[ { "text": "Optimal architecture for diamond-based wide-field thermal imaging: Nitrogen-Vacancy centers in diamond possess an electronic spin resonance that\nstrongly depends on temperature, which makes them efficient temperature sensor\nwith a sensitivity down to a few mK/$\\sqrt{\\rm Hz}$. However, the high thermal\nconductivity of the host diamond may strongly damp any temperature variations,\nleading to invasive measurements when probing local temperature distributions.\nIn view of determining possible and optimal configurations for diamond-based\nwide-field thermal imaging, we here investigate, both experimentally and\nnumerically, the effect of the presence of diamond on microscale temperature\ndistributions. Three geometrical configurations are studied: a bulk diamond\nsubstrate, a thin diamond layer bonded on quartz and diamond nanoparticles\ndispersed on quartz. We show that the use of bulk diamond substrates for\nthermal imaging is highly invasive, in the sense that it prevents any\nsubstantial temperature increase. Conversely, thin diamond layers partly solve\nthis issue and could provide a possible alternative for microscale thermal\nimaging. Dispersions of diamond nanoparticles throughout the sample appear as\nthe most relevant approach as they do not affect the temperature distribution,\nalthough NV centers in nanodiamonds yield lower temperature sensitivities\ncompared to bulk diamond.", "category": "physics_app-ph" }, { "text": "Spin dynamic response to a time dependent field: The dynamic response of a parametric system constituted by a spin precessing\nin a time dependent magnetic field is studied by means of a perturbative\napproach that unveils unexpected features, and is then experimentally\nvalidated. The first-order analysis puts in evidence different regimes: beside\na tailorable low-pass-filter behaviour, a band-pass response with interesting\npotential applications emerges. Extending the analysis to the second\nperturbation order permits to study the response to generically oriented fields\nand to characterize several non-linear features in the behaviour of such kind\nof systems.", "category": "physics_app-ph" }, { "text": "Germanene termination of Ge${_2}$Pt crystals on Ge(110): We have investigated the growth of Pt on Ge(110) using scanning tunneling\nmicroscopy and spectroscopy. The deposition of several monolayers of Pt on\nGe(110) followed by annealing at 1100 K results in the formation of\nthree-dimensional metallic Pt-Ge nanocrystals. The outermost layer of these\ncrystals exhibits a honeycomb structure. The honeycomb structure is composed of\ntwo hexagonal sub-lattices that are displaced vertically by 0.2 {\\AA} with\nrespect to each other. The nearest-neighbor distance of the atoms in the\nhoneycomb lattice is 2.5${\\pm}$0.1 {\\AA}, i.e. very close to the predicted\nnearest-neighbor distance in germanene (2.4 {\\AA}). Scanning tunneling\nspectroscopy reveals that the atomic layer underneath the honeycomb layer is\nmore metallic than the honeycomb layer itself. These observations are in line\nwith a model recently proposed for metal di-(silicides/)germanides: a hexagonal\ncrystal with metal layers separated by semiconductor layers with a honeycomb\nlattice. Based on our observations we propose that the outermost layer of the\nGe2Pt nanocrystal is a germanene layer.", "category": "physics_app-ph" }, { "text": "Thermal stress around a smooth cavity in a plate subjected to uniform\n heat flux: The two-dimensional thermoelastic problem of an adiabatic cavity in an\ninfinite isotropic homogeneous medium subjected to uniform heat flux is\nstudied, where the shape of the cavity is characterized by the Laurent\npolynomial. By virtue of a novel tactics, the obtained K-M potentials can be\nexplicitly worked out to satisfy the boundary conditions precisely, and the\npossible translation of the cavity is also available. The new and explicit\nanalytical solutions are compared with the those reported in literature and\nsome serious problems are found and corrected. Finally, some discussions on the\nthermal stress concentration around the tips of three typical cavities are\nprovided.", "category": "physics_app-ph" }, { "text": "Atmospheric Pressure Mass Spectrometry by Single-Mode\n Nanoelectromechanical Systems: Weighing particles above MegaDalton mass range has been a persistent\nchallenge in commercial mass spectrometry. Recently, nanoelectromechanical\nsystems-based mass spectrometry (NEMS-MS) has shown remarkable performance in\nthis mass range, especially with the advance of performing mass spectrometry\nunder entirely atmospheric conditions. This advance reduces the overall\ncomplexity and cost, while improving the limit of detection. However, this\ntechnique required the tracking of two mechanical modes, and the accurate\nknowledge of mode shapes which may deviate from their ideal values especially\ndue to air damping. Here, we used a NEMS architecture with a central platform,\nwhich enables the calculation of mass by single mode measurements. Experiments\nwere conducted using polystyrene and gold nanoparticles to demonstrate the\nsuccessful acquisition of mass spectra using a single mode, with improved areal\ncapture efficiency. This advance represents a step forward in NEMS-MS, bringing\nit closer to becoming a practical application for mass sensing of\nnanoparticles.", "category": "physics_app-ph" }, { "text": "Graphyne and Borophene as Nanoscopic Materials for Electronics: Discussions based upon rigorous derivations show the validity range of the\nanalogy between solid state materials like graphene which possess K symmetry\ncrystallographic points in k-space, and the relativistic solutions for massive\nand low mass particles associated with the Dirac equation. Both eigenenergies\nand eigenvectors are examined for the nonrelativistic solutions of the\nSchrodinger equation using the tight-binding method, and the relativistic\nsolutions of the Dirac equation. Implications for exploring new materials are\ndrawn from the results. It is concluded Dirac materials are unlikely to fulfill\nthe needs of transistor action materials, but two prime candidates which may\nsatisfy those needs for 2D future electronics are proposed, graphyne and\nborophene.", "category": "physics_app-ph" }, { "text": "Thermal expansion in photo-assisted tunneling: visible light versus\n free-space terahertz pulses: Photo-assisted tunneling in scanning tunneling microscopy has attracted\nconsiderable interest to combine sub-picosecond and sub-nanometer resolutions.\nThe illumination of a junction with visible or infrared light, however, induces\nthermal expansion of the tip and the sample, which strongly affects the\nmeasurements. Employing free-space THz pulses instead of visible light has been\nproposed to solve these thermal issues while providing photo-induced currents\nof similar magnitude. Here we compared the impact of illuminating the same\ntunneling junction, reaching comparable photo-induced current, with red light\nand with THz radiations. Our data provide a clear and direct evidence of\nthermal expansion with red light-illumination, while such thermal effects are\nnegligible with THz radiations.", "category": "physics_app-ph" }, { "text": "Near-infrared Schottky silicon photodetectors based on two dimensional\n materials: Since its discovery in 2004, graphene has attracted the interest of the\nscientific community due to its excellent properties of high carrier mobility,\nflexibility, strong light-matter interaction and broadband absorption. Despite\nof its weak light optical absorption and zero band gap, graphene has\ndemonstrated impressive results as active material for optoelectronic devices.\nThis success pushed towards the investigation of new two-dimensional (2D)\nmaterials to be employed in a next generation of optoelectronic devices with\nparticular reference to the photodetectors. Indeed, most of 2D materials can be\ntransferred on many substrates, including silicon, opening the path to the\ndevelopment of Schottky junctions to be used for the infrared detection.\nAlthough Schottky near-infrared silicon photodetectors based on metals are not\na new concept in literature the employment of two-dimensional materials instead\nof metals is relatively new and it is leading to silicon-based photodetectors\nwith unprecedented performance in the infrared regime. This chapter aims, first\nto elucidate the physical effect and the working principles of these devices,\nthen to describe the main structures reported in literature, finally to discuss\nthe most significant results obtained in recent years.", "category": "physics_app-ph" }, { "text": "Designing Anisotropic Microstructures with Spectral Density Function: Materials' microstructure strongly influences its performance and is thus a\ncritical aspect in design of functional materials. Previous efforts on\nmicrostructure mediated design mostly assume isotropy, which is not ideal when\nmaterial performance is dependent on an underlying transport phenomenon. In\nthis article, we propose an anisotropic microstructure design strategy that\nleverages Spectral Density Function (SDF) for rapid reconstruction of high\nresolution, two phase, isotropic or anisotropic microstructures in 2D and 3D.\nWe demonstrate that SDF microstructure representation provides an intuitive\nmethod for quantifying anisotropy through a dimensionless scalar variable\ntermed anisotropy index. The computational efficiency and low dimensional\nmicrostructure representation enabled by our method is demonstrated through an\nactive layer design case study for Bulk Heterojunction Organic Photovoltaic\nCells (OPVCs). Results indicate that optimized design, exhibiting strong\nanisotropy, outperforms isotropic active layer designs. Further, we show that\nCross-sectional Scanning Tunneling Microscopy and Spectroscopy (XSTM/S) is as\nan effective tool for characterization of anisotropic microstructures.", "category": "physics_app-ph" }, { "text": "Integrated Optical Electric Field Sensors: Humidity Stability Mechanisms\n and Packaging Scheme: Integrated optical electric field sensors (IOES) play a crucial role in\nelectric field measurement. This paper introduces the principles of the IOES\nand quantitatively evaluates the impact of humidity on measurement accuracy.\nSensors with different levels of hydrophobicity coatings and hygroscopicity\nshells are fabricated and tested across the relative humidity (RH) range of 25%\nto 95%. Results reveal that humidity stability is primarily influenced by water\nvapor absorption through the sensor shell, which increases its conductivity.\nThis further results in amplitude deviation and phase shift of the sensor\noutput. To address this, an optimal humidity-stable packaging scheme is\nproposed, which involves using PEEK shell with room temperature vulcanized\nfluorinated silicone rubber coating. Compared with uncoated ceramic shell, the\nphase shift of the IOES reduces from 90$^\\circ$ to 1$^\\circ$ under a RH of 90%.\nThe amplitude deviation of electric field measurement decreases from 20% to\nnearly zero after a 20-hour humidity experiment conducted under RH of 90% at 30\n$^\\circ$C. The proposed packaging scheme could be used to improve the humidity\nstability of the sensors deployed in outdoor environments, especially on ships\nand coastal areas.", "category": "physics_app-ph" }, { "text": "A Monte Carlo Simulation Study of L-band Emission upon Gamma Radiolysis\n of Water: Several studies have confirmed visible light and ultraviolet emission during\nwater molecule radiolysis.However radiofrequency (RF) emissions have been\nscarcely investigated.This simulation study has revealed that the gamma\nradiolysis of water creates excited hydrogen atoms which emit radio\nrecombination Lband (1 GHz to 2 GHz) radio waves of sufficient strength that a\nradio-imaging device can detect.The physical and physicochemical stages of\nradiolysis of water have been modeled via application of Monte Carlo simulation\ntechniques up to 1ps from the onset of gamma photon interaction with water\nmolecules.", "category": "physics_app-ph" }, { "text": "Indacenodithiophene homopolymers via direct arylation: direct\n polycondensation versus polymer analogous reaction pathways: Indacenodithiophene (IDT) based materials are emerging high performance\nconjugated polymers for use in efficient organic photovoltaics and transistors.\nHowever, their preparation generally suffers from long reaction sequences and\nis often accomplished using disadvantageous Stille couplings. Herein, we\npresent detailed synthesis pathways to IDT homopolymers using C-H activation\nfor all C-C coupling steps. Polyketones are first prepared by direct arylation\npolycondensation (DAP) in quantitative yield and further cyclized polymer\nanalogously. This protocol is suitable for obtaining structurally well-defined\nIDT homopolymers, provided that the conditions for cyclization are chosen\nappropriately and that side reactions are suppressed. Moreover, this polymer\nanalogous pathway gives rise to asymmetric side chain patterns, which allows to\nfine tune physical properties. Alternatively, IDT homopolymers can be obtained\nvia oxidative direct arylation polycondensation of IDT monomers (oxDAP),\nleading to IDT homopolymers with similar properties but at reduced yield.\nDetailed characterization by NMR, IR, UV-vis and PL spectroscopy, and thermal\nproperties, is used to guide synthesis and to explain varying field-effect\ntransistor hole mobilities in the range of 10-6- 10-3 cm2/Vs.", "category": "physics_app-ph" }, { "text": "On-Chip Characterization of High-Loss Liquids between 750 GHz and 1100\n GHz: Terahertz spectroscopy is a promising tool for analyzing the picosecond\ndynamics of biomolecules, which is influenced by surrounding water molecules.\nHowever, water causes extreme losses to terahertz signals, preventing sensitive\nmeasurements at this frequency range. Here, we present sensitive on-chip\nterahertz spectroscopy of highly lossy aqueous solutions using a vector network\nanalyzer, contact probes, and a coplanar waveguide with a 0.1 mm wide\nmicrofluidic channel. The complex permittivities of various deionized\nwater/isopropyl alcohol concentration are extracted from a known reference\nmeasurement across the frequency range 750-1100 GHz and agrees well with\nliterature data. The results prove the presented method as a high-sensitive\napproach for on-chip terahertz spectroscopy of high-loss liquids, capable of\nresolving the permittivity of water.", "category": "physics_app-ph" }, { "text": "The formation of polymer-dopant aggregates as a possible origin of\n limited doping efficiency at high dopant concentration: The polymer (PBDTTT-c) p-doped with the molecular dopant (Mo(tfd-COCF3)3)\nexhibits a decline in transport properties at high doping concentrations, which\nlimits the performance attainable through organic semiconductor doping.\nScanning Electron Microscopy is used to correlate the evolution of hole\nconductivity and hopping transport activation energy with the formation of\naggregates in the layer. Transmission Electron Microscopy with\nenergy-dispersive X-ray analysis along with liquid-state Nuclear Magnetic\nResonance experiments are carried out to determine the composition of the\naggregates. This study offers an explanation to the limited efficiency of\ndoping at high dopant concentrations and reinforces the need to increase doping\nefficiency in order to be able to reduce the dopant concentration and not\nnegatively affect conductivity.", "category": "physics_app-ph" }, { "text": "Specially designed B4C/SnO2 nanocomposite for photocatalysis:\n traditional ceramic with unique properties: Boron carbide: A traditional ceramic material shows unique properties when\nexplored in nano-range. Specially designed boron based nanocomposite has been\nsynthesized by reflux method. The addition of SnO2 in base matrix increase the\ndefect states in boron carbide and shows unique catalytic properties. The\ncalculated texture coefficient and Nelson Riley factor shows that the\nsynthesized nanocomposite have very high defect states. Also this composite is\nexplored for the first time for catalysis degradation of industrial used dyes.\nThe industrial pollutants such as Novacron red and methylene blue dye\ndegradation analysis reveal that the composite is an efficient catalyst.\nDegradation study shows that 1 g/L catalyst concentration of B4C/SnO2 degrade\nNovacron red Huntsman dye upto 97.38% approximately in 20 minutes under\nsunlight irradiation time. This water insoluble catalyst can be recovered and\nreused.", "category": "physics_app-ph" }, { "text": "Capacitance-Voltage (C-V) Characterization of Graphene-Silicon\n Heterojunction Photodiodes: Heterostructures of two-dimensional (2D) and three-dimensional (3D) materials\nform efficient devices for utilizing the properties of both classes of\nmaterials. Graphene/silicon (G/Si) Schottky diodes have been studied\nextensively with respect to their optoelectronic properties. Here, we introduce\na method to analyze measured capacitance-voltage data of G/Si Schottky diodes\nconnected in parallel with G/silicon dioxide/Si (GIS) capacitors. We also\ndemonstrate the accurate extraction of the built-in potential ($\\Phi$$_{bi}$)\nand the Schottky barrier height from the measurement data independent of the\nRichardson constant.", "category": "physics_app-ph" }, { "text": "Electrically controllable router of interlayer excitons: Optoelectronic devices which allow rerouting, modulation and detection of the\noptical signals would be extremely beneficial for telecommunication technology.\nOne of the most promising platforms for such devices are excitonic devices, as\nthey offer very efficient coupling to light. Of especial importance are those\nbased on indirect excitons, because of their long lifetime. Here we demonstrate\nexcitonic transistor and router based on bilayer of WSe2. Due to their strong\ndipole moment, excitons in bilayer WSe2 can be controlled by transverse\nelectric field. At the same time, unlike indirect excitons in artificially\nstacked heterostructures based on transition metal dichalcogenides - naturally\nstacked bilayer offers long exciton lifetime, smaller non-radiative losses, and\nare much simpler in fabrication.", "category": "physics_app-ph" }, { "text": "X-ray Writing of Fiber Bragg Gratings (FBGs): Fabrication of nanoscale optical Fiber Bragg Gratings (FBGs) is one of the\nkey manufacturing processes for fiber optics, which has many important\napplications in data communication and distributed remote sensing at a distance\nup to hundreds of kms. However, the fabrication of the FBGs is challenging. To\nmeet such need, we propose a novel method to write the FBGs using high-flux\nsynchrotron x-ray with a nanoscale gold/Si gratings to modulate the x-ray flux\nand thus change the refractive index contrast of the optical fiber to form the\nFBGs. The nanoscale gold/Si with high aspect ratio has been fabricated at the\nCenter for Nanoscale Materials (CNM) at Argonne National Laboratory (ANL) and\nthe preliminary experiment of x-ray writing of the optical fiber FBGs has been\ncarried out at the Advanced Photon Source (APS) of ANL. The preliminary\nexperiment shows promising result of the x-ray writing method of the optical\nfiber FBGs.", "category": "physics_app-ph" }, { "text": "Correlation between slip precursors and topological length scales at the\n onset of frictional sliding: Understanding the interplay between concurrent length scales is a fundamental\nissue in many problems involving friction between sliding interfaces, from\ntribology to the study of earthquakes and seismic faults. On the one hand, a\nmacroscopic sliding event is preceded by slip precursors with a characteristic\npropagation length scale. On the other hand, the emergent frictional properties\ncan be modified by surface patterning depending on their geometric length\nscale. This suggests that macroscopic sliding of structured surfaces is\ngoverned by the interplay between the length scale of the slip precursors and\nthose characterizing the geometric features. In this paper, we investigate\nthese aspects by means of numerical simulations using a two-dimensional\nspring-block model. We discuss the influence of the geometric features on the\noccurrence and localization of slip precursors, extending the study to\ninterfaces characterized by two geometric length scales. We find that different\ntypes of detachment sequences are triggered by specific surface structures,\ndepending on their scales and relation to sliding direction, leading to a\nmacroscopically smooth transition to sliding in the case of hierarchical and/or\nanisotropic features. These concepts could be exploited in devices switching\nfrom static to dynamic sliding, and can contribute to an improvement in the\nunderstanding and interpretation of seismic data", "category": "physics_app-ph" }, { "text": "Wavelength-dependence of laser excitation process on silicon surface: We report a first-principle calculation for the wavelength-dependence of a\nlaser excitation process on a silicon surface.", "category": "physics_app-ph" }, { "text": "Hybridization of Epsilon-Near-Zero Modes via Resonant Tunneling in\n Layered Metal/Insulator Double Nanocavities: The coupling between multiple nanocavities in close vicinity leads to\nhybridization of their modes. Stacked Metal/Insulator/Metal (MIM) nanocavities\nconstitute a highly versatile and very interesting model system to study and\nengineer such mode coupling, since they can be realized by lithography-free\nfabrication methods with fine control on the optical and geometrical\nparameters. The resonant modes of such MIM cavities are epsilon-near-zero (ENZ)\nresonances, which are appealing for non-linear photophysics and a variety of\napplications. Here we study the hybridization of ENZ resonances in MIMIM\nnanocavities, obtaining a very large mode splitting reaching 0.477 eV, Q\nfactors of the order of 40 in the visible spectral range, and fine control on\nthe resonance wavelength and mode linewidth by tuning the thickness of the\ndielectric and metallic layers. A semi-classical approach that analyses the\nMIMIM structure as a double quantum well system allows to derive the exact\nanalytical dispersion relation of the ENZ resonances, achieving perfect\nagreement with numerical simulations and experiments. Interestingly, the\nasymmetry of the mode splitting in a symmetric MIMIM cavity is not reflected in\nthe classical model of coupled oscillators, which can be directly related to\nquantum mechanical tunneling for the coupling of the two cavities. Interpreting\nthe cavity resonances as resonant tunneling modes elucidates that can be\nexcited without momentum matching techniques. The broad tunability of\nhigh-quality ENZ resonances together with their strong coupling efficiency\nmakes such MIMIM cavities an ideal platform for exploring light-matter\ninteraction, for example, by integration of quantum emitters in the dielectric\nlayers.", "category": "physics_app-ph" }, { "text": "Prediction of tubular solar still performance by machine learning\n integrated with Bayesian optimization algorithm: Presented is a new generation prediction model of a tubular solar still (TSS)\nproductivity utilizing two machine learning (ML) techniques, namely:Random\nforest (RF) and Artificial neural network (ANN). Prediction models were\nconducted based on experimental data recorded under Egyptian climate.\nMeteorological and operational thermal parameters were utilized as input\nlayers. Moreover, Bayesian optimization algorithm (BOA) was used to obtain the\noptimal performance of RF and ANN models. In addition, these models results\nwere compared to those of a multilinear regression (MLR) model. As resulted,\nexperimentally, the average value accumulated productivity was 4.3 L/(m2day).\nFor models results, RF was less sensitive to hyper parameters than ANN as ANN\nperformance could be significantly improved by BOA more than RF. In addition,\nRF achieved better prediction performance of TSS on the current dataset. The\ndetermination coefficients (R2) of RF and ANN were 0.9964 and 0.9977,\nrespectively, which were much higher than MLR models, 0.9431. Based on the\nrobustness performance and high accuracy, RF is recommended as a stable method\nfor predicting the productivity of TSS.", "category": "physics_app-ph" }, { "text": "Towards the maximum efficiency design of a perovskite solar cell by\n material properties tuning: A multidimensional approach: To obtain significant increases in the Power Conversion Efficiency (PCE) of\nsolar cells, future cell research and development should be based on the\nconcomitant improvement of multiple material properties, rather than on the\nstate-of-the-art one or two-dimensional improvements. In this context,\nresearchers should know, which combined material properties and cell design\nparameters lead to the highest efficiency increase. For the same objective, it\nshould also be known which relationships in-between these variables have to be\nadjusted. Such knowledge becomes available by simulation and numerical\noptimization, which we present for a Perovskite Solar Cell(PSC)in a hypercube\nspace of variables.", "category": "physics_app-ph" }, { "text": "Highly efficient optical transition between excited states in wide InGaN\n quantum wells: There is a lack of highly efficient light emitting devices (LEDs) operating\nin the green spectral regime. The devices based on (In,Al)GaN show extremely\nhigh efficiencies in violet and blue colors but fall short for longer emission\nwavelengths due to the quantum confined Stark effect (QCSE). In this paper we\npresent a design of the active region based on wide InGaN quantum wells (QWs)\nwhich do not suffer from QCSE and profit from an enhancement in the internal\nquantum efficiency (IQE). The design exploits highly efficient optical\ntransitions between excited states. It is shown that, counterintuitively, the\ndevices with higher InGaN composition exhibit a higher enhancement in IQE.\nExperimental evidence is provided showing a gradual change in the nature of the\noptical transition with increasing thickness of the QW. Moreover, optical gain\nin long wavelength LDs incorporating standard and wide QWs is investigated to\nshow the utilization of our concept.", "category": "physics_app-ph" }, { "text": "Graphene Resonant Pressure Sensor with Ultrahigh Responsivity: Graphene has good mechanical properties including large Young's modulus,\nmaking it ideal for many resonant sensing applications. Nonetheless, the\ndevelopment of graphene based sensors has been limited due to difficulties in\nfabrication, encapsulation, and packaging. Here we report a graphene\nnanoresonator based resonant pressure sensor. The graphene nano resonator is\nfabricated on a thin silicon diaphragm that deforms due to pressure\ndifferential across it. The deformation-induced strain change results in a\nresonance frequency shift of the graphene nano resonator. The pressure sensing\nexperiments demonstrate a record high responsivity of 20Hz/Pa with a resolution\nof 90Pa. The resolution of the sensing scheme is 0.003% of the full-scale range\nof the pressure sensor. This exceptional performance is attributed to two\nfactors: maintaining a high-quality vacuum environment for the nanoresonator\nand introducing stimuli through a thin silicon diaphragm. The proposed pressure\nsensor design provides flexibility to adjust responsivity and range as needed.\nThe fabrication method is simple and has the potential to be integrated with\nstandard CMOS fabrication. The innovative substrate packaging allows the\ncoupling of the resonator's strain with pressure.", "category": "physics_app-ph" }, { "text": "One-dimensional topological quasiperiodic chain for directional wireless\n power transfer: As an important class of systems with unique topological effects beyond the\nperiodic lattices, quasiperiodic topological structures have attracted much\nattention in recent years. Due to the quasiperiodic modulation, the topological\nstates in the quasiperiodic topological structures have the characteristics of\nself-similarity, which can be used to observe the charming Hofstadter\nbutterfly. In addition, because of the asymmetric distribution, the edge states\nin quasiperiodic chain can be used to realize the adiabatic pumping. When the\ntopological parameters in quasiperiodic topological lattices are considered as\nsynthetic dimensions, they can also be used to study the topological properties\nwith higher dimensions. Here, by using ultra-subwavelength resonators, we\ndesign and fabricate a type of one-dimensional quasiperiodic Harper chain with\nasymmetric topological edge states for the directional wireless power transfer\n(WPT). By further introducing a power source into the system, we selectively\nlight up two Chinese characters which is composed of LED lamps at both ends of\nthe chain. Moreover, the directional WPT implemented by the topological\nquasiperiodic chain has the property of topological protection, which is immune\nto the internal disorder perturbation of the structure. Not only do we apply\nthe asymmetric edge state for directional WPT, but also may further actively\ncontrol the directional WPT by using the external voltage. In addition, this\nwork provides a flexible platform for designing new WPT devices, such as using\nthe corner states in high-order topological structures or the skin effect in\nthe non-Hermitian topological lattices.", "category": "physics_app-ph" }, { "text": "Next-generation high transmission neutron optical devices utilizing\n micro-machined structures: Neutrons have emerged as a unique probe at the forefront of modern material\nscience, unrivaled in their penetrating abilities. A major challenge stems from\nthe fact that neutron optical devices are limited to refractive indices on the\norder of $n\\approx 1 \\pm 10^{-5}$. By exploiting advances in precision\nmanufacturing, we have designed and constructed a micro-meter period triangular\ngrating with a high aspect ratio of $14.3$. The manufacturing quality is\ndemonstrated with white-light interferometric data and microscope imaging.\nNeutron scattering experiment results are presented, showing agreement to\nrefraction modelling. The capabilities of neutron Fresnel lenses based on this\ndesign are contrasted to existing neutron focusing techniques and the path\nseparation of a prism-based neutron interferometer is estimated.", "category": "physics_app-ph" }, { "text": "Physical Mechanism behind the Hysteresis-free Negative Capacitance\n Effect in Metal-Ferroelectric-Insulator-Metal Capacitors with Dielectric\n Leakage and Interfacial Trapped Charges: The negative capacitance (NC) stabilization of a ferroelectric (FE) material\ncan potentially provide an alternative way to further reduce the power\nconsumption in ultra-scaled devices and thus has been of great interest in\ntechnology and science in the past decade. In this article, we present a\nphysical picture for a better understanding of the hysteresis-free charge boost\neffect observed experimentally in metal-ferroelectric-insulator-metal (MFIM)\ncapacitors. By introducing the dielectric (DE) leakage and interfacial trapped\ncharges, our simulations of the hysteresis loops are in a strong agreement with\nthe experimental measurements, suggesting the existence of an interfacial oxide\nlayer at the FE-metal interface in metal-ferroelectric-metal (MFM) capacitors.\nBased on the pulse switching measurements, we find that the charge enhancement\nand hysteresis are dominated by the FE domain viscosity and DE leakage,\nrespectively. Our simulation results show that the underlying mechanisms for\nthe observed hysteresis-free charge enhancement in MFIM may be physically\ndifferent from the alleged NC stabilization and capacitance matching. Moreover,\nthe link between Merz's law and the phenomenological kinetic coefficient is\ndiscussed, and the possible cause of the residual charges observed after pulse\nswitching is explained by the trapped charge dynamics at the FE-DE interface.\nThe physical interpretation presented in this work can provide important\ninsights into the NC effect in MFIM capacitors and future studies of low-power\nlogic devices.", "category": "physics_app-ph" }, { "text": "Potential of the three-terminal heterojunction bipolar transistor solar\n cell for space applications: Multi-terminal multi-junction solar cells (MJSC) offer higher efficiency\npotential than series connected (two-terminal) ones. In addition, for\nterrestrial applications, the efficiency of multi-terminal solar cells is less\nsensitive to solar spectral variations than the two-terminal series-connected\none. In space, generally, cells are always illuminated with AM0 spectrum and no\nimpact is expected from spectral variations. Still, in space, the\nmulti-terminal approach offers some advantages in comparison with the\nseries-connected architecture approach derived from a higher end of life (EOL)\nefficiency. In this work we review the potential of multi-terminal solar cells\nfor achieving extended EOL efficiencies with emphasis in the potential of the\nthree-terminal heterojunction bipolar transistor solar cell, a novel\nmulti-terminal MJSC architecture with a simplified structure not requiring, for\nexample, tunnel junctions.", "category": "physics_app-ph" }, { "text": "Mechanistic Insight to the Chemical Treatments of Monolayer Transition\n Metal Disulfides for Photoluminescence Enhancement: There is a growing interest in obtaining high quality monolayer transition\nmetal disulfides (TMDSs) for optoelectronic device applications. Surface\nchemical treatments using a range of chemicals on monolayer TMDSs have proven\neffective to improve their photoluminescence (PL) yield. However, the\nunderlying mechanism for PL enhancement by these treatments is not clear, which\nprevents a rational design of passivation strategies. In this work, a simple\nand effective approach to significantly enhance PL of TMDSs is demonstrated by\nusing a family of cation donors, which we show to be much more effective than\ncommonly used p-dopants which achieve PL enhancement through electron transfer.\nWe develop a detailed mechanistic picture for the action of these cation donors\nand demonstrate that one of them, Li-TFSI (bistriflimide), enhances the PL of\nboth MoS2 and WS2 to a level double that compared to the widely discussed and\ncurrently best performing super acid H-TFSI treatment. In addition, the ionic\nsalts used in chemical treatments are compatible with a range of greener\nsolvents and are easier to handle than super-acids, which provides the\npossibility of directly treating TMDSs during device fabrication. This work\nsets up rational selection rules for ionic chemicals to passivate TMDSs and\nincreases the potential of TMDSs in practical optoelectronic applications.", "category": "physics_app-ph" }, { "text": "Implementation and Characterization of a Two-Dimensional Printed Circuit\n Dynamic Metasurface Aperture for Computational Microwave Imaging: We present the design, fabrication, and experimental characterization of a\ntwo-dimensional, dynamically tuned, metasurface aperture, emphasizing its\npotential performance in computational imaging applications. The dynamic\nmetasurface aperture (DMA) consists of an irregular, planar cavity that feeds a\nmultitude of tunable metamaterial elements, all fabricated in a compact,\nmultilayer printed circuit board process. The design considerations for the\nmetamaterial element as a tunable radiator, the associated biasing circuitry,\nas well as cavity parameters are examined and discussed. A sensing matrix can\nbe constructed from the measured transmit patterns, the singular value spectrum\nof which provides insight into the information capacity of the apertures. We\ninvestigate the singular value spectra of the sensing matrix over a variety of\noperating parameters, such as the number of metamaterial elements, number of\nmasks, and number of radiating elements. After optimizing over these key\nparameters, we demonstrate computational microwave imaging of simple test\nobjects.", "category": "physics_app-ph" }, { "text": "Ultrashort Pulse Detection and Response Time Analysis Using Plasma-wave\n Terahertz Field Effect Transistors: We report on the response characteristics of plasmonic terahertz field-effect\ntransistors (TeraFETs) fed with femtosecond and picosecond pulses. Varying the\npulse width (tpw) from 10-15 s to 10-10 s under a constant input power\ncondition revealed two distinctive pulse detection modes. In the short pulse\nmode (tpw << L/s, where L is the gated channel length, s is the plasma\nvelocity), the source-to-drain voltage response is a sharp pulse oscillatory\ndecay preceded by a delay time on the order of L/s. The plasma wave travels\nalong the channel like the shallow water wave with a relatively narrow wave\npackage. In the long pulse mode (tpw > L/s), the response profile has two\noscillatory decay processes and the propagation of plasma wave is analogues to\noscillating rod with one side fixed. The ultimate response time at the long\npulse mode is significantly higher than that under the short pulse conditions.\nThe detection conditions under the long pulse mode are close to the step\nresponse condition, and the response time conforms well to the analytical\ntheory for the step function response. The simulated waveform agrees well with\nthe measured pulse response. Our results show that the measurements of the\npulse response enable the material parameter extraction from the pulse response\ndata (including the effective mass, kinematic viscosity and momentum relaxation\ntime).", "category": "physics_app-ph" }, { "text": "Mechanical activity and odd elasticity of passive, 2D chiral\n metamaterials: We demonstrate a general route to making active, odd elastic solids from\npassive chiral elements that can act as sources of mechanical work by violating\nstatic equilibrium without internal sources of energy or momentum. We further\ndemonstrate that by starting from a discrete, Newtonian mechanics viewpoint of\nthe chiral unit cell, we can develop the continuum field equations for\nisotropic 2D chiral metamaterials that reveal odd elasticity, while elucidating\nthe structure-property relationships underpinning the chiral, elastic moduli\nthat enable the mechanical activity of the chiral metamaterials. By\ndemonstrating the energy gain of chiral metamaterials as they undergo\nquasistatic deformation cycles, we show a new route to designing active,\nnon-reciprocal mechanical metamaterials that can operate at zero frequency.", "category": "physics_app-ph" }, { "text": "Preparation of the AlTiNiCuCox system high-entropy alloys and structural\n analysis: This study aimed to explore and develop a new material with high\ncost-effectiveness, excellent strength, light weight, high hardness, great wear\nresistance, corrosion resistance, and favorable oxidation resistance.\nStructural analysis suggested that, with the change in Co addition amount, the\nsurface morphology and structure of the alloy system changed. XRD analysis\nindicated that, the alloy system was the FCC+BCC mixed structure. In addition,\nmetallographical demonstrated that, with the increase in Co content, the\ndendritic crystal transformed from big block to dendritic structure, then to\nsnowflake, gradually to petal-like, and finally to petal shape. SEM-EDS\nanalysis revealed that, Cu element was enriched in interdendritic site, while\nTi, Ni, Al and Co elements were enriched in dendrite. Besides, TEM and TEM-EDS\nanalysis indicated that, there was nano-size precipitate of small particles in\nthe Cu-enriched block region, along with dislocation; further, there was twin\nstructure inside the dendrite, as well as the second phase with different\nmorphology, and the second phase showed coherency with the matrix. The above\nanalysis suggested that, the intercrystalline structure was the Cu-enriched\nphase of FCC structure; the internal matrix of grain was the NiTi and TiCo\nphases of BCC structure; and the second phases inside the grain were the\nAlCu2Ti,AlNi2Ti,AlCo2Ti and CuNi phases of FCC structure. Taken together, the\nAlTiNiCuCox system novel alloys have changed phase structures and phase types\nof the alloy system.", "category": "physics_app-ph" }, { "text": "Dynamics of hybrid magnetic skyrmion driven by spin-orbit torque in\n ferrimagnets: Magnetic skyrmions are magnetic textures with topological protection, which\nare expected to be information carriers in future spintronic devices. In this\nwork, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in\nferrimagnets, and we study theoretically and numerically the dynamics of the\nHMS driven by spin-orbit torque. It is revealed that the skyrmion Hall effect\ndepends on the skyrmion helicity and the net angular momentum ({\\delta}s),\nallowing the effective modulation of the HMS motion through tuning\nDzyaloshinskii-Moriya interaction and {\\delta}s. Thus, the Hall effect can be\nsuppressed through selecting suitable materials to better control the HMS\nmotion. Moreover, Magnus force for finite {\\delta}s suppresses the transverse\nmotion and enhances the longitudinal propagation, resulting in the HMS dynamics\nin ferrimagnets faster than that in antiferromagnets.", "category": "physics_app-ph" }, { "text": "High quality superconducting Nb co-planar resonators on sapphire\n substrate: We present measurements and simulations of superconducting Nb co-planar\nwaveguide resonators on sapphire substrate down to millikelvin temperature\nrange with different readout powers. In the high temperature regime, we\ndemonstrate that the Nb film residual surface resistance is comparable to that\nobserved in the ultra-high quality, bulk Nb 3D superconducting radio frequency\ncavities while the resonator quality is dominated by the BCS thermally excited\nquasiparticles. At low temperature both the resonator quality factor and\nfrequency can be well explained using the two-level system models. Through the\nenergy participation ratio simulations, we find that the two-level system loss\ntangent is $\\sim 10^{-2}$, which agrees quite well with similar studies\nperformed on the Nb 3D cavities.", "category": "physics_app-ph" }, { "text": "A dynamic picture of energy conversion in photovoltaic devices: Studies of emerging photovoltaics, such as organic and perovskite solar\ncells, have recently shown that the separation of photo-generated charge\ncarriers is correlated with non-thermal, coherent oscillations within the\nilluminated device. We consider this experimental evidence in light of results\nfrom the theory of open quantum systems that point to the need for a\nself-oscillating internal capacitor, acting as a microscopic piston, to explain\nhow an illuminated solar cell operates as an autonomous heat engine. We propose\na picture of work extraction by photovoltaic devices that supersedes the\nquasi-static descriptions prevalent in the literature. Finally, we argue that\nsuch a dialogue between condensed matter physics and quantum thermodynamics may\noffer a guide for the design of new energy transducers.", "category": "physics_app-ph" }, { "text": "Gold Nanoparticles Aggregation on Graphene Using Reactive Force Field: A\n Molecular Dynamic Study: We examine the aggregation behavior of AuNPs of different sizes on graphene\nas function of temperature using molecular dynamic simulations with Reax Force\nField (ReaxFF). In addition, the consequences of such aggregation on the\nmorphology of AuNPs and the charge transfer behavior of AuNP-Graphene hybrid\nstructure are analyzed. The aggregation of AuNPs on graphene is confirmed from\nthe center of mass distance calculation. The simulation results indicate that\nthe size of AuNPs and temperature significantly affect the aggregation behavior\nof AuNPs on graphene. The strain calculation showed that shape of AuNPs changes\ndue to the aggregation and the smaller size AuNPs on graphene exhibit more\nshape changes than larger AuNPs at all the temperatures studies in this work.\nThe charge transfer calculation reveals that, the magnitude of charge transfer\nis higher for larger AuNPs-graphene composite when compared with smaller\nAuNPs-graphene composite. The charge transfer trend and the trends seen in the\nnumber of Au atoms directly in touch with graphene are identical. Hence, our\nresults conclude that, quantity of Au atoms directly in contact with graphene\nduring aggregation is primarily facilitates charge transfer between AuNPs and\ngraphene.", "category": "physics_app-ph" }, { "text": "High precision atom interferometer-based dynamic gravimeter measurement\n by eliminating the cross-coupling effect: A dynamic gravimeter with an atomic interferometer (AI) can perform absolute\ngravity measurements with high precision. AI-based dynamic gravity measurement\nis a type of joint measurement that uses AI sensors and a classical\naccelerometer. The coupling of the two sensors may degrade the measurement\nprecision. In this study, we analyzed the cross-coupling effect and introduced\na recovery vector to suppress this effect. We improved the phase noise of the\ninterference fringe by a factor of 1.9 by performing marine gravity\nmeasurements using an AI-based gravimeter and optimizing the recovery vector.\nMarine gravity measurements were performed, and high gravity measurement\nprecision was achieved. The external and inner coincidence accuracies of the\ngravity measurement are 0.42 mGal and 0.46 mGal, which were improved by factors\nof 4.18 and 4.21 by optimizing the cross-coupling effect.", "category": "physics_app-ph" }, { "text": "Design for tunable optofluidic optical coupler with large dynamic range: A novel scheme for tunable optofluidic optical coupler is proposed, by using\ndirectional coupling waveguide structure and microfluidic channel with two\ntapers at end points. The normalized optical power at two output ports can be\ndynamically manipulated by controlling the refractive index of liquid mixture\nin microfluidic channel. The optical performance of the designed device is\nnumerically investigated by employing the beam propagation method (BPM). The\nsimulated results demonstrate that large dynamic range and low optical loss for\nboth TE and TM mode can be easily achieved, and furthermore the dependence of\npolarization states and operation wavelength is very low in our designed\ndevice. In addition, the tunable optofluidic coupler has advantages including\nsimple structure and large fabrication tolerance. Accordingly, our proposed\ndevice offers a new approach for manipulation of optical power output, which\nhas wide potential application in optofluidic systems.", "category": "physics_app-ph" }, { "text": "A highly sensitive magnetic sensor using a 2D van der Waals\n ferromagnetic material: Two-dimensional (2D) van der Waals ferromagnetic materials are emerging as\npromising candidates for applications in ultra-compact spintronic nanodevices,\nnanosensors, and information storage. Our recent discovery of the strong room\ntemperature ferromagnetism in single layers of VSe2 grown on graphite or MoS2\nsubstrate has opened new opportunities to explore these ultrathin magnets for\nsuch applications. In this paper, we present a new type of magnetic sensor that\nutilizes the single layer VSe2 film as a highly sensitive magnetic core. The\nsensor relies in changes in resonance frequency of the LC circuit composed of a\nsoft ferromagnetic microwire coil that contains the ferromagnetic VSe2 film\nsubject to applied DC magnetic fields. The sensitivity of the sensor reaches an\nextremely high value of 16x10^6 Hz/Oe, making it an excellent candidate for a\nwide range of magnetic sensing applications.", "category": "physics_app-ph" }, { "text": "Minor Actinides Transmutation in Candidate Accident Tolerant\n Fuel-Claddings U3Si2-FeCrAl and U3Si2-SiC: An advanced transmutation method is suggested that the long-lived Minor\nActinides (MAs) in the spent fuel can be efficiently transmuted in the\ncandidate Accident Tolerant Fuel (ATF). The transmutation of MAs is\ninvestigated through the Monte Carlo simulations in two potential\nfuel-claddings of ATF, U3Si2-FeCrAl and U3Si2-SiC. The critical loadings of MAs\nare determined through the Linear Reactivity Model (LRM) in order to keep the\nsame reactivity as the current UO2-zircaloy system at the End of Cycle (EOC).\nIn all cases, excellent transmutation efficiencies are found for the most\nimportant three MAs, 237Np, 241Am, and 243Am, of which the total transmutation\nrates are around 60%, 90%, and 60%, respectively. If only the longest-lived\nisotope 237Np is considered, one U3Si2-SiC assembly can transmute 237Np from\nsix normal assemblies. The loading of MAs has little influences on the\nneutronic properties, such as the power distributions inside an assembly and\ninside a fuel rod. The transmutation of MAs in the ATF assembly is shown to be\nmore efficient and safe comparing with the normal assembly, while other\nimportant properties are kept, such as the cycle length and the power\ndistribution.", "category": "physics_app-ph" }, { "text": "Short wavelength infrared avalanche photodetector using Sb-based\n strained layer superlattice: We demonstrate a low noise short wavelength infrared (SWIR) Sb based type II\nsuperlattice (T2SL) avalanche photodiodes (APD). The SWIR GaSb/(AlAsSb/GaSb)\nAPD structure was designed based on impact ionization engineering and grown by\nmolecular beam epitaxy on GaSb substrate. At room temperature, the device\nexhibits a 50 % cut-off wavelength of 1.74 micron. The device revealed to have\nelectron dominated avalanching mechanism with a gain value of 48 at room\ntemperature. The electron and hole impact ionization coefficients were\ncalculated and compared to give better prospect of the performance of the\ndevice. Low excess noise, as characterized by the carrier ionization ratio of ~\n0.07, has been achieved.", "category": "physics_app-ph" }, { "text": "Photochemical Upcycling of Ultrastrong Polyethylene Nanomembranes into\n Fibrous Carbon at Ambient Conditions: The escalating global issue of plastic waste accumulation, specifically\npolyolefins, necessitates an urgent solution for upcycling these materials into\nbeneficial compounds. Yet, achieving such upcycling without introducing carbon\ndioxide into the environment remains a formidable challenge. In this study, we\ndemonstrate an eco-friendly approach for the photochemical conversion of\nultrastrong, ultratransparent, and ultrathin polyethylene membrane into fibrous\ncarbon nanomembrane at ambient conditions. The membrane was sputter-coated with\nplatinum and cuprous oxide nanoparticles and exposed to simulated sunlight,\nresulting in a porous carbon membrane decorated with Pt nanoparticles. The new\ncarbonized nanomembrane maintained the pristine membrane's morphology. The\nmembrane exhibited high activity (2.11 mA/cm2) for electrochemical ethanol\noxidation with stability over 1000 cycles. This work holds significance for\nsustainable plastic waste management and the design of new polyolefin materials\nin a circular economy.", "category": "physics_app-ph" }, { "text": "Boosting thermal conductivity by surface plasmon polaritons propagating\n along a thin Ti film: We experimentally demonstrate a boosted in-plane thermal conduction by\nsurface plasmon polaritons (SPPs) propagating along a thin Ti film on a glass\nsubstrate. Owing to a lossy nature of metal, SPPs can propagate over\ncentimeter-scale distance even with a supported metal film, and resulting\nballistic heat conduction can be quantitatively validated. Further, for a\n100-nm-thick Ti film on glass substrate, a significant enhancement of in-plane\nthermal conductivity compared to bulk value ($\\sim 35\\%$) is experimentally\nshown. This study will provide a new avenue to employ SPPs for heat dissipation\nalong a supported thin film, which can be readily applied to mitigate hot-spot\nissues in microelectronics.", "category": "physics_app-ph" }, { "text": "Acoustic radiation-free surface phononic crystal resonator for in-liquid\n low-noise gravimetric detection: Acoustic wave resonators are promising for gravimetric biosensing. However,\nthey generally suffer from strong acoustic radiation in liquid, which limits\ntheir quality factor and increases their frequency noise. This article presents\nan acoustic-radiation-free gravimetric biosensor based on a locally-resonant\nsurface phononic crystal (SPC) consisting of periodic high aspect ratio\nelectrodes to ad-dress the above issue. The acoustic wave generated in the SPC\nis slower than the sound wave in water, hence preventing acoustic propagation\nin the fluid and resulting in energy confinement near the electrode surface.\nThis energy confinement results in a significant quality factor improvement and\nthus reduces the frequency noise. The proposed SPC resonator is numerically\nstudied by finite element analysis and experimentally implemented by an\nelectroplating based fabrication process. Experimental results show that the\nSPC resonator exhibits an in-liquid quality factor 15 times higher than a\nconventional Rayleigh wave resonator with a similar operating frequency. The\nproposed radiation suppression method using SPC can also be applied in other\ntypes of acoustic wave resonators. It can thus serve as a general technique for\nboosting the in-liquid quality factor and the sensing performance of many\nacoustic biosensors.", "category": "physics_app-ph" }, { "text": "Intense white luminescence in ZnTe embedded porous silicon: Porous silicon layers were embedded with ZnTe using the isothermal close\nspace sublimation technique. The presence of ZnTe was demonstrated using\ncross-sectional energy dispersive spectroscopy maps. ZnTe embedded samples\npresent intense room temperature photoluminescence along the whole visible\nrange. We ascribe this PL to ZnTe nanocrystals of different sizes grown on the\ninternal pore surface. Such crystals, with different orientations and sizes,\nwere observed in transmission electron microscopy images, while transmission\nelectron diffraction images of the same regions reveal ZnTe characteristic\npatterns.", "category": "physics_app-ph" }, { "text": "Efficient Extraction of Hot Carriers in Perovskite Quantum Dot through\n Building State Coupled Complex: Utilizing hot carriers is the crucial approach for solar cell to exceed the\nthermodynamic detailed balance limit, yet effective extraction of hot carriers\nin absorber materials via most commonly used semiconductor acceptors has been a\nchallenge in both materials and photophysics research for many years. Herein,\nwe build series of CsPbI3 quantum dot and fullerene derivative systems to\nexplore the decisive factors of this process and have for the first time\nrealized efficient hot carrier extraction in these systems (maximum extraction\nefficiency ~ 84%). We find building the systems as state-coupled complexes\ncreates new carrier transport channels at about 0.22 eV above CsPbI3 quantum\ndot bandgap, which facilitates highly efficient HC extraction. Our research\ndirectly visualizes the inner connection of molecule interaction and ultrafast\nhot carrier extraction. The knowledge and strategy gained here are of universal\nmeaning, taking an important step forward true hot carrier photovoltaics.", "category": "physics_app-ph" }, { "text": "Explainable machine learning to enable high-throughput electrical\n conductivity optimization of doped conjugated polymers: The combination of high-throughput experimentation techniques and machine\nlearning (ML) has recently ushered in a new era of accelerated material\ndiscovery, enabling the identification of materials with cutting-edge\nproperties. However, the measurement of certain physical quantities remains\nchallenging to automate. Specifically, meticulous process control,\nexperimentation and laborious measurements are required to achieve optimal\nelectrical conductivity in doped polymer materials. We propose a ML approach,\nwhich relies on readily measured absorbance spectra, to accelerate the workflow\nassociated with measuring electrical conductivity. The first ML model\n(classification model), accurately classifies samples with a conductivity >~25\nto 100 S/cm, achieving a maximum of 100% accuracy rate. For the subset of\nhighly conductive samples, we employed a second ML model (regression model), to\npredict their conductivities, yielding an impressive test R2 value of 0.984. To\nvalidate the approach, we showed that the models, neither trained on the\nsamples with the two highest conductivities of 498 and 506 S/cm, were able to,\nin an extrapolative manner, correctly classify and predict them at satisfactory\nlevels of errors. The proposed ML workflow results in an improvement in the\nefficiency of the conductivity measurements by 89% of the maximum achievable\nusing our experimental techniques. Furthermore, our approach addressed the\ncommon challenge of the lack of explainability in ML models by exploiting\nbespoke mathematical properties of the descriptors and ML model, allowing us to\ngain corroborated insights into the spectral influences on conductivity.\nThrough this study, we offer an accelerated pathway for optimizing the\nproperties of doped polymer materials while showcasing the valuable insights\nthat can be derived from purposeful utilization of ML in experimental science.", "category": "physics_app-ph" }, { "text": "Mathematical Operations and Equation Solving with Reconfigurable\n Metadevices: Performing analog computations with metastructures is an emerging wave-based\nparadigm for solving mathematical problems. For such devices, one major\nchallenge is their reconfigurability, especially without the need for a priori\nmathematical computations or computationally-intensive optimization. Their\nequation-solving capabilities are applied only to matrices with special\nspectral (eigenvalue) distribution. Here we report the theory and design of\nwave-based metastructures using tunable elements capable of solving\nintegral/differential equations in a fully-reconfigurable fashion. We consider\ntwo architectures: the Miller architecture, which requires the singular-value\ndecomposition, and an alternative intuitive direct-complex-matrix (DCM)\narchitecture introduced here, which does not require a priori mathematical\ndecomposition. As examples, we demonstrate, using system-level simulation\ntools, the solutions of integral and differential equations. We then expand the\nmatrix inverting capabilities of both architectures toward evaluating the\ngeneralized Moore-Penrose matrix inversion. Therefore, we provide evidence that\nmetadevices can implement generalized matrix inversions and act as the basis\nfor the gradient descent method for solutions to a wide variety of problems.\nFinally, a general upper bound of the solution convergence time reveals the\nrich potential that such metadevices can offer for stationary iterative\nschemes.", "category": "physics_app-ph" }, { "text": "Quantifying the Trade-offs between Energy Consumption and Salt Removal\n Rate in Membrane-free Cation Intercalation Desalination: Electrochemical desalination devices that use redox-active cation\nintercalation electrodes show promise for desalination of salt-rich water\nresources with high water recovery and low energy consumption. While previous\nmodeling and experiments used ion-exchange membranes to maximize charge\nefficiency, here a membrane-free alternative is evaluated to reduce capital\ncost by using a porous diaphragm to separate Na$_{1+x}$NiFe(CN)$_6$ electrodes.\nTwo-dimensional porous-electrode modeling shows that, while charge efficiency\nlosses are inherent to a diaphragm-based architecture, charge efficiency values\napproaching the anion transference number (61$\\%$ for NaCl) are achievable for\ndiaphragms with sufficiently low salt conductance. Closed-form equations are\nthereby derived that relate charge efficiency to the non-dimensional P\\`{e}clet\nand Damk\\\"ohler numbers that enable the selection of current and flow velocity\nto produce a desired degree of desalination. Simulations using these conditions\nare used to quantify the tradeoffs between energy consumption and salt removal\nrate for diaphragm-based cells operated at a range of currents. The simulated\ndistributions of reactions are shown to result from the local salt\nconcentration variations within electrodes using diffusion-potential theory. We\nalso simulate the cycling dynamics of various flow configurations and show that\nflow-through electrodes exceed the degree-of-desalination compared with flow-by\nand flow-behind configurations due to solution stagnation within electrodes.", "category": "physics_app-ph" }, { "text": "The ElectroHydroDynamic force distribution in surface AC Dielectric\n Barrier Discharge actuators: do streamers dictate the ionic wind profiles?: We show that the spatio-temporal ElectroHydroDynamic (EHD) force production\nin surface AC-Dielectric Barrier Discharge (AC-DBD) actuators is strongly\ninfluenced by both the streamer regime during the positive phase and the\nmicro-discharge regime during the negative phase. Focusing on the spatial EHD\nforce profiles, we demonstrate that the ionic wind spatial distribution can\nonly be explained by the positive contribution of the streamer regime. The\nlocation of maximum ionic wind is found to be directly linked with the maximum\nelongation of the streamers at several millimeters from the exposed electrode.\nIn both positive and negative phases of the AC-DBD operation, residual\nvolumetric and surface charges once again linked to the streamer formation and\nafterburn, result to a variety of positive EHD force zones which, when\ntime-averaged in one AC period, contribute to the generation of the\nexperimentally observed induced thin wall jet. Through a thorough elaboration\nof our numerical results, we provide an illustrative explanation of the EHD\nforce spatio-temporal evolution, showcase the importance of streamers and\nretrieve a correct representation of the ionic wind spatial profiles when\ncompared to experiments.", "category": "physics_app-ph" }, { "text": "Neuron-inspired flexible memristive device on silicon (100): Comprehensive understanding of the world's most energy efficient powerful\ncomputer, the human brain, is an elusive scientific issue. Still, already\ngained knowledge indicates memristors can be used as a building block to model\nthe brain. At the same time, brain cortex is folded allowing trillions of\nneurons to be integrated in a compact volume. Therefore, we report flexible\naluminium oxide based memristive devices fabricated and then derived from\nwidely used bulk mono-crystalline silicon (100). We use complementary metal\noxide semiconductor based processes to layout the foundation for ultra large\nscale integration (ULSI) of such memory devices to advance the task of\ncomprehending a physical model of human brain.", "category": "physics_app-ph" }, { "text": "Planar alignment of Liquid Crystals on h-BN for Near-Eye Displays: Liquid crystals alignment on 2D materials is known due to their intrinsic van\nder Waals interaction. Here, we demonstrate that direction of electric field\ncan tune the alignment of liquid crystal adsorbed on 2D surface. Due to\ndegeneracy of alignment liquid crystal on hexagonal surface, it prefers to\nalign in three multiple states. We utilized this concept and control the\nalignment of grains of chemical vapor deposition grown boron nitride (h-BN) to\ncontrol the incident light. It was demonstrated that electric field can\nreorient the direction of liquid crystal alignment on Zigzag and armchair edges\nof h-BN. The ab initio calculations confirmed the favorable adsorption\nconfigurations of liquid crystal molecule on hexagonal boron nitride surface.\nThis concept provides a pathway towards dynamic high-quality pixels with low\npower consumption and could define a new avenue in near-eye displays.", "category": "physics_app-ph" }, { "text": "Hierarchically Arranged Helical Fiber Actuators Derived from Commercial\n Cloth: The first hygroscopic tunable cloth actuator is realized via modification of\ncommercial cloth template by a 3D nanoporous polymer hybrid. The nanoporous\nhybrid guarantees fast water diffusion and amplifies deformation. The cloth\nactuator achieves a large-scale size production, tunable motion, high tensile\nstrength and mechanical flexibility with a breadth of utilities (e.g., electric\ngenerator and smart materials).", "category": "physics_app-ph" }, { "text": "Characterization and Modeling of Self-Heating in Nanometer Bulk-CMOS at\n Cryogenic Temperatures: This work presents a self-heating study of a 40-nm bulk-CMOS technology in\nthe ambient temperature range from 300 K down to 4.2 K. A custom test chip was\ndesigned and fabricated for measuring both the temperature rise in the MOSFET\nchannel and in the surrounding silicon substrate, using the gate resistance and\nsilicon diodes as sensors, respectively. Since self-heating depends on factors\nsuch as device geometry and power density, the test structure characterized in\nthis work was specifically designed to resemble actual devices used in\ncryogenic qubit control ICs. Severe self-heating was observed at deep-cryogenic\nambient temperatures, resulting in a channel temperature rise exceeding 50 K\nand having an impact detectable at a distance of up to 30 um from the device.\nBy extracting the thermal resistance from measured data at different\ntemperatures, it was shown that a simple model is able to accurately predict\nchannel temperatures over the full ambient temperature range from\ndeep-cryogenic to room temperature. The results and modeling presented in this\nwork contribute towards the full self-heating-aware IC design-flow required for\nthe reliable design and operation of cryo-CMOS circuits.", "category": "physics_app-ph" }, { "text": "All-Linear Multistate Magnetic Switching Induced by Electrical Current: We present an alternative mechanism to control the domain wall motion, whose\ndirections are manipulated by the amplitude of electrical currents when\nmodulating the ratio of D/A (constants of Dzyaloshinskii-Moriya interaction\nover exchange interaction). To confirm this mechanism, we observe this type of\ndomain wall motion and demonstrate linear magnetic switching without hysteresis\neffect via adjusting the D/A of Ta/Pt/Co/Ta multilayer device with ion\nimplantations. We further find field-free biased and chirally controllable\nmultistate switching at the lateral interface of ion exposed and unexposed\narea, which is due to the current induced Neel wall motion and a strong\nexchange coupling at this interface.", "category": "physics_app-ph" }, { "text": "Fabrication and micro-Raman spectroscopy of arrays of copper\n phthalocyanine molecular-magnet microdisks: Phthalocyanines as organic semiconductors and molecular magnets provide\nplenty of industrial or high-tech applications from dyes and pigments up to gas\nsensors, molecular electronics, spintronics and quantum computing. Copper\nphthalocyanine (CuPc) belongs among the most used phthalocyanines, typically in\nthe form of powder or films but self-grown nanowires are also known. Here we\ndescribe an opposite, i.e., top-down approach based on fabrication of ordered\narrays of CuPc microstructures (microdisks) using electron beam lithography and\nother steps. Among critical points of this approach belongs a choice of a\nproper resist and a solvent. Fabricated CuPc microdisks have a diameter of 5\n${\\mu}$m and heights from 7 up to 70 nm. Micro-Raman spectroscopy of the films\nand microdisks reveals a crystalline ${\\beta}$ phase associated with a\nparamagnetic form. Additional measurements with an increasing laser power show\na significant shift (${\\Delta}{\\omega}$ ~ 7.1 cm$^{-1}$ ) and broadening of a\npeak at 1532 rel$\\cdot$cm$^{-1}$ corresponding to the phonon B1g mode. The\nobserved smooth changes exclude a phase transition and confirm the thermally\nstable polymorph. Our versatile fabrication technique using the common\nlithographic resist brings new possibilities for the fabrication of various\nmicro/nanostructures such as micromagnets, heterostructures or organic\nelectronic devices.", "category": "physics_app-ph" }, { "text": "Thermal Annealing Effect on Electrical and Structural Properties of\n Tungsten Carbide Schottky Contacts on AlGaN/GaN heterostructures: Tungsten carbide (WC) contacts have been investigated as a novel gold-free\nSchottky metallization for AlGaN/GaN heterostructures. The evolution of the\nelectrical and structural/compositional properties of the WC/AlGaN contact has\nbeen monitored as a function of the annealing temperature in the range from 400\nto 800{\\deg}C. The Schottky barrier height ($\\Phi$B) at WC/AlGaN interface,\nextracted from the forward current-voltage characteristics of the diode,\ndecreased from 0.8 eV in the as-deposited and 400{\\deg}C annealed sample, to\n0.56 eV after annealing at 800 {\\deg}C. This large reduction of $\\Phi$B was\naccompanied by a corresponding increase of the reverse bias leakage current.\nTransmission electron microscopy coupled to electron energy loss spectroscopy\nanalyses revealed the presence of oxygen (O) uniformly distributed in the WC\nlayer, both in the as-deposited and 400{\\deg}C annealed sample. Conversely,\noxygen accumulation in a 2-3 nm thin W-O-C layer at the interface with AlGaN\nwas observed after the annealing at 800 {\\deg}C, as well as the formation of\nW2C grains within the film (confirmed by X-ray diffraction analyses). The\nformation of this interfacial W-O-C layer is plausibly the main origin of the\ndecreased $\\Phi$B and the increased leakage current in the 800{\\deg}C annealed\nSchottky diode, whereas the decreased O content inside the WC film can explain\nthe reduced resistivity of the metal layer. The results provide an assessment\nof the processing conditions for the application of WC as Schottky contact for\nAlGaN/GaN heterostructures.", "category": "physics_app-ph" }, { "text": "Numerical investigation of transient, low-power metal vapour discharges\n occurring in near limit ignitions of flammable gas: This article presents an investigation of a transient (30 {\\mu}s - 5 ms)\nelectrical discharge in metal vapour with low voltage (< 50 V) and current (< 1\nA), drawn between two separating electrodes. Discharges of this type are rarely\nstudied, but are important in electrical explosion safety, as they can ignite\nflammable gasses. An empirical model is developed based on transient recordings\nof discharge voltages and currents and high speed broadband image data. The\nmodel is used for predicting the electrical waveforms and spatial power\ndistribution of the discharge. The predicted electrical waveforms show good\naccuracy under various scenarios. To further investigate the underlying\nphysics, the model is then incorporated into a simplified 3-D gas dynamics\nsimulation including molecular diffusion, heat transfer and evaporation of\nmetal from the electrode surface. The local thermodynamic equilibrium (LTE)\nassumption is next used to calculate electrical conductivity from the simulated\ntemperature fields, which in turn is integrated to produce electrical\nresistance over time. This resistance is then compared to that implied by the\nvoltage and current waveforms predicted by the empirical model. The comparison\nshows a significant discrepancy, yielding the important insight that the\nstudied discharge very likely deviates strongly from LTE.", "category": "physics_app-ph" }, { "text": "Effects of Alloying Elements on Surface Oxides of Hot-Dip Galvanized\n Press Hardened Steel: Effects of steel alloying elements on the formation of the surface oxide\nlayer of hot-dip galvanized press hardened steel after austenitization\nannealing were examined with various advanced microscopy and spectroscopy\ntechniques. The main oxides on top of the original thin Al2O3 layer,\noriginating from the primary galvanizing process, are identified as ZnO and\n(Mn,Zn)Mn2O4 spinel. For some of the investigated steel alloys, a non-uniform,\nseveral nanometer thick Cr enriched, additional film was found at the Al2O3\nlayer. At a sufficiently high concentration, Cr can act as a substitute for Al\nduring annealing, strengthening and regenerating the original Al2O3 layer with\nCr2O3. Further analysis with secondary ion mass spectrometry allowed a reliable\ndistinction between ZnO and Zn(OH)2.", "category": "physics_app-ph" }, { "text": "Two-Dimensional Wide Dynamic Range Displacement Sensor using Dielectric\n Resonator Coupled Microwave Circuit: In this paper, the authors propose a two-dimensional, wide dynamic range,\nlinear displacement sensor using microwave methods. The microwave sensor\ncircuit employs a cylindrical dielectric resonator proximity coupled to a pair\nof orthogonal microstrip lines formed on a microwave substrate. The DR rests on\nthe substrate and is free to be displaced between the strips on the 2D plane of\nthe substrate. The strips excite the particular resonant mode of the DR, the\nintensity of which varies with the DRs proximity to the strips. The DRs\nposition can thus be read out in terms of the 2 port S parameters of the\ncircuit, at a fixed frequency determined by the resonant mode of DR. Such fixed\nfrequency sensors are robust in operation and cost effective in realization, an\nimportant aspect of this sensor. Initial one-dimensional positioning\nsimulations of the sensor through three fixed representative paths on the\nsubstrate reveal that the S parameters vary monotonically with the\ndisplacement. Prototype measurements reveal a dynamic range of 23 mm for\nhorizontal or vertical displacement, and 30 mm for diagonal displacement at the\nresonant frequency of 3.67 GHz. Next, 2D positioning test is conducted and a\ntechnique for one to one mapping from the S parameters to the 2D position is\ndemonstrated. To conclude, the proposed sensors performance is compared with\nthat of existing 2D sensors.", "category": "physics_app-ph" }, { "text": "Monolithic photonic chips for multi-channel frequency mixers and single\n photon detectors: Lithium niobate photonic chip could realize diverse optical engineering for\nvarious applications benefiting from its excellent optical performances. In\nthis letter, we demonstrate monolithic photonic chips for multi-channel\nsum-frequency conversion based on reverse-proton-exchange periodically poled\nlithium niobate waveguides, with the different channels showing uniform and\nexcellent conversion efficiencies. To obtain a robust device and provide a\nconvenient interface for applications, the integrated chip is fiber coupled\nwith two fiber arrays. The packaged chip then forms the core of a multi-channel\nup conversion single photon detector. In each channel the input signal\ninteracts with a 1950-nm single frequency pump laser and the sum frequency\noutput is spectrally filtered and detected by a silicon avalanche photodiode.\nAverage detection efficiency (DE) of 23.2 % and noise count rate (NCR) of 557\ncounts per second (cps) are achieved, with a standard deviation of 2.73 % and\n48 cps over the 30 channels, as well as optical isolation (OI) between nearby\nchannels of more than 71 dB, which are excellent for the extensive applications\nof monolithic photonic chips in fields including deep space laser\ncommunication, high-rate quantum key distribution and single-photon imaging.", "category": "physics_app-ph" }, { "text": "A pseudo-capacitive chalcogenide-based electrode with dense\n 1-dimensional nanoarrays for enhanced energy density in asymmetric\n supercapacitors: To achieve the further development of supercapacitors (SCs), which have\nintensively received attention as a next-generation energy storage system, the\nrational design of active electrode materials with electrochemically more\nfavorable structure is one of the most important factors to improve the SC\nperformance with high specific energy and power density. We propose and\nsuccessfully grow copper sulfide (CuS) nanowires (NWs) as a chalcogenide-based\nelectrode material directly on a Cu mesh current collector using the\ncombination of a facile liquid-solid chemical oxidation process and an anion\nexchange reaction. We found that the as-prepared CuS NWs have well-arrayed\nstructures with nanosized crystal grains, a high aspect ratio and density, as\nwell as a good mechanical and electrical contact to the Cu mesh. The obtained\nCuS NW based electrodes, with additional binder- and conductive material-free,\nexhibit a much higher areal capacitance of 378.0 mF/cm2 and excellent\ncyclability of an approximately 90.2 percentage retention during 2000\ncharge/discharge cycles due to their unique structural, electrical, and\nelectrochemical properties. Furthermore, for practical SC applications, an\nasymmetric supercapacitor is fabricated using active carbon as an anode and CuS\nNWs as a cathode, and exhibits the good capacitance retention of 91% during\n2000 charge/discharge processes and the excellent volumetric energy density of\n1.11 mW h/cm3 compared to other reported pseudo-capacitive SCs.", "category": "physics_app-ph" }, { "text": "True Differential Superconducting On-Chip Output Amplifier: The true-differential superconductor on-chip amplifier has complementary\noutputs that float with respect to chip ground. This improves signal integrity\nand compatibility with the receiving semiconductor stage. Both\nsource-terminated and non-source-terminated designs producing 4mV demonstrated\nrejection of a large common mode interference in the package. Measured margins\nare $\\pm$8.5% on the output bias, and $\\pm$28% on AC clock amplitude. Waveforms\nand eye diagrams are taken at 2.9-10Gb/s. Direct measurement of bit-error rates\nare better than the resolution limit of 1e-12 at 2.9Gb/s, and better than 1e-9\nat 10Gb/s.", "category": "physics_app-ph" }, { "text": "Designing heat transfer pathways for advanced thermoregulatory textiles: Thermal comfort of textiles plays an indispensable role in the process of\nhuman civilization. Advanced textile for personal thermal management shapes\nbody microclimates by merely regulating heat transfer between the skin and\nlocal ambient without wasting excess energy. Therefore, numerous efforts have\nrecently been devoted to the development of advanced thermoregulatory textiles.\nIn this review, we provide a unified perspective on those state-of-the-art\nefforts by emphasizing the design of diverse heat transfer pathways. We focus\non engineering certain physical quantities to tailor the heat transfer\npathways, such as thermal emittance/absorptance, reflectance and transmittance\nin near-infrared and mid-infrared radiation, as well as thermal conductance in\nconduction. Tuning those heat transfer pathways can achieve different\nfunctionalities for personal thermal management, such as passive cooling,\nwarming, or even dual-mode (cooling-warming), either static switching or\ndynamic adapting. Finally, we point out the challenges and opportunities in\nthis emerging field, including but not limited to the impact of evaporation and\nconvection with missing blocks of heat pathways, the bio-inspired and\nartificial-intelligence-guided design of advanced functional textiles.", "category": "physics_app-ph" }, { "text": "Investigation of gating effect in Si spin MOSFET: A gate voltage application in a Si-based spin metal-oxide-semiconductor\nfield-effect transistor (spin MOSFET) modulates spin accumulation voltages,\nwhere both electrical conductivity and drift velocity are modified while\nkeeping constant electric current. An unprecedented reduction in the spin\naccumulation voltages in a Si spin MOSFET under negative gate voltage\napplications is observed in a high electric bias current regime. To support our\nclaim, the electric bias current dependence of the spin accumulation voltage\nunder the gate voltage applications is investigated in detail and compared to a\nspin drift diffusion model including the conductance mismatch effect. We proved\nthat the drastic decrease of the mobility and spin lifetime in the Si channel\nis due to the optical phonon emission at the high electric bias current, which\nconsequently reduced the spin accumulation voltage.", "category": "physics_app-ph" }, { "text": "Cu$_2$O Microcrystals Grown on Silicon as Platform for\n Quantum-Degenerate Excitons and Rydberg States: Cuprous oxide (Cu$_2$O) is a semiconductor with large exciton binding energy\nand significant technological importance in applications such as photovoltaics\nand solar water splitting. It is also a superior material system for quantum\noptics that enabled the observation of two intriguing phenomena, i.e. Rydberg\nexcitons as solid-state analogue to highly-excited atomic states and dense\nexciton gases showing quantum degeneracy when approaching the phase transition\nto Bose-Einstein condensation. Previous experiments focused on natural bulk\ncrystals due to major difficulties in growing high-quality synthetic samples.\nHere, we present Cu$_2$O microcrystals with excellent optical material quality\ncapable of hosting both quantum-degenerate excitons and excited Rydberg states.\nGrowth of Cu$_2$O with exceedingly low point defect levels was achieved on\nsilicon by a scalable thermal oxidation process compatible with lithographic\npatterning. Using the latter, we demonstrate Rydberg excitons in\nsite-controlled Cu$_2$O microstructures, paving the way for a plethora of\napplications in integrated quantum photonics.", "category": "physics_app-ph" }, { "text": "Tetrahedral amorphous carbon resistive memories with graphene-based\n electrodes: Resistive-switching memories are alternative to Si-based ones, which face\nscaling and high power consumption issues. Tetrahedral amorphous carbon (ta-C)\nshows reversible, non-volatile resistive switching. Here we report polarity\nindependent ta-C resistive memory devices with graphene-based electrodes. Our\ndevices show ON/OFF resistance ratios$\\sim$4x$10^5$, ten times higher than with\nmetal electrodes, with no increase in switching power, and low power\ndensity$\\sim$14$\\mu$W/$\\mu$m$^2$. We attribute this to a suppressed tunneling\ncurrent due to the low density of states of graphene near the Dirac point,\nconsistent with the current-voltage characteristics derived from a quantum\npoint contact model. Our devices also have multiple resistive states. This\nallows storing more than one bit per cell. This can be exploited in a range of\nsignal processing/computing-type operations, such as implementing logic,\nproviding synaptic and neuron-like mimics, and performing analogue signal\nprocessing in non-von-Neumann architectures", "category": "physics_app-ph" }, { "text": "Monolithic superconducting emitter of tunable circularly polarized\n terahertz radiation: We propose an approach to control the polarization of terahertz (THz)\nradiation from intrinsic Josephson-junction stacks in single crystalline\nhigh-temperature superconductor $Bi_2Sr_2CaCu_2O_{8+\\delta}$. By monolithically\ncontrolling the surface current distributions in the truncated square mesa\nstructure, we can modulate the polarization of the emitted THz wave as a result\nof two orthogonal fundamental modes excited inside the mesa. Highly polarized\ncircular terahertz waves with a degree of circular polarization of more than\n99% can be generated using an electrically controlled method. The emitted\nradiation has a high intensity and a low axial ratio (AR<1 dB). The intuitive\nresults obtained from the numerical simulation based on the conventional\nantenna theory are consistent with the observed emission characteristics.", "category": "physics_app-ph" }, { "text": "Airborne Ultrasound Focusing Aperture with Binary Amplitude Mask Over\n Planar Ultrasound Emissions: Phased arrays of airborne ultrasound transducers are widely utilized as a key\ntechnology to achieve mid-air convergence of intense ultrasound, which is\napplied to a variety of systems, such as contactless tactile presentation,\nacoustic-levitation and its application, mid-air-flow acceleration, etc.\nHowever, it requires considerably precise phase control with temporally severe\nsynchronization between elements, which leads to difficulty in scaling up the\nentire system beyond the tabletop size as most of the current application\nsystems. Here, we propose a much simpler and easier scaling-up method of\nairborne ultrasound convergence, where a binary amplitude mask that serves as a\nFresnel Zone Plate (FZP) is placed on the planar in-phase ultrasound sources.\n We experimentally demonstrate that the FZP-based ultrasound focusing achieved\na spatial resolution that is comparable to conventional methods, based on the\nuse of phase-controlled transducers. The ultrasound foci created using FZPs are\nsufficiently intense for most application scenarios that are currently in\npractical use. We also determine favorable side effects of our method\nsuppressing grating lobes, which is inevitable with the conventional\nphase-controlling method.\n The FZPs and planar ultrasound sources are both readily implemented with\ninexpensive ingredients and components. The result of our study contributes to\nupsizing dimensions in which a mid-air convergent ultrasound field is\nsuccessfully generated. Accordingly, unprecedented application scenarios that\ntarget the entire room as the workspace will be possible.", "category": "physics_app-ph" }, { "text": "Porous aluminium decorated with rhodium nanoparticles, preparation and\n use as platform for UV plasmonics: There is a high current interest for novel plasmonic platforms and materials\nable to extend their applicability into the ultraviolet (UV) region of the\nelectromagnetic spectrum. In the UV it is possible to explore spectral\nproperties of biomolecules with small cross section in the visible spectral\nrange. However, most used metals in plasmonics have their resonances at\nwavelengths > 350 nm. Aluminum and rhodium are two interesting candidate\nmaterials for UV plasmonics, and in this work we developed a simple and\nlow-cost preparation of functional substrates based on nanoporous aluminum\ndecorated with rhodium nanoparticles. We demonstrate that these functionalized\nnanoporous metal films can be exploited as plasmonic materials suitable for\nenhanced UV Raman spectroscopy", "category": "physics_app-ph" }, { "text": "High performance photonic microwave filters based on a 50GHz optical\n soliton crystal Kerr micro-comb: We demonstrate a photonic radio frequency (RF) transversal filter based on an\nintegrated optical micro-comb source featuring a record low free spectral range\nof 49 GHz yielding 80 micro-comb lines across the C-band. This record-high\nnumber of taps, or wavelengths for the transversal filter results in\nsignificantly increased performance including a QRF factor more than four times\nhigher than previous results. Further, by employing both positive and negative\ntaps, an improved out-of-band rejection of up to 48.9 dB is demonstrated using\nGaussian apodization, together with a tunable centre frequency covering the RF\nspectra range, with a widely tunable 3-dB bandwidth and versatile dynamically\nadjustable filter shapes. Our experimental results match well with theory,\nshowing that our transversal filter is a competitive solution to implement\nadvanced adaptive RF filters with broad operational bandwidths, high frequency\nselectivity, high reconfigurability, and potentially reduced cost and\nfootprint. This approach is promising for applications in modern radar and\ncommunications systems.", "category": "physics_app-ph" }, { "text": "High-efficiency Ventilated Metamaterial Absorber at Low Frequency: We demonstrate a ventilated metamaterial absorber operating at low frequency\n(< 500 Hz).With only two layers of the absorption units, high-efficiency\nabsorption (> 90%) has been achieved in both simulations and experiments. This\nhigh-efficiency absorption under ventilation condition is originated from the\nweak coupling of the two identical split tube resonators constituting the\nabsorber, which leads to the hybridization of the degenerate eigenmodes and\nbreaks the absorption upper limit of 50% for conventional transmissive\nsymmetric acoustic absorbers. The absorber can also be extended to an array and\nwork in free space. The absorber should have potential applications in acoustic\nengineering where both noise reduction and ventilation are required.", "category": "physics_app-ph" }, { "text": "The Design of Programmable Transmitarray with Independent Controls of\n Transmission Amplitude and Phase: A design method of programmable transmitarray with independent controls of\ntransmission amplitude and phase is proposed in C-band. The unit cell with\ncascaded structures mainly consists of four parts, including the receiving\nantenna, reconfigurable attenuator with PIN diodes, reconfigurable phase\nshifter with varactors and transmitting antenna. Correspondingly, various\nmanipulations of spatial electromagnetic (EM) fields are achieved by varying\nthe bias voltages of PIN diodes and varactors in the transmitarray. The\nfabricated unit cell is measured in a standard waveguide, and the whole array\nwith 8*8 unit cells is measured with two horns for calibration of the\nprogrammable EM features. The experimental results show that the transmission\nmagnitude can range from -16 dB to -3.6 dB and the transmission phase achieves\n270-degree coverage independently under the 16-bit programmable control. To\nfurther exhibit the capability and functionality of the proposed transmitarray,\nthe waveform engineering of adaptive beamforming and power-allocation\nbeamforming are separately realized in the experiment. The measured results\nhave good agreements with our theoretical calculations, verifying the validity\nof our design method.", "category": "physics_app-ph" }, { "text": "An analytical relation between Weibull's and Basquin's laws for smooth\n and notched specimens and application to constant amplitude fatigue: Starting from the classical definition of stress-life Wohler curve in the\nform of Basquin's law, an analytical procedure for the calibration of the four\nparameters Wohler curve (Weibull's law) for a plain specimen is proposed. The\nobtained parameters are then adjusted by means of an additional slope factor\npreserving the inflection point of the curve while changing its slope in order\nto model the experimental observations in which an increase of the scatter in\nlife prediction is observed when reducing the stress amplitude. The same\napproach has then been adopted to calibrate the Weibull's law parameters for a\nnotched specimen, and the fitting slope factor has been found to be a value\nthat changes with the material but remains constant with the stress\nconcentration factor. The findings have been validated with existing\nexperimental data on 2024-T3 aluminum alloy and normalized SAE 4130 steel.", "category": "physics_app-ph" }, { "text": "Gain-Loss-Induced Bipolar Non-Hermitian Skin Effect With Purely\n Imaginary Eigenenergies: We study one-dimensional non-Hermitian lattices characterized by\n$\\mathcal{PT}$-symmetric gain and loss, where the real-gap transforms into an\nimaginary-gap with increasing strength of gain/loss. The energy spectrum, under\nopen boundary conditions, consists of real eigenenergies in the presence of\n$\\mathcal{PT}$-symmetry, and the corresponding eigenstates are bulk modes. As\nthe gain/loss is increased, $\\mathcal{PT}$-symmetry breaks, leading to an\nincrease in the proportion of imaginary eigenenergies and the appearance of\nbipolar Non-Hermitian skin effect (NHSE). Notably, the NHSE depending on the\nsign of their imaginary energy components. For Im$(E_{OBC})>(<)0$, the\neigenstates localize at the right (left) boundary. These findings not only\naffirm the validity of our theoretical framework but also showcase the\ncapability of engineered circuit systems to replicate intricate non-Hermitian\nphenomena. Our study unveils the unique characteristics of gain/loss-induced\nbipolar NHSE, shedding light on the exotic properties of non-Hermitian systems.", "category": "physics_app-ph" }, { "text": "Rectangular Photonic Crystal Nanobeam Cavities in Bulk Diamond: We demonstrate the fabrication of photonic crystal nanobeam cavities with\nrectangular cross section into bulk diamond. In simulation, these cavities have\nan unloaded quality factor (Q) of over 1 million. Measured cavity resonances\nshow fundamental modes with spectrometer-limited quality factors larger than\n14,000 within 1nm of the NV center's zero phonon line at 637nm. We find high\ncavity yield across the full diamond chip with deterministic resonance trends\nacross the fabricated parameter sweeps.", "category": "physics_app-ph" }, { "text": "500MHz resonant photodetector for high-quantum-effciency, low-noise\n homodyne measurement: We design and demonstrate a resonant-type differential photodetector for\nlow-noise quantum homodyne measurement at 500MHz optical sideband with 17MHz of\nbandwidth. By using a microwave monolithic amplifier and a discrete voltage\nbuffer circuit, a low-noise voltage amplifier is realized and applied to our\ndetector. 12dB of signal-to-noise ratio of the shot noise to the electric noise\nis obtained with 5mW of continuous-wave local oscillator. We analyze the\nfrequency response and the noise characteristics of a resonant photodetector,\nand the theoretical model agrees with the shot noise measurement.", "category": "physics_app-ph" }, { "text": "Influence of Temperature and Frequency on Electric Field Reduction\n Method via a Nonlinear Field Dependent Conductivity Layer Combined with\n Protruding Substrate for Power Electronics Modules: As shown in our previous studies, geometrical field grading techniques such\nas stacked and protruding substrate designs cannot well mitigate high electric\nstress issue within power electronics modules. However, it was shown that a\ncombination of protruding substrate design and applying a nonlinear\nfield-dependent conductivity layer could address the issue. Electric field (E)\nsimulations were carried out according to IEC 61287-1 for the partial discharge\ntest measurement step, where a 50/60 Hz AC voltage was applied. However,\ndielectrics, including ceramic substrate and silicone gel, in power devices\nundergo high temperatures up to a few hundred degrees and frequencies up to 1\nMHz. Thus, E values obtained with electrical parameters of the mentioned\ndielectrics for room temperature and under 50/60 Hz may not be valid for high\ntemperatures and frequencies mentioned above. In this paper, we address this\ntechnical gap through developing a finite element method (FEM) E calculation\nmodel developed in COMSOL Multiphysics where E calculations are carried out for\ndifferent temperatures up to 250 C and frequencies up to 1 MHz. Using the\nmodel, the influence of temperature and frequency on our proposed electric\nfield mitigation technique mentioned above is evaluated.", "category": "physics_app-ph" }, { "text": "An Electrically Conductive Oleogel Paste for Edible Electronics: Edible electronics will facilitate point-of-care testing through safe and\ncheap devices that are digested or degraded in the body or environment after\nperforming a specific function. Its thrive depends on creating a library of\nmaterials that are the basic building blocks for eatable technologies. Edible\nelectrical conductors fabricated with green methods that allow production at a\nlarge scale and composed of food derivatives, ingestible in large amounts\nwithout risk for human health are needed. Here, conductive pastes made with\nmaterials with a high tolerable upper intake limit (major of mg/kg body weight\n/day) are proposed. Conductive oleogel paste composites, made with\nbiodegradable and food-grade materials like natural waxes, oils, and activated\ncarbon conductive fillers, are presented. The proposed pastes are compatible\nwith manufacturing processes such as direct ink writing and thus are suitable\nfor an industrial scale-up. These conductors are built without the use of\nsolvents, and with tunable electromechanical features and adhesion depending on\nthe composition. They have antibacterial and hydrophobic properties, so that\nthey can be used in contact with food preventing contamination and preserving\nits organoleptic properties. As a proof-of-principle application, the edible\nconductive pastes are demonstrated to be effective edible contacts for food\nimpedance analysis, to be integrated for example in smart fruit labels for\nripening monitoring.", "category": "physics_app-ph" }, { "text": "Graphene Effusion-based Gas Sensor: Porous, atomically thin graphene membranes have interesting properties for\nfiltration and sieving applications because they can accommodate small pore\nsizes, while maintaining high permeability. These membranes are therefore\nreceiving much attention for novel gas and water purification applications.\nHere we show that the atomic thickness and high resonance frequency of porous\ngraphene membranes enables an effusion based gas sensing method that\ndistinguishes gases based on their molecular mass. Graphene membranes are used\nto pump gases through nanopores using optothermal forces. By monitoring the\ntime delay between the actuation force and the membrane mechanical motion, the\npermeation time-constants of various gases are shown to be significantly\ndifferent. The measured linear relation between the effusion time constant and\nthe square root of the molecular mass provides a method for sensing gases based\non their molecular mass. The presented microscopic effusion based gas sensor\ncan provide a small, low-power alternative for large, high-power,\nmass-spectrometry and optical spectrometry based gas sensing methods.", "category": "physics_app-ph" }, { "text": "Rigorous Analytical Model for Metasurface Microscopic Design with\n Interlayer Coupling: We present a semianalytical method for designing meta-atoms in multilayered\nmetasurfaces (MSs), relying on a rigorous model developed for multielement\nmetagratings. Notably, this model properly accounts for near-field coupling\neffects, allowing reliable design even for extremely small interlayer spacings,\nverified via commercial solvers. This technique forms an appealing alternative\nto the common full-wave optimization employed for MS microscopic design to\ndate.", "category": "physics_app-ph" }, { "text": "Stress-driven two-phase integral elasticity for Timoshenko curved beams: In this research, the size-dependent static behaviour of elastic curved\nstubby beams is investigated by Timoshenko kinematics. Stress-driven two-phase\nintegral elasticity is adopted to model size effects which soften or stiffen\nclassical local responses. The corresponding governing equations of nonlocal\nelasticity are established and discussed, non-classical boundary conditions are\ndetected and an effective coordinate-free solution procedure is proposed. The\npresented mixture approach is elucidated by solving simple curved small-scale\nbeams of current interest in Nanotechnology. The contributed results could be\nuseful for design and optimization of modern sensors and actuators.", "category": "physics_app-ph" }, { "text": "Anti-Stokes excitation of solid-state quantum emitters for nanoscale\n thermometry: Color centers in solids are the fundamental constituents of a plethora of\napplications such as lasers, light emitting diodes and sensors, as well as the\nfoundation of advanced quantum information and communication technologies.\nTheir photoluminescence properties are usually studied under Stokes excitation,\nin which the emitted photons are at a lower energy than the excitation ones. In\nthis work, we explore the opposite Anti-Stokes process, where excitation is\nperformed with lower energy photons. We report that the process is sufficiently\nefficient to excite even a single quantum system, namely the germanium-vacancy\ncenter in diamond. Consequently, we leverage the temperature-dependent,\nphonon-assisted mechanism to realize an all-optical nanoscale thermometry\nscheme that outperforms any homologous optical method employed to date. Our\nresults frame a promising approach for exploring fundamental light-matter\ninteractions in isolated quantum systems, and harness it towards the\nrealization of practical nanoscale thermometry and sensing.", "category": "physics_app-ph" }, { "text": "Lithium-Metal Batteries Using Sustainable Electrolyte Media and Various\n Cathode Chemistries: Lithium-metal batteries employing concentrated glyme-based electrolytes and\ndifferent cathode chemistries are herein evaluated in view of a safe use of the\nhighly energetic alkali-metal anode. Indeed, diethylene-glycol dimethyl-ether\n(DEGDME) and triethylene-glycol dimethyl-ether (TREGDME) dissolving lithium\nbis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO3) in\nconcentration approaching the solvents saturation limit are used in lithium\nbatteries employing either a conversion sulfur-tin composite (S:Sn 80:20 w/w)\nor a Li+ (de-)insertion LiFePO4 cathode. Cyclic voltammetry (CV) and\nelectrochemical impedance spectroscopy (EIS) clearly show the suitability of\nthe concentrated electrolytes in terms of process reversibility and low\ninterphase resistance, particularly upon a favorable activation. Galvanostatic\nmeasurements performed in the lithium-sulfur (Li/S) batteries reveal promising\ncapacities at room temperature (25 {\\deg}C) and a value as high as 1300 mAh\ngS-1 for DEGDME-based electrolyte at 35 {\\deg}C. On the other hand, the\nlithium-LiFePO4 (Li/LFP) cells exhibit satisfactory cycling behavior, in\nparticular when employing an additional reduction step at low voltage cutoff\n(i.e., 1.2 V) during the first discharge to consolidate the solid electrolyte\ninterphase (SEI). This procedure allows a coulombic efficiency near 100 %, a\ncapacity approaching 160 mAh g-1 and relevant retention particularly for the\ncell using TREGDME-based electrolyte. Therefore, this work suggests the use of\nconcentrated glyme-based electrolytes, the fine tuning of the operative\nconditions, and the careful selection of active materials chemistry as\nsignificant steps to achieve practical and safe lithium-metal batteries.", "category": "physics_app-ph" }, { "text": "The effect of RF-DC plasma N2-H2 in the selective hardening process for\n micro-patterned AISI420: The high density of RF-DC plasma N2-H2 was used to make precise\nmicro-texturing onto AISI420 has complex textured geometry. The original 2D\nmicro-patterns were drawn onto substrate surface by maskless patterning using\nby of nano-carbon ink. These micro-patterned specimens were further\nplasma-nitrided at 673 K for 5.4 ks by 70 Pa using the hollow cathode device.\nThe emissive light spectroscopy shows species in plasma were nitrogen atoms\ntogether with NH radicals and nitrogen molecular ions. Unprinted surface areas\nhad selectively nitrided, have high nitrogen solute contents up to 12 mass%.\nMasked area just corresponded to carbon-mapping from printed nano-carbon inks,\nwhile unprinted surface to nitrogen mapping. The hardness profile had stepwise\nchange across the borders between these printed and unprinted areas; e.g., the\nhardness on unprinted surface was 1200 Hv while it remained to be 350 Hv on\nprinted surface. This selective nitriding and hardening enabled to construct\nthe 3D textured miniature dies and products by chemical etching of printed\narea. These two peaks were related to extended martensitic lattice by high\nnitrogen extraordinary solid solution. The phase transformation from\nmartensitic lattice {\\alpha}prime-Fe through expanded phase into\n{\\epsilon}-Fe3N lattice.", "category": "physics_app-ph" }, { "text": "Electrostatic Force Suspended-Air Multilayer (EPAM) Structure for Highly\n Transparent Energy Efficient Windows: The poor thermal insulating building windows, especially single pane windows,\nare wasting ~7% of the total energy consumed by the U.S. every year. This paper\npresents an electrostatic force suspended polymer-air multilayer (EPAM)\nstructure as a highly transparent and energy efficient window retrofitting\nsolution for low-income single pane window users. To provide controllable and\nstable suspension force between large size compliant polymer films without\ndeteriorating their visual transmittance (Vt), corona discharge (CD) was\ninduced to permanently charge polymer films, leading to controllable permanent\nsurface potential difference between two sides of CD charged films.\nLiquid-solid contact electrification (CE) was combined with CD to realize\nprecise control of the surface potential of each side of polymer films. CD+CE\ntreated films can obtain programmable and stable electrostatic forces to form\nresilient EPAM structures for cost and energy effective window retrofitting\npurpose. The resilient EPAM retrofitted windows can provide U-factor lower than\n0.5 Btu/hr/ft2/{\\deg}F, Vt higher than 70%, haze lower than 1.6% at cost lower\nthan $7.4/ft2, at least 10 times cheaper than double pane windows. The energy\nsaved by EPAM can reach as much as the order of 106 kJ/m2 per year. The CD+CE\nsurface potential programming solution also provides a highly repeatable and\ncontrollable way for other electrical potential related technologies.", "category": "physics_app-ph" }, { "text": "Modeling the charging process of a coil by an HTS dynamo-type flux pump: The high-$T_c$ superconducting (HTS) dynamo exploits the nonlinear\nresistivity of an HTS tape to generate a DC voltage when subjected to a varying\nmagnetic field. This leads to the so-called flux pumping phenomenon and enables\nthe injection of DC current into a superconducting coil connected to the dynamo\nwithout current leads. In this work, the process of charging a coil by an HTS\ndynamo is examined in detail using two numerical models: the Minimum\nElectromagnetic Entropy Production and the segregated $\\textbf{H}$-formulation\nfinite element model. The numerical results are compared with an analytical\nmethod for various airgaps and frequencies. Firstly, the I-V curves of the\nmodeled HTS dynamo are calculated to obtain the open-circuit voltage,\nshort-circuit current and internal resistance. Afterward, the process of\ncharging a coil by the dynamo including the charging current curve and its\ndynamic behavior are investigated. The results obtained by the two models show\nexcellent quantitative and qualitative agreement with each other and with the\nanalytical method. Although the general charging process of the coil can be\nobtained from the I-V curve of the flux pump, the current ripples within a\ncycle of dynamo rotation, which can cause ripple AC loss in the HTS dynamo, can\nonly be captured via the presented models.", "category": "physics_app-ph" }, { "text": "Tensile material instabilities in elastic beam lattices lead to a\n bounded stability domain: Homogenization of the incremental response of grids made up of preloaded\nelastic rods leads to homogeneous effective continua which may suffer\nmacroscopic instability, occurring at the same time in both the grid and the\neffective continuum. This instability corresponds to the loss of ellipticity in\nthe effective material and the formation of localized responses as, for\ninstance, shear bands. Using lattice models of elastic rods, loss of\nellipticity has always been found to occur for stress states involving\ncompression of the rods, as usually these structural elements buckle only under\ncompression. In this way, the locus of material stability for the effective\nsolid is unbounded in tension, i.e. the material is always stable for a tensile\nprestress. A rigorous application of homogenization theory is proposed to show\nthat the inclusion of sliders (constraints imposing axial and rotational\ncontinuity, but allowing shear jumps) in the grid of rods leads to loss of\nellipticity in tension, so that the locus for material instability becomes\nbounded. This result explains (i.) how to design elastic materials passible of\nlocalization of deformation and shear banding for all radial stress paths;\n(ii.) how for all these paths a material may fail by developing strain\nlocalization and without involving cracking.", "category": "physics_app-ph" }, { "text": "Optothermal control of spin Hall nano-oscillators: We investigate the impact of localized laser heating on the auto-oscillation\nproperties of a 170 nm wide nano-constriction spin Hall nano-oscillators (SHNO)\nfabricated from a NiFe/Pt bilayer on a sapphire substrate. A 532 nm continuous\nwave laser is focused down to a spot size of about 500 nm at a power ranging\nfrom 0 to 12 mW. Through a comparison with resistive heating, we estimate a\nlocal temperature rise of about 8 K/mW. We demonstrate reversible laser tuning\nof the threshold current, the frequency, and the peak power, and find that the\nSHNO frequency can be tuned by up to 350 MHz, which is over three times more\nthan the current tuning alone. Increasing the temperature also results in\nincreased signal jitter, an increased threshold current, and a reduced maximum\ncurrent for auto-oscillations. Our results open up for optical control of\nsingle SHNOs in larger SHNO networks without the need for additional voltage\ngates.", "category": "physics_app-ph" }, { "text": "The Need for Speed: Efficient Exact Simulation of Silicon Dangling Bond\n Logic: The Silicon Dangling Bond (SiDB) logic platform, an emerging computational\nbeyond-CMOS nanotechnology, is a promising competitor due to its ability to\nachieve integration density and clock speed values that are several orders of\nmagnitude higher compared to current CMOS fabrication nodes. However, the exact\nphysical simulation of SiDB layouts, which is an essential component of any\ndesign validation workflow, is computationally expensive. In this paper, we\npropose a novel algorithm called QuickExact, which aims to be both, efficient\nand exact. To this end, we are introducing three techniques, namely 1)\nPhysically-informed Search Space Pruning, 2) Partial Solution Caching, and 3)\nEffective State Enumeration. Extensive experimental evaluations confirm that,\ncompared to the state-of-the-art algorithm, the resulting approach leads to a\nparamount runtime advantage of more than a factor of 5000 on randomly generated\nlayouts and more than a factor of 2000 on an established gate library.", "category": "physics_app-ph" }, { "text": "Enhancement of Water Repellence by Hierarchical Surface Structures\n Integrating Micro-dome and Micro-pillar Arrays with Nanoporous Coatings: Superhydrophobic surfaces with multi-scale topographies offer exceptionally\nhigh apparent water contact angles and low contact angle hysteresis by virtue\nof the small liquid{\\textendash}solid contact fractions they enable. Natural\nwater-repellent surfaces such as lotus leaves often feature dome-shaped\nmicro-scale protrusions, whose lack of sharp edges also facilitates smooth\ndroplet shedding without pinning. Engineered hydrophobic surfaces, however,\nhave not yet fully exploited the merits of protrusions with controlled\ncurvature. In this work, thermal re-flow of photoresist patterns followed by\nelastomeric casting was used to fabricate arrays of micro-domes with sizes\n20{\\textendash}50 {\\mu}m. These microstructures were coated with a nanoporous\nzinc oxide film and fluorosilanized to produce hierarchical surface\ntopographies with static water contact angles up to 169.7{\\pm}0.4{\\deg} and\ncontact angle hysteresis as low as 14.7{\\pm}1.3{\\deg}. Performance of the\nmicro-dome arrays significantly exceeded that of arrays of sharp-edged square\npillars and flat surfaces coated with the same nanoporous film. The highest\nperformance came from the smallest micro-domes (20 {\\mu}m) and closest spacings\n(10 {\\mu}m) investigated. For larger features, contact angles reduced and\nhysteresis increased {\\textemdash} unexpected trends not explained by contact\nfraction alone. This simple fabrication technique could be adapted to\nmanufacture large surfaces for droplet shedding, including in heat transfer\napplications.", "category": "physics_app-ph" }, { "text": "A novel superconducting magnetic levitation method to support the laser\n fusion capsule by using permanent magnets: A novel magnetic levitation support method is proposed, which can relieve the\nperturbation caused by traditional support methods and provide more accurate\nposition control of the capsule. This method can keep the perfect symmetry of\nthe octahedral spherical hohlraum and has the characteristics in stability,\ntunability and simplicity. It is also favorable that all the results, such as\nsupporting forces acting on the superconducting capsule, are calculated\nanalytically, and numerical simulations are performed to verify these results.\nA typical realistic design is proposed and discussed in detail. The\nsuperconducting coating material is suggested, and the required superconducting\nproperties are listed. Damped oscillation of the floating capsule in thin\nhelium gas is discussed, and the restoring time is estimated.", "category": "physics_app-ph" }, { "text": "Direct measurement of interfacial Dzyaloshinskii-Moriya interaction at\n the MoS$_{\\rm 2}$/Ni$_{80}$Fe$_{20}$ interface: We report on a direct measurement of sizable interfacial\nDzyaloshinskii-Moriya interaction (iDMI) at the interface of two-dimensional\ntransition metal dichalcogenide (2D-TMD), MoS$_{\\rm 2}$ and Ni$_{80}$Fe$_{20}$\n(Py) using Brillouin light scattering spectroscopy. A clear asymmetry in\nspin-wave dispersion is measured in MoS$_{\\rm 2}$/Py/Ta, while no such\nasymmetry is detected in the reference Py/Ta system. A linear scaling of the\nDMI constant with the inverse of Py thickness indicates the interfacial origin\nof the observed DMI. We further observe an enhancement of DMI constant in three\nto four layer MoS$_{\\rm 2}$/Py system (by 56$\\%$) as compared to 2 layer\nMoS$_{\\rm 2}$/Py which is caused by a higher density of MoO$_{\\rm 3}$ defect\nspecies in the case of three to four layer MoS$_{\\rm 2}$. The results open\npossibilities of spin-orbitronic applications utilizing the 2D-TMD based\nheterostructures.", "category": "physics_app-ph" }, { "text": "Controlling phase of microwaves with active graphene surfaces: In this letter, we report a method to control reflection phase of microwaves\nusing electrically tunable graphene devices. The device consists of mutually\ngated large-area graphene layers placed at a quarter-wave distance from a\nmetallic surface. This device structure yields electrically tunable resonance\nabsorbance and step-like phase shift around the resonance frequency when the\nimpedance of graphene matches with the free space impedance. Electrostatic\ncontrol of charge density on graphene yields an ability to control both\nintensity (> 50 dB) and phase (~pi) of the reflected electromagnetic waves with\nvoltage. Furthermore, using the asymmetry of the doping at opposite polarity of\nthe bias voltages, we showed bidirectional phase control with the applied\nvoltage. We anticipate that our results will pave a new directions to control\ninteraction of electromagnetic waves with matter for long wavelengths and could\nopen a new avenue for microwave devices.", "category": "physics_app-ph" }, { "text": "Enhanced pyroelectric and piezoelectric properties of PZT with aligned\n porosity for energy harvesting applications: This paper demonstrates the significant benefits of exploiting highly aligned\nporosity in piezoelectric and pyroelectric materials for improved energy\nharvesting performance. Porous lead zirconate (PZT) ceramics with aligned pore\nchannels and varying fractions of porosity were manufactured in a water-based\nsuspension using freeze casting. The aligned porous PZT ceramics were\ncharacterized in detail for both piezoelectric and pyroelectric properties and\ntheir energy harvesting performance figures of merit were assessed parallel and\nperpendicular to the freezing direction. As a result of the introduction of\nporosity into the ceramic microstrucutre, high piezoelectric and pyroelectric\nharvesting figures of merits were achieved for porous freeze-cast PZT compared\nto dense PZT due to the reduced permittivity and volume specific heat capacity.\nExperimental results were compared to parallel and series analytical models\nwith good agreement and the PZT with porosity aligned parallel to the freezing\ndirection exhibited the highest piezoelectric and pyroelectric harvesting\nresponse; this was a result of the enhanced interconnectivity of the\nferroelectric material along the poling direction and reduced fraction of\nunpoled material that leads to a higher polarization. A complete thermal energy\nharvesting system, composed of an parallel-aligned PZT harvester element and an\nAC/DC converter successfully demonstrated by charging a storage capacitor. The\nmaximum energy density generated by the 60 vol.% porous parallel-connected PZT\nwhen subjected to thermal oscillations was 1653 {\\mu}J/cm3 respectively, which\nwas 374% higher than that of the dense PZT with an energy density of 446\n{\\mu}J/cm3. The results are of benefit for the design and manufacture of high\nperformance porous pyroelectric and piezoelectric materials in devices for\nenergy harvesting and sensor applications.", "category": "physics_app-ph" }, { "text": "Gradient descent optimization of acoustic holograms for transcranial\n focused ultrasound: Acoustic holographic lenses, also known as acoustic holograms, can change the\nphase of a transmitted wavefront in order to shape and construct complex\nultrasound pressure fields, often for focusing the acoustic energy on a target\nregion. These lenses have been proposed for transcranial focused ultrasound\n(tFUS) to create diffraction-limited focal zones that target specific brain\nregions while compensating for skull aberration. Holograms for tFUS are\ncurrently designed using time-reversal approaches in full-wave time-domain\nnumerical simulations. However, such simulations need time-consuming\ncomputations, which severely limits the adoption of iterative optimization\nstrategies. Furthermore, in the time-reversal method, the number and\ndistribution of virtual sources can significantly influence the final sound\nfield. Because of the computational constraints, predicting these effects and\ndetermining the optimal arrangement is challenging. This study introduces an\nefficient method for designing acoustic holograms using a volumetric\nholographic technique to generate focused fields inside the skull. The proposed\nmethod combines a modified mixed-domain method for ultrasonic propagation with\na gradient descent iterative optimization algorithm. This approach enables\nsubstantially faster holographic computation than previously reported\ntechniques. The iterative process uses explicitly defined loss functions to\nbias the ultrasound field's optimization parameters to specific desired\ncharacteristics, such as axial resolution, transversal resolution, coverage,\nand focal region uniformity, while eliminating the uncertainty associated with\nvirtual sources in time-reversal techniques. Numerical studies are conducted on\nfour brain structures: the anterior insula, hippocampus, caudate nucleus, and\namygdala. The findings are further validated in underwater experiments with a\n3D-printed skull phantom.", "category": "physics_app-ph" }, { "text": "Mg-doping and free-hole properties of hot-wall MOCVD GaN: The hot-wall metal-organic chemical vapor deposition (MOCVD), previously\nshown to enable superior III-nitride material quality and high performance\ndevices, has been explored for Mg doping of GaN. We have investigated the Mg\nincorporation in a wide doping range ($2.45\\times{10}^{18}~cm^{-3}$ up to\n$1.10\\times{10}^{20}~cm^{-3}$) and demonstrate GaN:Mg with low background\nimpurity concentrations under optimized growth conditions. Dopant and impurity\nlevels are discussed in view of Ga supersaturation which provides a unified\nconcept to explain the complexity of growth conditions impact on Mg acceptor\nincorporation and compensation. The results are analysed in relation to the\nextended defects, revealed by scanning transmission electron microscopy (STEM),\nX-ray diffraction (XRD), and surface morphology, and in correlation with the\nelectrical properties obtained by Hall effect and capacitance-voltage (C-V)\nmeasurements. This allows to establish a comprehensive picture of GaN:Mg growth\nby hot-wall MOCVD providing guidance for growth parameters optimization\ndepending on the targeted application. We show that substantially lower H\nconcentration as compared to Mg acceptors can be achieved in GaN:Mg without any\nin-situ or post-growth annealing resulting in p-type conductivity in as-grown\nmaterial. State-of-the-art $p$-GaN layers with a low-resistivity and a high\nfree-hole density (0.77 $\\Omega$.cm and $8.4\\times{10}^{17}~cm^{-3}$,\nrespectively) are obtained after post-growth annealing demonstrating the\nviability of hot-wall MOCVD for growth of power electronic device structures.", "category": "physics_app-ph" }, { "text": "Highly efficient BiVO4 single-crystal nanosheets with dual modification:\n phosphorus doping and selective Ag modification: BiVO4, a visible-light response photocatalyst, has shown tremendous potential\nbecause of abundant raw material sources, good stability and low cost. There\nexist some limitations for further applicaitions due to poor capability to\nseparate electron-hole pairs. In fact, a single-component modification strategy\nis barely adequate to obtain highy efficient photocatalytic performance. In\nthis work, P substituted some of the V atoms from VO4 oxoanions, namely P was\ndoped into the V sites in the host lattice of BiVO4 by a hydrothermal route.\nMeanwhile, Ag as an attractive and efficient electron-cocatalyst was\nselectively modified on the (010) facet of BiVO4 nanosheets via facile\nphoto-deposition. As a result, the obtained dually modified BiVO4 sheets\nexhibited enhanced photocatalytic degradation property of methylene blue (MB).\nIn detail, photocatalytic rate constant (k) was 2.285 min-1g-1, which was 2.78\ntimes higher than pristine BiVO4 nanosheets. Actually, P-doping favored the\nformation of O vacancies, led to more charge carriers, and facilitated\nphotocatalytic reaction. On the other hand, metallic Ag loaded on (010) facet\neffectively transferred photogenerated electrons, which consequently helped\nelectron-hole pairs separation. The present work may enlighten new thoughts for\nsmart design and controllable synthesis of highly efficient photocatalytic\nmaterials.", "category": "physics_app-ph" }, { "text": "Dual mode microwave deflection cavities for ultrafast electron\n microscopy: This paper presents the experimental realization of an ultrafast electron\nmicroscope operating at a repetition rate of 75 MHz based on a single compact\nresonant microwave cavity operating in dual mode. This elliptical cavity\nsupports two orthogonal TM$_{110}$ modes with different resonance frequencies\nthat are driven independently. The microwave signals used to drive the two\ncavity modes are generated from higher harmonics of the same Ti:Sapphire laser\noscillator. Therefore the modes are accurately phase-locked, resulting in\nperiodic transverse deflection of electrons described by a Lissajous pattern.\nBy sending the periodically deflected beam through an aperture, ultrashort\nelectron pulses are created at a repetition rate of 75 MHz. Electron pulses\nwith $\\tau=(750\\pm10)$ fs pulse duration are created with only $(2.4\\pm0.1)$ W\nof microwave input power; with normalized rms emittances of\n$\\epsilon_{n,x}=(2.1\\pm0.2)$ pm rad and $\\epsilon_{n,y}=(1.3\\pm0.2)$ pm rad for\na peak current of $I_p=(0.4\\pm0.1)$ nA. This corresponds to an rms normalized\npeak brightness of $B_{np,\\textrm{rms}}=(7\\pm1)\\times10^6$ A/m$^2$ sr V, equal\nto previous measurements for the continuous beam. In addition, the FWHM energy\nspread of $\\Delta U = (0.90\\pm0.05)$ eV is also unaffected by the dual mode\ncavity. This allows for ultrafast pump-probe experiments at the same spatial\nresolution of the original TEM in which a 75 MHz Ti:Sapphire oscillator can be\nused for exciting the sample. Moreover, the dual mode cavity can be used as a\nstreak camera or time-of-flight EELS detector with a dynamic range $>10^4$.", "category": "physics_app-ph" }, { "text": "Magnetic Particle Spectroscopy (MPS) with One-stage Lock-in\n Implementation for Magnetic Bioassays with Improved Sensitivities: In recent years, magnetic particle spectroscopy (MPS) has become a highly\nsensitive and versatile sensing technique for quantitative bioassays. It relies\non the dynamic magnetic responses of magnetic nanoparticles (MNPs) for the\ndetection of target analytes in liquid phase. There are many research studies\nreporting the application of MPS for detecting a variety of analytes including\nviruses, toxins, and nucleic acids, etc. Herein, we report a modified version\nof MPS platform with the addition of a one-stage lock-in design to remove the\nfeedthrough signals induced by external driving magnetic fields, thus capturing\nonly MNP responses for improved system sensitivity. This one-stage lock-in MPS\nsystem is able to detect as low as 781 ng multi-core Nanomag50 iron oxide MNPs\n(micromod Partikeltechnologie GmbH) and 78 ng single-core SHB30 iron oxide MNPs\n(Ocean NanoTech). In addition, using a streptavidin-biotin binding system as a\nproof-of-concept, we show that these single-core SHB30 MNPs can be used for\nBrownian relaxation-based bioassays while the multi-core Nanomag50 cannot be\nused. The effects of MNP amount on the concentration dependent response\nprofiles for detecting streptavidin was also investigated. Results show that by\nusing lower concentration/amount of MNPs, concentration-response curves shift\nto lower concentration/amount of target analytes. This lower\nconcentrationresponse indicates the possibility of improved bioassay\nsensitivities by using lower amounts of MNPs.", "category": "physics_app-ph" }, { "text": "Photoelectrocatalytic detection of NADH on n-type silicon semiconductors\n facilitated by carbon nanotube fibers: NADH is a key biomolecule involved in many biocatalytic processes as cofactor\nand its quantification can be correlated to specific enzymatic activity. Many\nefforts have been taken to obtain clean electrochemical signals related to NADH\npresence and lower its redox overpotential to avoid interferences. Suppression\nof background and secondary signals can be achieved by including a switchable\nelectroactive surface, for instance, by using semiconductors able to harvest\nlight energy and drive the excited electrons only when irradiated. Here we\npresent the combination of a n-type Si semiconductor with fibers made of carbon\nnanotubes as electroactive surface for NADH quantification at low potentials\nonly upon irradiation. The resulting photoelectrode responded linearly to NADH\nconcentrations from 50 {\\mu} M to 1.6 mM with high sensitivity (54 $\\mu$ A\ncm$^{-2}$ mM${-1}$). This system may serve as a biosensing platform for\ndetection and quantification of dehydrogenases activity.", "category": "physics_app-ph" }, { "text": "Electrothermal equivalent three-dimensional Finite Element Model of a\n single neuron: Objective: We propose a novel approach for modelling the inter-dependence of\nelectrical and mechanical phenomena in nervous cells, by using electro-thermal\nequivalences in finite element (FE) analysis so that existing thermo-mechanical\ntools can be applied. Methods: First, the equivalence between electrical and\nthermal properties of the nerve materials is established, and results of a pure\nheat conduction analysis performed in Abaqus CAE Software 6.13-3 are validated\nwith analytical solutions for a range of steady and transient conditions. This\nvalidation includes the definition of equivalent active membrane properties\nthat enable prediction of the action potential. Then, as a step towards fully\ncoupled models, electromechanical coupling is implemented through the\ndefinition of equivalent piezoelectric properties of the nerve membrane using\nthe thermal expansion coefficient, enabling prediction of the mechanical\nresponse of the nerve to the action potential. Results: Results of the coupled\nelectro-mechanical model are validated with previously published experimental\nresults of deformation for the squid giant axon, crab nerve fibre and garfish\nolfactory nerve fibre. Conclusion: A simplified coupled electro-mechanical\nmodelling approach is established through an electro-thermal equivalent FE\nmodel of a nervous cell for biomedical applications. Significance: One of the\nkey findings is the mechanical characterization of the neural activity in a\ncoupled electro-mechanical domain, which provides insights into the\nelectromechanical behaviour of nervous cells, such as thinning of the membrane.\nThis is a first step towards modelling 3D electromechanical alteration induced\nby trauma at nerve bundle, tissue and organ levels.", "category": "physics_app-ph" }, { "text": "48 channels 100-GHz tunable laser by integrating 16 DFB lasers with high\n wavelength-spacing uniformity: We report a 48-channel 100-GHz tunable laser near 1550 nm by integrating 16\nDFB lasers. High wavelength-spacing uniformity is guaranteed by the\nreconstruction-equivalent-chirp technique, which enables a temperature tuning\nrange below 20 Celsius degree.", "category": "physics_app-ph" }, { "text": "Lock-in thermography using diamond quantum sensors: Precise measurement of temperature distribution and thermal behavior in\nmicroscopic regions is critical in many research fields. We demonstrate lock-in\nthermography using nitrogen-vacancy centers in diamond nanoparticles. We\nsuccessfully visualize thermal diffusion in glass coverslip and Teflon with\nmicrometer resolution and deduce their thermal diffusivity. By spreading\ndiamond nanoparticles over the sample surface, temperature variation can be\nmeasured directly without any physical contact, such as lead wires, making it\npossible to visualize the micrometer-scale thermal behavior of various\nmaterials.", "category": "physics_app-ph" }, { "text": "Bulk Electronic Structure of Lanthanum Hexaboride (LaB6) by Hard X-ray\n Angle-Resolved Photoelectron Spectroscopy: In the last decade rare-earth hexaborides have been investigated for their\nfundamental importance in condensed matter physics, and for their applications\nin advanced technological fields. Among these compounds, LaB$_6$ has a special\nplace, being a traditional d-band metal without additional f- bands. In this\npaper we investigate the bulk electronic structure of LaB$_6$ using hard x-ray\nphotoemission spectroscopy, measuring both core-level and angle-resolved\nvalence-band spectra. By comparing La 3d core level spectra to cluster model\ncalculations, we identify well-screened peak residing at a lower binding energy\ncompared to the main poorly-screened peak; the relative intensity between these\npeaks depends on how strong the hybridization is between La and B atoms. We\nshow that the recoil effect, negligible in the soft x-ray regime, becomes\nprominent at higher kinetic energies for lighter elements, such as boron, but\nis still negligible for heavy elements, such as lanthanum. In addition, we\nreport the bulk-like band structure of LaB$_6$ determined by hard x-ray\nangle-resolved photoemission spectroscopy (HARPES). We interpret HARPES\nexperimental results by the free-electron final-state calculations and by the\nmore precise one-step photoemission theory including matrix element and phonon\nexcitation effects. In addition, we consider the nature and the magnitude of\nphonon excitations in HARPES experimental data measured at different\ntemperatures and excitation energies. We demonstrate that one step theory of\nphotoemission and HARPES experiments provide, at present, the only approach\ncapable of probing true bulk-like electronic band structure of rare-earth\nhexaborides and strongly correlated materials.", "category": "physics_app-ph" }, { "text": "On the development of a new coplanar transmission line based on Gap\n Waveguide: A combination of gap waveguide technology and the traditional coplanar\nwaveguide is studied in detail and demonstrated experimentally for the first\ntime. This novel metamaterial transmission line is presented in three different\nconfigurations and offers a broadband operation, low loss, and low dispersion\ncharacteristics. Analytical expressions for its characteristic impedance and\neffective permittivity are provided and validated by Finite Element Method\nsimulations. The loss and dispersion of the line are analyzed with an Eigenmode\nsolver. The proposed line prevents the propagation of substrate modes in the\nband of operation at the same time it reduces the dielectric loss in the line\ndue to a higher concentration of the E-field over the air. Moreover, its\ncoplanar layout facilitates the integration of active components. As such, it\nis considered to constitute a potential key element in the development of more\nefficient, millimeter wave systems.", "category": "physics_app-ph" }, { "text": "Deformed Butler-Volmer Models for Convex Semilogarithmic\n Current-Overpotential Profiles of Li-ion Batteries: The Butler-Volmer (BV) equation links the current flux crossing an\nelectrochemical interface to the electric potential drop across it with the\nassumption of Arrhenius kinetics and the Boltzmann factor. Applying the\nsemilogarithmic Tafel analysis in which the logarithm of current is plotted vs.\nthe overpotential one expects straight lines from which the fundamental\nreaction rate of the kinetic process can be computed. However, some Li-ion\nbattery data, which is the focus here, show nonlinear convex profiles that\ncannot be adequately fitted with the standard BV model. We propose instead two\ndeformed BV models for the analysis of such types of behaviors constructed from\nthe superposition of cells exhibiting only local equilibrium and thus giving\nrise to the power-law $q$-exponential and $\\kappa$-exponential functions.\nNon-Boltzmann distributions have been successfully employed for the modeling of\na wide spectrum of physical systems in nonequilibrium situations, but not yet\nfor batteries. We verify the validity of the deformed BV models on experimental\ndata obtained from \\ce{LiFePO4} and \\ce{Li}-\\ce{O2} batteries.", "category": "physics_app-ph" }, { "text": "Cost-Effective Methods to Nanopattern Thermally Stable Platforms on\n Kapton HN Flexible Films Using Inkjet Printing Technology to Produce\n Printable Nitrate Sensors, Mercury Aptasensors, Protein Sensors, and Organic\n Thin Film Transistors: Kapton HN films, adopted worldwide due to their superior thermal durability\n(up to 400 {\\deg}C), allow the high temperature sintering of nanoparticle based\nmetal inks. By carefully selecting inks and Kapton substrates, outstanding\nthermal stability and anti-delaminating features are obtained in both aqueous\nand organic solutions and were applied to four novel devices: a solid state ion\nselective nitrate sensor, an ssDNA based mercury aptasensor, a low cost protein\nsensor, and a long lasting organic thin film transistor (OTFT). Many\nexperimental studies on parameter combinations were conducted during the\ndevelopment of the above devices. The results showed that the ion selective\nnitrate sensor displayed a linear sensitivity range with a limit of detection\nof 2 ppm. The mercury sensor exhibited a linear correlation between the RCT\nvalues and the increasing concentrations of mercury. The protein printed\ncircuit board (PCB) sensor provided a much simpler method of protein detection.\nFinally, the OTFT demonstrated a stable performance with mobility values for\nthe linear and saturation regimes, and the threshold voltage. These devices\nhave shown their value and reveal possibilities that could be pursued.", "category": "physics_app-ph" }, { "text": "Spin-orbit torque based physical unclonable function: This paper introduces the concept of spin-orbit-torque-MRAM (SOT-MRAM) based\nphysical unclonable function (PUF). The secret of the PUF is stored into a\nrandom state of a matrix of perpendicular SOT-MRAMs. Here, we show\nexperimentally and with micromagnetic simulations that this random state is\ndriven by the intrinsic nonlinear dynamics of the free layer of the memory\nexcited by the SOT. In detail, a large enough current drives the magnetization\nalong an in-plane direction. Once the current is removed, the in-plane magnetic\nstate becomes unstable evolving towards one of the two perpendicular stable\nconfigurations randomly. In addition, an hybrid CMOS/spintronics model is used\nto evaluate the electrical characteristics of a PUF realized with an array of\n16x16 SOT-MRAM cells. Beyond robustness against voltage and temperature\nvariations, hardware authentication based on this PUF scheme has additional\nadvantages over other PUF technologies such as non-volatility (no power\nconsumption in standby mode), reconfigurability (the secret can be rewritten),\nand scalability. We believe that this work is a step forward the design of\nspintronic devices for application in security.", "category": "physics_app-ph" }, { "text": "Two-dimensional thermal finite element model of directed energy\n deposition: matching melt pool temperature profile with pyrometer measurement: An open source two-dimensional (2D) thermal finite element (FE) model of the\nDirected Energy Deposition (DED) process is developed using the Python-based\nFEniCS framework. The model incrementally deposits material ahead of the laser\nfocus point according to the geometry of the part. The laser heat energy is\nsupplied by a Gaussian-distributed heat source while the phase change is\nrepresented by increased heat capacity around the solidus-liquidus temperature\nrange. Experimental validation of the numerical model is performed by matching\nwith the melt pool temperature measurements taken by a dual wavelength\npyrometer during the build process of a box-shaped Ti--6Al--4V part with large\ngeometrical voids. Effects of large geometrical voids on the melt pool shape\nand maximum melt pool temperature are examined. Both the numerical and\nexperimental data show an increase in the melt pool size and temperature during\ndeposition above large voids. The trailing edge of the melt pool's temperature\nprofile obtained using the developed numerical model closely matches pyrometer\nmeasurements.", "category": "physics_app-ph" }, { "text": "Numerical Analysis Investigation of Acoustic Shadow Moir\u00e9 Interference: Acoustic shadow moir\\'e has unique properties to be used for many potential\napplications in medical diagnostics, manufacturing, and material\ncharacterization. In this paper, numerical analysis, using Comsol, is used to\ninvestigate the principles of acoustic moir\\'e interference phenomenon. The\nstudy confirmed that the expected fringe images of shadow interference can be\ncreated at Talbot distances. The study confirms the experimental results\nreported by this group [1] and proves without any doubt that acoustic moir\\'e\ninterference phenomenon exists.", "category": "physics_app-ph" }, { "text": "Resistance of Hall Sensors Based on Graphene to Neutron Radiation: An in-situ study of Hall sensors based on single-layered graphene in neutron\nfluxes of a nuclear reactor to the fluence of 1.5e20 n/sq,m was conducted. The\nsensitivity of the sensors to the magnetic field remained stable throughout the\nexperiment, while the resistance changes correlated with the increase in sample\ntemperature due to radiation heating. The experiment confirmed the theoretical\nexpectations regarding the high stability of graphene sensors to neutron\nirradiation. Necessary further improvement of sensor technology to optimize\ntheir characteristics, as well as radiation testing to determine the maximum\npermissible neutron fluence.", "category": "physics_app-ph" }, { "text": "An Antenna Array Initial Condition Calibration Method for Integrated\n Optical Phased Array: This paper presents a modified rotating element electric field vector\n(modified REV) method to calibrate the antenna array initial condition of an\noptical phased array (OPA) device. The new method follows a similar sequential\nindividual antenna phase calibration process while it modifies the algorithm to\navoid possible {\\pi} phase error in traditional REV when large initial phase\ndistribution and finite optical power measurement accuracy present. We show\nthat the method produces statistically more accurate and predictable\ncalibration result which is highly desired in practice.", "category": "physics_app-ph" }, { "text": "Theoretical Analysis of Terahertz Detection of Resonant Tunneling Diodes: We analyze the terahertz detection characteristics of resonant tunneling\ndiodes (RTDs) using a set of simple equations that covers three detection\nmodes; (i) direct detection, (ii) amplified detection, and (iii) self-homodyne\n(coherent) detection. (i) and (ii) are based on the square-law detection, and\n(iii) is on the homodyne detection with the RTD used as an injection-locked\nlocal oscillator. The calculated results exhibit small- and large-signal areas\ndepending on irradiation power. In the small-signal area, the detection current\nis proportional to irradiated power for (i) and (ii), and to square root of\nirradiated power for (iii). The detection current has a peak at the bias\nvoltage at the boundary between (ii) and (iii). Effect of frequency fluctuation\nof irradiated wave is analyzed for (iii), and it is shown that the detection\ncurrent is proportional to irradiated power if the fluctuation becomes wider\nthan injection-locking range. The analytical results in this paper reasonably\nexplain the reported experiments.", "category": "physics_app-ph" }, { "text": "Structural Lens Based on Variable Thickness Structures: In this article, we report a lens design based on a concentric circular\nstructure with continuous changing of thickness defined in a thin plate\nstructure for focusing a plane wave into three spots (triple focusing) and for\nsplitting elastic waves emanating from a point source into three collimated\nbeams of different directions (three-beam splitting). Inspired by the principle\nof optical graded index triple focusing lens, the governing equations of the\ngradient refractive index profiles necessary for achieving such structural lens\nwere obtained. The refractive index profiles were realized by using a lens\ndesign with two concentric circular areas of different thickness variation\nprofiles defined in a thin plate. Analytical, numerical, and experimental\nstudies were conducted to investigate the functionalities of the variable\nthickness structural lens. The results showed that the lens developed in this\nstudy were able to perform triple focusing and three-beam splitting with\nbroadband property. Furthermore, the locations of focal points and directions\nof collimated beams can be engineered by changing the lens thickness profiles\naccording to the governing equations. In addition, the proposed lens is\nminiature and simple design, which overcome the limitations of previous triple\nfocusing and beam splitters.", "category": "physics_app-ph" }, { "text": "Upper Critical Field Based on the Width of $\u0394$H = $\u0394$B region\n in a Superconductor: We studied a method of measuring upper critical field (H$_{c2}$) of a\nsuperconductor based on the width of $\\Delta$H = $\\Delta$B region, which\nappears in the superconductor that volume defects are many and dominant. Here\nwe present the basic concept and details of the method. Although H$_{c2}$ of a\nsuperconductor is fixed according to kind of the superconductor, it is\ndifficult to measure H$_{c2}$ experimentally, and the results are different\ndepending on the experimental conditions. H$_{c2}$ was calculated from the\ntheory that pinned fluxes at volume defects are picked out and move into an\ninside of the superconductor when their arrangement is the same as that of\nH$_{c2}$ state of the superconductor. H$_{c2}$ of MgB$_2$ obtained by the\nmethod was 65.4 Tesla at 0 K. The reason that H$_{c2}$ obtained by the method\nis closer to ultimate H$_{c2}$ is based on that\n$\\Delta$F$_{pinning}$/$\\Delta$F$_{pickout}$ is more than 4 when pinned fluxes\nat volume defects of 163 nm radius are picked out. The method will help to find\nthe ultimate H$_{c2}$ of volume defect-dominating superconductors.", "category": "physics_app-ph" }, { "text": "Numerical modeling of active thermo-plasmonics experiments: In this paper, we present a simple and robust numerical method able to\npredict, with high accuracy, the photo-thermal effects occurring for a gold\nnanoparticles arrangement under externally applied strain. The physical system\nis numerically implemented in the COMSOL Multiphysics simulation platform. The\ngold nanoparticles distributions are excited by linearly polarized light. By\nconsidering the system at rest and under the action of a mechanical stress, we\nanalyze the extinction cross section, and we observe the production of heat at\nthe nanoscale. The purpose of this work is to describe how sensitive the local\ntemperature of the gold nanoparticles arrangement is to the formation of\nlocalized photo-thermal hot spots.", "category": "physics_app-ph" }, { "text": "Sensitive capacitive pressure sensors based on graphene membrane arrays: The high flexibility, impermeability and strength of graphene membranes are\nkey properties that can enable the next generation of nanomechanical sensors.\nHowever, for capacitive pressure sensors the sensitivity offered by a single\nsuspended graphene membrane is too small to compete with commercial sensors.\nHere, we realize highly sensitive capacitive pressure sensors consisting of\narrays of nearly ten thousand small, freestanding double-layer graphene\nmembranes. We fabricate large arrays of small diameter membranes using a\nprocedure that maintains the superior material and mechanical properties of\ngraphene, even after high-temperature anneals. These sensors are readout using\na low cost battery-powered circuit board, with a responsivity of up to 47.8 aF\nPa$^{-1}$ mm$^{-2}$, thereby outperforming commercial sensors.", "category": "physics_app-ph" }, { "text": "High Performance Direct-Current Generator Based on Dynamic PN Junctions: After the electromagnetic generator, searching for novel electric generators\nwithout strong magnetic field is highly demanded. The generator without strong\nmagnetic field calls for a physical picture distinct from the traditional\ngenerators. As the counterpart of the static PN junction has been widely used\nin the integrated circuits, we develop an electric generator named dynamic PN\ngenerator with a high current density and voltage output, which converts\nmechanical energy into electricity by sliding two semiconductors with different\nFermi level. A dynamic N-GaAs/SiO2/P-Si generator with the open-circuit voltage\nof 3.1 V and short-circuit density of 1.0 A/m2 have been achieved. The physical\nmechanism of the dynamic PN generator is proposed based on the built-in\nelectric field bounding back diffusing carriers in dynamic PN junctions, which\nbreaks the equilibrium between drift and diffusion current in the PN junction.\nMoreover, the dynamic MoS2/AlN/Si generator with the open-circuit voltage of\n5.1 V and short-circuit density of 112 A/m2 (11.2 mA/cm2) have also been\nachieved, which can effectively output a direct-current and light up a blue\nlight-emitting diode directly. This dynamic MoS2/AlN/Si generator can\ncontinuously work for hours without obvious degradation, demonstrating its\nunique mechanism and potential applications in many fields where the mechanical\nenergy is available.", "category": "physics_app-ph" }, { "text": "Nanomechanical Design Strategy for Single-Mode Optomechanical\n Measurement: The motion of a mechanical resonator is intrinsically decomposed over a\ncollection of normal modes of vibration. When the resonator is used as a\nsensor, its multimode nature often deteriorates or limits its performance and\nsensitivity. This challenge is frequently encountered in state-of-the-art\noptomechanical sensing platforms. We present a mechanical design strategy that\nensures that optomechanical measurements can retrieve information on a single\nmechanical degree of freedom, and implement it in a sliced photonic crystal\nnanobeam resonator. A spectral design approach is used to make mechanical\nsymmetries robust against practical disorder. The effectiveness of the method\nis evaluated by deriving a relevant figure of merit for continuous and pulsed\nmeasurement application scenarios. The method can be employed in any mechanical\ndesign that presents unwanted spurious mechanical modes. In the nanobeam\nplatform, we experimentally show an increase of the signal to noise ratio of\nthe mode of interest over the first spurious mode by four orders of magnitudes.", "category": "physics_app-ph" }, { "text": "Shaping THz emission spectra by using sub-wavelength nanopatterned\n spintronic THz emitters: We show in theory and experiment that in periodically patterned spintronic\nTHz emitters (STE), charge dynamics can modify the emission spectrum in a\nwell-controlled way. Characterization of sub-wavelength patterned STE at\nfrequencies up to 30 THz shows that the STE's emission spectrum systematically\nchanges with emitter size. The spectral intensity exhibits significant\nreductions at frequencies below 4 THz, accompanied by pronounced dips at around\n15 THz and 24 THz. While reducing the STE size enhances the modulation of all\nfeatures, it does not alter the dip frequencies. The effect originates from the\ncharging of the structure's edges by THz currents, causing a backflow that\ninterferes with the primary current pulse. An analytical model quantitatively\nreproduces these results and agrees well with control experiments. Our findings\nenable a detailed investigation of the charge dynamics in STE and provide\nadditional means for controlled shaping of STE emission spectra by nano\npatterning.", "category": "physics_app-ph" }, { "text": "Formation of Uniform Crystal and Reduction of Electrical Variation in\n HfZrO$_2$ Ferroelectric Memory by Thermal Engineering: In this paper we proclaim excellent variation control in\nHf$_{0.5}$Zr$_{0.5}$O$_2$ based ferroelectric films obtained by germination of\nlarge ferroelectric domain via extended duration of thermal annealing. 10nm\nthick Hf$_{0.5}$Zr$_{0.5}$O$_2$ based ferroelectric capacitors with TiN as\nbottom and top electrodes are fabricated and characterized. The duration of\nrapid thermal annealing (RTA) is varied to observe its effect on crystal\nformation and device electrical properties at 700C. The device to device\nvariation in terms of coercive voltage and peak capacitance are reduced from\n0.4V to 0.01V and from 2*$10^{-5}$nF/cm$^2$ to 4*$10^{-6}$nF/cm$^2$,\nrespectively, by increasing the RTA duration. High resolution transmission\nelectron micrograph clearly shows large and uniform ferroelectric domains with\nRTA of 180 seconds. Extended duration of RTA likely allows uniform crystal to\nform, which mitigates the stochasticity of the distribution of ferroelectric\nand paraelectric domains, and deterministic switching has been infused. This\nimprovement paves the way for implementing Hf$_{0.5}$Zr$_{0.5}$O$_2$ based\ndeeply scaled devices for memory and steep slope device applications.", "category": "physics_app-ph" }, { "text": "Reducing the metal-graphene contact resistance through laser-induced\n defects: Graphene has been extensively studied for a variety of electronic and\noptoelectronic applications. The reported contact resistance between metal and\ngraphene, or rather its specific contact resistance (R{_C}), ranges from a few\ntens of {\\Omega} {\\mu}m up to a few k{\\Omega} {\\mu}m. Manufacturable solutions\nfor defining ohmic contacts to graphene remain a subject of research. Here, we\nreport a scalable method based on laser irradiation of graphene to reduce the\nR{_C} in nickel-contacted devices. A laser with a wavelength of {\\lambda} = 532\nnm is used to induce defects at the contact regions, which are monitored\n\\textit{in-situ} using micro-Raman spectroscopy. Physical damage is observed\nusing \\textit{ex-situ} atomic force and scanning electron microscopy. The\ntransfer line method (TLM) is used to extract R{_C} from back-gated graphene\ndevices with and without laser treatment under ambient and vacuum conditions. A\nsignificant reduction in R{_C} is observed in devices where the contacts are\nlaser irradiated, which scales with the laser power. The lowest R{_C} of about\n250 {\\Omega} {\\mu}m is obtained for the devices irradiated with a laser power\nof 20 mW, compared to 900 {\\Omega} {\\mu}m for the untreated devices. The\nreduction is attributed to an increase in defect density, which leads to the\nformation of crystallite edges and in-plane dangling bonds that enhance the\ninjection of charge carriers from the metal into the graphene. Our work\nsuggests laser irradiation as a scalable technology for R{_C} reduction in\ngraphene and potentially other two-dimensional materials.", "category": "physics_app-ph" }, { "text": "Realization of Flattened Structural Luneburg Lens Based on\n Quasi-Conformal Transformation: Conventional structural Luneburg lens is a symmetric circular gradient-index\nlens with refractive indices decreasing from the centre along the radial\ndirection. In this paper, a flattened structural Luneburg lens (FSLL) based on\nstructural thickness variations is designed by using the quasi-conformal\ntransformation (QCT) technique. Through numerical simulations and experimental\nstudies, the FSLL is demonstrated to have excellent beam steering performance\nfor the manipulation of flexural wave propagation at desired angles.", "category": "physics_app-ph" }, { "text": "Analytical solutions for single and multiple scattering from\n rib-stiffened plates in water: The interaction of an acoustic plane wave with a pair of plates connected by\nperiodically spaced stiffeners in water is considered. The rib-stiffened\nstructure is called a \"flex-layer\" because its low frequency response is\ndominated by bending stiffness. The quasi-static behavior is equivalent a\nhomogeneous layer of compressible fluid, which we identify as air for the\npurposes of comparison. In this way an air layer is acoustically the same as a\npair of thin elastic plates connected by a periodic spacing of ribs. At\ndiscrete higher frequencies the flex-layer exhibits perfect acoustic\ntransmission, the cause of which is identified as fluid-loaded plate waves\npropagating back and forth between the ribs. Both the low and finite frequency\nbehavior of the flex-layer are fully explained by closed-form solutions for\nreflection and transmission. The analytical model is extended to two\nflex-layers in series, introducing new low and high frequency phenomena that\nare explained in terms of simple lumped parameter models.", "category": "physics_app-ph" }, { "text": "Spatial Mapping of Powder Layer Density for Metal Additive Manufacturing\n via X-ray Microscopy: Uniform powder spreading is a requisite for creating consistent, high-quality\ncomponents via powder bed additive manufacturing (AM), wherein layer density\nand uniformity are complex functions of powder characteristics, spreading\nkinematics, and mechanical boundary conditions. High spatial variation in\nparticle packing density, driven by the stochastic nature of the spreading\nprocess, impedes optical interrogation of these layer attributes. Thus, we\npresent transmission X-ray imaging as a method for directly mapping the\neffective depth of powder layers at process-relevant scale and resolution.\nSpecifically, we study layers of nominal 50-250 micrometer thickness, created\nby spreading a selection of commercially obtained Ti-6Al-4V, 316 SS, and\nAl-10Si-Mg powders into precision-depth templates. We find that powder layer\npacking fraction may be predicted from a combination of the relative thickness\nof the layer as compared to mean particle size, and flowability assessed by\nmacroscale powder angle of repose. Power spectral density analysis is\nintroduced as a tool for quantification of defect severity as a function of\nmorphology, and enables separate consideration of layer uniformity and\nsparsity. Finally, spreading is studied using multi-layer templates, providing\ninsight into how particles interact with both previously deposited material and\nabrupt changes in boundary condition. Experimental results are additionally\ncompared to a purpose-built discrete element method (DEM) powder spreading\nsimulation framework, clarifying the competing role of adhesive and\ngravitational forces in layer uniformity and density, as well as particle\nmotion within the powder bed during spreading.", "category": "physics_app-ph" }, { "text": "Laboratory application of sampling approaches to inverse scattering: This study presents an experimental investigation of the recently established\ngeneralized linear sampling method (GLSM) for non-destructive evaluation of\ndamage in elastic materials. To this end, ultrasonic shear waves are generated\nin a prismatic slab of charcoal granite featuring a discontinuity interface\ninduced by the three-point bending (3PB). The interaction of probing waves with\nthe 3PB-induced damage gives rise to transient velocity responses measured on\nthe sample's boundary by a 3D scanning laser Doppler vibrometer. Thus obtained\nwaveform data are then carefully processed to retrieve the associated spectra\nof scattered displacement fields. On deploying multifrequency sensory data, the\nGLSM indicators are computed and their counterparts associated with the\nclassical linear sampling method (LSM) for comparative analysis. Verified with\nin-situ observations, the GLSM map successfully exposes the support of hidden\nscatterers in the specimen with a remarkable clarity and resolution compared to\nits predecessor LSM. It is further shown that the GLSM remains robust for\nsparse and partial-aperture data inversion, thanks to its rigorous formulation.\nFor completeness, the one-sided reconstruction by both indicators is\ninvestigated.", "category": "physics_app-ph" }, { "text": "Arc Discharge Carbon Nanoonions Purification by Liquid-Liquid Extraction: Carbon nanoonions are novel carbon nanoestructures that have potential\napplications in fields like electronics and chemical catalysis. Here we report\na very simple but effective method of purifying carbon nanoonions produced by\nsubmerged arc discharge in water based on the water-toluene liquid-liquid\nextraction. Purified and non-purified samples were characterized by atomic\nforce microscopy, high resolution transmission electronic microscopy and\nBrunauer-Emmett-Teller gas adsorption isotherms method. Microscopy results\nshowed a good purification and allowed the assessment of the particles diameter\ndistribution. Specific surface area was measured showing a great increment from\n(14.7 +- 0.3) m2/g for the non-purified sample to (170 +- 3) m2/g for the\npurified sample. Average particles diameter was also assessed from the\nadsorption isotherms; the diameter values obtained by the three techniques were\nin good agreement being between 20 to 30 nm.", "category": "physics_app-ph" }, { "text": "Nanomechanical Spectroscopy of Ultrathin Silicon Nitride Suspended\n Membranes: Mechanical properties of a nanomechanical resonator have a significant impact\non the performance of a resonant Nano-electromechanical system (NEMS) device.\nHere we study the mechanical properties of suspended membranes fabricated out\nof low-pressure chemical vapor deposited silicon nitride thin films.\nDoubly-clamped membranes of silicon nitride with thickness less than 50 nm and\nlength varying from 5 um to 60 um were fabricated. The elastic modulus and\nstress in the suspended membranes were measured using Atomic Force Microscope\n(AFM)-based nanomechanical spectroscopy. The elastic modulus of the suspended\nmembranes was found to be significantly higher than those of corresponding thin\nfilms on the substrate. A reduction in the net stress after the fabrication of\nsuspended membrane was observed and is explained by estimating the\ncontributions of thermal stress and intrinsic stress. We establish a\nmathematical model to calculate the normalized elastic modulus of a suspended\nmembrane. Lastly, we study the capillary force-gradient between the SiNx\nsuspended membrane-Si substrate that could collapse the suspended membrane.", "category": "physics_app-ph" }, { "text": "Active metamaterials with negative static electric susceptibility: Well-established textbook arguments suggest that static electric\nsusceptibility must be positive in \"all bodies\" [1]. However, it has been\npointed out that media that are not in thermodynamic equilibrium are not\nnecessarily subject to this restriction; negative static electric\nsusceptibility has been predicted theoretically in systems with inverted\npopulations of atomic and molecular energy levels [2,3], though this has never\nbeen confirmed experimentally. Here we exploit the design freedom afforded by\nmetamaterials to fabricate active structures that exhibit the first\nexperimental evidence of negative static electric susceptibility. Unlike the\nsystems envisioned previously---which were expected to require reduced\ntemperature and pressure---negative values are readily achieved at room\ntemperature and pressure. Further, values are readily tuneable throughout the\nnegative range of stability -1<\\chi^{(0)}<0, resulting in magnitudes that are\nover one thousand times greater than predicted previously [4]. This opens the\ndoor to new technological capabilities such as stable electrostatic levitation.", "category": "physics_app-ph" }, { "text": "Correlation of interface transmission in THz spintronic emitters with\n spin mixing conductance in spin pumping experiments: The field of THz spintronics is a novel direction in the research field of\nspintronics that combines magnetism with optical physics and ultrafast\nphotonics. The experimental scheme of the field involves the use of femtosecond\nlaser pulses to trigger ultrafast spin and charge dynamics in bilayers composed\nof ferromagnetic (FM) and non-magnetic (NM) thin films where the NM layer\nfeatures a strong spin-orbit coupling. The key technological and scientific\nchallenges of THz spintronic emitters is to increase their intensity and\nfrequency bandwidth. To achieve this the control of the source of the\nradiation, namely the transport of the ultrafast spin current is required.\nHowever, the transfer of a spin current from a FM to a NM layer is a highly\ninterface-sensitive effect. In this work we study the properties of the spin\ncurrent transport through the interface measuring the strength of the THz\nemission and compare it to the effective spin mixing conductance, one of the\nkey concepts in the spin current transport through interfaces. The results show\nan enhancement of the spin mixing conductance for interfaces with higher degree\nof epitaxy similarly to the improvement of the THz emission. The\nproportionality between spin mixing conductance and THz emission can define new\ndirections in engineering the emission of spintronic THz emitters.", "category": "physics_app-ph" }, { "text": "Power-law density of states in organic solar cells revealed by the\n open-circuit voltage dependence of the ideality factor: The density of states (DOS) is fundamentally important for understanding\nphysical processes in organic disordered semiconductors, yet hard to determine\nexperimentally. We evaluated the DOS by considering recombination via tail\nstates and using the temperature and open-circuit voltage ($V_\\mathrm{oc}$)\ndependence of the ideality factor in organic solar cells. By performing\nSuns-$V_\\mathrm{oc}$ measurements, we find that gaussian and exponential\ndistributions describe the DOS only at a given quasi-Fermi level splitting. The\nDOS width increases linearly with the DOS depth, revealing the power-law DOS in\nthese materials.", "category": "physics_app-ph" }, { "text": "Detecting fatigue in aluminum alloys based on internal friction\n measurement using an electromechanical impedance method: Detecting mechanical fatigue of metallic components is always a challenge in\nindustries. In this work, we proposed to monitor the low-cycle fatigue of a\n6061 aluminum alloy based on internal friction (IF) measurement, which is\nrealized by a quantitative electromechanical impedance (Q-EMI) method using a\nsmall piezoelectric wafer bonded on the specimen. Large strain amplitude\n(3.3*10^-3) was employed thus the fatigue life can always be below 10^5 cycles.\nIt was found that except for the initial testing stage, the IF always increases\nsteadily with the increasing fatigue cycles. Before the fatigue failure, the IF\ncan reach 2.5 to 3.4 times of the initial value, which is thought to be caused\nby the micro-cracks forming and growing. In comparison, the resonance frequency\nof the specimen just drops less than 2% compared with the initial value.\nFinally, a general fatigue criterion based on IF measurement is suggested for\nall the metallic materials.", "category": "physics_app-ph" }, { "text": "Interaction of surface acoustic waves and magnetic thin films: Surface acoustic waves (SAWs) have emerged as innovative and energy-efficient\nmeans to manipulate domain walls (DWs) and skyrmions in thin films with\nperpendicular magnetic anisotropy (PMA) owing to the magnetoelastic coupling\neffect. This thesis focuses on the complex interplay between SAWs and magnetic\nthin films. The effects of the standing SAWs on the magnetisation dynamics in a\nTa/Pt/Co/Ir/Ta thin film with PMA were first investigated. SAWs with frequency\nof 93.35 MHz significantly reduced the coercivity of the thin film by 21% and\nenhanced the magnetisation reversal speed by 11-fold. Standing SAWs introduce a\ndynamic energy landscape with a unique spatial distribution, forming striped\ndomain patterns in the thin film. The use of rf signals for generating SAWs\ninevitably causes a heating effect in the device. This heating effect was\nexamined in situ in a SAW device featuring a Ta/Pt/Co/Ta thin film with PMA\nusing an on-chip platinum thermometer. The temperature increased by 10 K in the\npresence of SAWs at centre frequency of 48 MHz. The DW velocity was\nsignificantly enhanced in the presence of the standing SAWs by a factor of 4\ncompared to that with temperature change alone owing to the magnetoelastic\ncoupling effect. To understand the SAW-enhanced DW motion, comprehensive\nmicromagnetic simulations were performed on thin films in the presence of\ntravelling SAWs. The findings highlighted that SAW-induced vertical Bloch lines\nwithin DWs can simultaneously boost DW depinning and dissipate energy at the DW\nvia spin rotation. The SAW-induced strain gradient can be exploited to control\nskyrmion motion in a current-free manner. Micromagnetic simulations revealed\nthat the use of orthogonal SAWs, combining horizontal travelling and vertical\nstanding waves, offered a promising approach to direct skyrmion motion along\ndesired trajectories, avoiding undesirable Hall-like motion.", "category": "physics_app-ph" }, { "text": "Designing a boron nitride polyethylene composite for shielding neutrons: Neutrons are encountered in many different fields, including condensed matter\nphysics, space exploration, nuclear power, and healthcare. Neutrons interacting\nwith a biological target produce secondary charged particles that are damaging\nto human health. The most effective way to shield neutrons is to slow them to\nthermal energies and then capture the thermalized neutrons. These factors lead\nus to consider potential materials solutions for neutron shields that maximize\nthe protection of humans while minimizing the shield mass, and which adapt well\nto modern additive manufacturing techniques. Using hexagonal boron nitride\n(hBN) as a capture medium and high-density polyethylene (HDPE) as a\nthermalization medium, we aim to design the optimal internal structure of\nh$^{10}$BN/HDPE composites by minimizing the effective dose, which is a measure\nof the estimated radiation damage exposure for a human. Through Monte Carlo\nsimulations in Geant4, we find that the optimal structure reduces the effective\ndose up to a factor of 72x over aluminum (Al) and 4x over HDPE; this is a\nsignificant improvement in shielding effectiveness that could dramatically\nreduce the radiation exposure of occupational workers.", "category": "physics_app-ph" }, { "text": "Carrier loss mechanisms in textured crystalline Si-based solar cells: A quite general device analysis method that allows the direct evaluation of\noptical and recombination losses in crystalline silicon (c-Si)-based solar\ncells has been developed. By applying this technique, the optical and physical\nlimiting factors of the state-of-the-art solar cells with ~20% efficiencies\nhave been revealed. In the established method, the carrier loss mechanisms are\ncharacterized from the external quantum efficiency (EQE) analysis with very low\ncomputational cost. In particular, the EQE analyses of textured c-Si solar\ncells are implemented by employing the experimental reflectance spectra\nobtained directly from the actual devices while using flat optical models\nwithout any fitting parameters. We find that the developed method provides\nalmost perfect fitting to EQE spectra reported for various textured c-Si solar\ncells, including c-Si heterojunction solar cells, a dopant-free c-Si solar cell\nwith a MoOx layer, and an n-type passivated emitter with rear locally diffused\n(PERL) solar cell. The modeling of the recombination loss further allows the\nextraction of the minority carrier diffusion length and surface recombination\nvelocity from the EQE analysis. Based on the EQE analysis results, the carrier\nloss mechanisms in different types of c-Si solar cells are discussed.", "category": "physics_app-ph" }, { "text": "Radioplasmonics: design of plasmonic milli-particles in air and\n absorbing media for antenna communication and human-body in-vivo applications: Surface plasmons with MHz-GHz energies are predicted by using milliparticles\nmade of metamaterials that behave like metals in the radiofrequency range. In\nthis work, the so-called Radioplasmonics is exploited to design scatterers\nembedded in different realistic media with tunable absorption or scattering\nproperties. High-quality scattering/absorption based on plasmon excitation is\ndemonstrated through a few simple examples, useful to build antennas with\nbetter performance than conventional ones. Systems embedded in absorbing media\nas saline solutions or biological tissues are also considered to improve\nbiomedical applications and contribute with real-time, in-vivo monitoring tools\nin body tissues. In this regard, any possible implementation is criticized by\ncalculating the radiofrequency heating with full thermal simulations. As proof\nof the versatility offered by radioplasmonic systems, plasmon \"hybridization\"\nis used to enhance near-fields to unprecedented values or to tune resonances as\nin optical spectra, minimizing the heating effects. Finally, a monitorable\ndrug-delivery in human tissue is illustrated with a hypothetical example. This\nstudy has remarkable consequences on the conception of plasmonics at\nmacroscales. The recently-developed concept of \"spoof\" plasmons achieved by\ncomplicated structures is simplified in Radioplasmonics since bulk materials\nwith elemental geometries are considered.", "category": "physics_app-ph" }, { "text": "Effects of withdrawal speeds on the structural, morphological,\n electrical, and optical properties of CuO thin films synthesized by\n dip-coating for CO2 gas sensing: Copper oxide (CuO) thin films have been deposited on glass substrates by a\nfacile sol-gel dip-coating technique with varying withdrawal speeds from 0.73\nto 4.17 mm/s. The variation of film thickness manifested by dip-coating\nwithdrawal speeds was investigated in detail to investigate its effect on the\nstructural, morphological, optoelectrical, and wettability properties of CuO\nthin films for carbon dioxide (CO2) gas-sensing applications. The\ncrystallinity, as well as phase purity of dip-coated CuO, were confirmed by\nboth X-ray diffraction (XRD) and Raman spectral analyses. The surface\nmorphology of the films characterized by the scanning electron microscopy (SEM)\nrevealed that pore density decreases with the increase of withdrawal speeds and\ngrain size is found to increase with the increase of film thickness\ncorroborating the XRD results. The optical bandgap of dip-coated CuO films was\nestimated in the range of 1.47 - 1.52 eV from the UV-VIS-NIR transmission data\nand it is found to decrease with the increment of Urbach tail states\naccompanied by the increase of film thickness. The ratio of the electrical and\noptical conductivity of CuO films is found to decrease with increasing\nwithdrawal speeds due to the variation of carrier concentration. Among all the\nstudied films, the sample deposited to a 0.73 mm/s withdrawal speed exhibited\nthe highest crystallinity, porous morphology, highest pore density,\noptoelectrical conductivity as well as water contact angle, and therefore\nmaximum gas sensing response of CO2 vapor in the air recorded at room\ntemperature.", "category": "physics_app-ph" }, { "text": "Dynamic Equation in Thermo-piezoelectric Dissipative Media from Energy\n Conservation: A methodology is proposed for formulating dynamic equations in\nthermo-piezoelectric and dissipative media from the first principle of energy\nconservation. The results are in agreement with those from Hamiltonian\nprinciple. Our formulations based on energy conservation are much easier to\nunderstand. What is more is that, the energy conservation based framework is\nable to handle dissipation problems, which is usually behind the scope of\nHamiltonian principle. In our case, the mechanical, electric and thermal\nphenomena firstly are taken into account, and then the medium with dissipation\nis included. The formulations on acoustic dynamic equation and the associated\nconstitutive relations of the medium will also pave an alternative way in\ncomputational dynamic modelling based on weak formulations. In addition, our\nmethodology may be extended to other dynamic equation formulations, such as in\nelectrodynamics, fluid mechanics and quantum mechanics. This is especially true\nfor tackling the problems with multi-physical field interactions and coupling.", "category": "physics_app-ph" }, { "text": "Effects of CVD Growth Parameters on Global and Local Optical Properties\n of MoS$_2$ Monolayers: Semiconducting transition metal dichalcogenides (TMDs) combine strong\nlight-matter interaction with good chemical stability and scalable fabrication\ntechniques, and are thus excellent prospects for optoelectronic, photonic and\nlight-harvesting applications. Controllable fabrication of high-quality TMD\nmonolayers with low defect content is still challenging and hinders their\nadoption for technological application. The optical properties of chemical\nvapor deposition (CVD) grown monolayer MoS$_2$ are largely influenced by the\nstoichiometry during CVD by controlled sulfurization of molybdenum (Mo)\nprecursors. Here, we investigate how the sulfur concentration influences the\nsample morphology and, both globally and locally, their optical response. We\nconfirm that samples grown under a Mo:S > 1:2 stoichiometric ratio have regular\nmorphology facilitated by a moderate coverage of triangular monocrystals with\nexcellent optical response. Our data-driven approach correlates growth\nconditions with crystal morphology and its optical response, providing a\npractical and necessary pathway to address the challenges towards the\ncontrolled synthesis of 2D TMDs and their alloys with desired optical and\nelectronic properties.", "category": "physics_app-ph" }, { "text": "A discrete memristor model and its application in the Rulkov neuron: Continuous time memristor have been widely used in fields such as chaotic\noscillating circuitsand neuromorphic computing systems, but research on the\napplication of discretememristors haven't been noticed yet. In this paper, we\ndesigned a new chaoticneuron by applying the discrete model to two-dimensional\nRulkov chaotic neuron,and analyzed its dynamical behaviors by extensive\nexperiments involves phasediagram, bifurcation diagram, and spectral entropy\ncomplexity algorithm. The experimental results show that the charge of the\nmemristor has an importanteffect on the system dynamics, delaying the\noccurrence of bifurcation, and evenin the case of full memory, leading to the\ndisappearance of the bifurcation thus makethe system reach a fixed point.\nBesides, the increase of the current magnification,can also bring about the\nincrease in discharge frequency ofneurons, and a wider and larger range of\nspectral entropy complexity. The results of our study show the performance of\nRulkov chaotic neuronis improved by applying thediscrete memristor, and may\nprovide new insights into the mechanism of memoryand cognition in the nervous.", "category": "physics_app-ph" }, { "text": "Cold Isostatic Pressing to Improve the Mechanical Performance of\n Additively Manufactured Metallic Components: Additive manufacturing is becoming a technique with great prospects for the\nproduction of components with new designs or shapes that are difficult to\nobtain by conventional manufacturing methods. One of the most promising\ntechniques for printing metallic components is binder jetting, due to its time\nefficiency and its ability to generate complex parts. In this process, a liquid\nbinding agent is selectively deposited to adhere the powder particles of the\nprinting material. Once the metallic piece is generated, it undergoes a\nsubsequent process of curing and sintering to increase its density (hot\nisostatic pressing). In this work, we propose subjecting the manufactured\ncomponent to an additional post-processing treatment involving the application\nof a high hydrostatic pressure (5000 bar) at room temperature. This\npost-processing technique, so-called cold isostatic pressing (CIP), is shown to\nincrease the yield load and the maximum carrying capacity of an additively\nmanufactured AISI 316L stainless steel. The mechanical properties, with and\nwithout CIP processing, are estimated by means of the small punch test, a\nsuitable experimental technique to assess the mechanical response of small\nsamples. In addition, we investigate the porosity and microstructure of the\nmaterial according to the orientations of layer deposition during the\nmanufacturing process. Our observations reveal a homogeneous distribution\nindependent of these orientations, evidencing thus an isotropic behaviour of\nthe material.", "category": "physics_app-ph" }, { "text": "Wave beaming and diffraction in quasicrystalline elastic metamaterial\n plates: In this paper, we present numerical and experimental evidence of directional\nwave behavior, i.e. beaming and diffraction, along high-order rotational\nsymmetries of quasicrystalline elastic metamaterial plates. These structures\nare obtained by growing pillars on an elastic plate following a particular\nrotational symmetry arrangement, such as 8-fold and 10-fold rotational\nsymmetries, as enforced by a design procedure in reciprocal space. We estimate\nthe dispersion properties of the waves propagating in the plates through\nFourier transformation of transient wave-fields. The procedure identifies, both\nnumerically and experimentally, the existence of anisotropic bands\ncharacterized by high energy density at isolated regions in reciprocal space\nthat follow their higher order rotational symmetry. Specific directional\nbehavior is showcased at the identified frequency bands, such as wave beaming\nand diffraction. This work expands the wave directionality phenomena beyond the\nsymmetries of periodic configurations (e.g., 4-fold and 6-fold), and opens new\npossibilities for applications involving the unusual high-order wave features\nof the quasicrystals such as superior guiding, focusing, sensing and imaging.", "category": "physics_app-ph" }, { "text": "Hydrodynamic Analysis and Responsivity improvement of a\n metal/semiconductor/metal plasmonic detector: Characteristics improvement of photon/plasmon detectors have been the subject\nof several investigations in the area of plasmonic integrated circuits. Among\ndifferent suggestions, Silicon-based Metal-Semiconductor-Metal (MSM) waveguides\nare one of the most popular structures for implementation of high-quality\nphoton/plasmon detectors in infrared wavelengths. In this paper, an integrated\nSilicon Germanium (SiGe) core MSM plasmon detector is proposed to detect\nlambda=1550 nm with internal photoemission mechanism. Performance\ncharacteristics of the new device are simulated with a simplified hydrodynamic\nmodel. In a specific bias point (V=3 V and the incident optical power of 0.31\nmW), the output current is 404.3 uA (276 uA detection current and 128.3 uA dark\ncurrent), responsivity is 0.89 A/W and the 3-dB electrical bandwidth is 120\nGHz. Simulation results for the proposed Plasmon detector, in comparison with\nthe empirical results of a reported Si-based MSM device, demonstrate\nconsiderable responsivity enhancement.", "category": "physics_app-ph" }, { "text": "Deeply Sub-Wavelength Localization with Reverberation-Coded-Aperture: Accessing sub-wavelength information about a scene from the far-field without\ninvasive near-field manipulations is a fundamental challenge in wave\nengineering. Yet it is well understood that the dwell time of waves in complex\nmedia sets the scale for the waves' sensitivity to perturbations. Modern\ncoded-aperture imagers leverage the degrees of freedom (DoF) offered by complex\nmedia as natural multiplexor but do not recognize and reap the fundamental\ndifference between placing the object of interest outside or within the complex\nmedium. Here, we show that the precision of localizing a sub-wavelength object\ncan be improved by several orders of magnitude simply by enclosing it in its\nfar field with a reverberant chaotic cavity. We identify deep learning as\nsuitable noise-robust tool to extract sub-wavelength information encoded in\nmultiplexed measurements, achieving resolutions well beyond those available in\nthe training data. We demonstrate our finding in the microwave domain:\nharnessing the configurational DoF of a simple programmable metasurface, we\nlocalize a sub-wavelength object inside a chaotic cavity with a resolution of\n$\\lambda/76$ using intensity-only single-frequency single-pixel measurements.\nOur results may have important applications in photoacoustic imaging as well as\nhuman-machine interaction based on reverberating elastic waves, sound or\nmicrowaves.", "category": "physics_app-ph" }, { "text": "Magnetic, magnetoelastic and corrosion resistant properties of (Fe-Ni)\n based metallic glasses for structural health monitoring applications: We have performed a study of the magnetic, magnetoelastic, and corrosion\nresistance properties of seven different composition magnetoelastic-resonant\nplatforms. For some applications, such as structural health monitoring, these\nmaterials must have not only good magnetomechanical properties, but also a high\ncorrosion resistance. In the fabricated metallic glasses of composition\nFe(73-x)NixCr5Si10B12, the Fe/Ni ratio was varied (Fe + Ni = 73% at.) thus\nchanging the magnetic and magnetoelastic properties. A small amount of chromium\n(Cr5) was added in order to achieve the desired good corrosion resistance. As\nexpected, all the studied properties change with the composition of the\nsamples. Alloys containing a higher amount of Ni than Fe do not show magnetic\nbehavior at room temperature, while iron-rich alloys have demonstrated not only\ngood magnetic properties, but also good magnetoelastic ones, with\nmagnetoelastic coupling coefficient as high as 0.41 for x=0 in the\nFe73Ni0Cr5Si10B12 (the sample containing only Fe but not Ni). Concerning\ncorrosion resistance, we have found a continuous degradation of these\nproperties as the Ni content increases in the composition. Thus, the corrosion\npotential decreases monotonously from 46.74 mV for the x=0 composition,\nFe73Ni0Cr5Si10B12 to -239.47 mV for the x=73 composition Fe0Ni73Cr5Si10B12.", "category": "physics_app-ph" }, { "text": "Solar cell efficiency, diode factor and interface recombination:\n insights from photoluminescence: Metastable defects can decisively influence the diode factor and thus the\nefficiency of a solar cell. The diode factor is also influenced by the doping\nlevel and the recombination mechanisms in the solar cell. Here we quantify how\nthe various parameters change the diode factor by photoluminescence\nmeasurements and simulations. In addition, we show that backside recombination\nreduces the open circuit voltage in CuInSe2 solar cells by more than 40 mV.\nPassivation by a Ga gradient is shown to be as efficient as a passivation by\ndielectric layers. Increased backside recombination reduces the diode factor,\nnot because of less metastable defect transformation but because of a sublinear\nincrease in photo generated carriers with excitation. This reduction in diode\nfactor is unwanted, since the increased recombination reduces the voltage. A\nhigher doping level, on the other hand, reduces the diode factor, thereby\nincreasing the fill factor, and at the same time increases the voltage.", "category": "physics_app-ph" }, { "text": "Activation of Microwave Fields in a Spin-Torque Nano-Oscillator by\n Neuronal Action Potentials: Action potentials are the basic unit of information in the nervous system and\ntheir reliable detection and decoding holds the key to understanding how the\nbrain generates complex thought and behavior. Transducing these signals into\nmicrowave field oscillations can enable wireless sensors that report on brain\nactivity through magnetic induction. In the present work we demonstrate that\naction potentials from crayfish lateral giant neuron can trigger microwave\noscillations in spin-torque nano-oscillators. These nanoscale devices take as\ninput small currents and convert them to microwave current oscillations that\ncan wirelessly broadcast neuronal activity, opening up the possibility for\ncompact neuro-sensors. We show that action potentials activate microwave\noscillations in spin-torque nano-oscillators with an amplitude that follows the\naction potential signal, demonstrating that the device has both the sensitivity\nand temporal resolution to respond to action potentials from a single neuron.\nThe activation of magnetic oscillations by action potentials, together with the\nsmall footprint and the high frequency tunability, makes these devices\npromising candidates for high resolution sensing of bioelectric signals from\nneural tissues. These device attributes may be useful for design of\nhigh-throughput bi-directional brain-machine interfaces.", "category": "physics_app-ph" }, { "text": "Adiabatic edge-to-edge transformations in time-modulated elastic\n lattices and non-Hermitian shortcuts: The temporal modulation of a relevant parameter can be employed to induce\nmodal transformations in Hermitian elastic lattices. When this is combined with\na proper excitation mechanism, it allows to drive the energy transfer across\nthe lattice with tunable propagation rates. Such a modal transformation,\nhowever, is limited by the adiabaticity of the process, which dictates an upper\nbound for the modulation speed. In this manuscript, we employ a non-Hermitian\nshortcut by way of a tailored gain and loss to violate the adiabatic limit and,\ntherefore, to achieve superfast modal transformations. A quantitative condition\nfor adiabaticity is firstly derived and numerically verified for a pair of\nweakly coupled time-dependent mechanical oscillators, which can be interpreted\nin the light of modal interaction between crossing states. It is shown that for\nsufficiently slow time-modulation, the elastic energy can be transferred from\none oscillator to the other. A non-Hermitian shortcut is later induced to break\nthe modal coupling and, therefore, to speed-up the modal transformation. The\nstrategy is then generalized to elastic lattices supporting topological edge\nstates. We show that the requirements for a complete edge-to-edge energy\ntransfer are lifted from the adiabatic limit toward higher modulation\nvelocities, opening up new opportunities in the context of wave manipulation\nand control.", "category": "physics_app-ph" }, { "text": "Time profile of temperature rise in assemblies of nanomagnets: We compute the heat generated by (non-interacting) nanomagnets subjected to\nan alternating magnetic field (AMF) and study its transfer to the hosting\nmedium and environment. For the first task, we compute the heat generated by\nthe nanomagnets (or the specific absorption rate) using the ac susceptibility\nin the linear regime. For the second task, the loss of heat to the environment\nis modeled with the help of a balance (macroscopic) equation based on Newton's\nlaw of cooling. This equation is solved both numerically and analytically for a\ngeneric ferrofluid and the analytical solution renders a very good\napproximation to the general balance equation. Then, we investigate the effects\nof AMF frequency and amplitude on the temperature elevation during its temporal\nevolution. Finally, using the available experimental data for maghemite and\nmagnetite ferrofluids, we discuss the behavior of Newton's heat transfer\ncoefficient in terms of the AMF amplitude and frequency. These results could\ntrigger experimental investigations of this coefficient which characterizes the\nrate of heating in a ferrofluid, with the aim to build more refined models for\nthe mechanisms of heat generation and its diffusion in ferrofluids used in\nmagnetic hyperthermia.", "category": "physics_app-ph" }, { "text": "lambda DNA through a plasmonic nanopore What can be detected by means of\n Surface Enhanced Raman Scattering?: Engineered electromagnetic fields in plasmonic nanopores enable enhanced\noptical detection and their use in single molecule sequencing. Here, a\nplasmonic nanopore prepared in a thick nanoporous film is used to investigate\nthe interaction between the metal and a long-chain double strand DNA molecule.\nWe discuss how the matrix of nanoporous metal can interact with the molecule\nthanks to: i) transient aspecific interactions between the porous surface and\nDNA and ii) optical forces exerted by the localized field in a metallic\nnanostructure. A duration of interaction up to tens of milliseconds enables to\ncollect high signal-to-noise Raman vibrations allowing an easy label-free\nreading of information from the DNA molecule. Moreover, in order to further\nincrease the event of detection rate, we tested a polymeric porous hydrogel\nplaced beneath the solid-state membrane. This approach enables a slowdown of\nthe molecule diffusion, thus increasing the number of detected interactions by\na factor of about 20.", "category": "physics_app-ph" }, { "text": "Transmittable Nonreciprocal Cloaking: Cloaking is typically reciprocal. We introduce here the concept of\n\\emph{transmittable nonreciprocal cloaking} whereby the cloaking system\noperates as a standard omnidirectional cloak for external illumination, but can\ntransmit light from its center outwards at will. We demonstrate a specific\nimplementation of such cloaking that consists in a set of concentric\nbianisotropic metasurfaces whose innermost element is nonreciprocal and\ndesigned to simultaneously block inward waves and pass -- either\nomnidirectionaly or directionally -- outward waves. Such cloaking represents a\nfundamental diversification of conventional cloaking and may find applications\nin areas such as stealth, blockage avoidance, illusion and cooling.", "category": "physics_app-ph" }, { "text": "Acoustically Driven and Modulation Inducible Radiating Elements: The low propagation loss of electromagnetic radiation below 1 MHz offers\nsignificant opportunities for low power, long range communication systems to\nmeet growing demands for IoT applications. Especially in the very low frequency\n(VLF: 3-30 kHz) range and lower, propagation through tens of meters of\nseawater, hundreds of meters of earth, and hundreds of kilometers of air with\nonly 2-3 dB of loss is possible. However, the fundamental reduction in\nefficiency as the size of electrical antennas decreases below a wavelength (30\nm at 1 MHz) has made portable communication systems in the VLF and low\nfrequency (LF: 30-300 kHz) ranges impractical for decades. A paradigm shift\nfrom electrical to piezoelectric antennas utilizing strain-driven currents at\nresonant wavelengths up to five orders of magnitude smaller than electrical\nantennas offers the promise for orders of magnitude efficiency improvement over\nthe electrical state-of-the-art. This work demonstrates a lead zirconate\ntitanate transmitter >6000 times more efficient than a comparably sized\nelectrical antenna and capable of bit rates up to 60 bit/s using\nfrequency-shift keying. Detailed analysis of design parameters offers a roadmap\nfor significant future improvement in both radiation efficiency and data rate\nin the new field of acoustically driven antennas.", "category": "physics_app-ph" }, { "text": "Highly flexible electromagnetic interference shielding films based on\n ultrathin Ni/Ag composites on paper substrates: Highly flexible electromagnetic interference (EMI) shielding material with\nexcellent shielding performance is of great significance to practical\napplications in next-generation flexible devices. However, most EMI materials\nsuffer from insufficient flexibility and complicated preparation methods. In\nthis study, we propose a new scheme to fabricate a magnetic Ni particle/Ag\nmatrix composite ultrathin film on a paper surface. For a ~2 micro meter thick\nfilm on paper, the EMI shielding effectiveness (SE) was found to be 46.2 dB at\n8.1 GHz after bending 200,000 times over a radius of ~2 mm. The sheet\nresistance (Rsq) remained lower than 2.30 Ohm after bending 200,000 times.\nContrary to the change in Rsq, the EMI SE of the film generally increased as\nthe weight ratio of Ag to Ni increased, in accordance with the principle that\nEMI SE is positively related with an increase in electrical conductivity.\nDesirable EMI shielding ability, ultrahigh flexibility, and simple processing\nprovide this material with excellent application prospects.", "category": "physics_app-ph" }, { "text": "Design and Fabrication of a Differential MOEMS Accelerometer Based on\n Fabry Perot micro-cavities: In this paper, a differential MOEMS accelerometer based on the Fabry-Perot\n(FP) micro-cavities is presented. The optical system of the device consists of\ntwo FP cavities and the mechanical system is composed of a proof mass that is\nsuspended by four springs. The applied acceleration tends to move the PM from\nits resting position. This mechanical displacement can be measured by the FP\ninterferometer formed between the proof mass cross-section and the optical\nfiber end face. The proposed sensor is fabricated on a silicon on insulator\n(SOI) wafer using the bulk micromachining method. The results of the sensor\ncharacterization show that the accelerometer has a linear response in the range\nof 1g. Also, the optical sensitivity and resolution of the sensor in the static\ncharacterization are 6.52 nm/g and 153ug. The sensor sensitivity in the power\nmeasurement is 49.6 mV/g and its resonant is at 1372 Hz. Using the differential\nmeasurement method increases the sensitivity of the accelerometer. Based on\nexperimental data, the sensor sensitivity is two times as high as that of a\nsimilar MOEMS accelerometer with one FP cavity.", "category": "physics_app-ph" }, { "text": "Wood Anomalies and Surface-Wave Excitation with a Time-Grating: In order to confine waves beyond the diffraction limit, advances in\nfabrication techniques have enabled subwavelength structuring of matter,\nachieving near-field control of light and other types of waves. The price is\noften expensive fabrication needs and the irreversibility of device\nfunctionality, as well as the introduction of impurities, a major contributor\nto losses. In this Letter, we propose temporal inhomogeneities, such as a\nperiodic drive in the electromagnetic properties of a surface which supports\nguided modes, to circumvent the need for subwavelength fabrication in the\ncoupling of propagating waves to evanescent modes across the light line,\nachieving the temporal counterpart of the Wood anomaly. We show analytically\nand numerically how this concept is valid for any material platform and at any\nfrequency, and propose and model a realistic experiment in graphene to couple\nterahertz radiation to plasmons with unit efficiency, demonstrating that\ntime-modulation of material properties could be a tunable, lower-loss and\nfast-switchable alternative to the subwavelength structuring of matter for\nnear-field wave control.", "category": "physics_app-ph" }, { "text": "Steering of beam trajectory by distorted photonic crystals: Electromagnetic waves follow linear paths in homogenous index media, with the\nexception of band edges. In this study, we introduced spatially distorted\nphotonic crystals (D-PCs) that are capable of beam-steering light waves, even\nwhen a homogeneous refractive index is maintained. We analyzed their\nequifrequency contours to investigate the correspondence between the direction\nof distortion and the direction of the group velocity vector in the D-PC.\nThereafter, we experimentally verified the beam-steering phenomenon in the\nterahertz range using an all-silicon D-PC. Our structures serve as on-chip beam\ntrajectory control without the need for any specially-engineered materials,\nusing only lattice distortion.", "category": "physics_app-ph" }, { "text": "Atomistic Insights into the Effects of Phosphorous Doping of Graphene\n Anode in a Lithium Ion Battery: Inspired by a recent experimental and theoretical study [Yang et al., 2017],\nwherein protrusions in graphene have been proposed as an effective strategy to\nenhance the performance of sodium ion batteries, a comprehensive study of the\neffects of phosphorus doping in graphene on adsorption and diffusion behaviour\nof Li is carried out by using density functional theory. We find that\nprotrusion introduced by P-dopant in graphene enhances the adsorption of a\nsingle Li atom onto the anode due to an additional partial covalent bonding\ncharacter between Li and carbon atoms of the substrate. However, with increase\nin concentration of Li atoms, they tend to form clusters which may lead to\ndendrite growth and hence battery failure. Finite density of states at Fermi\nlevel ensures the electronic conductivity of the P-doped graphene before and\nafter the adsorption of a Li atom. No momentous variation in DOS is observed\nexcept a small up shift in Fermi level with increased Li concentration. The\npresence of such protrusions acts as trapping centres for Li and hinders their\nmigration over the substrate, leading to poor cycling performance of anode.\nThis atomic level study will act as a useful guideline for further development\nof anode materials for novel battery technologies.", "category": "physics_app-ph" }, { "text": "Topological rainbow trapping for elastic energy harvesting in graded SSH\n systems: We amalgamate two fundamental designs from distinct areas of wave control in\nphysics, and place them in the setting of elasticity. Graded elastic\nmetasurfaces, so-called metawedges, are combined with the now classical\nSu-Schrieffer-Heeger (SSH) model from the field of topological insulators. The\nresulting structures form one-dimensional graded-SSH-metawedges that support\nmultiple, simultaneous, topologically protected edge states. These robust,\nenhanced localised modes are leveraged for applications in elastic energy\nharvesting using the piezoelectric effect. The designs we develop are first\nmotivated by applying the SSH model to mass-loaded Kirchhoff-Love thin elastic\nplates. We then extend these ideas to using graded resonant rods, and create\nSSH models, coupled to elastic beams and full elastic half-spaces.", "category": "physics_app-ph" }, { "text": "The Essential Work of Fracture Parameters for 3D printed polymer sheets: Additive manufacturing is becoming increasingly popular in academia and\nindustry. Accordingly, there has been a growing interest in characterizing 3D\nprinted samples to determine their structural integrity behaviour. We employ\nthe Essential Work of Fracture (EWF) to investigate the mechanical response of\npolymer sheets obtained through additive manufacturing. Our goal is twofold;\nfirst, we aim at gaining insight into the role of fibre reinforcement on the\nfracture resistance of additively manufactured polymer sheets. Deeply\ndouble-edge notched tensile (DDEN-T) tests are conducted on four different\npolymers: Onyx, a crystalline, nylon-reinforced polymer, and three standard\npolymers used in additive manufacturing - PLA, PP and ABS. Results show that\nfibre-reinforcement translates into a notable increase in fracture resistance,\nwith the fracture energy of Onyx being an order of magnitude higher than that\nreported for non-reinforced polymers. On the other hand, we propose the use of\na miniature test specimen, the deeply double-edge notched small punch specimens\n(DDEN-SP), to characterize the mechanical response using a limited amount of\nmaterial. The results obtained exhibit good alignment with the DDEN-T data,\nsuggesting the suitability of the DDEN-SP test for measuring fracture\nproperties of additively manufactured polymers in a cost-effective manner.", "category": "physics_app-ph" }, { "text": "Wave-field representations with Green's functions, propagator matrices,\n and Marchenko-type focusing functions: Classical acoustic wave-field representations consist of volume and boundary\nintegrals, of which the integrands contain specific combinations of Green's\nfunctions, source distributions and wave fields. Using a unified matrix-vector\nwave equation for different wave phenomena, these representations can be\nreformulated in terms of Green's matrices, source vectors and wave-field\nvectors. The matrix-vector formalism also allows the formulation of\nrepresentations in which propagator matrices replace the Green's matrices.\nThese propagator matrices, in turn, can be expressed in terms of Marchenko-type\nfocusing functions. An advantage of the representations with propagator\nmatrices and focusing functions is that the boundary integrals in these\nrepresentations are limited to a single open boundary. This makes these\nrepresentations a suitable basis for developing advanced inverse scattering,\nimaging and monitoring methods for wave fields acquired on a single boundary.", "category": "physics_app-ph" }, { "text": "Elastic Wave Eigenmode Solver for Acoustic Waveguides: A numerical solver for the elastic wave eigenmodes in acoustic waveguides of\ninhomogeneous cross-section is presented. Operating under the assumptions of\nlinear, isotropic materials, it utilizes a finite-difference method on a\nstaggered grid to solve for the acoustic eigenmodes of the vector-field elastic\nwave equation. Free, fixed, symmetry, and anti-symmetry boundary conditions are\nimplemented, enabling efficient simulation of acoustic structures with\ngeometrical symmetries and terminations. Perfectly matched layers are also\nimplemented, allowing for the simulation of radiative (leaky) modes. The method\nis analogous to eigenmode solvers ubiquitously employed in electromagnetics to\nfind waveguide modes, and enables design of acoustic waveguides as well as\nseamless integration with electromagnetic solvers for optomechanical device\ndesign. The accuracy of the solver is demonstrated by calculating\neigenfrequencies and mode shapes for common acoustic modes in several simple\ngeometries and comparing the results to analytical solutions where available or\nto numerical solvers based on more computationally expensive methods.", "category": "physics_app-ph" }, { "text": "Visible-blind ZnMgO Colloidal Quantum Dot Downconverters expand Silicon\n CMOS Sensors Spectral Coverage into Ultraviolet and enable UV Band\n Discrimination: Selective spectral detection of ultraviolet (UV) radiation is highly\nimportant across numerous fields from health and safety to industrial and\nenvironmental monitoring applications. Herein, we report a non-toxic,\nvisible-blind, inorganic quantum dot (QD)-based sensing scheme that expands the\nspectral coverage of Silicon CMOS sensors into the UV, enabling efficient UV\ndetection without affecting the sensor performance in the visible and UV-band\ndiscrimination. The reported scheme employs zinc magnesium oxide (ZnMgO) QDs\nwith compositionally tunable absorption across UV and high photoluminescence\nquantum yield (PLQY) in the visible. The efficient luminescence and large\nstokes shift of these QDs have been exploited herein to act as an efficient\ndownconverting material that enhances the UV sensitivity of Si-photodetector\n(Si-PD). A Si-PD integrated with the QDs results in a nine-fold improvement in\nphotoresponsivity from 0.83 mA/W to 7.5 mA/W at 260 nm. Leveraging the\ntunability of these QDs we further report on a simple UV band identification\nscheme, using two distinct band gap ZnMgO QDs stacked in a tandem architecture\nwhose spectral emission color depends on the UV-band excitation light. The\ndownconverting stack enables facile discrimination of UV light using a standard\nCMOS image sensor (camera) or by the naked eye and avoids the use of complex\noptics.", "category": "physics_app-ph" }, { "text": "Exceptional Degeneracy in a Waveguide Periodically Loaded with Discrete\n Gain and Radiation Loss Elements: We demonstrate that a periodic waveguide comprising of uniform lossless\nsegments together with discrete gain and radiating elements supports\nexceptional points of degeneracy (EPDs). We provide analytical expressions for\nall possible conditions that guarantee the occurrence of an EPD, i.e., the\ncoalescence of eigenvalues and eigenvectors. We show that EPDs are not only\nachieved using symmetric gain and radiation periodic loading, but they are also\nobtained using asymmetric gain and radiation loss conditions. We illustrate the\ncharacteristics of the degenerate electromagnetic modes, showing the dispersion\ndiagram and discussing the tunability of the EPD frequency. We show a special\ncondition, we refer to it as parity-time (PT)-glide symmetry, which leads to a\ndegeneracy that is occurring at all frequencies of operation. The class of EPDs\nproposed in this work is very promising for many applications that incorporate\ndiscrete-distributed coherent sources and radiation-loss elements; operating in\nthe vicinity of such special degeneracy conditions leads to potential\nperformance enhancement in a variety of microwave and optical resonators,\nantennas, and devices and can be extended to a new class of active integrated\nantenna arrays and radiating laser arrays.", "category": "physics_app-ph" }, { "text": "Basic and extendable framework for effective charge transport in\n electrochemical systems: We consider basic and easily extendible transport formulations for lithium\nbatteries consisting of an anode (Li-foil), a separator (polymer electrolyte),\nand a composite cathode (composed of electrolyte and intercalation particles).\nOur mathematical investigations show the following novel features: (i)\n\\emph{complete and very basic description of mixed transport processes} relying\non a neutral, binary symmetric electrolyte resulting in a non-standard Poisson\nequation for the electric potential together with interstitial diffusion\napproximated by classical diffusion; (ii) \\emph{ upscaled and basic composite\ncathode equations allowing to take geometric and material features of\nelectrodes into account}; (iii) \\emph{the derived effective macroscopic model\ncan be numerically solved with well-known numerical strategies for homogeneous\ndomains} and hence does not require to solve a high-dimensional numerical\nproblem or to depend on a computationally involved multiscale discretisation\nstrategies where highly heterogeneous and realistic, nonlinear, and reactive\nboundary conditions are still unexplored. We believe that the here proposed\nbasic and easily extendible formulations will serve as a basic and simple setup\ntowards a systematic theoretical and experimental understanding of complex\nelectrochemical systems and their optimization, e.g. Li-batteries.", "category": "physics_app-ph" }, { "text": "High-precision local transfer of van der Waals materials on nanophotonic\n structures: Prototyping of van der Waals materials on dense nanophotonic devices requires\nhigh-precision monolayer discrimination to avoid bulk material contamination.\nWe use the glass transition temperature of polycarbonate, used in the standard\ndry transfer process, to draw an in situ point for the precise pickup of two\ndimensional materials. We transfer transition metal dichalcogenide monolayers\nonto a large-area silicon nitride spiral waveguide and silicon nitride ring\nresonators to demonstrate the high-precision contamination-free nature of the\nmodified dry transfer method. Our improved local transfer technique is a\nnecessary step for the deterministic integration of high-quality van der Waals\nmaterials onto nanocavities for the exploration of few-photon nonlinear optics\non a high-throughput, nanofabrication-compatible platform.", "category": "physics_app-ph" }, { "text": "Passive Aperiodic Optical Phased Array based on Uniform Random Shuffle: Grating lobes arise from the periodic nature of element spacing in the\noptical phased array. Essentially, the phased array performs the Spatial\nFourier Transform on light; the steering capability of the main lobe is\ngoverned by phase shift variations among waveguides, and the Sidelobe\nSuppression Ratio (SLSR) correlates with the uniformity of emitter positions.\nLeveraging this understanding, we have optimized a 1x64 channel passive\naperiodic OPAs with the uniform random shuffle in the emitter's position. Our\nconceptual simulations highlight a robust steering capability (18.60{\\deg} /\n10nm) and SLSR (-13.46 dB @ 0{\\deg} / -8.27 dB @ +/-45{\\deg}), and initial\nmeasurements demonstrate the steering capability (9.8 {\\deg} / 10nm, with\nsmaller phase shifts design) and SLSR (-6.1dB @ -33.4{\\deg}) from the\npreliminary fabrication.", "category": "physics_app-ph" }, { "text": "Circuit architecture of a sub-GHz resolution panoramic C band on-chip\n spectral sensor: Monitoring the state of the optical network is a key enabler for\nprogrammability of network functions, protocols and efficient use of the\nspectrum. A particular challenge is to provide the SDN-EON controller with a\npanoramic view of the complete state of the optical spectrum. This paper\ndescribes the architecture for compact on-chip spectrometry targeting high\nresolution across the entire C-band to reliably and accurately measure the\nspectral profile of WDM signals in fixed and flex-grid architectures. An\nindustry standard software tool is used to validate the performance of the\nspectrometer. The fabrication of the proposed design is found to be practical.", "category": "physics_app-ph" }, { "text": "High performance integrated graphene electro-optic modulator at\n cryogenic temperature: High performance integrated electro-optic modulators operating at low\ntemperature are critical for optical interconnects in cryogenic applications.\nExisting integrated modulators, however, suffer from reduced modulation\nefficiency or bandwidth at low temperatures because they rely on tuning\nmechanisms that degrade with decreasing temperature. Graphene modulators are a\npromising alternative, since graphene's intrinsic carrier mobility increases at\nlow temperature. Here we demonstrate an integrated graphene-based electro-optic\nmodulator whose 14.7 GHz bandwidth at 4.9 K exceeds the room-temperature\nbandwidth of 12.6 GHz. The bandwidth of the modulator is limited only by high\ncontact resistance, and its intrinsic RC-limited bandwidth is 200 GHz at 4.9 K.", "category": "physics_app-ph" }, { "text": "Doping Graphene via Organic Solid-Solid Wetting Deposition: Organic Solid-Solid Wetting Deposition (OSWD) enables the fabrication of\nsupramolecular architectures without the need for solubility or vacuum\nconditions. The technique is based on a process which directly generates\ntwo-dimensional monolayers from three-dimensional solid organic powders.\nConsequently, insoluble organic pigments and semiconductors can be made to\ninduce monolayer self-assembly on substrate surfaces, such as graphene and\ncarbon nanotubes, under ambient conditions. The above factuality hence opens up\nthe potential of the OSWD for bandgap engineering applications within the\ncontext of carbon based nanoelectronics. However, the doping of graphene via\nOSWD has not yet been verified, primarily owing to the fact that the classical\nOSWD preparation procedures do not allow for the analysis via Raman\nspectroscopy, one of the main techniques to determine graphene doping. Hence,\nhere we describe a novel approach to induce OSWD on graphene leading to samples\nsuitable for Raman spectroscopy. The analysis reveals peak shifts within the\nRaman spectrum of graphene, which are characteristics for p-type doping.\nAdditional evidence for chemical doping is found via Scanning Tunneling\nSpectroscopy. The results open up a very easily applicable, low-cost, and\neco-friendly way for doping graphene via commercially available organic\npigments.", "category": "physics_app-ph" }, { "text": "A frequency-preserving and time-invariant metamaterial-based nonlinear\n acoustic diode: We present the realization of an acoustic diode or rectifier, exploiting\nsymmetry-breaking nonlinear effects like harmonic generation and wave mixing\nand the filtering capabilities of metamaterials. The essential difference and\nadvantage compared with previous acoustic diode realizations is that the\npresent is simultaneously a time invariant, frequency preserving and switchable\ndevice. This allows its application also as an on-off or amplitude-tuning\nswitch. We evaluate its properties by means of a numerical study and\ndemonstrate its feasibility in a preliminary experimental realization. This\nwork may provide new opportunities for the practical realization of structural\ncomponents with one-way wave propagation properties.", "category": "physics_app-ph" }, { "text": "Combined funnel, concentrator, and particle valve functional element for\n magnetophoretic bead transport based on engineered magnetic domain patterns: Controlled actuation of superparamagnetic beads (SPBs) within a microfluidic\nenvironment using tailored dynamic magnetic field landscapes (MFLs) is a potent\napproach for the realization of point-of-care diagnostics within Lab-on-a-chip\n(LOC) systems. Making use of an engineered magnetic domain pattern as the MFL\nsource, a functional LOC-element with combined magnetophoretic funnel,\nconcentrator, and valve functions for micron-sized SPBs is presented. A\nparallel-stripe domain pattern design with periodically increasing/decreasing\nstripe lengths has been fabricated in a topographically flat continuous\nexchange biased (EB) thin film system by ion bombardment induced magnetic\npatterning (IBMP). It is demonstrated that, upon application of external\nmagnetic field pulses, a fully reversible concentration of SPBs at the domain\npattern focal point occurs. In addition, it is shown that this functionality\nmay be used as an SPB funnel, allowing only a maximum number of particles to\npass through the focal point. Adjusting the pulse time length, the focal point\ncan be clogged up for incoming SPBs, resembling an on-and-off switchable\nparticle valve. The observations are supported by quantitative theoretical\nforce considerations.", "category": "physics_app-ph" }, { "text": "Using fuel cells to power electric propulsion systems: The origin of fuel cell technology has a notable connection to the history of\nspaceflight, having been used in remarkable programs such as Gemini, Apollo and\nthe Space Shuttle. With the constant growth of the electric propulsion\ntechnology in the last years, one natural application for fuel cells to be\nconsidered would be the electrical feeding of those thrusters for different\nmission profiles. In this article we explore in details this possibility,\nshowing what would the necessary characteristics of such a device be in order\nto improve mission parameters, as payload ratio and thrust, among others. In\nthe first section, a brief review of the applications of fuel cells in the\nspace industry is shown, and the classical analytical modeling of these devices\nis presented. In the second part, two case studies illustrating most of the\npossible ways to use fuel cells in conjunction with electric propulsion systems\nare shown , and the possible advantages and limitations of the applications are\ndemonstrated analytically. The result of the analysis shows that, in the case\nwhere the fuel cell reaction products are disposed of and the propulsion has\nits own feed system, the application of fuel cell technology would bring no\nadvantages for most kinds of missions. On the other hand, when the case where\nthe fuel cell exhaust is used as a propellant is considered, it is shown that\nit is possible to improve mission parameters, such as thrust and specific\nimpulse, if certain conditions are met.", "category": "physics_app-ph" }, { "text": "Atypical electrical behavior of few layered WS2 nanosheets based\n platform subject to heavy metal ion treatment: An atypical electrical behavior of WS2 nanosheets deposited on Cu electrodes\nis reported here. The characteristic Raman peaks at 355cm-1 and 421.8cm-1\nconfirm the few-layer structure of WS2. The addition of heavy metal ions of ~30\nmicro Liter on this platform results in non-ohmic behavior in I-V\ncharacteristics, accompanied by a dramatic rise of current from nA to micro\nAmpere Additionally, this atypical behavior is found to be reversible.\nSubsequent to removal of these ions from the nanosheets, it again exhibits\nnormal ohmic I-V characteristics. It is envisioned that this unusual\ncharacteristic will pave way for more research in the sensing direction as well\nas relevant fields.", "category": "physics_app-ph" }, { "text": "Four-Dimensional Higher-Order Chern Insulator and Its Acoustic\n Realization: We present a theoretical study and experimental realization of a system that\nis simultaneously a four-dimensional (4D) Chern insulator and a higher-order\ntopological insulator (HOTI). The system sustains the coexistence of\n(4-1)-dimensional chiral topological hypersurface modes (THMs) and\n(4-2)-dimensional chiral topological surface modes (TSMs). Our study reveals\nthat the THMs are protected by second Chern numbers, and the TSMs are protected\nby a topological invariant composed of two first Chern numbers, each belonging\na Chern insulator existing in sub-dimensions. With the synthetic coordinates\nfixed, the THMs and TSMs respectively manifest as topological edge modes (TEMs)\nand topological corner modes (TCMs) in the real space, which are experimentally\nobserved in a 2D acoustic lattice. These TCMs are not related to quantized\npolarizations, making them fundamentally distinctive from existing examples. We\nfurther show that our 4D topological system offers an effective way for the\nmanipulation of the frequency, location, and the number of the TCMs, which is\nhighly desirable for applications.", "category": "physics_app-ph" }, { "text": "Water vapour pressure as determining control parameter to fabricate high\n efficiency perovskite solar cells at ambient conditions: Although perovskite solar cells have demonstrated impressive efficiencies in\nresearch labs (above 23%), there is a need of experimental procedures that\nallow their fabrication at ambient conditions, which would decrease\nsubstantially manufacturing costs. However, under ambient conditions, a\ndelicate control of the moisture level in the atmosphere has to be enforced to\nachieve efficient and highly stable devices. In this work, we show that it is\nthe absolute content of water measured in the form of partial water vapour\npressure (WVP) the only determining control parameter that needs to be\nconsidered during preparation. Following this perspective, MAPbI3 perovskite\nfilms were deposited under different WVP by changing the relative humidity (RH)\nand the lab temperature. We found that efficient and reproducible devices can\nbe obtained at given values of WVP. Furthermore, it is demonstrated that small\ntemperature changes, at the same value of the RH, result in huge changes in\nperformance, due to the non-linear dependence of the WVP on temperature. We\nhave extended the procedure to accomplish high-efficient FA0.83MA0.17PbI3\ndevices at ambient conditions by adjusting DMSO proportion in precursor\nsolution as a function of WVP only. As an example of the relevance of this\nparamater, a WVP value of around of 1.6 kPa appears to be an upper limit for\nsafe fabrication of high efficiency devices at ambient conditions, regardless\nthe RH and lab temperature.", "category": "physics_app-ph" }, { "text": "Observation of gapless corner modes in synthetic translation dimensions: The introduction of synthetic dimensions in topological photonic systems\nenriches the exploration of topological phase of light in higher-dimensional\nspace beyond three-dimensional real-space. Recently, the gapless corner modes\nof topological photonic crystals under translational deformation have been\nproposed, but their experimental observation is still absent. Here, we observe\nthe gapless corner modes in a photonic crystal slab under translational\ndeformation. The corner mode exhibits a frequency dependence that can be tuned\nthrough the translation of the slab. Importantly, we find that the existence of\ngapless corner modes is independent of the specific corner configuration. The\ngapless corner modes are experimentally imaged via the near-field scanning\nmeasurement, and validated numerically by full-wave simulations. Our work\ncontributes to the advancement of topological photonics and provides valuable\ninsights into the exploration of gapless corner modes in synthetic dimensions.", "category": "physics_app-ph" }, { "text": "Modulation of heterogeneous surface charge and flow pattern in\n electrically gated converging-diverging nanochannel: The present study aims at utilizing field effect phenomenon to induce\nheterogeneous surface charge and consequently changing the fluid flow in a\nsolid state nanochannel with converging-diverging periodicity. It is shown that\nthe proposed geometry causes non-uniform radial field adjacent to channel walls\nwhich is stronger around the diverging section and weaker next to the\nconverging part of the wall. The later generates heterogeneous surface charge\nat channel walls depending on the applied gate potential i.e. applying low gate\npotential enables effective modulation of surface charge with the same polarity\nof the intrinsic charge at channel walls, while moderate gate potential causes\ncharge inversion in diverging sections of the channel and generates reverse\nflow and thus results in fluid flow circulation. The potential application of\nflow circulation for trapping and rejection of particles is also demonstrated.", "category": "physics_app-ph" }, { "text": "Resonate and Fire Neuron with Fixed Magnetic Skyrmions: In the brain, the membrane potential of many neurons oscillates in a\nsubthreshold damped fashion and fire when excited by an input frequency that\nnearly equals their eigen frequency. In this work, we investigate theoretically\nthe artificial implementation of such \"resonate-and-fire\" neurons by utilizing\nthe magnetization dynamics of a fixed magnetic skyrmion in the free layer of a\nmagnetic tunnel junction (MTJ). To realize firing of this nanomagnetic\nimplementation of an artificial neuron, we propose to employ voltage control of\nmagnetic anisotropy or voltage generated strain as an input (spike or\nsinusoidal) signal, which modulates the perpendicular magnetic anisotropy\n(PMA). This results in continual expansion and shrinking (i.e. breathing) of a\nskyrmion core that mimics the subthreshold oscillation. Any subsequent input\npulse having an interval close to the breathing period or a sinusoidal input\nclose to the eigen frequency drives the magnetization dynamics of the fixed\nskyrmion in a resonant manner. The time varying electrical resistance of the\nMTJ layer due to this resonant oscillation of the skyrmion core is used to\ndrive a Complementary Metal Oxide Semiconductor (CMOS) buffer circuit, which\nproduces spike outputs. By rigorous micromagnetic simulation, we investigate\nthe interspike timing dependence and response to different excitatory and\ninhibitory incoming input pulses. Finally, we show that such resonate and fire\nneurons have potential application in coupled nanomagnetic oscillator based\nassociative memory arrays.", "category": "physics_app-ph" }, { "text": "New method for characterization of magnetic nanoparticles by scanning\n magnetic microscopy: In this paper, we present a new method for the magnetic characterization of\nbulk materials, microstructures, and nanostructures. We investigated the\nmagnetic and morphological properties of two colloidal dispersions of iron\noxide (Fe3O4) magnetic nanoparticles (MNPs), synthesized by chemical\nprecipitation (co-precipitation) and pulsed laser ablation (PLA) in liquid, by\nscanning magnetic microscopy (SMM) applied to a small sample with mass on the\norder of tens of {\\mu}g. We evaluated the performance of this technique by\ncomparing magnetization curves and measurements obtained with commercial\nmagnetometers, considered standard. The errors obtained for the saturation and\nremanent magnetization were approximately 0.18 Am2/kg and 0.6 Am2/kg,\nrespectively. The average size distribution of the NPs estimated from the\nmagnetization curve measurements is consistent with the results obtained by\ntraditional transmission electron microscopy (TEM). The technique can be\nextended to measure and analyze magnetization curves (hysteresis loops), thus\nenabling an even more accurate estimation of overall NP sizes.", "category": "physics_app-ph" }, { "text": "Large scale changes in overtone resonances and resonant peak burning of\n HBAR with mass loading and its potential for applications: This report presents the realization and characterization of a robust\ncomposite resonator i.e. high overtone bulk acoustic wave resonator (HBAR) and\nthe changes happening to the resonance peaks once it undergoes mass loading\nwhich has got the potential for application in material characterization,\ncommunication system and sensing. Mass loading effect on a HBAR based on\nBaxSr1-xTiO3 (BST) have been demonstrated by coating photoresist of various\nthicknesses and characterization of resonance modes present in the frequency\nspectrum of the resonator. Upon investigation, HBAR proves to be one of the\nmost promising and robust systems for gravimetric sensing. Burning effect in\nthe resonances occurs and it shifts significantly according to the amount of\nmass loaded (increasing thickness of the photoresist coated) on the resonator\nsystem. Some of the most important parameters like effective coupling\ncoefficient, spacing of parallel resonance frequency (SPRF) and quality factor\nof the resonator and its numerous modes have been investigated meticulously.", "category": "physics_app-ph" }, { "text": "Crystallization of Cuprous Oxide Thin Films by Continuous-Wave Laser\n Diode with Micro-Chevron Laser Beam (\u03bc-CLB): Crystallization of thin film materials by exploiting laser induced\ncrystallization has been advancing for the past four decades. This unique thin\nfilm technique has been predominantly used in processing thin film materials\nmade of a single chemical element; however, harnessing this technique to extend\nits use for thin film materials containing multiple chemical elements (e.g.,\nmetal oxides) unlocks applications currently not accessible. In this study,\nlaser crystallization of a Cu2O strip was demonstrated. A continuous-wave laser\ndiode with a micrometer-scale chevron-shaped beam profile (micro chevron laser\nbeam) was used to crystallize CuO thin films covered with an amorphous carbon\n(a-C) cap layer, deposited on fused silica substrates. Electron backscatter\ndiffraction, Raman spectroscopy, photoluminescence spectroscopy, and UV-Vis\nspectroscopy were used to investigate the crystallinity and optical properties\nof the Cu2O thin films revealing their unique characteristics associated with\nthe crystallization process.", "category": "physics_app-ph" }, { "text": "Conformal Transformation Electromagnetics Based on Schwarz-Christoffel\n Mapping for the Synthesis of Doubly Connected Metalenses: An innovative transformation electromagnetics (TE) paradigm, which leverages\non the Schwarz-Christoffel (SC) theorem, is proposed to design effective and\nrealistic field manipulation devices (FMDs). Thanks to the conformal property,\nsuch a TE design method allows one to considerably mitigate the anisotropy of\nthe synthesized metalenses (i.e., devices with artificially engineered\nmaterials covering an antenna to modify its radiation features) with respect to\nthose yielded by the competitive state-of-the-art TE techniques. Moreover,\ndevices with doubly connected contours, thus including masts with arbitrary\nsections and lenses with holes/forbidden regions in which the material\nproperties cannot be controlled, can be handled. A set of numerical experiments\nis presented to assess the features of the proposed method in terms of\nfield-manipulation capabilities and complexity of the lens material in a\ncomparative fashion.", "category": "physics_app-ph" }, { "text": "Time constant of the cross field demagnetization of superconducting\n stacks of tapes: Stacks of REBCO tapes can trap large amounts of magnetic fields and can stay\nmagnetized for long periods of times. This makes them an interesting option for\nmajor engineering applications such as motors, generators and magnetic\nbearings. When subjected to transverse alternating fields, superconducting\ntapes face a reduction in the trapped field, and thus it is the goal of this\npaper to understand the influence of all parameters in cross field\ndemagnetization of stacks of tapes. Major parameter dependencies considered for\nthe scope of this paper are ripple field amplitude, frequency, tape width, tape\nthickness (from 1 to 20 $\\mu$m), and number of tapes (up to 20). This article\nalso provides a systemic study of the relaxation time constant $\\tau$, which\ncan be used to estimate the cross-field demagnetization decay for high number\nof cycles. Modeling is based on the Minimum Electro-Magnetic Entropy Production\nmethod, and it is shown that the 2D model gives very accurate results for long\nsamples when compared with 3D model. Analytical formulas for large number of\ncycles have been devised. The results show that when the ripple field amplitude\nis above the penetration field of one tape, the stack always fully\ndemagnetizes, roughly in exponential decay. Increasing the number of tapes only\nincreases the relaxation time. The formulas derived also hold when validated\nagainst numerical results, and can be used for quick approximation of decay\nconstant. They also show that the cause of the decreases of cross-field\ndemagnetization with number of tapes is the increase in the self-inductance of\nthe magnetization currents. The trends and insights obtained for cross field\ndemagnetization for stacks are thus very beneficial for engineers and\nscientists working with superconducting magnet design and applications.", "category": "physics_app-ph" }, { "text": "Approaching intrinsic threshold breakdown voltage and ultra-high gain in\n graphite/InSe Schottky photodetector: Realizing both ultra-low breakdown voltage and ultra-high gain has been one\nof the major challenges in the development of high-performance avalanche\nphotodetector. Here, we report that an ultra-high avalanche gain of 3*10^5 can\nbe realized in the graphite/InSe Schottky photodetector at a breakdown voltage\ndown to 5.5 V. Remarkably, the threshold breakdown voltage can be further\nreduced down to 1.8 V by raising the operating temperature, approaching the\ntheoretical limit of 1.5E_g/e with E_g the band gap of semiconductor. We\ndevelop a two-dimensional impact ionization model and uncover that observation\nof high gain at low breakdown voltage arises from reduced dimensionality of\nelectron-phonon (e-ph) scattering in the layered InSe flake. Our findings open\nup a promising avenue for developing novel weak-light detectors with low energy\nconsumption and high sensitivity.", "category": "physics_app-ph" }, { "text": "Electrical evolution of W and WC Schottky contacts on 4H-SiC at\n different annealing temperatures: In this paper, we investigate the electrical evolution of tungsten (W) and\ntungsten carbide (WC) Schottky contacts on 4H-SiC subjected to thermal\ntreatments at different annealing temperatures from 475 to 700 {\\deg} C. For\neach annealing temperature, the uniformity of the Schottky barrier height\n(${\\phi_B}$) and ideality factor (n) was monitored by current-voltage (I-V)\nmeasurements in forward bias, performed over sets of equivalent diodes. Good\nvalues of n (below 1.05) were found for both contacts up to thermal annealing\nat 700 {\\deg} C. On the other hand, the barrier of the two contacts behaves\ndifferently. For the W/4H-SiC diode, the ${\\phi_B}$ increases with the\nannealing temperature (from 1.14 eV at 475 {\\deg} C to 1.25 eV at 700 {\\deg}\nC), whereas the Schottky barrier in WC/4H-SiC features a slight reduction\nalready with thermal annealing at 475 {\\deg} C, remaining almost constant at\naround 1.06 eV up to annealing at 700 {\\deg} C. A deeper characterization was\nperformed on the 700 {\\deg} C-annealed contacts by studying the\ntemperature-dependence of the Schottky parameters by\ncurrent-voltage-temperature (I-V-T) characterization. The ${\\phi_B}$ and n\nbehaviour with temperature indicates the presence of a nanoscale lateral\ninhomogeneity for both Schottky contacts, which can be described by Tung's\nmodel. Finally, the temperature-dependence of the reverse characteristics could\nbe described by the thermionic field emission model (TFE), accounting for the\ntemperature dependent barrier height determined from forward characterization.", "category": "physics_app-ph" }, { "text": "Simulation of corrosion and mechanical degradation of additively\n manufactured Mg scaffolds in simulated body fluid: A simulation strategy based in the finite element model was developed to\nmodel the corrosion and mechanical properties of biodegradable Mg scaffolds\nmanufactured by laser power bed fusion after immersion in simulated body fluid.\nCorrosion was simulated through a phenomenological, diffusion-based model which\ncan take into account pitting. The elements in which the concentration of Mg\nwas below a certain threshold (representative of the formation of Mg(OH)2)\nafter the corrosion simulation were deleted for the mechanical simulations, in\nwhich Mg was assumed to behave as an isotropic, elastic-perfectly plastic solid\nand fracture was introduced through a ductile failure model. The parameters of\nthe models were obtained from previous experimental results and the numerical\npredictions of the strength and fracture mechanisms of WE43 Mg alloy porous\nscaffolds in the as-printed condition and after immersion in simulated body\nfluid were in good agreement with the experimental results. Thus, the\nsimulation strategy is able to assess the effect of corrosion on the mechanical\nbehavior of biodegradable scaffolds, which is critical for design of\nbiodegradable scaffolds for biomedical applications.", "category": "physics_app-ph" }, { "text": "Understanding anti-parity-time symmetric systems with a conventional\n heat transfer framework -- comment on \"Anti-parity-time symmetry in diffusive\n systems\": Inspired by non-Hermitian physics, Li et al. (Science 364, 170-173)\ntheoretically predicted and experimentally demonstrated a stationary\ntemperature profile in a diffusive heat transfer system - seemingly indicating\nthat heat \"stops\" diffusing. By analogy to the wave physics framework, the\nmotionless and moving temperature profiles are manifestations of the\nanti-parity-time APT symmetry and symmetry breaking states, respectively. Their\nexperimental setup consists of two thermally coupled rings rotating in the\nopposite direction. At a particular rotation speed, known as the exceptional\npoint, the APT symmetry of the system changes, resulting in the temperature\nprofile switching between stationary and moving states. In fact, this seemingly\nunusual and exotic behavior can be elegantly captured and predicted using a\nconventional heat transfer framework with similarity and scaling analysis. In\nthis work, we show the system behavior can be characterized into three zones by\ntwo widely-used dimensionless parameters on a regime map. The exceptional\npoint, discovered using wave physics, is located precisely on the zone boundary\non the regime map, indicating a balance between the contribution of thermal\ncoupling and mechanical motion. Furthermore, the observed cessation of thermal\ndiffusion is merely a result of the long diffusion time constant of the\nexperimental setup. The unfamiliarity of concepts in another scientific field\nas well as the remarkable equivalence of the two points of view prompts this\nin-depth discussion of the analogy between wave physics and heat transfer. We\nbelieve that this work can help bridge the gap and promote new developments in\nthe two distinctly different disciplines.", "category": "physics_app-ph" }, { "text": "Quantum efficiency modeling for a thick back-illuminated astronomical\n CCD: The quantum efficiency and reflectivity of thick, back-illuminated CCD's\nbeing fabricated at LBNL for astronomical applications are modeled and compared\nwith experiment. The treatment differs from standard thin-film optics in that\n(a) absorption is permitted in any film, (b) the 200--500~$\\mu$m thick silicon\nsubstrate is considered as a thin film in order to observe the fringing\nbehavior at long wavelengths, and (c) by using approximate boundary conditions,\nabsorption in the surface films is separated from absorption in the substrate.\nFor the quantum efficiency measurements the CCD's are normally operated as\nCCD's, usually at $T = -140^\\circ$C, and at higher temperatures as photodiodes.\nThey are mounted on mechanical substrates. Reflectivity is measured on\nair-backed wafer samples at room temperature. The agreement between model\nexpectation and quantum efficiency measurement is in general satisfactory.", "category": "physics_app-ph" }, { "text": "Graphene-based Soft Wearable Antennas: Electronic textiles (e-textiles) are about to face tremendous environmental\nand resource challenges due to the complexity of sorting, the risk to supplies\nand metal contamination in textile recycling streams. This is because\ne-textiles are heavily based on the integration of valuable metals, including\ngold, silver and copper. In the context of exploring sustainable materials in\ne-textiles, we tested the boundaries of multi-layer (ML) graphene in wearable\ncommunication applications, in which metal assemblies are leading the way in\nwearable communication. This study attempts to create a soft, textile-based\ncommunication interface that does not disrupt tactile comfort and conformity by\nintroducing ML graphene sheets. The antenna design proposed is based on a\nmultidisciplinary approach that merges electromagnetic engineering and material\nscience and integrates graphene, a long-lasting alternative to metal\ncomponents. The designed antenna covers a wide bandwidth ranging from 3 GHz to\n9 GHz, which is a promising solution for a high data rate and efficient\ncommunication link. We also described the effects of bending and proximity to\nthe human body on the antenna performance. Overall, the results suggested that\ngraphene-based soft antennas are a viable solution for a fully integrated\ntextile-based communication interface that can replace the current rigid,\nrestrictive and toxic approaches, leading to a future where eco-friendliness\nand sustainability is the only way forward!", "category": "physics_app-ph" }, { "text": "Superconducting Pulse Conserving Logic and Josephson-SRAM: Superconducting digital Pulse-Conserving Logic (PCL) and Josephson SRAM\n(JSRAM) memory together enable scalable circuits with energy efficiency 100x\nbeyond leading-node CMOS. Circuit designs support high throughput and low\nlatency when implemented in an advanced fabrication stack with\nhigh-critical-current-density Josephson junctions of 1000$\\mu$A/$\\mu$m$^2$.\nPulse-conserving logic produces one single-flux-quantum output for each input,\nand includes a three-input, three-output gate producing logical or3, majority3\nand and3. Gate macros using dual-rail data encoding eliminate inversion latency\nand produce efficient implementations of all standard logic functions. A full\nadder using 70 Josephson junctions has a carry-out latency of 5ps corresponding\nto an effective 12 levels of logic at 30 GHz. JSRAM (Josephson SRAM) memory\nuses single-flux-quantum signals throughout an active array to achieve\nthroughput at the same clock rate as the logic. The unit cell has eight\nJosephson junctions, signal propagation latency of 1ps, and a footprint of\n2$\\mu$m$^2$. Projected density of JSRAM is 4 MB/cm$^2$, and computational\ndensity of pulse-conserving logic is on par with leading node CMOS accounting\nfor power densities and clock rates.", "category": "physics_app-ph" }, { "text": "A nonlinear magnonic nano-ring resonator: The field of magnonics, which aims at using spin waves as carriers in data\nprocessing devices, has attracted increasing interest in recent years. We\npresent and study micromagnetically a nonlinear nanoscale magnonic ring\nresonator device for enabling implementations of magnonic logic gates and\nneuromorphic magnonic circuits. In the linear regime, this device efficiently\nsuppresses spin-wave transmission using the phenomenon of critical resonant\ncoupling, thus exhibiting the behavior of a notch filter. By increasing the\nspin-wave input power, the resonance frequency is shifted leading to\ntransmission curves, depending on the frequency, reminiscent of the activation\nfunctions of neurons or showing the characteristics of a power limiter. An\nanalytical theory is developed to describe the transmission curve of magnonic\nring resonators in the linear and nonlinear regimes and validated by a\ncomprehensive micromagnetic study. The proposed magnonic ring resonator\nprovides a multi-functional nonlinear building block for unconventional\nmagnonic circuits.", "category": "physics_app-ph" }, { "text": "The physical limits of nanoLEDs and nanolasers for optical\n communications: Nanoscale light sources are being intensively investigated for their\npotential to enable low-energy, high-density optical communication and sensing\nsystems. Both nano-light-emitting diodes (nanoLEDs) and nanolasers have been\nconsidered, based on advanced nanophotonic concepts such as photonic crystals\nand plasmonic structures, with dimensions well into the sub-micrometer domain.\nWith decreasing dimensions, light-matter interaction becomes stronger,\npotentially leading to efficient and ultrafast radiative emission, both in the\nspontaneous and stimulated regime. These features have created wide\nexpectations for the practical prospects of such nanoscale light sources, in\nparticular for optical interconnects. In this article we examine the limits to\nthe downscaling of LEDs and lasers, and ask ourselves which type of source is\nmost suited to ultralow-power optical communications. Based on simple physical\nconsiderations on the scaling of spontaneous and stimulated emission rates for\nsemiconductor active regions at room temperature, we analyze the speed and\nenergy limits for nanoLEDs and nanolasers as a function of their size. The role\nof spontaneous emission enhancement (Purcell effect) in practical nanophotonic\nsources is also revisited. The main conclusion is that nanoLEDs reach a\nfundamental energy/speed limit for data rates exceeding a few Gb/s, whereas\nnanolasers with active dimensions in the range of few 100s nm may enable direct\nmodulation rates larger than 40 Gb/s at power levels adequate for\nshort-distance and low-energy optical interconnects.", "category": "physics_app-ph" }, { "text": "Spectral emissivity of copper and nickel in the mid-infrared range\n between 250 and 900 $^{\\circ}$C: A study on the radiative properties of two pure metals, copper and nickel,\nusing a high accuracy radiometer is carried out. Their spectral emissivity\nbetween 3 and 21 {\\mu}m and its dependence on emission angle and temperature\nbetween 250 and 900 $^{\\circ}$C is measured. An evolution of the samples\nemissivity associated to the surface stress relaxation is observed, which is\nrelieved after two or three heating cycles. Spectral emissivity of metals\nusually decreases as wavelength increases, but in the case of copper an\nirregular behaviour has been found. Its spectral emissivity shows a broad\nplateau around 10 {\\mu}m, which can be due to the anomalous skin effect. On the\nother hand, the emissivity usually increases with temperature, but in the case\nof nickel the emissivity changes little and even slightly decreases for T > 700\n$^{\\circ}$C. The exper-imental directional emissivity of both metals shows the\ndependence on the emission angle predicted by the electromagnetic theory for\nmetallic samples. By increasing the emission angle, the emissivity dependence\non the wavelength strongly decreases. Furthermore, in the case of nickel, an\nemissivity increase with wavelength is observed for k > 20 {\\mu}m. The\nelectrical resistivity for both metals is obtained by fitting the experimental\nemissivity curves with the Hagen Rubens equation. The results agree fairly well\nwith direct electrical resistivity measurements for copper but show a poor\nagreement in the case of nickel.", "category": "physics_app-ph" }, { "text": "Transition Metal Chalcogenide Tin Sulfide Nanodimensional Films Align\n Liquid Crystals: Transition metal chalcogenide tin sulfide (SnS) films as alternative\nnoncontact alignment layer for liquid crystals, have been demonstrated and\ninvestigated. The SnS has an anisotropic atomic chain structure similar to\nblack Phosphorous which causes the liquid crystal molecules to align without\nthe need for any additional surface treatments. The high anisotropic nature of\nSnS promotes the alignment of the easy axis of liquid crystal molecules along\nthe periodic atomic grooves of the SnS layer. The atomically thin SnS layers\nwere deposited on indium tin oxide films on glass substrates, at room\ntemperature by chemical vapor deposition. The device characteristics are\ncomparable to those commercially available, which use photo-aligning polymer\nmaterials. We measured threshold voltage of 0.92V, anchoring energy of\n1.573x10^(-6) J/m^2, contrast ratio better than 71:1 and electro-optical\nrise/fall times of 80/390ms, respectively for ~11 micron thick liquid crystal\ndevice as expected.", "category": "physics_app-ph" }, { "text": "An low-cost spectrum analyzer for trouble shooting noise sources in\n scanning probe microscopy: Scanning probe microscopes are notoriously sensitive to many types of\nexternal and internal interference including electrical, mechanical and\nacoustic noise. Sometimes noise can even be misinterpreted as real features in\nthe images. Therefore, quantification of the frequency and magnitude of any\nnoise is key to discovering the source and eliminating it from the system.\nWhile commercial spectrum analyzers are perfect for this task, they are rather\nexpensive and not always available. We present a simple, cost effective\nsolution in the form of an audio output from the instrument coupled to a smart\nphone spectrum analyzer application. Specifically, the scanning probe signal,\ne.g. the tunneling current of a scanning tunneling microscope is fed to the\nspectrum analyzer which Fourier transforms the time domain acoustic signal into\nthe frequency domain. When the scanning probe is in contact with the sample,\nbut not scanning, the output is a spectrum containing both the amplitude and\nfrequency of any periodic noise affecting the microscope itself, enabling\ntroubleshooting to begin.", "category": "physics_app-ph" }, { "text": "High-index-contrast single-mode optical waveguides fabricated on lithium\n niobate by photolithography assisted chemo-mechanical etching (PLACE): We report fabrication of low loss single mode waveguides on lithium niobate\non insulator (LNOI) cladded by a layer of SiO2. Our technique, termed\nphotolithography assisted chemo-mechanical etching (PLACE), relies on\npatterning of a chromium film into the mask shape by femtosecond laser\nmicromachining and subsequent chemo-mechanical etching of the lithium niobate\nthin film. The high-index-contrast single mode waveguide is measured to have a\npropagation loss of 0.13 dB/cm. Furthermore, waveguide tapers are fabricated\nfor boosting the coupling efficiency.", "category": "physics_app-ph" }, { "text": "Multi-level resistance switching and random telegraph noise analysis of\n nitride based memristors: Resistance switching devices are of special importance because of their\napplication in resistive memories (RRAM) which are promising candidates for\nreplacing current nonvolatile memories and realize storage class memories.\nThese devices exhibit usually memristive properties with many discrete\nresistance levels and implement artificial synapses. The last years,\nresearchers have demonstrated memristive chips as accelerators in computing,\nfollowing new in-memory and neuromorphic computational approaches. Many\ndifferent metal oxides have been used as resistance switching materials in MIM\nor MIS structures. Understanding of the mechanism and the dynamics of\nresistance switching is very critical for the modeling and use of memristors in\ndifferent applications. Here, we demonstrate the bipolar resistance switching\nof silicon nitride thin films using heavily doped Si and Cu as bottom and\ntop-electrodes, respectively. Analysis of the current-voltage characteristics\nreveal that under space-charge limited conditions and appropriate current\ncompliance setting, multi-level resistance operation can be achieved.\nFurthermore, a flexible tuning protocol for multi-level resistance switching\nwas developed applying appropriate SET/RESET pulse sequences. Retention and\nrandom telegraph noise measurements performed at different resistance levels.\nThe present results reveal the attractive properties of the examined devices.", "category": "physics_app-ph" }, { "text": "Localized heat diffusion in topological thermal materials: Various unusual behaviors of artificial materials are governed by their\ntopological properties, among which the edge state at the boundary of a\nphotonic or phononic lattice has been captivated as a popular notion. However,\nthis remarkable bulk-boundary correspondence and the related phenomena are\nmissing in thermal materials. One reason is that heat diffusion is described in\na non-Hermitian framework because of its dissipative nature. The other is that\nthe relevant temperature field is mostly composed of modes that extend over\nwide ranges, making it difficult to be rendered within the tight-binding theory\nas commonly employed in wave physics. Here, we overcome the above challenges\nand perform systematic studies on heat diffusion in thermal lattices. Based on\na continuum model, we introduce a state vector to link the Zak phase with the\nexistence of the edge state, and thereby analytically prove the thermal\nbulk-boundary correspondence. We experimentally demonstrate the predicted edge\nstates with a topologically protected and localized heat dissipation capacity.\nOur finding sets up a solid foundation to explore the topology in novel heat\ntransfer manipulations.", "category": "physics_app-ph" }, { "text": "Integration of hBN quantum emitters in monolithically fabricated\n waveguides: Hexagonal boron nitride (hBN) is gaining interest for potential applications\nin integrated quantum nanophotonics. Yet, to establish hBN as an integrated\nphotonic platform several cornerstones must be established, including the\nintegration and coupling of quantum emitters to photonic waveguides. Supported\nby simulations, we study the approach of monolithic integration, which is\nexpected to have coupling efficiencies that are 4 times higher than those of a\nconventional hybrid stacking strategy. We then demonstrate the fabrication of\nsuch devices from hBN and showcase the successful integration of hBN single\nphoton emitters with a monolithic waveguide. We demonstrate coupling of single\nphotons from the quantum emitters to the waveguide modes and on-chip detection.\nOur results build a general framework for monolithically integrated hBN single\nphoton emitter and will facilitate future works towards on-chip integrated\nquantum photonics with hBN.", "category": "physics_app-ph" }, { "text": "A new metric for the comparison of permittivity models in terahertz\n time-domain spectroscopy: We present a robust method, as well as a new metric, for the comparison of\npermittivity models in terahertz timedomain spectroscopy (THz-TDS). In this\nwork, we perform an extensive noise analysis of a THz-TDS system, we remove and\nmodel the unwanted deterministic noises and implement them into our fitting\nprocess. This is done using our open-source software, Fit@TDS, available at :\nhttps://github.com/THzbiophotonics/Fit-TDS. This work is the first step towards\nthe derivation of uncertainties, and therefore the use of error bars. We hope\nthat this will lead to performing analytical analysis with THz-TDS, as results\nobtained from different setups will be comparable. Finally, we apply this\nprotocol to the study of a $\\alpha$-lactose monohydrate pellet in order to give\nmore insight on the molecular dynamics behind the absorption peaks. The\ncomparison with simulation results is made easier thanks to the probabilities\nderived from the metric.", "category": "physics_app-ph" }, { "text": "High-energy optical transitions and optical constants of\n CH$_3$NH$_3$PbI$_3$ measured by spectroscopic ellipsometry and\n spectrophotometry: Optoelectronics based on metal halide perovskites (MHPs) have shown\nsubstantial promise, following more than a decade of research. For prime routes\nof commercialization such as tandem solar cells, optical modeling is essential\nfor engineering device architectures, which requires accurate optical data for\nthe materials utilized. Additionally, a comprehensive understanding of the\nfundamental material properties is vital for simulating the operation of\ndevices for design purposes. In this article, we use variable angle\nspectroscopic ellipsometry (SE) to determine the optical constants of\nCH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) thin films over a photon energy range of 0.73\nto 6.45 eV. We successfully model the ellipsometric data using six Tauc-Lorentz\noscillators for three different incident angles. Following this, we use\ncritical-point analysis of the complex dielectric constant to identify the\nwell-known transitions at 1.58, 2.49, 3.36 eV, but also additional transitions\nat 4.63 and 5.88 eV, which are observed in both SE and spectrophotometry\nmeasurements. This work provides important information relating to optical\ntransitions and band structure of MAPbI$_3$, which can assist in the\ndevelopment of potential applications of the material.", "category": "physics_app-ph" }, { "text": "Laser-patterned multifunctional sensor array with graphene nanosheets as\n a smart biomonitoring fashion accessory: Biomonitoring wearable sensors based on two-dimensional nanomaterials have\nlately elicited keen research interest and potential for a new range of\nflexible nanoelectronic devices. Practical nanomaterial-based devices suited\nfor real-world service, which have first-rate performance while being an\nattractive accessory, are still distant. We report a multifunctional flexible\nwearable sensor fabricated using an ultra-thin percolative layer of microwave\nexfoliated graphene nanosheets on laser-patterned gold circular inter-digitated\nelectrodes for monitoring vital human physiological parameters. This Graphene\non Laser-patterned Electrodes (GLE) sensor displays an ultra-high strain\nresolution of 0.024% and a record gauge factor of 6.3e7 and exceptional\nstability and repeatability in its operating range. The sensor was subjected to\nbiomonitoring experiments like measurement of heart rate, breathing rate, body\ntemperature, and hydration level, which are vital health parameters, especially\nconsidering the current pandemic scenario. The sensor also served in\napplications such as a pedometer, limb movement tracking, and control switch\nfor human interaction. The innovative laser-etch process used to pattern gold\nthin-film electrodes and shapes, with the multifunctional incognizable graphene\nlayer, provides a technique for integrating multiple sensors in a wearable\nfashion accessory. The reported work marks a giant leap from the conventional\nbanal devices to a highly marketable multifunctional sensor array as a\nbiomonitoring fashion accessory.", "category": "physics_app-ph" }, { "text": "Quantitative optical imaging method for surface acoustic waves using\n optical path modulation: A Rayleigh-type surface acoustic wave (SAW) is used in various fields as\nclassical and quantum information carriers because of its surface localization,\nhigh electrical controllability, and low propagation loss. Coupling and\nhybridization between the SAW and other physical systems such as magnetization,\nelectron charge, and electron spin are the recent focuses in phononics and\nspintronics. A precise measurement of the surface wave amplitude is often\nnecessary to discuss the coupling strengths. However, there are only a few such\nmeasurement techniques and they generally require a rather complex analysis.\nHere we develop and demonstrate a straightforward measurement technique that\ncan quantitatively characterize the SAW. The technique optically detects the\nsurface waving due to the coherently driven SAW by the optical path modulation.\nFurthermore, when the measurement system operates in the shot-noise-limited\nregime, the surface slope and displacement at the optical spot can be deduced\nfrom the optical path modulation signal. Our demonstrated technique will be an\nimportant tool for SAW-related research.", "category": "physics_app-ph" }, { "text": "Ion hydration-controlled large osmotic power with arrays of Angstrom\n scale capillaries of vermiculite: In the osmotic power generation field, reaching the industrial benchmark has\nbeen challenging because of the need for capillaries close to the sizes of ions\nand molecules. Here, we fabricated well-controlled 'along-the-capillary'\nmembranes of Na-vermiculite with a capillary size of ~5 Angstrom. They exhibit\n1600 times enhanced conductivity compared to commonly studied\n'across-the-capillary' membranes. Interestingly, they show a very high cation\nselectivity of 0.83 for NaCl solutions, which resulted in large power densities\nof 9.6 W.m^-2 and 12.2 W.m^-2 at concentration gradients of 50 and 1000,\nrespectively, at 296 K, for an unusually large membrane length of 100 micron.\nThe power density shows an exponential increase with temperature, reaching 65.1\nW.m-2 for a concentration gradient of 50 at 333 K. This markedly differs from\nthe classical behavior and indicates the role of ion (de)hydration in enhancing\npower density, opening new possibilities for exploiting such membranes for\nenergy harvesting applications.", "category": "physics_app-ph" }, { "text": "Characterization and Modeling of Silicon-on-Insulator Lateral Bipolar\n Junction Transistors at Liquid Helium Temperature: Conventional silicon bipolars are not suitable for low-temperature operation\ndue to the deterioration of current gain ($\\beta$). In this paper, we\ncharacterize lateral bipolar junction transistors (LBJTs) fabricated on\nsilicon-on-insulator (SOI) wafers down to liquid helium temperature (4 K). The\npositive SOI substrate bias could greatly increase the collector current and\nhave a negligible effect on the base current, which significantly alleviates\n$\\beta$ degradation at low temperatures. We present a physical-based compact\nLBJT model for 4 K simulation, in which the collector current\n($\\textit{I}_\\textbf{C}$) consists of the tunneling current and the additional\ncurrent component near the buried oxide (BOX)/silicon interface caused by the\nsubstrate modulation effect. This model is able to fit the Gummel\ncharacteristics of LBJTs very well and has promising applications in amplifier\ncircuits simulation for silicon-based qubits signals.", "category": "physics_app-ph" }, { "text": "Nano-assembled open quantum dot nanotube devices: A pristine suspended carbon nanotube is a near ideal environment to host\nlong-lived quantum states. For this reason, they have been used as the core\nelement of qubits and to explore numerous condensed matter physics phenomena.\nOne of the most advanced technique to realize complex carbon nanotube based\nquantum circuits relies on a mechanical integration of the nanotube into the\ncircuit. Despite the high-quality and complexity of the fabricated circuits,\nthe range of possible experiments was limited to the closed quantum dot regime.\nHere, by engineering a transparent metal-nanotube interface, we developed a\ntechnique that overcomes this limitation. We reliably reach the open quantum\ndot regime as demonstrated by measurements of Fabry-Perot interferences and\nKondo physics in multiple devices. A circuit-nanotube alignment precision of\n+/-200nm is demonstrated. Our technique allows to envision experiments\nrequiring the combination of complex circuits and strongly coupled carbon\nnanotubes such as the realization of carbon nanotube superconducting qubits or\nflux-mediated optomechanics experiments.", "category": "physics_app-ph" }, { "text": "Effect of Graphene Interface on Potassiation in a Graphene- Selenium\n Heterostructure Cathode for Potassium-ion Batteries: Selenium (Se) cathodes are an exciting emerging high energy density storage\nsystem for Potassium ion batteries(KIB), where potassiation reactions are less\nunderstood. Here, we present an atomic-level investigation of KxSe cathode\nenclosed in hexagonal lattices of carbon(C) characteristic of multilayered\ngraphene matrix and multiwalled carbon nanotubes (MW-CNTs). Microstructural\nchanges directed by graphene substrate in KxSe cathode are contrasted with\ngraphene-free cathode. Graphene's binding affinity for long-chain polyselenides\n(Se-Se-Se = -2.82 eV and Se-Se = -2.646 eV) and ability to induce reactivity\nbetween Se and K are investigated. Furthermore, intercalation voltage for\ngraphene enclosed KxSe cathode reaction intermediates are calculated with K2Se\nas the final discharged product. Our results indicate a single-step reaction\nnear a voltage of 1.55 V between K and Se cathode. Our findings suggest that\noperating at higher voltages (~2V) could result in the formation of reaction\nintermediates where intercalation/deintercalation of K could be a challenge,\nand therefore cause irreversible capacity losses in the battery. Primary issues\nare the high binding energy of long-chain polyselenides with graphene that\ndiscourage K storage and Se-Se bond dissociation at low K concentrations. A\ncomparison with graphene-free cathode highlights the substantial changes a van\nder Waals (vdW) graphene interface can bring in atomic-structure and\nelectrochemistry of the KxSe cathode.", "category": "physics_app-ph" }, { "text": "Temporal Evolution of Self-Assembled Lead Halide Perovskite Nanocrystal\n Superlattices: Effects on Photoluminescence and Energy Transfer: Excitonic/electronic coupling and cooperative interactions in self-assembled\nlead halide perovskite nanocrystals were reported to give rise to a collective\nlow energy emission peak with accelerated dynamics. Here we report that similar\nspectroscopic features could appear as a result of the nanocrystal reactivity\nwithin the self-assembled superlattices. This is demonstrated by using CsPbBr3\nnanocrystal superlattices under room temperature and cryogenic\nmicro-photoluminescence spectroscopy. It is shown that keeping such structures\nunder vacuum, a gradual contraction of the superlattices and subsequent\ncoalescence of the nanocrystals occurs over several days. As a result, a\nnarrow, low energy emission peak is observed at 4 K with a concomitant\nshortening of the photoluminescence lifetime due to the energy transfer between\nnanocrystals. When exposed to air, self-assembled CsPbBr3 nanocrystals develop\nbulk-like CsPbBr3 particles on top of the superlattices. At 4 K, these\nparticles produce a distribution of narrow, low energy emission peaks with\nshort lifetimes and excitation fluence-dependent, oscillatory decays,\nresembling the features of superfluorescence. Overall, the reactivity of\nCsPbBr3 nanocrystals dramatically alters the emission of their assemblies,\nwhich should not be overlooked when studying collective optoelectronic\nproperties nor confused with superfluorescence effects.", "category": "physics_app-ph" }, { "text": "Single quantum dot selection and tailor-made photonic device integration\n using nanoscale focus pinspot: Among the diverse platforms of quantum light sources, epitaxially grown\nsemiconductor quantum dots (QDs) are one of the most attractive workhorses for\nrealizing various quantum photonic technologies owing to their outstanding\nbrightness and scalability. There exist various material systems for these QDs\nbased on their appropriate emission bandwidth; however, only a few material\nsystems have successfully grown single or low-density QDs, which are essential\nfor quantum light sources. In most other material systems, it is difficult to\nrealize low-density QDs, and the mesa-etching process is usually undergone in\norder to reduce their density. Nevertheless, the etching process irreversibly\ndestroys the medium near the QD, which is detrimental to in-plane device\nintegration. In this study, we apply a nondestructive luminescence picking\nmethod termed as nanoscale focus pinspot (NFP) using helium ion microscopy to\nreduce the luminous QD density while retaining the surrounding medium. Given\nthat the NFP can precisely manipulate the luminescence at nanoscale resolution,\na photonic device can be deterministically fabricated on the target QD matched\nfrom both spatial and spectral points of view. After applying the NFP, we\nextract only a single QD emission out of the high-density ensemble QD emission.\nMoreover, the photonic structure of a circular Bragg reflector is\ndeterministically integrated with the selected QD, and the extraction\nefficiency of the QD emission has been improved 27 times. Furthermore, this\ntechnique does not destroy the medium and only controls the luminescence.\nHence, it is highly applicable to various photonic structures, including\nphotonic waveguides or photonic crystal cavities regardless of their materials.", "category": "physics_app-ph" }, { "text": "$\u03c0$/2 Mode Converters and Vortex Generators for Electrons: In optics, mode conversion is an elegant way to switch between Hermite\nGaussian and Laguerre Gaussian beam profiles and thereby impart orbital angular\nmomentum onto the beam and to create vortices. In optics such vortex beams can\nbe produced in a setup consisting of two identical cylinder lenses. In electron\noptics, quadrupole lenses can be used for the same purpose. Here we investigate\ngeneralized asymmetric designs of a quadrupole mode converter that may be\nrealized within the constraints of existing electron microscopes and can steer\nthe development of dedicated vortex generators for high brilliance electron\nvortex probes of atomic scale.", "category": "physics_app-ph" }, { "text": "Physical Design and Experimental Verification of a Huygens' Metasurface\n Two-lens System for Phased-array Scan-angle Enhancement: Over the past decades, many radome designs to extend the angular scan range\nof phased-array antennas have been devised by utilizing dielectric materials\nand metamaterials. More recently, metasurface technology such as planar lenses\nand beam deflectors have been applied to phased arrays, enabling scan-angle\nenhancers to have a low profile. In this work, a physical Huygens' metasurface\n(HMS) two-lens system for scanangle doubling of a phased array is presented.\nFor the HMS unit cells, the wire-loop topology is deployed to achieve high\ntransmission for the required phase-angle shift. The proposed two-lens system\nis analyzed by full-wave simulations and experiments. The simulation results\ndemonstrate that the scan angle doubles when the incident angle is below\n15{\\deg} in accordance to the design specification. Furthermore, the\ndirectivity degradation of the refracted beams by the two-HMS lenses is in good\nagreement with theory. Finally, a fabricated two-lens system with two\n15{\\lambda} long by 15{\\lambda} wide metasurface lenses and a\n16{\\times}16-element patch antenna array as a source is experimentally verified\nat 10 GHz. The experimental results are in good agreement with the simulated\nresults by showing angle-doubling performance with {\\pm}2{\\deg} scan errors.", "category": "physics_app-ph" }, { "text": "Proton Irradiation-Decelerated Intergranular Corrosion of Ni-Cr Alloys\n in Molten Salt: The effects of ionizing radiation on materials often reduce to \"bad news.\"\nRadiation damage usually leads to detrimental effects such as embrittlement,\naccelerated creep, phase instability, and radiation-altered corrosion. This\nlast point merits special attention. Elucidating synergies between radiation\nand corrosion has been one of the most challenging tasks impeding the\ndeployment of advanced reactors, stemming from the combined effects of high\ntemperature, corrosive coolants, and intense particle fluxes. Here we report\nthat proton irradiation significantly and repeatably decelerates intergranular\ncorrosion of Ni-Cr alloys in molten fluoride salt at 650C. We demonstrate this\neffect by showing that the depth of intergranular voids resulting from Cr\nleaching into the salt is reduced by the proton irradiation alone. Interstitial\ndefects generated from proton irradiation result in radiation-enhanced\ndiffusion, more rapidly replenishing corrosion-injected vacancies with alloy\nconstituents, thus playing the crucial role in decelerating corrosion. Our\nresults show that in industrially-relevant scenarios irradiation can have a\npositive impact, challenging our view that radiation damage always results in\nnegative effects.", "category": "physics_app-ph" }, { "text": "Roadmap on Material-Function Mapping for Photonic-Electronic Hybrid\n Neural Networks: Driven by machine-learning tasks neural networks have demonstrated useful\ncapabilities as nonlinear hypothesis classifiers. The underlying technologies\nperforming the dot product multiplication, the summation, and the nonlinear\nthresholding on the input data in electronics, however, are limited by the same\ncapacitive challenges known from electronic integrated circuits. The optical\ndomain, in contrast, provides low delay interconnectivity suitable for such\nnode distributed non Von Neumann architectures relying on dense node to node\ncommunication. Thus, once the neural network's weights are set, the delay of\nthe network is just given by the time of flight of the photon, which is in the\npicosecond range for photonic integrated circuits. However, the functionality\nof memory for storing the trained weights does not exists in optics, thus\ndemanding a fresh look to explore synergies between photonics and electronics\nin neural networks. Here we provide a roadmap to pave the way for emerging\nhybridized photonic electronic neural networks by taking a detailed look into a\nsingle node's perceptron, discussing how it can be realized in hybrid photonic\nelectronic heterogeneous technologies. We show that a set of materials exist\nthat exploit synergies with respect to a number of constrains including\nelectronic contacts, memory functionality, electrooptic modulation, optical\nnonlinearity, and device packaging. We find that the material ITO, in\nparticular, could provide a viable path for both the perceptron weights and the\nnonlinear activation function, while simultaneously being a foundry process\nnear material. We finally identify a number of challenges that, if solved,\ncould accelerate the adoption of such heterogeneous integration strategies of\nemerging memory materials into integrated photonics platforms for real time\nresponsive neural networks.", "category": "physics_app-ph" }, { "text": "Aerosol Jet Printing of High-Temperature Multimodal Sensors for Strain\n and Temperature Sensing: Integrating multiple sensing capabilities into a single multimodal sensor\ngreatly enhances its applications for in-situ sensing and structural health\nmonitoring. However, the fabrication of multimodal sensors is complicated and\nlimited by the available materials and existing manufacturing methods that\noften involve complex and expensive fabrication processes. In this study, a\nhigh-temperature multimodal sensor is demonstrated by aerosol jet printing of\ngold and ITO nanoparticle inks. The printed multimodal sensor for concurrent\nstrain and temperature sensing possesses a high gauge factor of 2.54 and\nthermopower of 55.64 V/{\\deg}C combined with excellent high-temperature thermal\nstability up to 540 {\\deg}C. Compared to traditional single-modality sensors,\nthe printed multimodal sensor significantly increases sensing capacity and\nimproves spatial resolution using microscale printed patterns. The study also\ndemonstrates that the strain sensor with integrated thermocouple enables\nin-situ compensation of the temperature effect on strain sensing, significantly\nimproving strain measurement accuracy at high temperatures. By combining\naerosol jet printing with nanomaterial inks, a wide range of multifunctional\ndevices can be developed for a broad range of emerging applications.", "category": "physics_app-ph" }, { "text": "Stabilizing ultrathin Silver (Ag) films on different substrates: This paper reports an effective method of stabilizing ultrathin Silver (Ag)\nfilms on substrates using a filler metal (Zn). Ag films with a thickness < 15\nnm were deposited by DC magnetron sputtering above a Zn filler metal on glass,\nquartz, silicon and PET (polyethylene terephthalate) substrates. Zinc is\nexpected to partially or fully fill the roughness associated with the\nsubstrates. The Zn filler material and ultrathin Ag film form a 3-D augmented\natomically chemically graded interface. 3-D interfaces have smoothly varying\nchemistry. The ability of Zn to partially or fully fill the substrate roughness\nimproves the adhesion of Zn along with the Ag to the substrate. Also, Zn acts\nas a barrier layer against the diffusion of Ag into the substrate. This\ntechnique leads to ultrathin Ag films with low sheet resistance (~ 3\n{\\Omega}/Sq.), low mean absolute surface roughness (~1 nm), good optical\ntransparency (~ 65 %), better stability and compatibility with the environment.\nThe results indicate significant potential for applying stable ultrathin Ag\nfilm/electrode as a practical and economically feasible design solution for\noptoelectronic (transparent and conductive electrodes for solar cells and LEDs)\nand plasmonic devices. This film shows good conductivity, transparency,\nstability, and flexibility.", "category": "physics_app-ph" }, { "text": "Critical Strain for Surface Nucleation of Dislocations in Silicon: A long-standing discrepancy exists between experiments and atomistic models\nconcerning the critical strain needed for surface nucleation of dislocations in\nsilicon-germanium systems. While dislocation nucleation is readily observed in\nhetero-epitaxial thin films with misfit strains less than 4%, existing\natomistic models predict that a critical strain over 7.8% is needed to overcome\nthe kinetic barrier for dislocation nucleation. Using zero-temperature energy\nbarrier calculations and finite-temperature Molecular Dynamics simulations, we\nshow that 3-dimensional surface features such as a sharply bent step can lower\nthe predicted critical nucleation strain of a shuffle-set dislocation to 6.4%,\nand that of a shuffle-glide dislocation complex to 5.3%. Consistent findings\nare obtained using both the Stillinger-Weber (SW) and modified embedded-atom\nmethod (MEAM) potentials, providing support to the physical relevance of the\nshuffle-glide dislocation complex, which was previously considered as an\nartifact of the SW potential.", "category": "physics_app-ph" }, { "text": "Local Electric Field Measurement in GaN Diodes by exciton Franz-Keldysh\n Photocurrent Spectroscopy: The eXciton Franz-Keldysh (XFK) effect is observed in GaN p-n junction diodes\nvia the spectral variation of photocurrent responsivity data that redshift and\nbroaden with increasing reverse bias. Photocurrent spectra are quantitatively\nfit over a broad photon energy range to an XFK model using only a single fit\nparameter that determines the lineshape, the local bias ($V_{l}$), uniquely\ndetermining the local electric field maximum and depletion widths. As expected,\nthe spectrally determined values of $V_{l}$ vary linearly with the applied bias\n($V$) and reveal a large reduction in the local electric field due to\nelectrostatic non-uniformity. The built-in bias ($V_{bi}$) is estimated by\nextrapolating $V_{l}$ at $V=0$, which compared with independent C-V\nmeasurements indicates an overall $\\pm$0.31 V accuracy of $V_{l}$. This\ndemonstrates sub-bandgap photocurrent spectroscopy as a local probe of electric\nfield in wide bandgap diodes that can be used to map out regions of device\nbreakdown (hot spots) for improving electrostatic design of high voltage\ndevices.", "category": "physics_app-ph" }, { "text": "Fabrication and transfer print based integration of free-standing GaN\n membrane micro-lenses onto semiconductor chips: We demonstrate the back-end integration of broadband, high-NA GaN\nmicro-lenses by micro-assembly onto non-native semiconductor substrates. We\ndeveloped a highly parallel micro-fabrication process flow to suspend micron\nscale plano-convex lens platelets from 6\" Si growth wafers and show their\nsubsequent transfer-printing integration. A growth process targeted at\nproducing unbowed epitaxial wafers was combined with optimisation of the\netching volume in order to produce flat devices for printing. Lens structures\nwere fabricated with 6 to 11 $\\mu$m diameter, 2 $\\mu$m height and\nroot-mean-squared surface roughness below 2 nm. The lenses were printed in a\nvertically coupled geometry on a single crystalline diamond substrate and with\n$\\mu$m-precise placement on a horizontally coupled photonic integrated circuit\nwaveguide facet. Optical performance analysis shows that these lenses could be\nused to couple to diamond nitrogen vacancy centres at micron scale depths and\ndemonstrates their potential for visible to infrared light-coupling\napplications.", "category": "physics_app-ph" }, { "text": "Interaction of nanoparticle properties and X-ray analytical techniques: In this work, Pt-Ti core-shell nanoparticles (NP) of 2 nm to 3 nm in size and\n30000 u \\pm 1500 u as specified single particle mass, deposited on flat silicon\nsubstrates by means of a mass-selected cluster beam source, were used for the\ninvestigation of the modification of the X-Ray Standing Wave (XSW) field\nintensity with increasing NP surface coverage. The focus of the investigation\nis on the determination of the range of validity of the undisturbed flat\nsurface approach of the XSW intensity in dependence of the actual coverage rate\nof the surface. Therefore, the nanoparticles were characterized using\nreference-free grazing incidence X-ray fluorescence analysis (GIXRF) employing\nradiometrically calibrated instrumentation. In addition, near-edge X-ray\nabsorption fine structure (NEXAFS) measurements were performed to investigate\nthe binding state of titanium in the core-shell nanoparticles which was found\nto be amorphous TiO2. The combination of GIXRF measurements and of the\ncalculated XSW field intensities allow for a quantification of the core-shell\nnanoparticle surface coverage. For six different samples, the peak surface\ncoverage could be determined to vary from 7 % to 130 % of a complete\nmonolayer-equivalent coverage. A result of the current investigation is that\ncore-shell nanoparticles modify the intensity distribution of the XSW field\nwith increasing surface coverage. This experimental result is in line with\ncalculated XSW field intensity distributions at different surface coverages\nusing an effective density approach.", "category": "physics_app-ph" }, { "text": "Refraction efficiency of Huygens' and bianisotropic terahertz\n metasurfaces: Metasurfaces are an enabling technology for complex wave manipulation\nfunctions, including in the terahertz frequency range, where they are expected\nto advance security, imaging, sensing, and communications technology. For\noperation in transmission, Huygens' metasurfaces are commonly used, since their\ngood impedance match to the surrounding media minimizes reflections and\nmaximizes transmission. Recent theoretical work has shown that Huygens'\nmetasurfaces are non-optimal, particularly for large angles of refraction, and\nthat to eliminate reflections and spurious diffracted beams it is necessary to\nuse a bianisotropic metasurface. However, it remains to be demonstrated how\nsignificant the efficiency improvement is when using bianisotropic\nmetasurfaces, considering all the non-ideal features that arise when\nimplementing the metasurface design with real meta-atoms. Here we compare\nconcrete terahertz metasurface designs based on the Huygens' and Omega-type\nbianisotropic approaches, demonstrating anomalous refraction angles for 55\ndegrees, and 70 degrees. We show that for the lower angle of 55 degrees, there\nis no significant improvement when using the bianisotropic design, whereas for\nrefraction at 70 degrees the bianisotropic design shows much higher efficiency\nand fidelity of refraction into the designed direction. We also demonstrate the\nstrong perturbations caused by near-field interaction, both between and within\ncells, which we compensate using numerical optimization.", "category": "physics_app-ph" }, { "text": "Systematic Characterization of Hydrophilized Polydimethylsiloxane: Flexible microfluidics have found extensive utility in the biological and\nbiomedical fields. A leading substrate material for compliant devices is\npolydimethylsiloxane (PDMS). Despite its many advantages, PDMS is inherently\nhydrophobic and consequently its use in passive (pumpless) microfluidics\nbecomes problematic. To this end, many physical and chemical modifications have\nbeen introduced to render PDMS hydrophilic, ranging from amphiphilic molecule\nadditions to surface plasma treatments. However, when transitioning from lab\nbenchtop to realized medical devices, these modifications must exhibit\nlong-term stability. Unfortunately, these modifications are often presented but\ntheir mechanisms and long-term stability are not studied in detail. We have\ninvestigated an array of PDMS modifications, utilizing contact angle goniometry\nto study surface energy over a 30-day evolution study. Samples were stored in\nair and water, and Fourier Transform Infrared-Attenuated Total Reflectance\n(FTIR-ATR) analysis was used to confirm surface functional group uniformity. We\nhave identified preferred modification techniques for long-lasting PDMS devices\nand characterized often overlooked material stability.", "category": "physics_app-ph" }, { "text": "Considering non-uniform current distributions in magnetoresistive sensor\n designs and their implications for the resistance transfer function: Non-uniform current distributions of spin valves with disk shaped free layers\nare investigated. In the context of spin valves, the vortex state, which is the\nground-state in many disk shaped magnetic bodies, allows for distinct parallel\nchannels of high and low resistivity. The readout current is thus able to evade\nhigh resistivity regions in favor of low resistivity regions, giving rise to\n'conductive inhomogeneities'. Therefore, the total resistance of the spin valve\ndoes not always correspond exactly to the total average magnetization of the\nfree layer. In addition, the resistance transfer function can be significantly\ninfluenced by the spatial placement of the electrodes, giving rise to\n'geometric inhomogeneities'. The resulting deviations from resistance to\nmagnetization transfer function are investigated for different spin valve\ngeometries and compared to measurements of comparable devices.", "category": "physics_app-ph" }, { "text": "Synthesis, Functionalization and Properties of Uniform Europium-doped\n Sodium Lanthanum Tungstate and Molybdate (NaLa(XO$_4$)$_2$, X= Mo,W) probes\n for Luminescent and X-ray Computed Tomography Bioimaging: A one-pot simple procedure for the synthesis of uniform, ellipsoidal\nEu3+-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X = W, Mo)\nnanophosphors, functionalized with carboxylate groups, is described. The method\nis based on a homogeneous precipitation process at 120 C from appropriate Na+,\nLn3+ and tungstate or molybdate precursors dissolved in ethylene glycol/water\nmixtures containing polyacrylic acid. A comparative study of the luminescent\nproperties of both luminescent materials as a function of the Eu3+ doping level\nhas been performed to find the optimum nanophosphor, whose efficiency as X-ray\ncomputed tomography contrast agent is also evaluated and compared with that of\na commercial probe. Finally, the cell viability and colloidal stability in\nphysiological pH medium of the optimum samples have also been studied to assess\ntheir suitability for biomedical applications.", "category": "physics_app-ph" }, { "text": "Meandering microstrip leaky-wave antenna with dual-band linear-circular\n polarization and suppressed open stopband: This paper proposes a dual-band frequency scanning meandering microstrip\nleaky-wave antenna with linear polarization in the Ku-band and circular\npolarization in the K-band. This is achieved by making use of two spatial\nharmonics for radiation. The unit cell of the periodic microstrip antenna\ncontains three meanders with mitred corners. To ensure circular polarization, a\ntheoretical formulation is developed taking into account the delay caused by\nmicrostrip length intervals. It defines the unit cell geometry by determining\nthe length of the meanders to ensure that axial ratio remains below 3 dB\nthroughout the operational band. Moreover, the meanders are used to provide\nbetter control over scanning rate (the ratio of change of angle of maximum\nradiation with frequency) and reduce spurious radiation of harmonics by\nensuring single harmonic operation within the operational band. To guarantee\ncontinuous scanning through broadside direction, open stopband is suppressed\nusing mitered angles. The antenna is designed on a 0.254-mm substrate making it\nsuitable for conformal applications. The fabricated antenna shows a backward to\nforward beam steering range of 72 deg (-42 deg to 30 deg) in the K-band\n(19.4-27.5 GHz) with circular polarization and of 75 deg (-15 deg to 60 deg) in\nthe Ku-band (11-15.5 GHz) with linear polarization.", "category": "physics_app-ph" }, { "text": "Design of auxetic cellular structures for in-plane response through\n out-of-plane actuation of stimuli-responsive bridge films: In this work, we propose novel designs of cellular structures exhibiting\nunconventional in-plane actuation responses to external stimuli. We\nstrategically introduce stimuli-responsive bilayer bridge films within\nconventional honeycombs to achieve the desired actuation. The films are\nincorporated such that, in response to an external field (thermal, electric,\nchemical, etc.), the bridge film bends out-of-plane, activating the honeycomb\nin the plane. The conventional out-of-plane deformation of the bridge film can\nlead to interesting and unconventional actuation in the plane. An analytical\nmodel of this coupled unit cell behaviour is developed using curved beam\ntheory, and the model is validated against finite element simulations. Several\napplications of such designs are presented. Unit cell architectures exhibiting\nboth positive and negative macroscopic actuation are proposed, and the\ncriterion for achieving such actuation is derived analytically. Furthermore, we\ndemonstrate that by altering the topology, unidirectional and bidirectional\nnegative actuation can be achieved. We also propose designs that result in the\nnegative actuation of the structure with both monotonically increasing and\nmonotonically decreasing stimuli. Finally, by combining two macroscopic\nstructures with positive and negative actuation, we design efficient\nactuators/sensors that bend in the plane in response to a stimulus.", "category": "physics_app-ph" }, { "text": "Plasmon-driven creation of magnetic topological structures: In the present research, we demonstrate the usage of plasmonic effects in\nthin film structures to control magnetic topological textures, specifically\nskyrmions and skyrmioniums. We investigate numerically the generation and\nalteration of these topological structures caused by hemisphere gold\nnanoparticle placed over a magnetic layer coated with a dielectric material.\nThe electromagnetic and photothermal models are used to clarify the processes\nof producing heat and absorption, and the results were implemented in\nmicromagnetic formalism to reveal the dynamics of magnetization under various\nconditions. Our findings demonstrate the significance of the laser pulse\nduration and the contact area between nanoparticles and the underlying magnetic\nlayer in forming topological textures. In particular, we show how to generate a\nsingle skyrmion, multiple skyrmions, and skyrmioniums, and how to dynamically\ntransition between these states. These results highlight the possibility of\nmanipulating magnetic textures by using plasmonic effects, which presents\nsignificant opportunities for spintronics and non-conventional computer\napplications.", "category": "physics_app-ph" }, { "text": "Semimetals for high performance photodetection: Semimetals are being explored for their unique advantages in low-energy\nhigh-speed photodetection, although they suffer from serious drawbacks such as\nan intrinsically high dark current. In this perspective, we envision the\nexploitation of topological effects in the photoresponse of these materials as\na promising route to circumvent these problems. We overview recent studies on\nphotodetection based on graphene and other semimetals, and further discuss the\nexciting opportunities created by the topological effects, along with the\nadditional requirements that they impose on photodetector designs.", "category": "physics_app-ph" }, { "text": "Mapping the global design space of nanophotonic components using machine\n learning pattern recognition: Nanophotonics finds ever broadening applications requiring complex component\ndesigns with a large number of parameters to be simultaneously optimized.\nRecent methodologies employing optimization algorithms commonly focus on a\nsingle design objective, provide isolated designs, and do not describe how the\ndesign parameters influence the device behaviour. Here we propose and\ndemonstrate a machine-learning-based approach to map and characterize the\nmulti-parameter design space of nanophotonic components. Pattern recognition is\nused to reveal the relationship between an initial sparse set of optimized\ndesigns through a significant reduction in the number of characterizing\nparameters. This defines a design sub-space of lower dimensionality that can be\nmapped faster by orders of magnitude than the original design space. As a\nresult, multiple performance criteria are clearly visualized, revealing the\ninterplay of the design parameters, highlighting performance and structural\nlimitations, and inspiring new design ideas. This global perspective on\nhigh-dimensional design problems represents a major shift in how modern\nnanophotonic design is approached and provides a powerful tool to explore\ncomplexity in next-generation devices.", "category": "physics_app-ph" }, { "text": "SPICE Simulation of tunnel FET aiming at 32 kHz crystal-oscillator\n operation: We numerically investigate the possibility of using Tunnel field-effect\ntransistor (TFET) in a 32 kHz crystal oscillator circuit to reduce power\nconsumption. A simulation using SPICE (Simulation Program with Integrated\nCircuit Emphasis) is carried out based on a conventional CMOS transistor model.\nIt is shown that the power consumption of TFET is one-tenth that of\nconventional low-power CMOS.", "category": "physics_app-ph" }, { "text": "Detecting triplet states in opto-electronic and photovoltaic materials\n and devices by transient optically detected magnetic resonance: Triplet excited states in organic semiconductor materials and devices are\nnotoriously difficult to detect and study with established spectroscopic\nmethods. Yet, they are a crucial intermediate step in next-generation organic\nlight emitting diodes (OLED) that employ thermally activated delayed\nfluorescence (TADF) to upconvert non-emissive triplets to emissive singlet\nstates. In organic photovoltaic (OPV) devices, however, triplets are an\nefficiency-limiting exciton loss channel and are also involved in device\ndegradation. Here, we introduce an innovative spin-sensitive method to study\ntriplet states in both, optically excited organic semiconductor films, as well\nas in electrically driven devices. The method of transient optically detected\nmagnetic resonance (trODMR) can be applied to all light-emitting materials\nwhose luminescence depends on paramagnetic spin states. It is thus an ideal\nspectroscopic tool to distinguish different states involved and determine their\ncorresponding time scales. We unravel the role of intermediate excited spin\nstates in opto-electronic and photovoltaic materials and devices and reveal\nfundamental differences in electrically and optically induced triplet states.", "category": "physics_app-ph" }, { "text": "Review of LiFi visible light communications : research and use cases: LiFi is a networked wireless communication technology transforming\nsolid-state indoor lighting into a backbone for information. The technology has\nreached maturity, with the first LiFi LED luminaire commercialized in 2016.\nReal life deployments with a variety of use cases, as well as staggering\nbandwidth improvements in the lab superior to 10 Gbps, hint to a luminous\nfuture for LiFi as a powerful complement or alternative to WiFi and 4G/5G.", "category": "physics_app-ph" }, { "text": "Complementary metasurfaces for guiding electromagnetic waves: Waveguides are critically important components in microwave, THz, and optical\ntechnologies. Due to recent progress in two-dimensional materials, metasurfaces\ncan be efficiently used to design novel waveguide structures which confine the\nelectromagnetic energy while the structure is open. Here, we introduce a\nspecial type of such structures formed by two penetrable metasurfaces which\nhave complementary isotropic surface impedances. We theoretically study guided\nmodes supported by the proposed structure and discuss the corresponding\ndispersion properties. Furthermore, we show the results for different scenarios\nin which the surface impedances possess non-resonant or resonant\ncharacteristics, and the distance between the metasurfaces changes from large\nvalues to the extreme limit of zero. As an implication of this work, we\ndemonstrate that there is a possibility to excite two modes with orthogonal\npolarizations having the same phase velocity within a broad frequency range.\nThis property is promising for applications in leaky-wave antennas and field\nfocusing.", "category": "physics_app-ph" }, { "text": "Analytical Modeling for Rapid Design of Bistable Buckled Beams: Double-clamped bistable buckled beams, as the most elegant bistable\nmechanisms, demonstrate great versatility in various fields, such as robotics,\nenergy harvesting, and MEMS. However, their design is always hindered by\ntime-consuming and expensive computations. In this work, we present a method to\neasily and rapidly design bistable buckled beams subjected to a transverse\npoint force. Based on the Euler-Bernoulli beam theory, we establish a\ntheoretical model of bistable buckled beams to characterize their snap-through\nproperties. This model is verified against the results from an FEA model, with\ndiscrepancy less than 7 %. By analyzing and simplifying our theoretical model,\nwe derive explicit analytical expressions for critical behavioral values on the\nforce-displacement curve of the beam. These behavioral values include critical\nforce, critical displacement, and travel, which are generally sufficient for\ncharacterizing the snap-through properties of a bistable buckled beam. Based on\nthese analytical formulas, we investigate the influence of a bistable buckled\nbeam's key design parameters, including its actuation position and\nprecompression, on its critical behavioral values, with our results validated\nby FEA simulations. This way, our method enables fast and computationally\ninexpensive design of bistable buckled beams and can guide the design of\ncomplex systems that incorporate bistable mechanisms.", "category": "physics_app-ph" }, { "text": "Properties and device performance of BN thin films grown on GaN by\n pulsed laser deposition: Wide and ultrawide-bandgap semiconductors lie at the heart of next-generation\nhigh-power, high-frequency electronics. Here, we report the growth of\nultrawide-bandgap boron nitride (BN) thin films on wide-bandgap gallium nitride\n(GaN) by pulsed laser deposition. Comprehensive spectroscopic (core level and\nvalence band XPS, FTIR, Raman) and microscopic (AFM and STEM) characterizations\nconfirm the growth of BN thin films on GaN. Optically, we observed that BN/GaN\nheterostructure is second-harmonic generation active. Moreover, we fabricated\nthe BN/GaN heterostructure-based Schottky diode that demonstrates rectifying\ncharacteristics, lower turn-on voltage, and an improved breakdown capability\n(234 V) as compared to GaN (168 V), owing to the higher breakdown electrical\nfield of BN. Our approach is an early step towards bridging the gap between\nwide and ultrawide-bandgap materials for potential optoelectronics as well as\nnext-generation high-power electronics.", "category": "physics_app-ph" }, { "text": "Structural Reconstruction in Lead-free Two-dimensional Tin Iodide\n Perovskites Leading to High Quantum Yield Emission: We report a structural reconstruction-induced high photoluminescence quantum\nyield of 25% in colloidal two-dimensional tin iodide nanosheets that are\nsynthesized by a hot-injection method. The as-synthesized red-colored\nnanosheets of octylammonium tin iodide perovskites at room temperature\ntransform to white hexagonal nanosheets upon washing or exposure to light. This\nstructural change increases the bandgap from 2.0 eV to 3.0 eV, inducing a large\nStokes shift and a broadband emission. Further, a long photoluminescence\nlifetime of about 1 microsecond is measured for the nanosheets. Such long-lived\nbroad and intense photoluminescence with large Stokes shift is anticipated to\noriginate from tin iodide clusters that are formed during the structural\nreconstruction. Stereoactive 5s2 lone pair of tin (II) ions perturbs the\nexcited state geometry of the white hexagonal nanosheets and facilitates the\nformation of self-trapped excitons. Such broadband and intensely emitting metal\nhalide nanosheets are promising for white light-emitting diodes.", "category": "physics_app-ph" }, { "text": "Performance analysis of heat and energy recovery ventilators using\n exergy analysis and nonequilibrium thermodynamics: The increased attention to energy savings has contributed to more widespread\nuse of energy recovery systems for building ventilation. We investigate the\nefficiency of such systems under different outdoor conditions using exergy\nanalysis and nonequilibrium thermodynamics. This analysis makes it possible to\nassess performance in terms of loss of work potential, to account for the\ndifferent quality of energy and to localize and compare the different sources\nof loss in the system. It also enables the use of exergy efficiency as a single\nperformance parameter, in contrast to the several indicators that are commonly\nused. These more common indicators are difficult to compare and relate to each\nother. Further, since there is no obvious optimal trade-off between them, it is\nchallenging to combine them and develop a global performance indicator that\nallows for a sensible comparison of different technical solutions and different\ntypes of recovery devices. We illustrate the concepts by applying the analysis\nto a heat recovery ventilator (HRV) and to a structurally similar membrane\nenergy recovery ventilator (MERV) that can exchange both heat and moisture. We\nshow how the exergy efficiency can be used to identify the range of operating\nconditions for which the recovery ventilator is not beneficial as the energy\ncost is greater than the energy recovery. This is not trivial using traditional\nperformance parameters, yet it is a natural outcome of exergy analysis. In\naddition, we identify the mechanism by which work potential is lost, which can\nhelp the eventual optimization of both the recovery process and the auxiliary\nsystems present in ventilation systems.", "category": "physics_app-ph" }, { "text": "The Spatiotemporal Evolution of Temperature During Transient Heating of\n Nanoparticle Arrays: Nanoparticle (NP) are promising agents to absorb external energy excitation\nand generate heat. Cluster of NPs or NP array heating have found essential\nroles for biomedical applications, diagnostic techniques and chemical\ncatalysis. Various studies have shed light on the heat transfer of\nnanostructures and greatly advanced our understanding of NP array heating.\nHowever, there is a lack of analytical tools and dimensionless parameters to\ndescribe the transient heating of NP arrays. Here we demonstrate a\ncomprehensive analysis of the transient NP array heating. Firstly, we developed\nanalytical solution for the NP array heating and provide a useful mathematical\ndescription of the spatial-temporal evolution of temperature for 2D, 3D and\nspherical NP array heating. Based on this, we proposed the idea of thermal\nresolution that quantifies the relationship between minimal heating time, NP\narray size, energy intensity and target temperature. Lastly, we define a\ndimensionless parameter that characterize the transition from confined heating\nto delocalized heating. This study advances the in-depth understanding of\nnanomaterials heating and provides guidance for rationally designing innovative\napproaches for NP array heating.", "category": "physics_app-ph" }, { "text": "Route to High-Performance Micro-solid Oxide Fuel Cells on Metallic\n Substrates: Micro-solid oxide fuel cells based on thin films have strong potential for\nuse in portable power devices. However, devices based on silicon substrates\ntypically involve thin-film metallic electrodes which are unstable at high\ntemperatures. Devices based on bulk metal substrates overcome these\nlimitations, though performance is hindered by the challenge of growing\nstate-of-the-art epitaxial materials on metals. Here, we demonstrate for the\nfirst time the growth of epitaxial cathode materials on metal substrates\n(stainless steel) commercially supplied with epitaxial electrolyte layers (1.5\n{um (Y2O3)0.15(ZrO2)0.85 (YSZ) + 50 nm CeO2). We create epitaxial mesoporous\ncathodes of (La0.60Sr0.40)0.95Co0.20Fe0.80O3 (LSCF) on the substrate by growing\nLSCF/MgO vertically aligned nanocomposite films by pulsed laser deposition,\nfollowed by selectively etching out the MgO. To enable valid comparison with\nthe literature, the cathodes are also grown on single-crystal substrates,\nconfirming state-of-the-art performance with an area specific resistance of\n100ohmegacm2 at 500dC and activation energy down to 0.97 eV. The work marks an\nimportant step toward the commercialization of high-performance micro-solid\noxide fuel cells for portable power applications.", "category": "physics_app-ph" }, { "text": "Ultrafast photocurrent and absorption microscopy of few-layer TMD\n devices isolate rate-limiting dynamics driving fast and efficient\n photoresponse: Despite inherently poor interlayer conductivity, photodetectors made from\nfew-layer devices of 2D transition metal dichalcogenides (TMDs) such as WSe$_2$\nand MoS$_2$ can still yield a desirably fast ($\\leq$90 ps) and efficient\n($\\epsilon$$>$40\\%) photoresponse. By combining ultrafast photocurrent (U-PC)\nand transient absorption (TA) microscopy, the competing electronic escape and\nrecombination rates are unambiguously identified in otherwise complex kinetics.\nBoth the U-PC and TA response of WSe$_2$ yield matching interlayer electronic\nescape times that accelerate from 1.6 ns to 86 ns with applied $E$-field to\npredict the maximum device PC-efficiency realized of $\\sim$44\\%. The slope of\nthe escape rates versus $E$-field suggests out-of-plane electron and hole\nmobilities of 0.129 and 0.031 cm$^2$/V$s$ respectively. Above $\\sim$10$^{11}$\nphotons/cm$^{2}$ incident flux, defect-assisted Auger scattering greatly\ndecreases efficiency by trapping carriers at vacancy defects. Both TA and PC\nspectra identify a metal-vacancy sub-gap peak with $\\sim$5.6 ns lifetime as a\nprimary trap capturing carriers as they hop between layers. Synchronous TA and\nU-PC microscopy show the\\ net PC collected is modelled by a kinetic rate-law of\nelectronic escape competing against the linear and nonlinear Auger\nrecombination rates. This simple rate-model further predicts the PC-based\ndynamics, nonlinear amplitude and efficiency, $\\epsilon$ over a 10$^5$ range of\nincident photon flux in few-layer WSe$_2$ and MoS$_2$ devices.", "category": "physics_app-ph" }, { "text": "Morphology modifcation of Si nanopillars under ion irradiation at\n elevated temperatures: plastic deformation and controlled thinning to 10 nm: Si nanopillars of less than 50 nm diameter have been irradiated in a helium\nion microscope with a focused Ne$^+$ beam. The morphological changes due to ion\nbeam irradiation at room temperature and elevated temperatures have been\nstudied with the transmission electron microscope. We found that the shape\nchanges of the nanopillars depend on irradiation-induced amorphization and\nthermally driven dynamic annealing. While at room temperature, the nanopillars\nevolve to a conical shape due to ion-induced plastic deformation and viscous\nflow of amorphized Si, simultaneous dynamic annealing during the irradiation at\nelevated temperatures prevents amorphization which is necessary for the viscous\nflow. Above the critical temperature of ion-induced amorphization, a steady\ndecrease of the diameter was observed as a result of the dominating forward\nsputtering process through the nanopillar sidewalls. Under these conditions the\nnanopillars can be thinned down to a diameter of 10 nm in a well-controlled\nmanner. A deeper understanding of the pillar thinning process has been achieved\nby a comparison of experimental results with 3D computer simulations based on\nthe binary collision approximation.", "category": "physics_app-ph" }, { "text": "Broadband time-modulated absorber beyond the Bode-Fano limit by energy\n trapping: Wide-band absorption is a popular topic in microwave engineering to protect\nsensitive devices against broadband sources. However, the Bode-Fano criterion\ndefines the trade-off between bandwidth and efficiency for all passive, linear,\ntime-invariant systems. In this letter, we propose a broadband absorber beyond\nthe Bode-Fano limit by creating an energy trap using time-modulated\nswitch/diodes. This work starts with an ideal circuit model to prove the\nconcept, followed by two EM realizations - a freuqnecy selective surface (FSS)\napproach for general bandwidth broadening and a low-profile PCB design. The\nprototype of the latter is built and measured, demonstrating a Bode-Fano\nintegral larger than one. This approach paves a way to many practical\nultra-wide band absorber designs.", "category": "physics_app-ph" }, { "text": "The influence of illumination conditions in the measurement of built-in\n electric field at p-n junctions by 4D-STEM: Momentum resolved 4D-STEM, also called center of mass (CoM) analysis, has\nbeen used to measure the long range built-in electric field of a silicon p-n\njunction. The effect of different STEM modes and the trade-off between spatial\nresolution and electric field sensitivity are studied. Two acquisition modes\nare compared: nanobeam and low magnification (LM) modes. A thermal noise free\nMedipix3 direct electron detector with high speed acquisition has been used to\nstudy the influence of low electron beam current and millisecond dwell times on\nthe measured electric field and standard deviation. It is shown that LM\nconditions can underestimate the electric field values due to a bigger probe\nsize used but provide an improvement of almost one order of magnitude on the\nsignal-to-noise ratio, leading to a detection limit of 0.011MV/cm. It is\nobserved that the CoM results do not vary with acquisition time or electron\ndose as low as 24 $e^-/A^2$, showing that the electron beam does not influence\nthe built-in electric field and that this method can be robust for studying\nbeam sensitive materials, where a low dose is needed.", "category": "physics_app-ph" }, { "text": "Photophysical comparison of liquid and mechanically exfoliated WS$_2$\n monolayers: Semiconducting transition metal dichalcogenides (TMDs) are desired as active\nmaterials in optoelectronic devices due to their strong excitonic effects. They\ncan be exfoliated from their parent layered materials with low-cost and for\nmass production via a liquid exfoliation method. However, the device\napplication of TMDs prepared by liquid phase exfoliation is limited by their\npoor photoluminescence quantum efficiencies (PLQE). It is crucial to understand\nthe reason to low PLQE for their practical device development. Here we evaluate\nthe quality of monolayer-enriched liquid phase exfoliated (LPE) WS$_2$\ndispersions by systematically investigating their optical and photophysical\nproperties and contrasting with mechanically exfoliated (ME) WS2 monolayers. An\nin-depth understanding of the exciton dynamics is gained with ultrafast\npump-probe measurements. We reveal that the energy transfer between monolayer\nand few-layers in LPE WS$_2$ dispersions is a substantial reason for their\nquenched PL. In addition, we show that LPE WS$_2$ is promising to build high\nperformance optoelectronic devices with excellent optical quality.", "category": "physics_app-ph" }, { "text": "Towards integrated metatronics: a holistic approach on precise optical\n and electrical properties of Indium Tin Oxide: The class of transparent conductive oxides includes the material indium tin\noxide (ITO) and has become a widely used material of modern every-day life such\nas in touch screens of smart phones and watches, but also used as an optically\ntransparent low electrically-resistive contract in the photovoltaics industry.\nMore recently ITO has shown epsilon-near-zero (ENZ) behavior in the\ntelecommunication frequency band enabling both strong index modulation and\nother optically-exotic applications such as metatronics. However the ability to\nprecisely obtain targeted electrical and optical material properties in ITO is\nstill challenging due to complex intrinsic effects in ITO and as such no\nintegrated metatronic platform has been demonstrated to-date. Here we deliver\nan extensive and accurate description process parameters of RF-sputtering,\nshowing a holistic control of the quality of ITO thin films in the visible and\nparticularly near-infrared spectral region. We further are able to\ncustom-engineer the ENZ point across the telecommunication band by explicitly\ncontrolling the sputtering process conditions. Exploiting this control we\ndesign a functional sub-wavelength-scale filter based on lumped\ncircuit-elements, towards the realization of integrated metatronic devices and\ncircuits.", "category": "physics_app-ph" }, { "text": "Refractive-index-sensing radio-frequency comb with intracavity\n multi-mode interference fibre sensor: Optical frequency combs have attracted attention as optical frequency rulers\ndue to their tooth-like discrete spectra together with their inherent\nmode-locking nature and phase-locking control to a frequency standard. Based on\nthis concept, their applications until now have been demonstrated in the fields\nof optical frequency metrology and optical distance metrology. However, if the\nutility of optical combs can be further expanded beyond their\noptical-frequency-ruler-based application by exploiting new aspects of optical\ncombs, this will lead to new developments in optical metrology and\ninstrumentation. Here, we report a fibre sensing application of optical combs\nbased on a coherent frequency link between the optical and radio-frequency\nregions, enabling high-precision refractive index measurement of a liquid\nsample based on frequency measurement in radio-frequency region. Our technique\nencodes a refractive index change of a liquid sample into a radio-frequency\ncomb by a combination of an intracavity multi-mode-interference fibre sensor\nand wavelength dispersion of a cavity fibre. Then, the change in refractive\nindex is read out by measuring the repetition frequency of the radio-frequency\ncomb with a frequency counter and a frequency standard. Use of an optical comb\nas a photonic radio-frequency converter will lead to the development of new\napplications in high-precision fibre sensing with the help of functional fibre\nsensors and precise radio-frequency measurement.", "category": "physics_app-ph" }, { "text": "Broad Band Single Germanium Nanowire Photodetectors with Surface Oxide\n Controlled High Optical Gain: We have investigated photoconductive properties of single Germanium\nNanowires(NWs)of diameter less than 100 nm in the spectral range of 300 to 1100\nnm showing ultra large peak Responsivity in excess of 10^{7}AW^{-1}.The NWs\nwere grown by Vapor Liquid Solid method using Au nanoparticle as catalyst. In\nthis report we discuss the likely origin of the ultra large responsivity that\nmay arise from a combination of various physical effects which are a): Ge and\nGeO_{x} interface states which act as scavengers of electrons from the\nphoto-generated pairs,leaving the holes free to reach the electrodes,b)\nSchottky barrier at the metal and NW interface which gets lowered substantially\ndue to carrier diffusion in contact region and (c) photodetector length being\nsmall (approximately few {\\mu}m), negligible loss of photogenerated carriers\ndue to recombination at defect sites. We have observed from power dependence of\nthe optical gain that the gain is controlled by trap states. We find that the\nsurface of the nanowire has presence of a thin layer of GeO_{x} (as evidenced\nfrom HRTEM study) which provide interface states. It is observed that these\nstate play a crucial role to provide a radial field for separation of\nphotogenerated electron and hole pair which in turn leads to very high\neffective photoconductive gain that reaches a very high at low illumination\ndensity.", "category": "physics_app-ph" }, { "text": "Small-size reflectionless band-pass filter: The paper presents a reflectionless stripline filter with reduced dimensions\nhaving a single bandwidth over a wide frequency range. The filter consists of\ncoupled strip lines and RLC circuits included in the diagonal ports of the\ncoupled strip lines. Calculations and measurements of the reflectionless\nstripline filter layout in the frequency range up to 4.8 GHz have been carried\nout. The obtained results show that the dimensions are reduced by a factor of\ntwo compared to previously developed reflectionless stripline filter designs.\nIt is achieved by folding the coupled lines in the form of a meander formed by\nhorizontally and vertically arranged conductors on horizontally and vertically\noriented dielectric substrates. The proposed reflectionless stripline filter\nallows to solve the problem of improving the mass-dimensional parameters of the\nequipment and to provide signal selection with minimum reflection at\nout-of-band frequencies. It can be in demand in multichannel systems of\nwireless communications, radar, and measurements.", "category": "physics_app-ph" }, { "text": "Pulsed Self-Oscillating Nonlinear Systems for Robust Wireless Power\n Transfer: While wired-power-transfer devices ensure robust power delivery even if the\nreceiver position or load impedance changes, achieving the robustness of\nwireless power transfer (WPT) is challenging. Conventional solutions are based\non additional control circuits for dynamic tuning. Here, we propose a robust\nWPT system in which no additional tuning circuitry is required for robust\noperation. This is achieved by our systematically designing the load and the\ncoupling link to be parts of the feedback circuit. Therefore, the WPT operation\nis automatically adjusted to the optimal working condition under a wide range\nof load and receiver positions. In addition, pulsed oscillations instead of\nsingle-harmonic oscillation are adopted to increase the overall efficiency. An\nexample system is designed with the use of a capacitive coupling link. It\nrealizes a virtual, nearly-ideal oscillating voltage source at the load site,\ngiving efficient power transfer comparable to that of the ideal\nwired-connection scenario. We numerically and experimentally verify the\nrobustness of the WPT system under the variations of load and coupling, where\ncoupling is changing by our varying the alignment of aluminum plates. The\nworking frequency and the transferred power agree well with analytical models.\nThe proposed paradigm can have a significant impact on future high-performance\nWPT devices. The designed system can also work as a smart table supporting\nmultiple receivers with robust and efficient operation.", "category": "physics_app-ph" }, { "text": "Neutronic Analysis on Potential Accident Tolerant Fuel-Cladding\n Combination U$_3$Si$_2$-FeCrAl: Neutronic performance is investigated for a potential accident tolerant fuel\n(ATF),which consists of U$_3$Si$_2$ fuel and FeCrAl cladding. In comparison\nwith current UO$_2$-Zr system, FeCrAl has a better oxidation resistance but a\nlarger thermal neutron absorption cross section. U$_3$Si$_2$ has a higher\nthermal conductivity and a higher uranium density, which can compensate the\nreactivity suppressed by FeCrAl. Based on neutronic investigations, a possible\nU$_3$Si$_2$-FeCrAl fuel-cladding systemis taken into consideration. Fundamental\nproperties of the suggested fuel-cladding combination are investigated in a\nfuel assembly.These properties include moderator and fuel temperature\ncoefficients, control rods worth, radial power distribution (in a fuel rod),\nand different void reactivity coefficients. The present work proves that the\nnew combination has less reactivity variation during its service lifetime.\nAlthough, compared with the current system, it has a little larger deviation on\npower distribution and a little less negative temperature coefficient and void\nreactivity coefficient and its control rods worth is less important, variations\nof these parameters are less important during the service lifetime of fuel.\nHence, U$_3$Si$_2$-FeCrAl system is a potential ATF candidate from a neutronic\nview.", "category": "physics_app-ph" }, { "text": "Detection of Influenza A Virus Nucleoprotein Through the Self-Assembly\n of Nanoparticles in Magnetic Particle Spectroscopy-Based Bioassays: A Method\n for Rapid, Sensitive, and Wash-free Magnetic Immunoassays: Magnetic nanoparticles (MNPs) with proper surface functionalization have been\nextensively applied as labels for magnetic immunoassays, carriers for\ncontrolled drug/gene delivery, tracers and contrasts for magnetic imaging, etc.\nHere, we introduce a new biosensing scheme based on magnetic particle\nspectroscopy (MPS) and the self-assembly of MNPs to quantitatively detect H1N1\nnucleoprotein molecules. MPS monitors the harmonics of oscillating MNPs as a\nmetric for the freedom of rotational motion, thus indicating the bound states\nof MNPs. These harmonics can be readily collected from nanogram quantities of\niron oxide nanoparticles within 10 s. H1N1 nucleoprotein molecule hosts\nmultiple different epitopes that forms binding sites for many IgG polyclonal\nantibodies. Anchoring IgG polyclonal antibodies onto MNPs triggers the\ncross-linking between MNPs and H1N1 nucleoprotein molecules, thereby forming\nMNP self-assemblies. Using MPS and the self-assembly of MNPs, we achieved the\nsensitivity of 44 nM (442 pmole) for detecting H1N1 nucleoprotein. In addition,\nthe morphologies and the hydrodynamic sizes of the MNP self-assemblies are\ncharacterized to verify the MPS results. Different MNP self-assembly models\nsuch as classical cluster, open ring tetramer, chain model as well as multimers\n(from dimer to pentamer) are proposed in this paper. Herein, we claim the\nfeasibility of using MPS and the self-assembly of MNPs as a new biosensing\nscheme for detecting ultralow concentrations of target biomolecules, which can\nbe employed as rapid, sensitive, and wash-free magnetic immunoassays.", "category": "physics_app-ph" }, { "text": "A light-weight and high thermal performance graphene heat pipe: Heat pipe is one of the most efficient tools for heat dissipation in\nelectronics and power systems. Currently, heat pipes are usually made of\ncopper, aluminum or stainless steel. Due to their relatively high density and\nlimited heat transmission capacity, heat pipes are facing urgent challenges in\npower electronics and power modules. In this paper, we report a new class of\ngraphene enhanced heat pipes that can cope with these issues. The graphene\nenhanced heat pipes are made of high thermal conductivity graphene assembled\nfilm and graphene laminated copper films with nanostructure enhanced inner\nsurfaces. The study shows that the dramatically improved heat dissipation\ncapacity, 6100 W m-2 K-1 g-1, about 3 times higher than that of copper based\ncommercial heat pipes can be achieved. This paves the way for using graphene\nenhanced heat pipes in light-weight and large capacity cooling applications, as\nrequired in many systems such as avionics, automotive electronics, laptop\ncomputers, handsets and space electronics.", "category": "physics_app-ph" }, { "text": "Controlling Cherenkov angles with resonance transition radiation: Cherenkov radiation provides a valuable way to identify high energy particles\nin a wide momentum range, through the relation between the particle velocity\nand the Cherenkov angle. However, since the Cherenkov angle depends only on\nmaterial's permittivity, the material unavoidably sets a fundamental limit to\nthe momentum coverage and sensitivity of Cherenkov detectors. For example, Ring\nImaging Cherenkov detectors must employ materials transparent to the frequency\nof interest as well as possessing permittivities close to unity to identify\nparticles in the multi GeV range, and thus are often limited to large gas\nchambers. It would be extremely important albeit challenging to lift this\nfundamental limit and control Cherenkov angles as preferred. Here we propose a\nnew mechanism that uses constructive interference of resonance transition\nradiation from photonic crystals to generate both forward and backward\nCherenkov radiation. This mechanism can control Cherenkov angles in a flexible\nway with high sensitivity to any desired range of velocities. Photonic crystals\nthus overcome the severe material limit for Cherenkov detectors, enabling the\nuse of transparent materials with arbitrary values of permittivity, and provide\na promising option suited for identification of particles at high energy with\nenhanced sensitivity.", "category": "physics_app-ph" }, { "text": "Demonstration of broadband topological slow light: Slow-light devices are able to significantly enhance light-matter interaction\ndue to the reduced group velocity of light, but a very low group velocity is\nusually achieved in a narrow bandwidth, accompanied by extreme sensitivity to\nimperfections that causes increased disorder-induced attenuation. Recent\ntheories have suggested an ideal solution to this problem - unidirectional\nchiral photonic states, previously discovered in structures known as photonic\ntopological insulators, not only resist backscattering from imperfections but\ncan also be slowed down in the entire topological bandgap with multiple\nwindings in the Brillouin zone. Here, we report on the experimental\ndemonstration of broadband topological slow light in a photonic topological\ninsulator. When coupled with periodic resonators that form flat bands, the\nchiral photonic states can wind many times around the Brillouin zone, achieving\nan ultra-low group velocity in the entire topological bandgap. This\ndemonstration extends the scope of topological photonics into slow light\nengineering and opens a unique avenue in the dispersion manipulation of chiral\nphotonic states.", "category": "physics_app-ph" }, { "text": "Spin selectivity through chiral polyalanine monolayers on semiconductors: Electrical generation of polarized spins in nonmagnetic materials is of great\ninterest for the underlying physics and device potential. One such mechanism is\nchirality-induced spin selectivity (CISS), with which structural chirality\nleads to different electric conductivities for electrons of opposite spins. The\nresulting effect of spin filtering has been reported for a number of chiral\nmolecules. However, the microscopic mechanism and manifestation of CISS in\npractical device structures remain controversial; in particular, the Onsager\nrelation is understood to preclude linear-response detection of CISS by a\nferromagnet. Here, we report direct evidence of CISS in two-terminal devices of\nchiral molecules on the magnetic semiconductor (Ga,Mn)As: In vertical\nheterojunctions of (Ga,Mn)As/AHPA-L molecules/Au, we observed characteristic\nlinear- and nonlinear-response magnetoconductance, which directly verifies spin\nfiltering by the AHPA-L molecules and spin detection by the (Ga,Mn)As. The\nresults constitute definitive signature of CISS-induced spin valve effect, a\ncore spintronic functionality, in apparent violation of the Onsager\nreciprocity. The results present a promising route to semiconductor spintronics\nfree of any magnetic material.", "category": "physics_app-ph" }, { "text": "Screening current effect on the stress and strain distribution in REBCO\n high-field magnets: experimental verification and numerical analysis: Besides screening-current-induced magnetic fields (SCIF), the shielding\neffect in high-Tc coated conductors also has an strong influence on its strain\ndistribution in a coil winding, especially during high-field operations. To\ndemonstrate this phenomenon, a special experimental setup was designed. With an\nLTS background magnet and a small HTS insert coil, we were able to carry out\ndirect observations on the hoop strains of a 10-mm wide REBCO sample. Measured\ndata was compared against numerical solutions solved by electromagnetic models\nbased on T -A formulation and homogeneous mechanical models, showing good\nagreements. An analytical expression was proposed to estimate the maximum\nradial Lorentz force considering shielding effect. Using the developed\nnumerical models, we further studied the potential effects of two of the mostly\ninvestigated methods, which were formerly introduced to reduce SCIF, including\nmulti-filamentary conductors and current sweep reversal (CSR) approach.", "category": "physics_app-ph" }, { "text": "Fast Activation of Graphene with Corrugated Surface and its Role in\n Improved Aqueous Electrochemical Capacitors: In graphene based materials, the energy storage capacity is usually improved\nby rich porous structures with extremely high surface area. By utilizing\nsurface corrugations, this work shows an alternative strategy to activate\ngraphene materials for large capacitance. We demonstrate how to simply\nfabricate such activated graphene and how these surface structures helped to\nrealize considerable specific capacitance (e.g., electrode capacitance of ~340\nF g-1 at 5 mV s-1 and device capacitance of ~ 343 F g-1 at 1.7 A g-1) and power\nperformance (e.g., power density of 50 and 2500 W kg-1 at the energy density of\n~10.7 and 1.53 Wh kg-1, respectively) in aqueous system, which are comparable\nto and even better than those of highly activated graphene materials with\nultra-high surface area. This work demonstrates a new path to enhance the\ncapacity of carbon-based materials, which could be developed and combined with\nother systems for various improved energy storage applications.", "category": "physics_app-ph" }, { "text": "Cooperative near- and far-field thermal management via diffusive\n superimposed dipoles: Active metadevices with external excitations exhibit significant potential\nfor advanced heat regulation. Nonetheless, conventional inputs, like\nheating/cooling and introducing convection by rotating plate, display inherent\nlimitations. One is the only focus on far-field control to eliminate\ntemperature distortion in the background while neglecting near-field regulation\nin the functional region. Another is lacking adaptability due to complex\ndevices like thermoelectric modules and stepping motors. To tackle these\nchallenges, the concept of diffusive superimposed dipoles characterized by\northogonal thermal dipole moments is proposed. Cooperative near- and far-field\nregulation of temperature fields is achieved by designing superimposed dipole\nmoments, enabling transparency and cloaking functionalities. Simulation and\nexperiment outcomes affirm the efficacy of this adaptive thermal field control\ntechnique, even when interface thermal resistance is taken into account.\nAdaptivity stems from dipole moment decomposability, allowing metadevices to\noperate in various heat flux directions and background thermal conductivity.\nThese findings could pave the way for cooperative and adaptive thermal\nmanagement and hold potential applications in other Laplace fields, including\ndirect current and hydrodynamics.", "category": "physics_app-ph" }, { "text": "The GeSn Alloy and its Optoelectronic Properties: A Critical Review of\n the Current Understanding: GeSn is nowadays recognized as a promising candidate to enable monolithic\non-chip Si photonics operating in the near-infrared (NIR) and short-wave\ninfrared (SWIR) wavelengths. The addition of Sn to the Ge lattice induces a\nred-shift in the material bandgap, extending the absorption cut-off wavelength\ntowards the infrared. In addition, above 7-9 at.% Sn, the GeSn alloy acquires a\ndirect bandgap, enabling its use as active material in SWIR light-emitting\ndevices. Ge-rich GeSn alloys have been demonstrated in a plethora of\noptoelectronic devices including photodetectors, lasers and light emitting\ndiodes (LEDs). Furthermore, the high theoretical mobility of GeSn motivated\nresearch for GeSn high-mobility field-effect transistors (FETs), while the\npossibility of monolithic integration on Si platforms has also pushed the\ninvestigation of GeSn for on-chip thermoelectric applications. However, despite\nmore than 15 years of intensive research in the field, there exists no\ncommercial device to date based on GeSn. In fact, there are numerous challenges\nhindering the rise of this material for the next-generation (opto)electronics.\nHere, we give a concise review of the historical achievements in GeSn research\nand the withstanding challenges. This is followed by a detailed description of\nthe GeSn physical properties relevant for its use in optoelectronic devices. We\nconclude with a discussion of the open questions in the field.", "category": "physics_app-ph" }, { "text": "Energy Efficient Skyrmion based Oscillator on Thermocoupled Nanotrack: The magnetic skyrmion-based spin transfer nano-oscillators (STNO) are the\npotential candidates for next-generation microwave signal generator and has\ngained popularity due to their performance, integrability and compatibility\nwith existing CMOS technology. However, these devices suffer from the Joule\nheating problem that neglects their non-volatility advantage in spintronic\ndevices. Therefore, it is necessary to investigate the alternative driving\nmechanisms for the development of energy-efficient skyrmion based\nnano-oscillators. In this paper, a skyrmion-based nano-oscillator has been\ndesigned that utilizes thermal power to drive skyrmion on a thermocoupled\nnanotrack. The thermocoupled nanotrack is designed in such a way that both the\nupper and lower nanotracks have different values of damping constants and a\ntemperature difference is maintained between the extreme ends, in order to\ncreate a temperature gradient in the two nanotracks. By employing this\ntechnique, skyrmion is able to exhibit the periodic motion on the nanotrack\nwith the maximum achievable frequency of 2.5GHz without any external stimuli.\nMoreover, the proposed device offers low thermal energy consumption of\n0.84fJ/oscillation. Hence, this work provides the pathway for the development\nof energy-efficient future spintronic devices.", "category": "physics_app-ph" }, { "text": "Validation of a temperature-dependent elasto-viscoplastic material model\n for a talcum-filled polypropylene/polyethylene co-polymer using glove box\n flap component tests: In the automotive industry, thermoplastic polymers are used for a significant\nnumber of interior and exterior parts. These components have to pass all\nunderlying crash and safety relevant tests, where a proper performance is\ndesired in the range of low to high ambient temperatures. Today, the vehicle\ndesign is heavily aided by numerical simulation methods for advancing towards a\nprototype free vehicle development. This requires an accurate modeling of the\ntemperature- and ratedependent, elasto-viscoplastic mechanical response of the\npolymer structures. In this work, the validation of a novel elasto-viscoplastic\ntemperature-dependent material model is performed using glove box flap segments\nsubjected to impact loading by a spherical punch in a custom-build loading\nframe. The proposed material model shows a very good prediction of the\nexperimental results.", "category": "physics_app-ph" }, { "text": "32x100 GHz WDM filter based on ultra-compact silicon rings with a high\n thermal tuning efficiency of 5.85 mW/pi: To the best of our knowledge, this paper has achieved the lowest thermal\ntuning power (5.85 mW/pi) for silicon rings with FSR>=3.2 THz, and the first\nsilicon ring-based WDM-32x100 GHz filter.", "category": "physics_app-ph" }, { "text": "Electrically Controlled Reversible Strain Modulation in MoS$_2$\n Field-effect Transistors via an Electro-mechanically Coupled Piezoelectric\n Thin Film: Strain can efficiently modulate the bandgap and carrier mobilities in\ntwo-dimensional (2D) materials. Conventional mechanical strain-application\nmethodologies that rely on flexible, patterned or nano-indented substrates are\nseverely limited by low thermal tolerance, lack of tunability and/or poor\nscalability. Here, we leverage the converse piezoelectric effect to\nelectrically generate and control strain transfer from a piezoelectric thin\nfilm to electro-mechanically coupled ultra-thin 2D MoS$_2$. Electrical bias\npolarity change across the piezoelectric film tunes the nature of strain\ntransferred to MoS$_2$ from compressive $\\sim$0.23% to tensile $\\sim$0.14% as\nverified through peak shifts in Raman and photoluminescence spectroscopies and\nsubstantiated by density functional theory calculations. The device\narchitecture, built on a silicon substrate, uniquely integrates an MoS$_2$\nfield-effect transistor on top of a metal-piezoelectric-metal stack enabling\nstrain modulation of transistor drain current 130$\\times$, on/off current ratio\n150$\\times$, and mobility 1.19$\\times$ with high precision, reversibility and\nresolution. Large, tunable tensile (1056) and compressive (-1498) strain gauge\nfactors, easy electrical strain modulation, high thermal tolerance and\nsubstrate compatibility make this technique promising for integration with\nsilicon-based CMOS and micro-electro-mechanical systems.", "category": "physics_app-ph" }, { "text": "Efficient and Stable PbS Quantum Dot Solar Cells by Triple-Cation\n Perovskite Passivation: Solution-processed quantum dots (QDs) have a high potential for fabricating\nlow cost, flexible and large-scale solar energy harvesting devices. It has\nrecently been demonstrated that hybrid devices employing a single monovalent\ncation perovskite solution for PbS QD surface passivation exhibit enhanced\nphotovoltaic performance when compared to standard ligand passivation. Herein\nwe demonstrate that the use of a triple cation\nCs0.05(MA0.17FA0.83)0.95Pb(I0.9Br0.1)3 perovskite composition for surface\npassivation of the quantum dots results in highly efficient solar cells, which\nmaintain 96 % of their initial performance after 1200h shelf storage. We\nconfirm perovskite shell formation around the PbS nanocrystals by a range of\nspectroscopic techniques as well as high-resolution transmission electron\nmicroscopy. We find that the triple cation shell results in a favorable\nenergetic alignment to the core of the dot, resulting in reduced recombination\ndue to charge confinement without limiting transport in the active layer.\nConsequently, photovoltaic devices fabricated via a single-step film deposition\nreached a maximum AM1.5G power conversion efficiency of 11.3 % surpassing most\nprevious reports of PbS solar cells employing perovskite passivation.", "category": "physics_app-ph" }, { "text": "Topology Optimization for Microwave Control With Reconfigurable\n Intelligent Metasurfaces In Complex Media: Reconfigurable intelligent metasurfaces have been proposed as an efficient\nsolution for improving wireless telecommunication systems in multiple\nscattering or reverberating media. Concurrently, topology optimization has been\nsuccessfully employed as an inverse design technique in many fields, and\nparticularly in electromagnetics. In this work, we apply a gradient-based\ntopology optimization for tuning the binary elements of a metasurface for a\nfocusing goal in a complex environment. First, the metasurface unit-cells are\napproximated as point sources and, then, the optimization problem is\nformulated. Afterwards, the proposed method is applied to find the optimal\nparameter sets on three distinct environments of an ascending complexity and\nthe resulting focus for each case is demonstrated via simulations. The\ncombination of reverberating cavity and a metasurface inside the latter reveals\nvery powerful since everything can be solved analytically for focusing outside\nthe cavity.", "category": "physics_app-ph" }, { "text": "Observing polarization patterns in the collective motion of\n nanomechanical arrays: In recent years, nanomechanics has evolved into a mature field, with\nwide-ranging impact from sensing applications to fundamental physics, and it\nhas now reached a stage which enables the fabrication and study of ever more\nelaborate devices. This has led to the emergence of arrays of coupled\nnanomechanical resonators as a promising field of research, serving as model\nsystems to study collective dynamical phenomena such as synchronization or\ntopological transport. From a general point of view, the arrays investigated so\nfar represent scalar fields on a lattice. Moving to a scenario where these\ncould be extended to vector fields would unlock a whole host of conceptually\ninteresting additional phenomena, including the physics of polarization\npatterns in wave fields and their associated topology. Here we introduce a new\nplatform, a two-dimensional array of coupled nanomechanical pillar resonators,\nwhose orthogonal vibration directions encode a mechanical polarization degree\nof freedom. We demonstrate direct optical imaging of the collective dynamics,\nenabling us to analyze the emerging polarization patterns and follow their\nevolution with drive frequency.", "category": "physics_app-ph" }, { "text": "Membrane-electrode assemblies for flow-electrode capacitive deionization: Scale-up of flow-electrode capacitive deionization is hindered due to the\nreliance on thick brittle graphite current collectors. Inspired by developments\nof electrochemical technologies we present the use of flexible membrane\nelectrode assemblies (MEA) to solve these limitations. We tested different\ncarbon-fiber fabrics as current collectors and laminated them successfully with\nion-exchange membranes. The use of thinner ion-exchange membranes is now\npossible due to the reinforcement with the carbon fiber fabric. Desalination\nexperiments reveal that a MEA setup can achieve salt transfer rates equal to\nstandard setups. Hence, we deduce that charge percolation also acts outside the\nelectric field. In a single point of contact, ionic and electric charges are\nexchanged at the carbon surface of the MEA. The use of thinner membranes leads\nto a reduced potential drop. Together with a more homogeneous electric field\nacross the feed water section, this can compensate for the reduction of contact\nsurface between flow electrode and current collector.", "category": "physics_app-ph" }, { "text": "Strain-Based Room-Temperature Non-Volatile MoTe$_2$ Ferroelectric Phase\n Change Transistor: The primary mechanism of operation of almost all transistors today relies on\nelectric-field effect in a semiconducting channel to tune its conductivity from\nthe conducting 'on'-state to a non-conducting 'off'-state. As transistors\ncontinue to scale down to increase computational performance, physical\nlimitations from nanoscale field-effect operation begin to cause undesirable\ncurrent leakage that is detrimental to the continued advancement of computing.\nUsing a fundamentally different mechanism of operation, we show that through\nnanoscale strain engineering with thin films and ferroelectrics (FEs) the\ntransition metal dichalcogenide (TMDC) MoTe$_2$ can be reversibly switched with\nelectric-field induced strain between the 1T'-MoTe$_2$ (semimetallic) phase to\na semiconducting MoTe$_2$ phase in a field effect transistor geometry. This\nalternative mechanism for transistor switching sidesteps all the static and\ndynamic power consumption problems in conventional field-effect transistors\n(FETs). Using strain, we achieve large non-volatile changes in channel\nconductivity (G$_{on}$/G$_{off}$~10$^7$ vs. G$_{on}$/G$_{off}$~0.04 in the\ncontrol device) at room temperature. Ferroelectric devices offer the potential\nto reach sub-ns nonvolatile strain switching at the attojoule/bit level, having\nimmediate applications in ultra-fast low-power non-volatile logic and memory\nwhile also transforming the landscape of computational architectures since\nconventional power, speed, and volatility considerations for microelectronics\nmay no longer exist.", "category": "physics_app-ph" }, { "text": "Actively controllable topological phase transition in phononic beam\n systems: Topological insulators, which allow edge or interface waves but forbid bulk\nwaves, have revolutionized our scientific cognition of acoustic/elastic\nsystems. Due to their nontrivial topological characteristics, edge\n(interface)waves are topologically protected against defects and disorders.\nThis superior and unique characteristic could lead to a wealth of new\nopportunities in applications of quantum and acoustic/elastic information\nprocessing. However, current acoustic/elastic topological insulators are still\nat an infancy stage where the theory and prediction only work in laboratories\nand there are still many problems left open before promoting their practical\napplications. One of the apparent disadvantages is their narrow working\nfrequency range, which is the main concern in this paper. We design a\none-dimensional phononic beam system made of a homogeneous epoxy central beam\nsandwiched by two homogeneous piezoelectric beams, and covered with extremely\nthin electrodes, periodically and separately placed. These electrodes are\nconnected to external electric circuits with negative capacitors. We show that\na topological phase transition can be induced and tuned by changing the values\nof the negative capacitors. It follows that the working frequency of the\ntopologically protected interface mode can be widely changed, such that the\nworking frequency range of the topological insulator can be considerably\n`broadened'. This intelligent topological device may also find wide\napplications in intelligent technologies that need controllable information\nprocessing of high precision.", "category": "physics_app-ph" }, { "text": "Broadband optical-fiber-compatible photodetector based on a\n graphene-MoS2-WS2 heterostructure with a synergetic photo-generating\n mechanism: Integrating two-dimensional (2D) crystals into optical fibers can grant them\noptoelectronic properties and extend their range of applications. However, our\nability to produce complicated structures is limited by the challenges of\nchemical vapor deposition (CVD) manufacturing. Here, we successfully\ndemonstrate a 2D-material heterostructure created on a fiber endface by\nintegrating a microscale multilayer graphene-MoS2-WS2 van der Waals (vdW)\nheterostructure film on it. Hence, based on simple layer-by-layer transferring,\na visible-to-infrared gating-free all-in-fiber photodetector (FPD) is produced.\nOur FPD exhibits an ultrahigh photoresponsivity of 6.6X107 A/W and a relatively\nfast response speed of 7 ms at 400 nm light wavelength, due to the strong light\nabsorption and the built-in electric field of the heterostructure. Moreover,\nowning to the type-II staggered band alignments in the MoS2-WS2\nheterostructure, the interlayer optical transition between the MoS2 and WS2\nlayers enable our FPD to sense the infrared light power, displaying a\nphotoresponsivity of 17.1 A/W at 1550 nm. In addition, an inverse photoresponse\nis observed under an illuminating power higher than 1 mW at 1550 nm, indicating\na competingphotocurrent generation mechanism, comprising the photoconductive\nand photo-bolometric effects. These findings offer a new strategy for\ndeveloping broadband and gating-free photodetectors and other novel\noptoelectronic devices based on 2D crystals. Furthermore, our fabrication\nmethod may provide a new platform for the integration of optical fibers with\nsemiconducting materials.", "category": "physics_app-ph" }, { "text": "Poynting-Robertson damping of laser beam driven lightsails: Lightsails using Earth-based lasers for propulsion require passive\nstabilization to stay within the beam. This can be achieved through the sail's\nscattering properties, creating optical restoring forces and torques. Undamped\nrestoring forces produce uncontrolled oscillations, which could jeopardize the\nmission, but it is not obvious how to achieve damping in the vacuum of space.\nUsing a simple two-dimensional model we show that the Doppler effect and\nrelativistic aberration of the propelling laser beam create damping terms in\nthe optical forces and torques. The effect is similar to the Poynting-Robertson\neffect causing loss of orbital momentum of dust particles around stars, but can\nbe enhanced by design of the sail's geometry.", "category": "physics_app-ph" }, { "text": "Nanoscale magnetophotonics: This Perspective surveys the state-of-the-art and future prospects of science\nand technology employing the nanoconfined light (nanophotonics and\nnanoplasmonics) in combination with magnetism. We denote this field broadly as\nnanoscale magnetophotonics. We include a general introduction to the field and\ndescribe the emerging magneto-optical effects in magnetoplasmonic and\nmagnetophotonic nanostructures supporting localized and propagating plasmons.\nSpecial attention is given to magnetoplasmonic crystals with transverse\nmagnetization and the associated nanophotonic non-reciprocal effects, and to\nmagneto-optical effects in periodic arrays of nanostructures. We give also an\noverview of the applications of these systems in biological and chemical\nsensing, as well as in light polarization and phase control. We further review\nthe area of nonlinear magnetophotonics, the semiconductor spin-plasmonics, and\nthe general principles and applications of opto-magnetism and nano-optical\nultrafast control of magnetism and spintronics.", "category": "physics_app-ph" }, { "text": "Review on Modeling of Mechanical and Thermal Properties of Nano- and\n Micro-Composites: This article deals with the prediction of thermomechanical properties of\nfiber reinforced composites using several micromechanics models. These include\nstrength of material approach, Halpin-Tsai equations, multi-phase mechanics of\nmaterials approaches, multi-phase Mori-Tanaka models, composite cylindrical\nassemblage model, Voigt-Reuss models, modified mixture rule, Cox model,\neffective medium approach and method of cells. Several composite systems\nreinforced with short and long, aligned, random and wavy reinforcements were\nconsidered. In addition, different aspects such as fiber-matrix interphase,\nfiber-matrix interfacial thermal resistance, fiber geometry, and multiple types\nof reinforcements were considered to model the composites systems. The current\nstudy also presents some important preliminary concepts and application of\ndeveloped micromechanics models to advanced nanocomposites such as carbon\nnanotube reinforced composite. Main contribution of the current work is the\ninvestigation of several analytical micromechanical models, while most of the\nexisting studies on the subject deal with only one or two approaches\nconsidering few aspects.", "category": "physics_app-ph" }, { "text": "Radiation-induced secondary emissions in solid-state devices as a\n possible contribution to quasiparticle poisoning of superconducting circuits: This report estimates the potential for secondary emission processes induced\nby ionizing radiation to result in the generation of quasiparticles in\nsuperconducting circuits. These estimates are based on evaluation of data\ncollected from a small superconducting detector and a fluorescence measurement\nof typical read-out circuit board materials. Specifically, we study cosmic ray\nmuons interacting with substrate or mechanical support materials present within\nthe vicinity of superconducting circuits. We evaluate the potential for\nsecondary emission, such as scintillation and/or fluorescence, from these\nnearby materials to occur at sufficient energy (wavelength) and rate (photon\nflux) to ultimately lead to the breaking of superconducting Copper pairs (i.e.,\nproduction of quasiparticles). This evaluation leads to a conclusion that\nmaterial fluorescence in the vicinity of superconducting circuits is a\npotential contributor to undesirable elevated quasiparticle populations. A\nco-design approach evaluating superconducting circuit design and the material\nenvironment within the immediate vicinity of the circuit would prove beneficial\nfor mitigating undesired environmentally-induced influences on superconducting\ndevice performance, such as in direct detection dark matter sensors or quantum\ncomputing bits (qubits).", "category": "physics_app-ph" }, { "text": "Burst Eddy Current Testing with a Diamond Magnetometry: In this work, a burst eddy current testing technique based on the employment\nof a diamond nitrogen vacancy (NV) center magnetometer with the Hahn echo (HE)\nsequence is demonstrated. With the confocal experiment apparatus, the HE-based\nNV magnetometer attained a magnetic sensitivity of $4.3 ~ \\mathrm{nT} /\n\\sqrt{\\mathrm{Hz}}$ and a volume-normalized sensitivity of $3.6 ~ \\mathrm{pT} /\n\\sqrt{\\mathrm{Hz} \\cdot \\mathrm{mm}^{-3}}$, which are 5 times better than the\nalready existing method under the same conditions. Based on the proposed\nmagnetometer configuration, a burst eddy current (BEC) testing prototype\nachieves a minimum detectable sample smaller than ${300~{\\mu} \\mathrm{m}}$ and\nmeasurement accuracy of $9.85~\\mathrm{\\mu} \\mathrm{m}$., which is employed to\nimage different metallic specimens and detect the layered internal structures.\nSince our prototype comprises superb high sensitivity, it exhibits various\npotential applications in the fields of deformation monitoring, security\nscreening, and quality control. Moreover, its biocompatibility and promising\nnanoscale resolution paves the way for electromagnetic testing in the fields of\nbiomaterials.", "category": "physics_app-ph" }, { "text": "SOT-MRAM-Enabled Probabilistic Binary Neural Networks for Noise-Tolerant\n and Fast Training: We report the use of spin-orbit torque (SOT) magnetoresistive random-access\nmemory (MRAM) to implement a probabilistic binary neural network (PBNN) for\nresource-saving applications. The in-plane magnetized SOT (i-SOT) MRAM not only\nenables field-free magnetization switching with high endurance (> 10^11), but\nalso hosts multiple stable probabilistic states with a low device-to-device\nvariation (< 6.35%). Accordingly, the proposed PBNN outperforms other neural\nnetworks by achieving an 18* increase in training speed, while maintaining an\naccuracy above 97% under the write and read noise perturbations. Furthermore,\nby applying the binarization process with an additional SOT-MRAM dummy module,\nwe demonstrate an on-chip MNIST inference performance close to the ideal\nbaseline using our SOT-PBNN hardware.", "category": "physics_app-ph" }, { "text": "Requirements for functional pn-homojunctions in lead-halide perovskite\n solar cells: Cui et al. describe the fabrication and characterization of planar\npn-junction solar cells based on lead-halide perovskites. The doping densities\nmeasured using Hall effect measurements vary from $N_D = 10^{12} cm^{-3}$ to\n$8\\times 10^{12} cm^{-3}$ for the solution-processed n-type layer and $N_A =\n8\\times 10^9 cm^{-3}$ for the evaporated p-type layer. While these devices\noutperform their counterparts, that are supposedly un-doped, the results raise\nthree important questions: (i) Are the reported doping densities high enough to\nchange the electrostatic potential distribution in the device from that for the\nun-doped ones, (ii) are the doping densities high enough for the pn-junction to\nremain intact under typical photovoltaic operation conditions and (iii) is a\npn-junction beneficial for photovoltaic performance given the typical\nproperties of lead-halide perovskites.", "category": "physics_app-ph" }, { "text": "Fabrication and Characterization of AlN-based, CMOS compatible\n Piezo-MEMS Devices: This paper details the development of high-quality, c-axis oriented AlN thin\nfilms up to 2 {\\mu}m thick, using sputtering on platinum-coated SOI substrates\nfor use in piezoelectric MEMS. Our comprehensive studies illustrate how\nimportant growth parameters such as the base Pt electrode quality, deposition\ntemperature, power, and pressure, can influence film quality. With careful\nadjustment of these parameters, we managed to manipulate residual stresses\n(from compressive -1.2 GPa to tensile 230 MPa), and attain a high level of\norientation in the AlN thin films, evidenced by < 5deg FWHM X-Ray diffraction\npeak widths. We also report on film surface quality regarding roughness, as\nassessed by atomic force microscopy, and grain size, as determined through\nscanning electron microscopy. Having attained the desired film quality, we\nproceeded to a fabrication process to create piezoelectric micromachined\nultrasound transducers (PMUTs) with the AlN on SOI material stack, using deep\nreactive ion etching (DRIE). Initial evaluations of the vibrational behavior of\nthe created devices, as observed through Laser Doppler Vibrometry, hint at the\npotential of these optimized AlN thin films for MEMS transducer development.", "category": "physics_app-ph" }, { "text": "Considerations for the design of a heterojunction bipolar transistor\n solar cell: Independent current extraction in multi-junction solar cells has gained\nattention in recent years because it can deliver higher annual energy yield and\ncan work for more semiconductor material combinations than the more established\nseries-connected multi-junction technology. The heterojunction bipolar\ntransistor solar cell concept (HBTSC) was recently proposed as a simple,\ncompact and cost-effective multi-terminal device structure that allows\nindependent current extraction. It consists of only three main layers: emitter,\nbase and collector. In this work we use a drift-diffusion model to analyze\nimportant aspects in the design of an HBTSC structure based on typical III-V\nsemiconductor materials. We find that carrier injection from the emitter into\nthe collector (transistor effect) degrades the open-circuit voltage of the top\nsub-cell, but this risk can be eliminated by optimizing the base design. We\nfind requirements for the base layer which are, in principle, achievable in the\ncontext of current III-V semiconductor technology.", "category": "physics_app-ph" }, { "text": "Reduced ITO for Transparent Superconducting Electronics: Absorption of light in superconducting electronics is a major limitation on\nthe quality of circuit architectures that integrate optical components with\nsuperconducting components. A 10 nm thick film of a typical superconducting\nmaterial like niobium can absorb over half of any incident optical radiation.\nWe propose instead using superconductors which are transparent to the\nwavelengths used elsewhere in the system. In this paper we investigated reduced\nindium tin oxide (ITO) as a potential transparent superconductor for\nelectronics. We fabricated and characterized superconducting wires of reduced\nindium tin oxide. We also showed that a $\\SI{10}{nm}$ thick film of the\nmaterial would only absorb about 1 - 20\\% of light between 500 - 1700 nm.", "category": "physics_app-ph" }, { "text": "Breaking voltage-bandwidth limits in integrated lithium niobate\n modulators using micro-structured electrodes: Electro-optic modulators with low voltage and large bandwidth are crucial for\nboth analog and digital communications. Recently, thin-film lithium niobate\nmodulators have enable dramatic performance improvements by reducing the\nrequired modulation voltage while maintaining high bandwidths. However, the\nreduced electrode gaps in such modulators leads to significantly higher\nmicrowave losses, which limit electro-optic performance at high frequencies.\nHere we overcome this limitation and achieve a record combination of low RF\nhalf-wave voltage of 1.3 V while maintaining electro-optic response with 1.8-dB\nroll-off at 50 GHz. This demonstration represents a significant improvement in\nvoltage-bandwidth limit, one that is comparable to that achieved when switching\nfrom legacy bulk to thin-film lithium niobate modulators. Leveraging the\nlow-loss electrode geometry, we show that sub-volt modulators with $>$ 100 GHz\nbandwidth can be enabled.", "category": "physics_app-ph" }, { "text": "Optimization approach for optical absorption in three-dimensional\n structures including solar cells: The rigorous coupled-wave approach (RCWA) and the differential evolution\nalgorithm (DEA) were coupled in a practicable approach to maximize absorption\nin optical structures with three-dimensional morphology. As a model problem,\noptimal values of four geometric parameters and the bandgaps of three i-layers\nwere found for an amorphous-silicon, multi-terminal, thin-film tandem solar\ncell comprising three p-i-n junctions with a metallic hexagonally corrugated\nback-reflector. When the optical short-circuit current density was chosen as\nthe figure of merit to be maximized, only the bandgap of the topmost i-layer\nwas significant and the remaining six parameters played minor roles. While this\nconfiguration would absorb light very well, it would have poor electrical\nperformance. This is because the optimization problem allows for the\nthicknesses and bandgaps of the semiconductor layers to change. We therefore\ndevised another figure of merit that takes into account bandgap changes by\nestimating the open-circuit voltage. The resulting configuration was found to\nbe optimal with respect to all seven variable parameters. The RCWA+DEA\noptimization approach is applicable to other types of photovoltaic solar cells\nas well as optical absorbers, with the choice of the figure of merit being\nvital to a successful outcome.", "category": "physics_app-ph" }, { "text": "Effect of Low-Frequency Signal On Nanoscale Memristor Device: In the present report, we have investigated the effect of the low-frequency\nsignal on nanoscale memristor device. The frequency is varied from 2 Hz to 10\nHz and the corresponding effect on the current-voltage characteristics, time\ndomain state variable, charge-magnetic flux relation, memristance-charge\nrelation, memristance-voltage characteristics and memristance-magnetic flux\nrelation are studied. The results clearly suggested that the frequency of the\ninput stimulus plays an important role in the device dynamics.", "category": "physics_app-ph" }, { "text": "Towards a 2D Printer: A Deterministic Cross Contamination-free Transfer\n Method for Atomically Layered Materials: Precision and chip contamination-free placement of two-dimensional (2D)\nmaterials is expected to accelerate both the study of fundamental properties\nand novel device functionality. Current transfer methods of 2D materials onto\nan arbitrary substrate deploy wet chemistry and viscoelastic stamping. However,\nthese methods produce a) significant cross contamination of the substrate due\nto the lack of spatial selectivity b) may not be compatible with chemically\nsensitive device structures, and c) are challenged with respect to spatial\nalignment. Here, we demonstrate a novel method of transferring 2D materials\nresembling the functionality known from printing; utilizing a combination of a\nsharp micro-stamper and viscoelastic polymer, we show precise placement of\nindividual 2D materials resulting in vanishing cross contamination to the\nsubstrate. Our 2D printer-method results show an aerial cross contamination\nimprovement of two to three orders of magnitude relative to state-of-the-art\ndry and direct transfer methods. Moreover, we find that the 2D material quality\nis preserved in this transfer method. Testing this 2D material printer on\ntaped-out integrated Silicon photonic chips, we find that the micro-stamper\nstamping transfer does not physically harm the underneath Silicon nanophotonic\nstructures such as waveguides or micro-ring resonators receiving the 2D\nmaterial. Such accurate and substrate-benign transfer method for 2D materials\ncould be industrialized for rapid device prototyping due to its high\ntime-reduction, accuracy, and contamination-free process.", "category": "physics_app-ph" }, { "text": "Nonlinear waves in flexible mechanical metamaterials: Flexible mechanical metamaterials are compliant structures engineered to\nachieve unique properties via the large deformation of their components. While\ntheir static character has been studied extensively, the study of their dynamic\nproperties is still at an early stage, especially in the nonlinear regime\ninduced by their high deformability. Nevertheless, recent studies show that\nthese systems provide new opportunities for the control of large amplitude\nelastic waves. Here, we summarize the recent results on the propagation of\nnonlinear waves in flexible elastic metamaterials, and highlight possible new\nresearch directions.", "category": "physics_app-ph" }, { "text": "Experimental demonstration of multimode microresonator sensing by\n machine learning: A multimode microcavity sensor based on a self-interference microring\nresonator is demonstrated experimentally. The proposed multimode sensing method\nis implemented by recording wideband transmission spectra that consist of\nmultiple resonant modes. It is different from the previous dissipative sensing\nscheme, which aims at measuring the transmission depth changes of a single\nresonant mode in a microcavity. Here, by combining the dissipative sensing\nmechanism and the machine learning algorithm, the multimode sensing information\nextracted from a broadband spectrum can be efficiently fused to estimate the\ntarget parameter. The multimode sensing method is immune to laser frequency\nnoises and robust against system imperfection, thus our work presents a great\nstep towards practical applications of microcavity sensors outside the research\nlaboratory. The voltage applied across the microheater on the chip was adjusted\nto bring its influence on transmittance through the thermo-optic effects. As a\nproof-of-principle experiment, the voltage was detected by the multimode\nsensing approach. The experimental results demonstrate that the limit of\ndetection of the multimode sensing by the general regression neural network is\nreduced to 6.7% of that of single-mode sensing within a large measuring range.", "category": "physics_app-ph" }, { "text": "Novel Lithium-Sulfur Polymer Battery Operating at Moderate Temperature: A safe lithium-sulfur (Li-S) battery employs a composite polymer electrolyte\nbased on a poly(ethylene glycol) dimethyl ether (PEGDME) solid at room\ntemperature. The electrolyte membrane enables a stable and reversible Li-S\nelectrochemical process already at 50{\\deg}C, with low resistance at the\nelectrode/electrolyte interphase and fast Li+ transport. The relatively low\nmolecular weight of the PEGDME and the optimal membrane composition in terms of\nsalts and ceramic allow a liquid-like Li-S conversion reaction by heating at\nmoderately high temperature, still holding the solid-like polymer state of the\ncell. Therefore, the electrochemical reaction of the polymer Li-S cell is\ncharacterized by the typical dissolution of lithium polysulfides into the\nelectrolyte medium during discharge and the subsequent deposition of sulfur at\nthe electrode/electrolyte interphase during charge. On the other hand, the\nremarkable thermal stability of the composite polymer electrolyte (up to\n300{\\deg}C) suggests a lithium-metal battery with safety content significantly\nhigher than that using the common, flammable liquid solutions. Hence, the Li-S\npolymer battery delivers at 50{\\deg}C and 2 V a stable capacity approaching 700\nmAhgS-1, with a steady-state coulombic efficiency of 98%. These results suggest\na novel, alternative approach to achieve safe, high energy batteries with solid\npolymer configuration.", "category": "physics_app-ph" }, { "text": "MoS$_{2}$ pixel arrays for real-time photoluminescence imaging of redox\n molecules: Measuring the behavior of redox-active molecules in space and time is crucial\nfor better understanding of chemical and biological systems and for the\ndevelopment of new technologies. Optical schemes are non-invasive, scalable and\ncan be applied to many different systems, but usually have a slow response\ncompared to electrical detection methods. Furthermore, many fluorescent\nmolecules for redox detection degrade in brightness over long exposure times.\nHere we show that the photoluminescence of pixel arrays of an atomically thin\ntwo-dimensional (2D) material, a monolayer of MoS$_{2}$, can image spatial and\ntemporal changes in redox molecule concentration in real time. Because of the\nstrong dependence of MoS$_{2}$ photoluminescence on doping and sensitivity to\nsurface changes characteristic of 2D materials, changes in the local chemical\npotential significantly modulate the photoluminescence of MoS$_{2}$, with a\nsensitivity of 0.9 mV/$\\sqrt{Hz}$ on a 5 $\\mu$m by 5 $\\mu$m pixel,\ncorresponding to better than parts-per-hundred changes in redox molecule\nconcentration down to nanomolar concentrations at 100 ms frame rates. The\nreal-time imaging of electrochemical potentials with a fast response time\nprovides a new strategy for visualizing chemical reactions and biomolecules\nwith a 2D material screen.", "category": "physics_app-ph" }, { "text": "Theoretical compensation of static deformations of freeform multi mirror\n substrates: Varying temperatures influence the figure errors of freeform metal mirrors by\nthermal expansion. Furthermore, different materials lead to thermo-elastic\nbending effects. The article presents a derivation of a compensation approach\nfor general static loads. Utilizing perturbation theory this approach works for\nshape compensation of substrates which operate in various temperature\nenvironments. Verification is made using a finite element analysis which is\nfurther used to produce manufacturable CAD models. The remaining low spatial\nfrequency errors are deterministically correctable using diamond turning or\npolishing techniques.", "category": "physics_app-ph" }, { "text": "Distributed Quantum Fiber Magnetometry: Nitrogen-vacancy (NV) quantum magnetometers offer exceptional sensitivity and\nlong-term stability. However, their use to date in distributed sensing\napplications, including remote detection of ferrous metals, geophysics, and\nbiosensing, has been limited due to the need to combine optical, RF, and\nmagnetic excitations into a single system. Existing approaches have yielded\nlocalized devices but not distributed capabilities. In this study, we report on\na continuous system-in-a-fiber architecture that enables distributed magnetic\nsensing over extended lengths. Key to this realization is a thermally drawn\nfiber that has hundreds of embedded photodiodes connected in parallel and a\nhollow optical waveguide that contains a fluid with NV diamonds. This fiber is\nplaced in a larger coaxial cable to deliver the required RF excitation. We\nrealize this distributed quantum sensor in a water-immersible 90-meter-long\ncable with 102 detection sites. A sensitivity of 63 nT Hz-1/2 per site, limited\nby laser shot noise, was established along a 90 m test section. This fiber\narchitecture opens new possibilities as a robust and scalable platform for\ndistributed quantum sensing technologies.", "category": "physics_app-ph" }, { "text": "Transient and Steady-State Temperature Rise in Three-Dimensional\n Anisotropic Layered Structures in Pump-Probe Thermoreflectance Experiments: Recent developments of the pump-probe thermoreflectance methods (such as the\nbeam-offset and elliptical-beam approaches of the time-domain and\nfrequency-domain thermoreflectance techniques) enabled measurements of the\nthermal conductivities of in-plane anisotropic materials. Estimating the\ntemperature rise of anisotropic layered structures under surface heating is\ncritically important to make sure that the temperature rise is not too high to\nalias the signals in these experiments. However, a simple formula to estimate\nthe temperature rise in three-dimensional (3D) anisotropic layered systems\nheated by a non-circular laser beam is not available yet, which is the main\nproblem we aim to solve in this work. We first re-derived general formalisms of\nthe temperature rise of a multilayered structure based on the previous\nliterature work by solving the 3D anisotropic heat diffusion equation in the\nfrequency domain. These general formalisms normally require laborious numerical\nevaluation; however, they could be reduced to explicit analytical expressions\nfor the case of semi-infinite solids. We then extend the analytical expressions\nto multilayered systems, taking into account the effect of the top layers. This\nwork not only enhances our understanding of the physics of temperature rise due\nto surface laser heating but also enables quick estimation of the peak\ntemperature rise of 3D anisotropic layered systems in pump-probe\nthermoreflectance experiments and thus greatly benefits the thermoreflectance\nexperiments in choosing the appropriate heating power intensity for the\nexperiments.", "category": "physics_app-ph" }, { "text": "Encryption Device Based on Wave-Chaos for Enhanced Physical Security of\n Wireless Wave Transmission: We introduce an encryption device based on wave-chaos to enhance the physical\nsecurity of wireless wave transmission. The proposed encryption device is\ncomposed of a compact quasi-2D disordered cavity, where transmit signals pass\nthrough to be distorted in time before transmission. On the receiving end, the\nsignals can only be decrypted when they pass through an identical cavity. In\nthe absence of a proper decryption device, the signals cannot be properly\ndecrypted. If a cavity with a different shape is used on the receiving end,\nvastly different wave dynamics will prevent the signals from being decrypted,\ncausing them to appear as noise. We experimentally demonstrate the proposed\nconcept in an apparatus representing a wireless link.", "category": "physics_app-ph" }, { "text": "beta-Ga2O3 Double Gate Junctionless FET with an Efficient Volume\n Depletion Region: This paper presents a new \\b{eta}-Ga2O3 junctionless double gate\nMetal-Oxide-Field-Semiconductor-Effect-Transistor (\\b{eta}DG-JL-FET) that a P+\npacket embedded in the oxide layer (PO-\\b{eta}DG-JL-FET) for high-voltage\napplications. Our goal is to achieve an efficient volume depletion region by\nplacing a P+ layer of silicon. We show that the proposed structure has a\nsubthreshold swing ~ 64 mV/decade and it suppressed the band to band tunneling\n(BTBT) phenomenon. Also, the PO-\\b{eta}DG-JL-FET structure has a high Ion/Ioff\n~ 1.3e15. The embedded layer reduces the off-current (IOFF) by ~ 10-4, while\nthe on-current (ION) reduces slightly. Besides, we show that the proposed\nstructure has acceptable Ioff value in a range of gate work functions which\nhelp us to the optimization of designs in terms of area, power gain, and\nleakage current. The leakage current of the proposed structure is ~ 7e-17 A in\n400 K temperature. Furthermore, the fabrication process steps of the proposed\nstructure will be investigated.", "category": "physics_app-ph" }, { "text": "Effect of Graded Bias Voltage on the Microstructure of arc-PVD CrN Films\n and its Response in Electrochemical & Mechanical Behavior: The effect of graded or constant bias voltages (-40 V, -80 V and -40/60/80 V)\non size grain and surface defects of arc PVD deposited CrN films was\ninvestigated. Corrosion resistance evaluated using electrochemical impedance\nspectroscopy (EIS) and potentiodynamic curves (Tafel) and the mechanical\nbehavior evaluated by means of instrumented nanoindentation and scratch testing\nwas correlated with the microstructural changes. It was found that the bias\nvoltage variation affects corrosion behavior due to the presence of defects\n(i.e. open voids, droplets) which also affects the failure mechanisms and\nincreasing spallation. High bias voltage (-80 V) increases nano-hardness and\nthe elastic modulus due to the dense microstructure of the CrN coating.", "category": "physics_app-ph" }, { "text": "Controlling the electro-optic response of a semiconducting perovskite\n coupled to a phonon-resonant cavity: Optical cavities, resonant with vibrational or electronic transitions of\nmaterial within the cavity, enable control of light-matter interaction.\nPrevious studies have reported cavity-induced modifications of chemical\nreactivity, fluorescence, phase behavior, and charge transport. Here, we\nexplore the effect of resonant cavity-phonon coupling on the transient\nphotoconductivity in a hybrid organic-inorganic perovskite. To this end, we\nmeasure the ultrafast photoconductivity response of perovskite in a tunable\nFabry-Perot terahertz cavity, designed to be transparent for optical\nexcitation. The terahertz-cavity field-phonon interaction causes apparent Rabi\nsplitting between the perovskite phonon mode and the cavity mode. We explore\nwhether the cavity-phonon interaction affects the material electron-phonon\ninteraction by determining the charge carrier mobility through the\nphotoconductivity. Despite the apparent hybridization of cavity and phonon\nmodes, we show that the perovskite properties, in both ground (phonon response)\nand excited (photoconductive response) states, remain unaffected by the tunable\nlight-matter interaction. Yet the response of the integral perovskite-terahertz\noptical cavity system depends critically on the interaction strength of the\ncavity with the phonon: the transient terahertz response to optical excitation\ncan be increased up to 3-fold by tuning the cavity-perovskite interaction\nstrength. These results enable tunable switches and frequency-controlled\ninduced transparency devices.", "category": "physics_app-ph" }, { "text": "Gold/Parylene-C/Pentacene Capacitor under Constant-Voltage Stress: Degradation of metal-insulator-semiconductor (MIS) capacitors of\ngold/Parylene-C/Pentacene under constant voltage stress (CVS) was investigated\nto explore the electrical stability and reliability of Parylene C as a gate\ndielectric in flexible electronics. A stress voltage of fixed magnitude as high\nas 20 V, both negative and positive in polarity, was applied to each MIS\ncapacitor at room temperature for a fixed duration as long as 10 s. The CVS\neffects on the capacitance-voltage curve-shift, the time-dependent leakage\ncurrent, and the time-dependent dielectric breakdown were measured and\nanalyzed. CVS is observed to induce charge in Parylene-C and its interfaces\nwith gold and Pentacene. The net induced charge is positive and negative for,\nrespectively, negative and positive gate bias polarity during CVS. The\nmagnitude of the charge accumulated following positive gate CVS is\nsignificantly higher than that following negative gate bias CVS in the range of\n4 to 25 nC cm$^{-2}$. In contrast, the leakage current during the negative gate\nstress is three orders of magnitude higher than that during the positive gate\nstress for the same bias stress magnitude. The charge buildup and leakage\ncurrent are due to the trapping of electrons and holes near the\nParylene-C/Pentacene interface as well as in the Parylene-C layer. Before the\napplication of the CVS, a dielectric breakdown occurs at an electric field of\n1.62 MV cm$^{-1}$. After the application of the CVS, the breakdown voltage\ndecreases and the density of the trapped charges increases as the stress\nvoltage increases in magnitude, with the polarity of the trapped charges\nopposite to that of the stress voltage. The magnitude and direction of the\ncapacitance-voltage curve-shift depend on the trapping and recombination of\nelectrons and holes in the Parylene-C layer and in the proximity of the\nParylene-C/Pentacene interface during CVS.", "category": "physics_app-ph" }, { "text": "Anti-fatigue-fracture hydrogels: The emerging applications of hydrogels in devices and machines require these\nsoft materials to maintain robustness under cyclic mechanical loads. Whereas\nhydrogels have been made tough to resist fracture under a single cycle of\nmechanical load, these toughened gels still suffer from fatigue fracture under\nmultiple cycles of loads. The reported fatigue threshold (i.e., the minimal\nfracture energy at which crack propagation occurs under cyclic loads) for\nsynthetic hydrogels is on the order of 1-100 J/m2, which is primarily\nassociated with the energy required to fracture a single layer of polymer\nchains per unit area. Here, we demonstrate that the controlled introduction of\ncrystallinity in hydrogels can significantly enhance their fatigue thresholds,\nsince the process of fracturing crystalline domains for fatigue-crack\npropagation requires much higher energy than fracturing a single layer of\npolymer chains. The fatigue threshold of polyvinyl alcohol (PVA) with a\ncrystallinity of 18.9 wt.% in the swollen state can exceed 1,000 J/m2. We\nfurther develop a strategy to enhance the anti-fatigue-fracture properties of\nPVA hydrogels, but still maintain their high water contents and low moduli by\npatterning highly-crystalline regions in the hydrogels. The current work not\nonly reveals an anti-fatigue-fracture mechanism in hydrogels but also provides\na practical method to design anti-fatigue-fracture hydrogels for diverse\napplications.", "category": "physics_app-ph" }, { "text": "Efficiency limits of Perovskite Solar Cells with Transition Metal Oxides\n as Hole Transport Layers: Transition metal oxides (TMOs) like MoOx are increasingly explored as hole\ntransport layers for perovskite-based solar cells. Due to their large work\nfunction, the hole collection mechanism of such solar cells are fundamentally\ndifferent from other materials like PEDOT: PSS, and the associated device\noptimizations are not well elucidated. In addition, the prospects of such\narchitectures against the challenges posed by ion migration are yet to be\nexplored - which we critically examine in this contribution through detailed\nnumerical simulations. Curiously, we find that, for similar ion densities and\ninterface recombination velocities, ion migration is more detrimental for\nPerovskite solar cells with TMO contact layers with much lower achievable\nefficiency limits (21%). The insights shared by this work should be of broad\ninterest to the community in terms of long-term stability, efficiency\ndegradation and hence could help critically evaluate the promises and prospects\nof TMOs as hole contact layers for perovskite solar cells.", "category": "physics_app-ph" }, { "text": "Wide-field fluorescent nanodiamond spin measurements toward real-time\n large-area intracellular quantum thermometry: In this study, we analyze the operational process of nanodiamond (ND) quantum\nthermometry based on wide-field detection of optically detected magnetic\nresonance (ODMR) of nitrogen vacancy centers, and compare its performance with\nthat of confocal ODMR detection. We found that (1) the thermometry results are\nsignificantly affected by the shape and size of the camera region of interest\n(ROI) surrounding the target NDs and that (2) by properly managing the ROI and\nacquisition parameters of the camera, a temperature precision comparable to\nconfocal detection in living cells can be obtained by wide-field ODMR. Our\nresults are significant to the development of camera-based real-time large-area\nquantum thermometry of living cells.", "category": "physics_app-ph" }, { "text": "Topographic De-adhesion in the Viscoelastic Limit: The superiority of many natural surfaces at resisting soft, sticky\nbiofoulants has inspired the integration of dynamic topography with mechanical\ninstability to promote self-cleaning artificial surfaces. The physics behind\nthis novel mechanism is currently limited to elastic biofoulants where surface\nenergy, bending stiffness, and topographical wavelength are key factors.\nHowever, the viscoelastic nature of many biofoulants causes a complex interplay\nbetween these factors with time-dependent characteristics such as material\nsoftening and loading rate. Here, we enrich the current elastic theory of\ntopographic de-adhesion using analytical and finite element models to elucidate\nthe non-linear, time-dependent interaction of three physical, dimensionless\nparameters: biofoulant's stiffness reduction, product of relaxation time and\nloading rate, and the critical strain for short-term elastic de-adhesion.\nTheoretical predictions, in good agreement with numerical simulations, provide\ninsight into tuning these control parameters to optimize surface renewal via\ntopographic de-adhesion in the viscoelastic regime.", "category": "physics_app-ph" }, { "text": "A Nanoscale Room-Temperature Multilayer Skyrmionic Synapse for Deep\n Spiking Neural Networks: Magnetic skyrmions have attracted considerable interest, especially after\ntheir recent experimental demonstration at room temperature in multilayers. The\nrobustness, nanoscale size and non-volatility of skyrmions have triggered a\nsubstantial amount of research on skyrmion-based low-power, ultra-dense\nnanocomputing and neuromorphic systems such as artificial synapses.\nRoom-temperature operation is required to integrate skyrmionic synapses in\npractical future devices. Here, we numerically propose a nanoscale skyrmionic\nsynapse composed of magnetic multilayers that enables room-temperature device\noperation tailored for optimal synaptic resolution. We demonstrate that when\nembedding such multilayer skyrmionic synapses in a simple spiking neural\nnetwork (SNN) with unsupervised learning via the spike-timing-dependent\nplasticity rule, we can achieve only a 78% classification accuracy in the MNIST\nhandwritten data set under realistic conditions. We propose that this\nperformance can be significantly improved to about 98.61% by using a deep SNN\nwith supervised learning. Our results illustrate that the proposed skyrmionic\nsynapse can be a potential candidate for future energy-efficient neuromorphic\nedge computing.", "category": "physics_app-ph" }, { "text": "Hyperpolarization-enhanced NMR spectroscopy with femtomole sensitivity\n using quantum defects in diamond: Nuclear magnetic resonance (NMR) spectroscopy is a widely used tool for\nchemical analysis and molecular structure identification. Because it typically\nrelies on the weak magnetic fields produced by a small thermal nuclear spin\npolarization, NMR suffers from poor molecule-number sensitivity compared to\nother analytical techniques. Recently, a new class of NMR sensors based on\noptically-probed nitrogen-vacancy (NV) quantum defects in diamond have allowed\nmolecular spectroscopy from sample volumes several orders of magnitude smaller\nthan the most sensitive inductive detectors. To date, however, NV-NMR\nspectrometers have only been able to observe signals from pure, highly\nconcentrated samples. To overcome this limitation, we introduce a technique\nthat combines picoliter-scale NV-NMR with fully integrated Overhauser dynamic\nnuclear polarization (DNP) to perform high-resolution spectroscopy on a variety\nof small molecules in dilute solution, with femtomole sensitivity. Our\ntechnique advances mass-limited NMR spectroscopy for drug and natural product\ndiscovery, catalysis research, and single cell studies.", "category": "physics_app-ph" }, { "text": "Database-driven high-throughput study for hybrid perovskite coating\n materials: We developed a high-throughput screening scheme to acquire candidate coating\nmaterials for hybrid perovskites. From more than 1.8 million entries of an\ninorganic compound database, we collected 93 binary and ternary materials with\npromising properties for protectively coating halide-perovskite photoabsorbers\nin perovskite solar cells. These candidates fulfill a series of criteria,\nincluding wide band gaps, abundant and non-toxic elements, water-insoluble, and\nsmall lattice mismatch with surface models of halide perovskites.", "category": "physics_app-ph" }, { "text": "Improved Self-cleaning Properties of an Efficient and Easy to Scale up\n TiO2 Thin Films Prepared by Adsorptive Self-Assembly: Transparent titania coatings have self-cleaning and anti-reflection\nproperties (AR) that are of great importance to minimize soiling effect on\nphotovoltaic modules. In this work, TiO2 nanocolloids prepared by polyol\nreduction method were successfully used as coating thin films onto borosilicate\nglass substrates via adsorptive self-assembly process. The nanocolloids were\ncharacterized by transmission electron microscopy and x-ray diffraction. The\naverage particle size was around 2.6 nm. The films which have an average\nthickness of 76.2 nm and refractive index of 1.51 showed distinctive anti\nsoiling properties under desert environment. The film surface topography,\nuniformity, wettability, thickness and refractive index were characterized\nusing x-ray diffraction, atomic force microscopy, scanning electron microscopy,\nwater contact angle measurements and ellipsometry. The self-cleaning properties\nwere investigated by optical microscopy and UV-Vis spectroscopy. The optical\nimages show 56% reduction of dust deposition rate over the coated surfaces\ncompared with bare glass substrates after 7 days of soiling. The transmission\noptical spectra of these films collected at normal incidence angle show high\nanti-reflection properties with the coated substrates having transmission loss\nof less than 6% compared to bare clean glass.", "category": "physics_app-ph" }, { "text": "Co-evaporation as an optimal technique towards compact methylammonium\n bismuth iodide layers: The most studied perovskite-based solar cells reported up to date contain the\ntoxic lead in its composition. Photovoltaic research and development towards\nnon-toxic, lead-free perovskite solar cells are critical to finding\nalternatives to reduce human health concerns associated with them.\nBismuth-based perovskite variants, especially in the form of methylammonium\nbismuth iodide (MBI), is a good candidate for the non-toxic light absorber.\nHowever, the reported perovskite variant MBI thin flms prepared by the solution\nprocess so far suffers from poor morphology and surface coverage. In this work,\nwe investigate for the first time the optoelectronic, crystallographic and\nmorphological properties of MBI thin flms prepared via thermal co-evaporation\nof MAI and BiI3. We find by modifying the precursor ratio that the layer with\npure MBI composition lead to uniform, compact and homogeneous layers,\nbroadening the options of deposition techniques for lead-free based perovskite\nsolar cells.", "category": "physics_app-ph" }, { "text": "Electrically Tunable Harmonics in Time-modulated Metasurfaces for\n Wavefront Engineering: Modulation of metasurfaces in time gives rise to several exotic space-time\nscattering phenomena by violating the reciprocity and generation of\nhigher-order frequency harmonics. We introduce a new design paradigm for\ntime-modulated metasurfaces, offering electrically tunable engineering of the\ngenerated frequency harmonics and their emerging wavefronts by controlling the\nphase delay in modulation. It is demonstrated that the light acquires a\ndispersionless phase shift regardless of incident angle and polarization, upon\nundergoing frequency conversion in a time-modulated metasurface which is\nlinearly proportional to the modulation phase delay and the order of generated\nfrequency harmonic. The conversion efficiency to the frequency harmonics is\nindependent of modulation phase delay and only depends on the modulation depth\nand resonant characteristics of the metasurface element, with the highest\nefficiency occurring in the vicinity of resonance, and decreasing away from the\nresonant regime. The design approach allows for creating tunable spatially\nvarying phase discontinuties with 2{\\pi} span in the wavefronts of generated\nfrequency harmonics for a wide range of frequencies and incident angles.\nSpecifically, we apply this approach to a time-modulated metasurface in the\nTeraherz regime consisted of graphene-wrapped silicon microwires. For this\npurpose, we use an accurate and efficient semi-analytical framework based on\nmultipole scattering. We demonstrate the utility of the design for tunable beam\nsteering and focusing of the generated frequency harmonics. Furthermore, we\nrigorously verify the broadband and wide-angle performance of the metasurface\nin manipulation of the generated frequency harmonics. The proposed design\napproach enables a new class of high-efficiency tunable metasurfaces with wide\nangular and frequency bandwidth, wavefront engineering capabilities and\nmulti-functionality.", "category": "physics_app-ph" }, { "text": "Thermal Conductivity Enhancement by Surface Electromagnetic Waves\n Propagating along Multilayered Structures with Asymmetric Surrounding Media: Enhancement of thermal conductivity via surface electromagnetic waves (SEWs)\nsupported in nanostructures has recently drawn attention as a remedy for issues\nraised due to the reduction of thermal conductivity in nanoscale confinement.\nAmong them, multilayered structures on a substrate are prevalent in nano-sized\nsystems, such as electronic nanodevices, meaning that analysis on those\nstructures is indispensable. In this work, three basic multilayered structures\nare selected and the analytical expressions for SEWs supported in each\nstructure are derived. This analytical approach enables us to figure out which\nfactors are crucial for enhancing SEW thermal conductivity using multilayers.\nIt is also found that the solution can be extended to various materials and\nprovide the guidelines on which configurations are desirable for increasing the\nthermal conductivity. Furthermore, the analytical solutions reduce the\ncalculation time significantly such that the optimal configuration, which can\nadditionally yield SEW thermal conductivity of 1.27 W/m$\\cdot$K corresponding\nto 90\\% of the thermal conductivity of bulk glass, is found with the genetic\nalgorithm. This study thus provides a new method for efficiently managing\nthermal issues in nano-sized devices.", "category": "physics_app-ph" }, { "text": "Ideal spectral emissivity design for extreme radiative cooling: Radiative coolers that can passively cool objects by radiating heat into the\nouter space have recently received much attention. However, the ultimate limits\nof their performance as well as their ideal spectral design are still unknown.\nWe present the fundamental lower bound of the temperature of a radiatively\ncooled object on earth surfaces under general conditions, including\nnon-radiative heat transfer, and the upper bound of the net radiative power\ndensity of a radiative cooler as a function of temperature. We derive the ideal\nspectral emissivities that can realize such bounds and, contrary to common\nbelief, find that the ideal emission window is different from 8 to 13 um and\nforms disjointed sets of wavelengths, whose width diminishes at lower\ntemperatures. We show that ideal radiative coolers with perfect thermal\ninsulation against conduction and convection have a steady-state temperature of\n243.6 K in summer and 180.5 K in winter, much below previously measured values.\nWe also provide the ideal emission window for a single-band emitter and show\nthat this window should be much narrower than that of previous designs if the\nobjective is to build a radiative freezer that can operate in summer. We\nprovide a general guideline for designing spectral emissivity to achieve the\nmaximum temperature drop or the maximum net radiative power density.", "category": "physics_app-ph" }, { "text": "Environmental Modeling of Silicon Dangling Bond QCA Wires: Interactions of quantum cellular automata (QCA) circuits with their\nenvironment induce transitions in their quantum states that can cause errors in\ncomputation. The nature of these interactions depend on the specific physical\nimplementation of the circuit. In the case of silicon dangling bond QCA, one\nchannel of environmental interaction is between dangling bond cells and\nlongitudinal phonons in the silicon lattice. In the presence of this\nenvironmental interaction, short 4 cell wire simulations show reliable\noperation at liquid nitrogen temperature, however simulation and theoretical\narguments suggest long wires operated from thermal equilibrium are susceptible\nto exponential decay of cell polarization along their length regardless of\nclock zoning. Quantum annealing is suggested as a technique for bringing QCA\nwires into their ground state prior to information transmission to circumvent\nthis problem.", "category": "physics_app-ph" }, { "text": "Optimization of Raman amplifiers: a comparison between black-, grey- and\n white-box modeling: Designing and optimizing optical amplifiers to maximize system performance is\nbecoming increasingly important as optical communication systems strive to\nincrease throughput. Offline optimization of optical amplifiers relies on\nmodels ranging from white-box models deeply rooted in physics to black-box\ndata-driven physics-agnostic models. Here, we compare the capabilities of\nwhite-, grey- and black-box models to achieve a target frequency-distance\namplification in a bidirectional Raman amplifier. We show that any of the\nstudied methods can achieve down to 1 dB of frequency-distance flatness over\nthe C-band in a 100-km span. Then, we discuss the models' applicability,\nadvantages, and drawbacks based on the target application scenario, in\nparticular in terms of optimization speed and access to training data.", "category": "physics_app-ph" }, { "text": "Ultrasound Matrix Imaging-Part I: The focused reflection matrix, the\n F-factor and the role of multiple scattering: This is the first article in a series of two dealing with a matrix approach\nfor aberration quantification and correction in ultrasound imaging. Advanced\nsynthetic beamforming relies on a double focusing operation at transmission and\nreception on each point of the medium. Ultrasound matrix imaging (UMI) consists\nin decoupling the location of these transmitted and received focal spots. The\nresponse between those virtual transducers form the so-called focused\nreflection matrix that actually contains much more information than a confocal\nultrasound image. In this paper, a time-frequency analysis of this matrix is\nperformed, which highlights the single and multiple scattering contributions as\nwell as the impact of aberrations in the monochromatic and broadband regimes.\nInterestingly, this analysis enables the measurement of the incoherent\ninput-output point spread function at any pixel of this image. A fitting\nprocess enables the quantification of the single scattering, multiple\nscattering and noise components in the image. From the single scattering\ncontribution, a focusing criterion is defined, and its evolution used to\nquantify the amount of aberration throughout the ultrasound image. In contrast\nto the state-of-the-art coherence factor, this new indicator is robust to\nmultiple scattering and electronic noise, thereby providing a contrasted map of\nthe focusing quality at a much better transverse resolution. After a validation\nof the proof-of-concept based on time-domain simulations, UMI is applied to the\nin-vivo study of a human calf. Beyond this specific example, UMI opens a new\nroute for speed-of-sound and scattering quantification in ultrasound imaging.", "category": "physics_app-ph" }, { "text": "Simultaneous readout of two adjacent bit tracks with a spin-torque\n oscillator: We propose a novel setup for a spin-torque oscillator reader in magnetic hard\ndisk drive technology. Two adjacent bit tracks are to be read simultaneously,\nleading to high data transfer rate and increased resilience to noise as the\nlateral size of the oscillator device is allowed to remain larger than the bit\nwidth. We perform micromagnetic simulations of an example system and find that\nthe magnetization response has a clear unimodal character, which enables for\ndetection of two bit values at the same time. We analyze the frequency of the\ndevice under the influence of two different external fields and conduct a\nsimulation of a successful dynamic readout. We estimate the signal linewidth\nand signal-to-noise ratios of the setup and show that it may be potentially\nbeneficial for magnetic readout applications.", "category": "physics_app-ph" }, { "text": "Reversible Ionic Liquid Intercalation for Electrically Controlled\n Thermal Radiation from Graphene Devices: Using graphene as a tuneable optical material enables a series of optical\ndevices such as switchable radar absorbers, variable infrared emissivity\nsurfaces, or visible electrochromic devices. These devices rely on controlling\nthe charge density on graphene with electrostatic gating or intercalation. In\nthis paper, we studied the effect of ionic liquid intercalation on the\nlong-term performance of optoelectronic devices operating within a broad\ninfrared wavelength range. Our spectroscopic and thermal characterization\nresults reveal the key limiting factors for the intercalation process and the\nperformance of the infrared devices, such as the electrolyte ion-size asymmetry\nand charge distribution scheme and the effects of oxygen. Our results provide\ninsight for the limiting mechanism for graphene applications in infrared\nthermal management and tunable heat signature control.", "category": "physics_app-ph" }, { "text": "Optically-trapped microspheres are high-bandwidth acoustic transducers: We report on the use of an optically-trapped microsphere as an acoustic\ntransducer. A model for the hydrodynamic coupling between the microsphere and\nthe surrounding acoustic fluid flow is combined with thermo-mechanical\ncalibration of the microsphere's position detection to enable quantitative\nacoustic measurements. We describe our technique in detail, including the\nself-noise, sensitivity, and minimum detectable signals, using a model\nappropriate for both liquid and gas environments. We then test our approach in\nan air-based experiment and compare our measurements with two state-of-the-art\ncommercially-available acoustic sensors. Piezoelectrically-driven bursts of\npure tones and laser ablation provide two classes of test sounds. We find\naccurate measurements with a bandwidth of 1 MHz are possible using our\ntechnique, improving by several orders of magnitude the bandwidth of previous\nflow measurements based on optically-trapped microspheres.", "category": "physics_app-ph" }, { "text": "Graphene Plasmonic Fractal Metamaterials for Broadband Photodetectors: Metamaterials have recently established a new paradigm for enhanced light\nabsorption in state-of-the-art photodetectors. Here, we demonstrate broadband,\nhighly efficient, polarization-insensitive, and gate-tunable photodetection at\nroom temperature in a novel metadevice based on gold/graphene Sierpinski carpet\nplasmonic fractals. We observed an unprecedented internal quantum efficiency up\nto 100% from the near-infrared to the visible range with an upper bound of\noptical detectivity of $10^{11}$ Jones and a gain up to $10^{6}$, which is a\nfingerprint of multiple hot carriers photogenerated in graphene. Also, we show\na 100-fold enhanced photodetection due to highly focused (up to a record factor\nof $|E/E_{0}|\\approx20$ for graphene) electromagnetic fields induced by\nelectrically tunable multimodal plasmons, spatially localized in self-similar\nfashion on the metasurface. Our findings give direct insight into the physical\nprocesses governing graphene plasmonic fractal metamaterials. The proposed\nstructure represents a promising route for the realization of a broadband,\ncompact, and active platform for future optoelectronic devices including\nmultiband bio/chemical and light sensors.", "category": "physics_app-ph" }, { "text": "Cryogenic cleaning of tin-drop contamination on surfaces relevant for\n extreme ultraviolet light collection: Improvement of tool reliability and uptime is a current focus in development\nof extreme ultraviolet lithography. The lifetime of collection mirrors for\nextreme ultraviolet light in tin-based plasma light sources is limited\nconsiderably by contamination with thick tin deposits that cannot be removed\nsufficiently fast by plasma etching. For tin droplet splats sticking to large\nsubstrates, we have developed and compared several efficient cleaning\ntechniques based on cryogenic cooling. A silicon carbide substrate and\ndifferent silicon wafer samples with up to 6 inch diameter with the surface\nuncoated, multilayer-coated, unstructured and grating-structured were tested.\nAfter tin dripping onto heated samples, embrittlement of droplet contamination\nis induced in-situ by stresses during phase transformation, following the\ninitiation of tin pest with seed crystals of gray tin. Conversion of initially\nadhesive deposits to loose gray tin has been reached in less than 24 hours on\nall tested surfaces by continuous cooling with cold nitrogen vapor to\ntemperatures in the range of -30 to -50 {\\deg}C. Alternatively,\nstress-initiated tin-removal by delamination of beta-Sn droplet splats has been\nattained via contraction strain induced by strong cooling to temperatures of\naround -120 {\\deg}C. Profilometry has been used to analyze the bottom side of\ntin droplet splats removed from a grating-structured wafer. The in-situ tin\ncleaning techniques give results comparable to fast ex-situ cleaning that has\nbeen achieved either by sample immersion in liquid nitrogen or by splat removal\nafter CO2 snowflake aerosol impact using a hand-held jet-nozzle. The\nimplementation of the in-situ phase-conversion concept for the cleaning of\ncollector mirrors in commercial light sources for lithography is discussed.", "category": "physics_app-ph" }, { "text": "Integrated microwave acousto-optic frequency shifter on thin-film\n lithium niobate: Electrically driven acousto-optic devices that provide beam deflection and\noptical frequency shifting have broad applications from pulse synthesis to\nheterodyne detection. Commercially available acousto-optic modulators are based\non bulk materials and consume Watts of radio frequency power. Here, we\ndemonstrate an integrated 3-GHz acousto-optic frequency shifter on thin-film\nlithium niobate, featuring a carrier suppression over 30 dB. Further, we\ndemonstrate a gigahertz-spaced optical frequency comb featuring more than 200\nlines over a 0.6-THz optical bandwidth by recirculating the light in an active\nfrequency shifting loop. Our integrated acousto-optic platform leads to the\ndevelopment of on-chip optical routing, isolation, and microwave signal\nprocessing.", "category": "physics_app-ph" }, { "text": "Optical power meter using radiation pressure measurement: This paper describes a radiation pressure meter based on a diamagnetic\nspring. We take advantage of the diamagnetic property of pyrolytic carbon to\nmake an elementary levitated system. It is equivalent to a torsional\nspring-mass-damper system consisting of a small pyrolytic carbon disc levitated\nabove a permanent magnet array. There are several possible measurement modes.\nIn this paper, only the angular response to an optical power single-step is\ndescribed. An optical detection composed of a laser diode, a mirror and a\nposition sensitive detector (PSD) allow measurement of the angular deflection\nproportional to the voltage delivered by the PSD. Once the parameters of the\nlevitated system depending on its geometrical and physical characteristics have\nbeen determined regardless of any optical power, by applying a simple physical\nlaw, one can deduce the value of the optical power to be measured from the\nmeasurement of the first maximum of the output voltage amplitude.", "category": "physics_app-ph" }, { "text": "Laser radio transmitter: Since the days of Hertz, radio transmitters have evolved from rudimentary\ncircuits emitting around 50 MHz to modern ubiquitous Wi-Fi devices operating at\ngigahertz radio bands. As wireless data traffic continues to increase there is\na need for new communication technologies capable of high-frequency operation\nfor high-speed data transfer. Here we give a proof of concept of a new compact\nradio frequency transmitter based on a semiconductor laser frequency comb. In\nthis laser, the beating among the coherent modes oscillating inside the cavity\ngenerates a radio frequency current, which couples to the electrodes of the\ndevice. We show that redesigning the top contact of the laser allows one to\nexploit the internal oscillatory current to drive an integrated dipole antenna,\nwhich radiates into free space. In addition, direct modulation of the laser\ncurrent permits encoding a signal in the radiated radio frequency carrier.\nWorking in the opposite direction, the antenna can receive an external radio\nfrequency signal, couple it to the active region and injection lock the laser.\nThese results pave the way to new applications and functionality in optical\nfrequency combs, such as wireless radio communication and wireless\nsynchronization to a reference source.", "category": "physics_app-ph" }, { "text": "Multi-year Study of Environmental Stability of Ti$_3$C$_2$T$_x$ MXene\n Films: MXenes are a family of two-dimensional (2D) carbides and nitrides that\ndisplay extraordinary electrical, optical, chemical, and electrochemical\nproperties. There is a perception that MXenes are unstable and degrade quickly,\nlimiting potential applications and requiring specific storage conditions to\nlast for a long time. This was true for delaminated MXenes flakes in dilute\ndispersions prepared from defective precursors when MXene research was in its\ninfancy. Since then, significant developments in MXene synthesis, processing,\nand understanding of its chemistry led to dramatic increases in environmental\nstability. Herein, we analyze Ti$_3$C$_2$T$_x$ free-standing films aged from 4\nto 9 years through structural and morphological characterization along with\nelectrical conductivity measurements to reveal the effect, or lack thereof, of\nprolonged storage under ambient conditions. Further, we show that the decrease\nin electronic conductivity over time is largely caused by the uptake of water\nby the hydrophilic surface chemistry of MXenes, which can be easily removed and\nits effect reversed by vacuum annealing.", "category": "physics_app-ph" }, { "text": "Engineered diffraction gratings for acoustic cloaking: We show that engineered diffraction gratings can considerably simplify the\ndesign and performance of acoustic devices. Acoustic reflecting gratings based\non rectangular cavities drilled on an acoustically rigid surface are designed\nin such a way that all the incident energy is channeled towards the diffracted\nmode traveling in the oposite direction of the incident field (retroreflection\neffect), and this effect is used to cloak an object placed over a rigid\nsurface. Axisymmetric gratings consisting in rigid surfaces with just one\ngroove per unit cell are used to design acoustic thin acoustic carpet cloaks.\nFinally, full wave numerical simulations are performed and a conical carpet\ncloak is experimentally tested, showing an excellent scattering cancellation\neffect.", "category": "physics_app-ph" }, { "text": "Detailed Modelling of Ultraviolet Radiation (UV) from the Interaction of\n Multiple Lamps in Reactors, using Radiative Transfer Techniques: Trojan Technologies uses mercury-based ultraviolet (UV) lamps in reactors to\npurify water. When there are multiple closely spaced lamps in a reactor,\nsignificant UV emitted by the various lamps can reach, and 'interact' with\nneighbouring lamps. Although many of the optical phenomena occurring in a UV\nreactor are well understood and accounted for in current models, the fate of UV\nphotons from one lamp reaching the plasma of a neighbouring lamp after\ntravelling through the intervening air, quartz, and water has not been\ninvestigated in detail. These photons can be transmitted through the plasma,\nabsorbed and re-emitted, or lost. The goal of this project was to develop a\nmore accurate model, which accounts for these plasma interactions, to better\npredict the UV distribution throughout a reactor. We developed a Monte Carlo\ntheoretical model of the photon-plasma interactions; predictions of this model\nagree well with work in the literature. We further validated our model by\nperforming several optical experiments with UV lamps.", "category": "physics_app-ph" }, { "text": "Photonic Microwave and RF Channelizers using Kerr Micro-combs: We review recent work on broadband RF channelizers based on integrated\noptical frequency Kerr micro-combs combined with passive micro-ring resonator\nfilters, with microcombs having channel spacings of 200GHz and 49GHz. This\napproach to realizing RF channelizers offers reduced complexity, size, and\npotential cost for a wide range of applications to microwave signal detection.", "category": "physics_app-ph" }, { "text": "Spin Hall Magnetoresistance in Metallic Bilayers with In-plane\n Magnetized Ferromagnets: We revisit the theory and experiment on spin Hall magnetoresistance (SMR) in\nbilayers consisting of a heavy metal (H) coupled to in-plane magnetized\nferromagnetic metal (F), and determine contributions to the magnetoresistance\ndue to SMR and anisotropic magnetoresistance (AMR) in four different bilayer\nsystems: W/$\\text{Co}_{20}\\text{Fe}_{60}\\text{B}_{20}$, W/Co,\n$\\text{Co}_{20}\\text{Fe}_{60}\\text{B}_{20}$/Pt, and Co/Pt. To do this, the AMR\nis explicitly included in the diffusion transport equations in the ferromagnet.\nThe results allow precise determination of different contributions to the\nmagnetoresistance, which can play an important role in optimizing prospective\nmagnetic stray field sensors. They also may be useful in the determination of\nspin transport properties of metallic magnetic heterostructures in other\nexperiments based on magnetoresistance measurements.", "category": "physics_app-ph" }, { "text": "PDMS microfluidic film for in vitro engineering of mesoscale neuronal\n networks: Polydimethylsiloxane (PDMS) microfluidic devices have become a standard tool\nfor engineering cells and multicellular networks in vitro. However, the\nreservoirs, or through-holes where cells access the devices, are usually\nfabricated manually using a biopsy punch, making it difficult to create a\nlarge-scale array of small (<1 mm) reservoirs. Here, we present a fabrication\nprocess for a thin-film microfluidic device, or a microfluidic film ({\\mu}FF),\ncontaining an array of through-holes. Holes as small as 100 {\\mu}m by 100\n{\\mu}m spanning 10 mm by 10 mm are characterized. The geometry of the\nthrough-holes was precisely defined by the photoresist mould. A challenge in\nusing the {\\mu}FF for cell culture was air-bubble entrapments in the\nthrough-holes, which became more prominent with smaller holes. We show that\nthis issue can be overcome using ethanol-mediated wetting of the PDMS surface,\nand demonstrate functional recording of cultured neuronal networks grown in\n{\\mu}FFs. This technology opens new application of microfluidic devices to\nmesoscale systems comprised of several tens to hundreds of cells.", "category": "physics_app-ph" }, { "text": "Room temperature single-photon emitters in silicon nitride: Single-photon emitters are essential for enabling several emerging\napplications in quantum information technology, quantum sensing and quantum\ncommunication. Scalable photonic platforms capable of hosting intrinsic or\ndirectly embedded sources of single-photon emission are of particular interest\nfor the realization of integrated quantum photonic circuits. Here, we report on\nthe first-time observation of room-temperature single-photon emitters in\nsilicon nitride (SiN) films grown on silicon dioxide substrates. As SiN has\nrecently emerged as one of the most promising materials for integrated quantum\nphotonics, the proposed platform is suitable for scalable fabrication of\nquantum on-chip devices. Photophysical analysis reveals bright (>$10^5$\ncounts/s), stable, linearly polarized, and pure quantum emitters in SiN films\nwith the value of the second-order autocorrelation function at zero time delay\n$g^{(2)}(0)$ below 0.2 at room temperatures. The emission is suggested to\noriginate from a specific defect center in silicon nitride due to the narrow\nwavelength distribution of the observed luminescence peak. Single-photon\nemitters in silicon nitride have the potential to enable direct, scalable and\nlow-loss integration of quantum light sources with the well-established\nphotonic on-chip platform.", "category": "physics_app-ph" }, { "text": "Optically gated terahertz-field-driven switching of antiferromagnetic\n CuMnAs: We show scalable and complete suppression of the recently reported\nterahertz-pulse-induced switching between different resistance states of\nantiferromagnetic CuMnAs thin films by ultrafast gating. The gating\nfunctionality is achieved by an optically generated transiently conductive\nparallel channel in the semiconducting substrate underneath the metallic layer.\nThe photocarrier lifetime determines the time scale of the suppression. As we\ndo not observe a direct impact of the optical pulse on the state of CuMnAs, all\nobserved effects are primarily mediated by the substrate. The sample region of\nsuppressed resistance switching is given by the optical spot size, thereby\nmaking our scheme potentially applicable for transient low-power masking of\nstructured areas with feature sizes of ~100 nm and even smaller.", "category": "physics_app-ph" }, { "text": "Flow-electrode capacitive deionization enables continuous and\n energy-efficient brine concentration: Many industrial and agricultural applications require the treatment of water\nstreams containing high concentrations of ionic species for closing material\ncycles. High concentration factors are often desired, but hard to achieve with\nestablished thermal or membrane-based water treatment technologies at low\nenergy consumptions. Capacitive deionization processes are normally assumed as\nrelevant for the treatment of low salinity solutions only. Flow-electrode\ncapacitive deionization (FCDI), on the other hand, is an electrically driven\nwater desalination technology, which allows the continuous desalination and\nconcentration of saline water streams even at elevated salinities. Ions are\nadsorbed electrostatically in pumpable carbon flow electrodes, which enable a\nrange of new process designs.\n In this article, it is shown that continuously operated FCDI systems can be\napplied for the treatment of salt brines. Concentrations of up to 291.5~g/L\nNaCl were reached in the concentrate product stream. Based on this, FCDI is a\npromising technology for brine treatment and salt recovery. Additionally, a\nreduction of the energy demand by more than 70% is demonstrated by introducing\nmultiple cell pairs into a continuous FCDI system. While the economic\nfeasibility is not investigated here, the results show that FCDI systems may\ncompete with established technologies regarding their energy demand.", "category": "physics_app-ph" }, { "text": "A Disposable Soft Magnetic Ribbon Based Sensor for Corrosion Monitoring: We present a new approach for real-time monitoring of chemical corrosion\nbased on the radio-frequency (RF) impedance technology and soft ferromagnetic\nribbons. The impedance (Z) of a commercial magnetic ribbon was measured in real\ntime for 5 mul of drop-casted HNO3 of various concentrations. Variations in the\nconcentration of the drop-casted acid were assessed by considering the\ndifference in Z with and without the acid treatment. We found a large and\nlinear increase in deltaZ and a large linear decrease in measurement time with\nthe acid concentration, which are ideal for developing disposable chemical\nsensors for strength estimation of corrosive chemicals and for monitoring of a\ntime-dependent chemical corrosion process. Since the ribbon used is\ncommercially available at low cost and the measurement system is quick and low\npower consuming, the proposed sensor can be used as an easy, quick, and\nlow-cost chemical probe in industries and environmental hazard management\npurposes.", "category": "physics_app-ph" }, { "text": "Optimize electron beam energy toward in-situ imaging of large thick\n bio-samples with nanometer resolution: To optimize electron energy toward in-situ imaging large bio-samples up to\n10-um thickness with nanoscale resolution, we implemented an analytical model\nbased on elastic and inelastic characteristic angles [1]. This model can be\nused to predict the transverse beam size broadening as a function of electron\nenergy while the probe beam traverses through the sample. As result, the\noptimal choice of the electron beam energy can be realized. While the sample\nthickness is less than 10 um, there exists an optimal electron beam energy\nbelow 10 MeV regarding a specific sample thickness. However, for samples\nthicker than 10 um, the optimal beam energy is 10 MeV, and the ultimate\nresolution could become worse with the increase of the sample thickness.", "category": "physics_app-ph" }, { "text": "Tuning of the Quantum-Confined Stark Effect in Wurtzite $[000\\bar{1}]$\n Group-III-Nitride Nanostructures by the Internal-Field-Guarded-Active-Region\n Design: Recently, we suggested an unconventional approach [the so-called\nInternal-Field-Guarded-Active-Region Design (IFGARD)] for the elimination of\nthe crystal polarization field induced quantum confined Stark effect (QCSE) in\npolar semiconductor heterostructures. And in this work, we demonstrate by means\nof micro-photoluminescence techniques the successful tuning as well as the\nelimination of the QCSE in strongly polar $[000\\bar{1}]$ wurtzite GaN/AlN\nnanodiscs while reducing the exciton life times by more than two orders of\nmagnitude. The IFGARD based elimination of the QCSE is independent of any\nspecific crystal growth procedures. Furthermore, the cone-shaped geometry of\nthe utilized nanowires (which embeds the investigated IFGARD nanodiscs)\nfacilitates the experimental differentiation between quantum confinement- and\nQCSE-induced emission energy shifts. Due to the IFGARD, both effects become\nindependently adaptable.", "category": "physics_app-ph" }, { "text": "The modular SAXS data correction sequence for solids and dispersions: Data correction is probably the least favourite activity amongst users\nexperimenting with small-angle X-ray scattering (SAXS): if it is not done\nsufficiently well, this may become evident during the data analysis stage,\nnecessitating the repetition of the data corrections from scratch. A\nrecommended, comprehensive sequence of elementary data correction steps is\npresented here to alleviate the difficulties associated with data correction.\nWhen applied in the proposed order, the resulting data will provide a high\ndegree of accuracy for both solid samples and dispersions. The solution here\ncan be applied without modification to any pinhole-collimated instruments with\nphoton-counting, direct detection area detectors.", "category": "physics_app-ph" }, { "text": "Current-induced four-state magnetization switching by spin-orbit torques\n in perpendicular ferromagnetic trilayers: We demonstrated current-induced four-state magnetization switching in a\ntrilayer system using spin-orbit torques. The memory device contains two Co\nlayers with different perpendicular magnetic anisotropy, separated by a space\nlayer of Pt. Making use of the opposite spin current at the top and bottom\nsurface of the middle Pt layer, magnetization of both Co layers can be switched\noppositely by the spin-orbit torques with different critical switching\ncurrents. By changing the current pulse forms through the device, the four\nmagnetic states memory was demonstrated. Our device provides a new idea for the\ndesign of low power and high density spin-orbit torque devices.", "category": "physics_app-ph" }, { "text": "THz-Frequency Spin-Hall Auto-Oscillator Based on a Canted\n Antiferromagnet: We propose a design of a THz-frequency signal generator based on a layered\nstructure consisting of a current-driven platinum (Pt) layer and a layer of an\nantiferromagnet (AFM) with easy-plane anisotropy, where the magnetization\nvectors of the AFM sublattices are canted inside the easy plane by the\nDzyaloshinskii-Moriya interaction (DMI). The DC electric current flowing in the\nPt layer creates, due to the spin-Hall effect, a perpendicular spin current\nthat, being injected in the AFM layer, tilts the DMI-canted AFM sublattices out\nof the easy plane, thus exposing them to the action of a strong internal\nexchange magnetic field of the AFM. The sublattice magnetizations, along with\nthe small net magnetization vector $\\textbf{m}_{\\rm DMI}$ of the canted AFM,\nstart to rotate about the hard anisotropy axis of the AFM with the THz\nfrequency proportional to the injected spin current and the AFM exchange field.\nThe rotation of the small net magnetization $\\textbf{m}_{\\rm DMI}$ results in\nthe THz-frequency dipolar radiation that can be directly received by an\nadjacent (e.g. dielectric) resonator. We demonstrate theoretically that the\nradiation frequencies in the range $f=0.05-2$~THz are possible at the\nexperimentally reachable magnitudes of the driving current density, and\nevaluate the power of the signal radiated into different types of resonators,\nshowing that this power increases with the increase of frequency $f$, and that\nit could exceed 1~$\\mu$W at $f \\sim 0.5$~THz for a typical dielectric resonator\nof the electric permittivity $\\varepsilon \\sim 10$ and quality factor $Q \\sim\n750$.", "category": "physics_app-ph" }, { "text": "Optical properties of mist CVD grown $\u03b1$-Ga$_2$O$_3$: We report on the study of optical properties of mist CVD grown alpha Gallium\noxide with the observation of excitonic absorption in spectral responsivity\nmeasurements. 163 nm of Gallium oxide was grown on sapphire using Gallium\nacetylacetonate as the starting solution at a substrate temperature of 450 deg\nC. The film was found to be crystalline and of alpha phase with an on axis full\nwidth at half maximum of 92 arcsec as confirmed from X ray diffraction scans.\nThe Taucs plot extracted from absorption spectroscopy exhibited two transitions\nin the UV regime at 5.3 eV and 5.6 eV, corresponding to excitonic absorption\nand direct band to band transition respectively. The binding energy of exciton\nwas extracted to be 114 meV from spectral responsivity measurements. Further,\nmetal semiconductor metal photodetectors with lateral inter digitated geometry\nwere fabricated on the film. A sharp band edge was observed at 230 nm in the\nspectral response with peak responsivity of around 1 Amperes per Watt at a bias\nof 20 V. The UV to visible rejection ratio was found to be around 100 while the\ndark current was measured to be around 0.1 nA.", "category": "physics_app-ph" }, { "text": "Field emission from AlGaN nanowires with low turn-on field: We fabricate AlGaN nanowires by molecular beam epitaxy and we investigate\ntheir field emission properties by means of an experimental setup using\nnano-manipulated tungsten tips as electrodes, inside a scanning electron\nmicroscope. The tip-shaped anode gives access to local properties and allows\ncollecting electrons emitted from areas as small as 1$\\mu m^2$. The field\nemission characteristics are analyzed in the framework of Fowler-Nordheim\ntheory and we find a field enhancement factor as high as $\\beta$ = 556 and a\nminimum turn-on field $E_{turn-on}$ = 17 V/$\\mu$m for a cathode-anode\nseparation distance d = 500 nm. We show that for increasing separation\ndistance, $E_{turn-on}$ increases up to about 35 V/$\\mu$m and $\\beta$ decreases\nto 100 at d = 1600 nm. We also demonstrate the time stability of the field\nemission current from AlGaN nanowires for several minutes. Finally, we explain\nthe observation of modified slope of the Fowler-Nordheim plots at low fields in\nterms of non-homogeneous field enhancement factors due to the presence of\nprotruding emitters.", "category": "physics_app-ph" }, { "text": "An isogeometric finite element formulation for geometrically exact\n Timoshenko beams with extensible directors: An isogeometric finite element formulation for geometrically and materially\nnonlinear Timoshenko beams is presented, which incorporates in-plane\ndeformation of the cross-section described by two extensible director vectors.\nSince those directors belong to the space ${\\Bbb R}^3$, a configuration can be\nadditively updated. The developed formulation allows direct application of\nnonlinear three-dimensional constitutive equations without zero stress\nconditions. Especially, the significance of considering correct surface loads\nrather than applying an equivalent load directly on the central axis is\ninvestigated. Incompatible linear in-plane strain components for the\ncross-section have been added to alleviate Poisson locking by using an enhanced\nassumed strain (EAS) method. In various numerical examples exhibiting large\ndeformations, the accuracy and efficiency of the presented beam formulation is\nassessed in comparison to brick elements. We particularly use hyperelastic\nmaterials of the St. Venant-Kirchhoff and compressible Neo-Hookean types.", "category": "physics_app-ph" }, { "text": "Latent Pigments Strategy for Robust Active Layers in Solution-Processed,\n Complementary Organic Field-Effect Transistors: Solution-processed organic semiconductors enable the fabrication of\nlarge-area and flexible electronics by means of cost-effective, solution-based\nmass manufacturing techniques. However, for many applications an insoluble\nactive layer can offer technological advantages in terms of robustness to\nprocessing solvents. This is particularly relevant in field-effect transistors\n(FET), where processing of dielectrics or barriers from solution on top of the\nsemiconductor layer typically imposes the use of orthogonal solvents in order\nnot to interfere with the nanometer thick accumulation channel. To this end,\nthe use of latent pigments, highly soluble molecules which can produce\ninsoluble films after a post-deposition thermal cleavage of solubilizing\ngroups, is a very promising strategy. In this contribution, we demonstrate the\nuse of tert-Butyloxycarbonyl (t-Boc) functionalized diketopyrrolopyrrole and\nperylene-diimide small molecules for good hole and electron transporting films.\nt-Boc thermal cleavage produces a densification of the films, along with a\nstrong structural rearrangement of the deprotected molecules, strongly\nimproving charge mobility in both p- and n-type FET. We also highlight the\nrobustness of these highly insoluble semiconducting layers to typical and\naggressive processing solvents. These results can greatly enhance the degree of\nfreedom in the manufacturing of multi-layered organic electronic devices,\noffering enhanced stability to harsh processing steps.", "category": "physics_app-ph" }, { "text": "Measurement of effective thermal conductivity of LaNi$_5$ powder packed\n bed: Effective thermal conductivity of LaNi$_5$ powder packed bed was analyzed\nwith customized guarded hot-plate (GHP) apparatus. Here, GHP was designed for\nprecise measurement of effective thermal conductivity of metal-hydride powders\neven with small sample amounts (2.12$\\times$10$^4$ mm$^3$). Dimensions of\nsample container and apparatus were determined through two-dimensional (2-D)\nsteady-state heat conduction analysis. Calibration experiment and uncertainty\nanalysis were conducted to validate the accuracy of the GHP. Based on the\nmeasurements of the residual thermal conductivity of the LaNi$_5$ packed bed,\neffect of particle size on contact factor of LaNi$_5$ packed bed was estimated.\nBy applying the Yagi and Kunii (YK) model to the effective thermal conductivity\nof LaNi$_5$ packed bed, effect of contact factor and gas thermal conductivity\non characteristic length of gas film were newly analyzed. Factors of YK model\nwere modified in present work and validated through comparison with\nexperimental data from previous literature.", "category": "physics_app-ph" }, { "text": "Thermophysical properties of n-hexadecane: Combined Molecular Dynamics\n and experimental investigations: Investigating properties of phase change materials (PCMs) is an important\nissue due to their extensive use in heat storage systems and thermal regulation\ndevices. Improvement of the efficiency of such systems should be based on a\nbetter knowledge of the microscopic mechanisms governing the thermal and\nrheological characteristics of PCMs. This may be accomplished by the use of\nmolecular simulations of the aforementioned quantities and their linkage with\nmacroscale investigations. In this work, we studied thermophysical properties\nof $n$-hexadecane for different temperatures regimes using molecular dynamics\n(MD) and carry out several experimental measurements. Particularly, we focused\non the evaluation of various rheological and thermal properties such as thermal\nconductivity, $\\kappa$, viscosity, $\\eta$, diffusion coefficient, $D$, and heat\ncapacities $C_p$ and $C_v$. Special attention was paid to the comparison of the\nresults of simulations with experimental ones.", "category": "physics_app-ph" }, { "text": "A small-signal GFET equivalent circuit considering an explicit\n contribution of contact resistances: A small-signal equivalent circuit for graphene field-effect transistors is\nproposed considering the explicit contribution of effects at the metal-graphene\ninterfaces by means of contact resistances. A methodology to separate the\ncontact resistances from intrinsic parameters, obtained by a de-embedding\nprocess, and extrinsic parameters of the circuit is considered. The\nexperimental high-frequency performance of three devices from two different\nGFET technologies is properly described by the proposed small-signal circuit.\nSome model parameters scale with the device footprint. The correct detachment\nof contact resistances from the internal transistor enables to assess their\nimpact on the intrinsic cutoff frequency of the studied devices.", "category": "physics_app-ph" }, { "text": "Machine Learning for Metasurfaces Design and Their Applications: Metasurfaces (MTSs) are increasingly emerging as enabling technologies to\nmeet the demands for multi-functional, small form-factor, efficient,\nreconfigurable, tunable, and low-cost radio-frequency (RF) components because\nof their ability to manipulate waves in a sub-wavelength thickness through\nmodified boundary conditions. They enable the design of reconfigurable\nintelligent surfaces (RISs) for adaptable wireless channels and smart radio\nenvironments, wherein the inherently stochastic nature of the wireless\nenvironment is transformed into a programmable propagation channel. In\nparticular, space-limited RF applications, such as communications and radar,\nthat have strict radiation requirements are currently being investigated for\npotential RIS deployment. The RIS comprises sub-wavelength units or meta-atoms,\nwhich are independently controlled and whose geometry and material determine\nthe spectral response of the RIS. Conventionally, designing RIS to yield the\ndesired EM response requires trial and error by iteratively investigating a\nlarge possibility of various geometries and materials through thousands of\nfull-wave EM simulations. In this context, machine/deep learning (ML/DL)\ntechniques are proving critical in reducing the computational cost and time of\nRIS inverse design. Instead of explicitly solving Maxwell's equations, DL\nmodels learn physics-based relationships through supervised training data. The\nML/DL techniques also aid in RIS deployment for numerous wireless applications,\nwhich requires dealing with multiple channel links between the base station\n(BS) and the users. As a result, the BS and RIS beamformers require a joint\ndesign, wherein the RIS elements must be rapidly reconfigured. This chapter\nprovides a synopsis of DL techniques for both inverse RIS design and\nRIS-assisted wireless systems.", "category": "physics_app-ph" }, { "text": "Cryogenic characterization of 28nm FD-SOI ring oscillators with energy\n efficiency optimization: Extensive electrical characterization of ring oscillators (ROs) made in\nhigh-$\\kappa$ metal gate 28nm Fully-Depleted Silicon-on- Insulator (FD-SOI)\ntechnology is presented for a set of temperatures between 296 and 4.3K. First,\ndelay per stage ($\\tau_P$), static current ($I_{STAT}$), and dynamic current\n($I_{DYN}$) are analyzed for the case of the increase of threshold voltage\n($V_{TH}$) observed at low temperature. Then, the same analysis is performed by\ncompensating $V_{TH}$ to a constant, temperature independent value through\nforward body-biasing (FBB). Energy efficiency optimization is proposed for\ndifferent supply voltages ($V_{DD}$) in order to find an optimal operating\npoint combining both high RO frequencies and low power dissipation. We show\nthat the Energy-Delay product ($EDP$) can be significantly reduced at low\ntemperature by applying a forward body bias voltage ($V_{FBB}$). We demonstrate\nthat outstanding performance of RO in terms of speed ($\\tau_P$=37ps) and static\npower (7nA/stage) can be achieved at 4.3K with $V_{DD}$ reduced down to 0.325V.", "category": "physics_app-ph" }, { "text": "Preparation and Characterization of NixMn0.25-xMg0.75Fe2O4 Nano-ferrite\n as NO2 Gas Sensing Material: NixMn0.25-xMg0.75Fe2O4 nano-ferrites (where x = 0.00, 0.05, 0.10, 0.15 and\n0.20) were produced via sol-gel auto-combustion technique. Investigations were\ndone into how the incorporation of Ni ions affects the Mn0.25Mg0.75Fe2O4\nferrite's structure, morphological, magnetic, and NO2 gas sensing features. All\nthe samples are single-phase, based on the structural study utilizing the X-ray\ndiffraction (XRD) pattern. In terms of the structure of the cubic spinel,\naccording to the XRD study, the crystallite sizes range from 24.30 to 28.32 nm,\nindicating nano-crystallinity. The synthesis of spherical nanoparticles with a\nsmall modification in particle size distribution was verified via FE-SEM\nimages. The study found that the size of particles is tiny enough to act\nsuperparamagnetically. The area of hysteresis loop is almost non-existing, thus\nreflecting typical soft magnetic materials according to magnetic measurements\nby VSM carried out at room temperature. Furthermore, the conductance responses\nof the NixMn0.25-xMg0.75Fe2O4 nano-ferrite were measured by exposing the\nferrite to oxidizing (NO2) gas at different operating temperatures. The results\nshow that the sensor boasts shorter response and recovery times, as well as a\nhigher sensitivity 707.22% of the sample (x=0.20) for nano-ferrite.", "category": "physics_app-ph" }, { "text": "Site adaptation with machine learning for a Northern Europe gridded\n solar radiation product: Gridded global horizontal irradiance (GHI) databases are fundamental for\nanalysing solar energy applications' technical and economic aspects,\nparticularly photovoltaic applications. Today, there exist numerous gridded GHI\ndatabases whose quality has been thoroughly validated against ground-based\nirradiance measurements. Nonetheless, databases that generate data at latitudes\nabove 65$^{\\circ}$ are few, and those available gridded irradiance products,\nwhich are either reanalysis or based on polar orbiters, such as ERA5,\nCOSMO-REA6, or CM SAF CLARA-A2, generally have lower quality or a coarser time\nresolution than those gridded irradiance products based on geostationary\nsatellites. Among the high-latitude gridded GHI databases, the STR\\r{A}NG model\ndeveloped by the Swedish Meteorological and Hydrological Institute (SMHI) is\nlikely the most accurate one, providing data across Sweden. To further enhance\nthe product quality, the calibration technique called \"site adaptation\" is\nherein used to improve the STR\\r{A}NG dataset, which seeks to adjust a long\nperiod of low-quality gridded irradiance estimates based on a short period of\nhigh-quality irradiance measurements. This study, differing from the\nconventional statistical approaches, adopts machine learning for site\nadaptation. Nine machine-learning algorithms have been analysed and compared\nwith conventional statistical ones to identify Sweden's most favourable\ntechnique for site adaptation. Three weather stations of SMHI are used for\ntraining and validation. The results show that, due to the spatio-temporal\nheterogeneity in model performance, no universal model can be identified, which\nsuggests that site adaptation is a location-dependent procedure.", "category": "physics_app-ph" }, { "text": "Prospective phosphors for white LEDs based on double molybdates of the\n composition Ln2Zr3 (MoO4) 9 (Ln: Eu, Tb): The results of the investigation of the spectral characteristics of new\nluminescent substances based on rare-earth ions Eu3 + and Tb3 + in matrices of\ndouble molybdates are presented in the article. The luminescence and excitation\nspectra are considered, the decay times of the main transitions are determined,\nand the color coordinates are determined. The results show the possible\nsuitability of using these compounds as white phosphor phosphor components.", "category": "physics_app-ph" }, { "text": "Controllable gas sensitivity of Mg/CuO nanocomposite films measured in\n methanol vapor: The gas sensitivity of Mg/CuO nanocomposite films, characterized by varying\nmass ratios of Mg:CuO, was assessed under exposure to 1000 ppm of methanol\nvapor. Films were fabricated by the doctor blade method on conductive and\nnonconductive glass substrates. Structural and optical analyses were conducted\nusing XRD and UV-Visible spectrums. The XRD patterns facilitated the estimation\nof crystallite size, dislocation density and strain. The optical band gap of\nthe samples was determined from UV-Visible spectrums. Despite variations in\ncrystallite size, dislocation density and strain in response to changing Mg\nconcentrations in nanocomposites, no discernible shift in the band gap was\nobserved. The mass percentage of Mg in nanocomposite was incrementally altered\nfrom 10% to 20% in steps of 5%. Due to the adsorption of methanol vapor, the\nresistivity of the sample decreased significantly. Gas sensitivity exhibited\nvariance ranging from 3.79 for pure CuO to 1.23 for nanocomposite with 20%Mg.\nThe sample with 10%Mg quickly responded to methanol vapor compared to pure CuO\nand other nanocomposites.\n Keywords: CuO, nanocomposites, gas sensors, XRD, UV-Visible spectrums", "category": "physics_app-ph" }, { "text": "Parasitic Element Time-Modulation for Enhanced Effective Inter-Antenna\n Coupling: Utilization for Improved Gain-Bandwidth: Time variation has been recently introduced as an additional degree of\nfreedom for wave engineering, that enables going beyond the performances that\nare expected by linear time-invariant (LTI) systems. In this paper, we\nintroduce the concept of indirect time-modulation of antennas using an add-on\ntime-varying scatterer (parasitic element) that gives rise to an inherent\nfeedback mechanism via the airborne wave system. As opposed to a direct\nmodulated system where a time-dependent element is in contact with the other\nelements, in an indirect time modulation scheme \\emph{no} direct physical\ncontact between the original LTI network and the time-varying add-on scatterer\nis needed, thus leading to additional flexibility in the design. Using indirect\ntime modulation we demonstrate enhanced effective coupling between remote\nantenna elements, and the possibility to outperform the gain-bandwidth achieved\nfor the same antenna structure but without time-modulation.", "category": "physics_app-ph" }, { "text": "Voltage-Induced Inertial Domain Wall Motion in an Antiferromagnetic\n Nanowire: Racetrack memory based on magnetic domain walls (DWs) motion exhibits\nadvantages of small volume and high reading speed. When compared to\ncurrent-induced DW motion, voltage-induced DW motion exhibits lower\ndissipation. On the other hand, the DW in an antiferromagnet (AFM) moves at a\nhigh velocity with weak stray field. In this work, the AFM DW motion induced by\na gradient of magnetic anisotropy energy under a voltage pulse has been\ninvestigated in theory. The dynamics equation for the DW motion was derived.\nThe solution indicates that the DW velocity is higher than 100 m/s, and because\nof inertia, the DW is able to keep moving at a speed of around 100 m/s for\nseveral nano seconds after turning off the voltage in a period of pulse. The\nmechanism for this DW inertia is explained based on the Lagrangian route. On\nthe other hand, a spin wave is emitted while the DW is moving, yet the DW is\nstill able to move at an ever increasing velocity with enlarging DW width. This\nindicates energy loss from emission of spin wave is less than the energy gain\nfrom the effective field of the gradient of anisotropy energy.", "category": "physics_app-ph" }, { "text": "Photo-electrical properties of 2D Quantum Confined Metal Organic\n Chalcogenides Nanocrystal Films: 2D quantum confined hybrid materials are of great interest from a solid state\nphysics standpoint because of the rich multibody phenomena hosted, their\ntunability and easy synthesis allowing to create material libraries. In\naddition, from a technological standpoint, 2D hybrids are promising candidates\nfor efficient, tunable, low cost materials impacting a broad range of\noptoelectronic devices. Different approaches and materials have therefore been\ninvestigated, with the notable example of 2D metal halide hybrid perovskites.\nDespite the remarkable properties of such materials, the presence of toxic\nelements like lead are not desirable in applications and their ionic lattices\nmay represent a limiting factor for stability under operating conditions.\nAlternative, non-ionic 2D materials made of non-toxic elements are therefore\ndesirable. In order to expand the library of possible hybrid quantum wells\nmaterials, here we consider an alternative platform based on non-toxic,\nself-assembled, metal-organic chalcogenides. While the optical properties have\nbeen recently explored and some unique excitonic characters highlighted,\nphoto-generation of carriers and their transport in these lamellar\ninorganic/organic nanostructures, critical optoelectronic aspects, remain\ntotally unexplored. We hereby report the first electrical investigation of the\nair-stable [AgSePh] 2D coordination polymer in form of nanocrystal (NC) films\nreadily synthesized in situ and at low temperature, compatible with flexible\nplastic substrates. The wavelength-dependent photo-response of the NC films\nsuggests possible use of this materials as near-UV photodetector. We therefore\nbuilt a lateral photo-detector, achieving a sensitivity of 0.8 A/W at 370 nm\nthanks to a photoconduction mechanism, and a cutoff frequency of ~400 Hz, and\nvalidated its reliability as air-stable UV detector on flexible substrates.", "category": "physics_app-ph" }, { "text": "Photoacoustic spectroscopy of NO$_2$ using a mid-infrared pulsed optical\n parametric oscillator as light source: A photoacoustic (PA) sensor for spectroscopic measurements of NO$_2$-N$_2$ at\nambient pressure and temperature is demonstrated. The PA sensor is pumped\nresonantly by a nanosecond pulsed single-mode mid-infrared (MIR) optical\nparametric oscillator (OPO). Spectroscopic measurements of NO$_2$-N$_2$ in the\n3.25 $\\mu$m to 3.55 $\\mu$m wavelength region with a resolution bandwidth of 5\ncm$^{-1}$ and with a single shot detection limit of 1.6 ppmV ($\\mu$mol/mol) is\ndemonstrated. The measurements were conducted with a constant flow rate of 300\nml/min, thus demonstrating the suitability of the gas sensor for real time\ntrace gas measurements. The acquired spectra is compared with data from the\nHitran database and good agreement is found. An Allan deviation analysis shows\nthat the detection limit at optimum integration time for the PAS sensor is 14\nppbV (nmol/mol) at 170 seconds of integration time, corresponding to a\nnormalized noise equivalent absorption (NNEA) coefficient of 3.3$\\times\n10^{-7}$ W cm$^{-1}$ Hz$^{-1/2}$.", "category": "physics_app-ph" }, { "text": "Tailoring Interlayer Charge Transfer Dynamics in 2D Perovskites with\n Electroactive Spacer Molecules: The family of hybrid organic-inorganic lead-halide perovskites are the\nsubject of intense interest for optoelectronic applications, from\nlight-emitting diodes to photovoltaics to X-ray detectors. Due to the inert\nnature of most organic molecules, the inorganic sublattice generally dominates\nthe electronic structure and therefore optoelectronic properties of\nperovskites. Here, we use optically and electronically active carbazole-based\nCz-Ci molecules, where Ci indicates an alkylammonium chain and i indicates the\nnumber of CH2 units in the chain, varying from 3-5, as cations in the 2D\nperovskite structure. By investigating the photophysics and charge transport\ncharacteristics of (Cz-Ci)2PbI4, we demonstrate a tunable electronic coupling\nbetween the inorganic lead-halide and organic layers. The strongest interlayer\nelectronic coupling was found for (Cz-C3)2PbI4, where photothermal deflection\nspectroscopy results remarkably demonstrate an organic-inorganic charge\ntransfer state. Ultrafast transient absorption spectroscopy measurements\ndemonstrate ultrafast hole transfer from the photoexcited lead-halide layer to\nthe Cz-Ci molecules, the efficiency of which increases by varying the chain\nlength from i=5 to i=3. The charge transfer results in long-lived carriers\n(10-100 ns) and quenched emission, in stark contrast with the fast (sub-ns) and\nefficient radiative decay of bound excitons in the more conventional 2D\nperovskite (PEA)2PbI4, in which phenylethylammonium (PEA) acts as an inert\nspacer. Electrical charge transport measurements further support enhanced\ninterlayer coupling, showing increased out-of-plane carrier mobility from i=5\nto i=3. This study paves the way for the rational design of 2D perovskites with\ncombined inorganic-organic electronic proper-ties through the wide range of\nfunctionalities available in the world of organics.", "category": "physics_app-ph" }, { "text": "Atomic Defect-Aware Physical Design of Silicon Dangling Bond Logic on\n the H-Si(100)2x1 Surface: Although fabrication capabilities of Silicon Dangling Bonds have rapidly\nadvanced from manual labor-driven laboratory work to automated manufacturing in\njust recent years, sub-nanometer substrate defects still pose a hindrance to\nproduction due to the need for atomic precision. In essence, unpassivated or\nmissing surface atoms, contaminants, and structural deformations disturb the\nfabricated logic or prevent its realization altogether. Moreover, design\nautomation techniques in this domain have not yet adopted any defect-aware\nbehavior to circumvent the present obstacles. In this paper, we derive a\nsurface defect model for design automation from experimentally verified defect\ntypes that we apply to identify sensitivities in an established gate library in\nan effort to generate more robust designs. Furthermore, we present an automatic\nplacement and routing algorithm that considers scanning tunneling microscope\ndata obtained from physical experiments to lay out dot-accurate circuitry that\nis resilient against the presence of atomic surface defects. This culminates in\na holistic evaluation on surface data of varying defect rates that enables us\nto quantify the severity of such defects. We project that fabrication\ncapabilities must achieve defect rates of around 0.1 %, if charged defects can\nbe completely eliminated, or < 0.1 %, otherwise. This realization sets the pace\nfor future efforts to scale up this promising circuit technology.", "category": "physics_app-ph" }, { "text": "Top-down fabrication of ordered arrays of GaN nanowires by selective\n area sublimation: We demonstrate the top-down fabrication of ordered arrays of GaN nanowires by\nselective area sublimation of pre-patterned GaN(0001) layers grown by hydride\nvapor phase epitaxy on Al$_{2}$O$_{3}$. Arrays with nanowire diameters and\nspacings ranging from 50 to 90 nm and 0.1 to 0.7 $\\mu$m, respectively, are\nsimultaneously produced under identical conditions. The sublimation process,\ncarried out under high vacuum conditions, is analyzed \\emph{in situ} by\nreflection high-energy electron diffraction and line-of-sight quadrupole mass\nspectromety. During the sublimation process, the GaN(0001) surface vanishes,\ngiving way to the formation of semi-polar $\\lbrace1\\bar{1}03\\rbrace$ facets\nwhich decompose congruently following an Arrhenius temperature dependence with\nan activation energy of ($3.54 \\pm 0.07$) eV and an exponential prefactor of\n$1.58\\times10^{31}$ atoms cm$^{-2}$ s$^{-1}$. The analysis of the samples by\nlow-temperature cathodoluminescence spectroscopy reveals that, in contrast to\ndry etching, the sublimation process does not introduce nonradiative\nrecombination centers at the nanowire sidewalls. This technique is suitable for\nthe top-down fabrication of a variety of ordered nanostructures, and could\npossibly be extended to other material systems with similar crystallographic\nproperties such as ZnO.", "category": "physics_app-ph" }, { "text": "Apparatus for Operando X-ray Diffraction of Fuel Electrodes in High\n Temperature Solid State Electrochemical Cells: Characterizing electrochemical energy conversion devices during operation is\nan important strategy for correlating device performance with the properties of\ncell materials under real operating conditions. While operando characterization\nhas been used extensively for low temperature electrochemical cells, these\ntechniques remain challenging for solid oxide electrochemical cells due to the\nhigh temperatures and reactive gas atmospheres these cells require. Operando\nX-ray diffraction measurements of solid oxide electrochemical cells could\ndetect changes in the crystal structure of the cell materials, which can be\nuseful for understanding degradation process that limit device lifetimes, but\nthe experimental capability to perform operando X-ray diffraction on the fuel\nelectrodes of these cells has not been demonstrated. Here we present the first\nexperimental apparatus capable of performing X-ray diffraction measurements on\nthe fuel electrodes of high temperature solid oxide electrochemical cells\nduring operation under reducing gas atmospheres. We present data from an\nexample experiment with a model solid oxide cell to demonstrate that this\napparatus can collect X-ray diffraction spectra during electrochemical cell\noperation at high temperatures in humidified H2 gas. Measurements performed\nusing this apparatus can reveal new insights about solid oxide fuel cell and\nsolid oxide electrolyzer cell degradation mechanisms to enable the design of\ndurable, high performance devices.", "category": "physics_app-ph" }, { "text": "Effect of RF Sputtering Process Parameters on Silicon Nitride Thin Film\n Deposition: The objective of this work was to study the RF sputtering process parameters\noptimisation for deposition of Silicon Nitride thin films. The process\nparameters chosen to be varied were deposition power, deposition duration, flow\nrate of argon and flow rate of nitrogen. The parameters were varied at three\nlevels according to Taguchi L9 orthogonal array. Surface topology, film\ncomposition, coating thickness, coating resistivity and refractive index were\ndetermined using SEM, XRD, profilometer, Semiconductor device analyser and UV\nspectrometer respectively. The measured film thickness values ranged from\n127.8nm to 908.3nm with deposition rate varying from 1.47nm/min to a maximum\nvalue of 10.1nm/min. The resistivity of the film varied between 1.53x1013ohm-m\nto 7.85 x1013ohm-m. Refractive index of the film was calculated to be between\n1.84 to 2.08. From the results, it was seen that film properties tend to be\npoor when there is no nitrogen flow and tend to improve with small input of\nnitrogen. Also, SEM images indicated amorphous structure of silicon nitride\nwhich was confirmed by XRD pattern.", "category": "physics_app-ph" }, { "text": "Metal oxide nanomaterials for pseudocapacitors: With the rapid development of economy, the consumption of fossil fuels, and\nthe increasing environment pollution, there is in urgent need of seeking clean\nand renewable energy sources, as well as highly efficient and low-cost energy\nstorage technologies. Concerning electrochemically active materials, transition\nmetal oxides (TMOs) are regarded as the most promising candidates for the next\ngeneration SCs and have been widely reported. Therefore, in this review, we\nmainly pay attention to TMOs with excellent electrochemical performance. This\nreview is divided into four parts: (a) the background including energy storage\nmechanisms and electrochemical characterizations of SCs; (b) various kinds of\nTMOs for SCs are analyzed in detail involved in crystal structure,\nconductivity, and energy storage mechanism; (c) hybridizations with other\nmaterials to improve the electrochemical performance of TMOs are summarized and\ndiscussed; (d) a perspective and short remarks about the development and design\nof TMOs for superior performance SCs are shown.", "category": "physics_app-ph" }, { "text": "Observation of Temporal Reflections and Broadband Frequency Translations\n at Photonic Time-Interfaces: Time-reflection is a uniform inversion of the temporal evolution of a signal,\nwhich arises when an abrupt change in the properties of the host material\noccurs uniformly in space. At such a time-interface, a portion of the input\nsignal is time-reversed, and its frequency spectrum is homogeneously translated\nwhile its momentum is conserved, forming the temporal counterpart of a spatial\ninterface. Combinations of time-interfaces, forming time-metamaterials and\nFloquet matter, exploit the interference of multiple time-reflections for\nextreme wave manipulation, leveraging time as a new degree of freedom. Here, we\nreport the observation of photonic time-reflection and associated broadband\nfrequency translation in a switched transmission-line metamaterial whose\neffective capacitance is homogeneously and abruptly changed via a synchronized\narray of switches. A pair of temporal interfaces are combined to demonstrate\ntime-reflection-induced wave interference, realizing the temporal counterpart\nof a Fabry-Perot cavity. Our results establish the foundational building blocks\nto realize time-metamaterials and Floquet photonic crystals, with opportunities\nfor extreme photon manipulation in space and time.", "category": "physics_app-ph" }, { "text": "Transfer of Graphene with Protective Oxide Layers: Transfer of graphene, grown by Chemical Vapor Deposition (CVD), to a\nsubstrate of choice, typically involves deposition of a polymeric layer\n(typically, poly(methyl methacrylate, PMMA or polydimethylsiloxane, PDMS).\nThese polymers are quite hard to remove without leaving some residues behind.\nHere we study a transfer of graphene with a protective thin oxide layer. The\nthin oxide layer is grown by Atomic Deposition Layer (ALD) on the graphene\nright after the growth stage on Cu foils. One can further aid the\noxide-graphene transfer by depositing a very thin polymer layer on top of the\ncomposite (much thinner than the usual thickness) following by a more\naggressive polymeric removal methods, thus leaving the graphene intact. We\nreport on the nucleation growth process of alumina and hafnia films on the\ngraphene, their resulting strain and on their optical transmission. We suggest\nthat hafnia is a better oxide to coat the graphene than alumina in terms of\nuniformity and defects.", "category": "physics_app-ph" }, { "text": "Implementing Multiple Modes of the Perpendicular Magnetization Switching\n within a Single Spin Orbit Torque Device: Spin orbit torque (SOT) has been considered as one of the promising\ntechnologies for the next-generation magnetic random access memory (MRAM). So\nfar, SOT has been widely utilized for inducing various modes of magnetization\nswitching. However, it is challenging to integrate multiple modes of\nmagnetization switching together. In this work we propose a method for\nimplementing both unipolar and bipolar switching of the perpendicular\nmagnetization within a single SOT device. The mode of switching could be easily\naltered by tuning the amplitude of the applied current. We show that the\nfield-like torque plays an important role in the switching process. The\nfield-like torque induces the precession of the magnetization in the case of\nunipolar switching, whereas it helps to generate an effective z-component\ntorque in the case of bipolar switching. In addition, the influence of key\nparameters on the mode of switching is discussed. Our proposal could be used to\ndesign novel reconfigurable logic circuits in the near future.", "category": "physics_app-ph" }, { "text": "Acoustic helical dichroism in a one-dimensional lattice of chiral\n resonators: Circular dichroism and helical dichroism are intriguing chiroptical phenomena\nwith broad applications in optical sensing and imaging. Here, we generalize one\nof the phenomena-helical dichroism-to acoustics. We show that a one-dimensional\nlattice of chiral resonators with loss can induce differential absorption of\nhelical sounds (i.e. acoustic vortices) carrying opposite orbital angular\nmomentum (OAM). This acoustic helical dichroism strongly depends on the\nrotation symmetry of the chiral resonators. A breaking of the $C_4$ rotation\nsymmetry can induce coupling between the opposite chiral dipole modes of the\nresonators. This leads to OAM bandgaps and non-Hermitian exceptional points\nnear the Brillouin-zone center and boundaries, which together give rise to\nsignificantly enhanced helical dichroism. The underlying physics can be well\ncaptured by an effective Hamiltonian that quantitatively reproduces the complex\nband structures. The acoustic helical dichroism can find important applications\nin acoustic OAM manipulations and chiral sound-matter interactions.", "category": "physics_app-ph" }, { "text": "Three-dimensional Temperature Field Reconstruction for A Lithium-Ion\n Battery Pack: A Distributed Kalman Filtering Approach: Despite the ever-increasing use across different sectors, the lithium-ion\nbatteries (LiBs) have continually seen serious concerns over their thermal\nvulnerability. The LiB operation is associated with the heat generation and\nbuildup effect, which manifests itself more strongly, in the form of highly\nuneven thermal distribution, for a LiB pack consisting of multiple cells. If\nnot well monitored and managed, the heating may accelerate aging and cause\nunwanted side reactions. In extreme cases, it will even cause fires and\nexplosions, as evidenced by a series of well-publicized incidents in recent\nyears. To address this threat, this paper, for the first time, seeks to\nreconstruct the three-dimensional temperature field of a LiB pack in real time.\nThe major challenge lies in how to acquire a high-fidelity reconstruction with\nconstrained computation time. In this study, a three-dimensional thermal model\nis established first for a LiB pack configured in series. Although spatially\nresolved, this model captures spatial thermal behavior with a combination of\nhigh integrity and low complexity. Given the model, the standard Kalman filter\nis then distributed to attain temperature field estimation at substantially\nreduced computational complexity. The arithmetic operation analysis and\nnumerical simulation illustrate that the proposed distributed estimation\nachieves a comparable accuracy as the centralized approach but with much less\ncomputation. This work can potentially contribute to the safer operation of the\nLiB packs in various systems dependent on LiB-based energy storage, potentially\nwidening the access of this technology to a broader range of engineering areas.", "category": "physics_app-ph" }, { "text": "Wave momentum shaping for moving objects in heterogeneous and dynamic\n media: Light and sound waves have the fascinating property that they can move\nobjects through the transfer of linear or angular momentum. This ability has\nled to the development of optical and acoustic tweezers, with applications\nranging from biomedical engineering to quantum optics. Although impressive\nmanipulation results have been achieved, the stringent requirement for a highly\ncontrolled, low-reverberant, and static environment still hinders the\napplicability of these techniques in many scenarios. Here, we overcome this\nchallenge and demonstrate the manipulation of objects in disordered and dynamic\nmedia, by optimally tailoring the momentum of sound waves iteratively in the\nfar field. The method does not require information about the object's physical\nproperties or the spatial structure of the surrounding medium but relies only\non a real-time scattering matrix measurement and a positional guidestar. Our\nexperiment demonstrates the possibility of optimally moving and rotating\nobjects, extending the reach of wave-based object manipulation to complex and\ndynamic scattering media. We envision new opportunities for biomedical\napplications, sensing, or manufacturing.", "category": "physics_app-ph" }, { "text": "Single-source, solvent-free, room temperature deposition of black\n $\u03b3$-CsSnI$_3$ films: The presence of a non-optically active polymorph (yellow-phase) competing\nwith the optically active polymorph (black $\\gamma$-phase) at room temperature\nin CsSnI3 and the susceptibility of Sn to oxidation, represent two of the\nbiggest obstacles for the exploitation of CsSnI3 in optoelectronic devices.\nHere room-temperature single-source in vacuum deposition of smooth black\n$\\gamma$ - CsSnI3 thin films is reported. This has been done by fabricating a\nsolid target by completely solvent-free mixing of CsI and SnI2 powders and\nisostatic pressing. By controlled laser ablation of the solid target on an\narbitrary substrate at room temperature, the formation of CsSnI3 thin films\nwith optimal optical properties is demonstrated. The films present a band gap\nof 1.32 eV, a sharp absorption edge and near-infrared photoluminescence\nemission. These properties and X-ray diffraction of the thin films confirmed\nthe formation of the orthorhombic (B-$\\gamma$) perovskite phase. The thermal\nstability of the phase was ensured by applying in situ an Al2O$_3$ capping\nlayer. This work demonstrates the potential of pulsed laser deposition as a\nvolatility-insensitive single-source growth technique of halide perovskites and\nrepresents a critical step forward in the development and future scalability of\ninorganic lead-free halide perovskites.", "category": "physics_app-ph" }, { "text": "Mutual synchronization of constriction-based spin Hall nano-oscillators\n in weak in-plane fields: We study mutual synchronization in double nanoconstriction-based spin Hall\nnano-oscillators (SHNOs) under weak in-plane fields ($\\mu_0H_\\mathrm{IP}$ =\n30-40 mT) and also investigate its angular dependence. We compare SHNOs with\ndifferent nano-constriction spacings of 300 and 900 nm. In all devices, mutual\nsynchronization occurs below a certain critical angle, which is higher for the\n300 nm spacing than for the 900 nm spacing, reflecting the stronger coupling at\nshorter distances. Alongside the synchronization, we observe a strong second\nharmonic consistent with predictions that the synchronization may be mediated\nby the propagation of second harmonic spin waves. However, although Brillouin\nLight Scattering microscopy confirms the synchronization, it fails to detect\nany related increase of the second harmonic. Micromagnetic simulations instead\nexplain the angular dependent synchronization as predominantly due to\nmagneto-dipolar coupling between neighboring SHNOs.", "category": "physics_app-ph" }, { "text": "Scalable and Deterministic Fabrication of Quantum Emitter Arrays from\n Hexagonal Boron Nitride: We demonstrate the fabrication of large-scale arrays of single photon\nemitters (SPEs) in hexagonal boron nitride (hBN). Bottom-up growth of hBN onto\nnanoscale arrays of dielectric pillars yields corresponding arrays of hBN\nemitters at the pillar sites. Statistical analysis shows that the pillar\ndiameter is critical for isolating single defects, and diameters of ~250 nm\nproduce a near-unity yield of a single emitter at each pillar site. Our results\nconstitute a promising route towards spatially-controlled generation of hBN\nSPEs and provide an effective and efficient method to create large scale SPE\narrays. The results pave the way to scalability and high throughput fabrication\nof SPEs for advanced quantum photonic applications.", "category": "physics_app-ph" }, { "text": "Overlimiting current in non-uniform arrays of microchannels: Overlimiting current (OLC) through electrolytes interfaced with\nperm-selective membranes has been extensively researched in recent years for\nunderstanding the fundamental mechanisms of transport and developing efficient\napplications from electrochemistry to sample analysis and separation.\nPredominant mechanisms responsible for OLC include surface conduction,\nconvection by electro-osmotic flow, and electro-osmotic instability depending\non input parameters such as surface charge and geometric constrictions. This\nwork studies how a network of microchannels in a non-uniform array, which\nmimicks a natural pore configuration, can contribute to OLC. To this end,\nmicro/nanofluidic devices are fabricated with arrays of parallel microchannels\nwith non-uniform size distributions. All cases maintain the same surface and\nbulk conduction to allow probing the sensitivity only by the non-uniformity of\nthe channels. Both experimental and theoretical current-voltage relations\ndemonstrate that OLCs increase with increasing non-uniformity. Furthermore, the\nvisualization of internal recirculating flows indicates that the non-uniform\narrays induce flow loops across the network enhancing advective transport.\nThese evidences confirm a new driving mechanism of OLC, inspired by natural\nmicro/nanoporous materials with random geometric structure. Therefore, this\nresult can advance not only the fundamental understanding of\nnanoelectrokinetics but also the design rule of engineering applications of\nelectrochemical membrane.", "category": "physics_app-ph" }, { "text": "Ultra-high resolution and broadband chip-scale speckle enhanced\n Fourier-transform spectrometer: Recent advancements in silicon photonics are enabling the development of\nchip-scale photonics devices for sensing and signal processing applications,\namong which on-chip spectrometers are of particular interest for precision\nwavelength monitoring and related applications. Most chip-scale spectrometers\nsuffer from a resolution-bandwidth trade-off, thus limiting the uses of the\ndevice. Here we report on a novel passive, chip-scale, hybrid speckle-enhanced\nFourier transform device that exhibits a two order-of-magnitude improvement in\nfinesse (bandwidth/resolution) over the state-of-the art chip-scale speckle and\nFourier transform spectrometers. In our proof-of-principle device, we\ndemonstrate a spectral resolution of 140 MHz with 12-nm bandwidth for a finesse\nof $10^4$ that can operate over a range of 1500-1600 nm. This chip-scale\nspectrometer structure implements a typical spatial heterodyne discrete Fourier\ntransform interferometer network that is enhanced by speckle generated from the\nwafer substrate. This latter effect, which is extremely simple to invoke,\nsuperimposes the high wavelength resolution intrinsic to speckle generated from\na strongly guiding waveguide with a more broadband but lower resolution\ndiscrete Fourier transform modality of the overarching waveguide structure.\nThis hybrid approach signifies a new pathway for realizing chip-scale\nspectrometers capable of ultra-high resolution and broadband performance.", "category": "physics_app-ph" }, { "text": "Inference of highly time-resolved melt pool visual characteristics and\n spatially-dependent lack-of-fusion defects in laser powder bed fusion using\n acoustic and thermal emission data: With a growing demand for high-quality fabrication, the interest in real-time\nprocess and defect monitoring of laser powder bed fusion (LPBF) has increased,\nleading manufacturers to incorporate a variety of online sensing methods\nincluding acoustic sensing, photodiode sensing, and high-speed imaging.\nHowever, real-time acquisition of high-resolution melt pool images in\nparticular remains computationally demanding in practice due to the high\nvariability of melt pool morphologies and the limitation of data caching and\ntransfer, making it challenging to detect the local lack-of-fusion (LOF) defect\noccurrences. In this work, we propose a new acoustic and thermal\ninformation-based monitoring method that can robustly infer critical LPBF melt\npool morphological features in image forms and detect spatially-dependent LOF\ndefects within a short period. We utilize wavelet scalogram matrices of\nacoustic and photodiode clip data to identify and predict highly time-resolved\n(within a 1.0 ms window) visual melt pool characteristics via a well-trained\ndata-driven pipeline. With merely the acoustic and photodiode-collected thermal\nemission data as the input, the proposed pipeline enables data-driven inference\nand tracking of highly variable melt pool visual characteristics with\n$R^2=0.8$. We subsequently validate our proposed approach to infer local LOF\ndefects between two adjacent scanlines, showing that our proposed approach can\noutperform our selected baseline theoretical model based on previous\nliterature. Revealing the physical correlation between airborne acoustic\nemission, thermal emission, and melt pool morphology, our work demonstrates the\nfeasibility of creating an efficient and cost-effective acoustic- and\nthermal-based approach to facilitate online visual melt pool characterization\nand LOF defect detection.", "category": "physics_app-ph" }, { "text": "Twist-Controlled Wire Metasurfaces: Twistronics, originally conceptualized within the electronics domain to\nmodulate electronic properties through the twist angle between stacked\ntwo-dimensional (2D) materials, presents a groundbreaking approach in material\nscience. This concept's extension to photonics, especially using metasurfaces,\noffers a promising avenue for manipulating light at subwavelength scales across\na broad electromagnetic spectrum. Nevertheless, the possibilities that\ntwistronics presents within the realm of photonics are still significantly\nuntapped. In this work, we explore a photonic configuration consisting of a\ndual-layer wire metasurface operating within the microwave frequency spectrum,\nwhere the interlayer twist angle governs the system. Our findings reveal that\nsuch manipulation significantly alters the electromagnetic response of the\nstructure, leading to enhanced resonances, tunability, and mode coupling. This\ntwist-induced modulation results in a resonance shift towards the low-frequency\nrange, effectively miniaturizing the structure's electrical dimension. Our\nstudy demonstrates the feasibility of integrating twistronics into photonic\ndesigns and opens new pathways for developing tunable and reconfigurable\nphotonic devices.", "category": "physics_app-ph" }, { "text": "Giant tunneling magnetoresistance in Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi\n magnetic tunnel junction: We propose a theoretical model for an all-Heusler magnetic tunnel junction\nthat uses two Heusler compounds: Fe$_2$CrSi and Fe$_2$TiSi, both of which can\nbe experimentally synthesized. Fe$_2$CrSi is a half-metallic ferromagnet,\nmaking it a promising material for efficient spin injection in magnetic random\naccess memories and other spin-dependent devices. While, Fe$_2$TiSi is a\nnonmagnetic semiconductor that has the same lattice structure and comparable\nlattice constant with Fe$_2$CrSi, as it can be obtained by substituting the\n$Y$-site atoms in Fe$_2$CrSi. By using Fe$_2$TiSi as a tunneling barrier\nsandwiched by two pieces of semi-infinite Fe$_2$CrSi to construct an\nall-Heusler magnetic tunnel junction, the interface disorder is naturally\nreduced. Our calculations demonstrate that this magnetic tunnel junction can\nexhibit a giant tunneling magnetoresistance of up to 10$^{9}$\\% and remains\nrobust under finite bias voltage. These characteristics suggest that\nFe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi MTJ will be an ideal candidate for future\nspintronic applications. More importantly, such a device model can keep such a\ngiant tunneling magnetoresistance at and beyond room temperature due to the\nhigh Curie temperature of Fe$_2$CrSi.", "category": "physics_app-ph" }, { "text": "Layer-by-Layer Assembled Nanowire Networks Enable Graph Theoretical\n Design of Multifunctional Coatings: Multifunctional coatings are central for information, biomedical,\ntransportation and energy technologies. These coatings must possess\nhard-to-attain properties and be scalable, adaptable, and sustainable, which\nmakes layer-by-layer assembly (LBL) of nanomaterials uniquely suitable for\nthese technologies. What remains largely unexplored is that LBL enables\ncomputational methodologies for structural design of these composites.\nUtilizing silver nanowires (NWs), we develop and validate a graph theoretical\n(GT) description of their LBL composites. GT successfully describes the\nmultilayer structure with nonrandom disorder and enables simultaneous rapid\nassessment of several properties of electrical conductivity, electromagnetic\ntransparency, and anisotropy. GT models for property assessment can be rapidly\nvalidated due to (1) quasi-2D confinement of NWs and (2) accurate microscopy\ndata for stochastic organization of the NW networks. We finally show that\nspray-assisted LBL offers direct translation of the GT-based design of\ncomposite coatings to additive, scalable manufacturing of drone wings with\nstraightforward extensions to other technologies.", "category": "physics_app-ph" }, { "text": "Increasing TeraHertz spintronic emission with planar antennas: Spintronic THz emitters, consisting of Ta/Co/Pt trilayers patterned into\nrectangles of lateral size in the 10 ${\\mu}$m range, have been integrated in\nplanar electromagnetic antennas of various types (dipole, bow-tie, spiral).\nAntenna dimensions and shapes have been optimized with the help of\nelectromagnetic simulations so as to maximize antenna efficiency in both\nnarrow-band and broad-band geometries at/around 1 THz. The THz emission has\nbeen studied using a pump probe free space electro-optic sampling set up, both\nfor a single emitter geometry and for arrays of emitters. Results show an\nincrease of the detected THz signal for all antenna geometries, with\nenhancement ratios in the range of three to fifteen depending on antenna type\nand frequency range, together with changes of the emission bandwidth consistent\nwith simulated characteristics.", "category": "physics_app-ph" }, { "text": "Environmental Control of Triplet Emission in Donor-Bridge-Acceptor\n Organometallics: Carbene-metal-amides (CMAs) are a promising family of donor-bridge-acceptor\nmolecular charge-transfer emitters for organic light-emitting diodes (OLEDs).\nHere a universal approach is introduced to tune the energy of their\ncharge-transfer emission. A shift of up to 210 meV is achievable in the solid\nstate via dilution in a polar host matrix. The origin of this shift has two\ncomponents: constraint of thermally activated triplet diffusion, and\nelectrostatic interactions between the guest molecules and the polar host. This\nallows the emission of mid-green CMA archetypes to be blue shifted without\nchemical modifications. Monte-Carlo simulations based on a Marcus-type transfer\nintegral successfully reproduce the concentration- and temperature-dependent\ntriplet diffusion process, and reveal a substantial shift in the ensemble\ndensity of states in polar hosts. In gold-bridged CMAs this substantial shift\ndoes not lead to a significant change in luminescence lifetime, thermal\nactivation energy, reorganisation energy or intersystem crossing rate. These\ndiscoveries thus offer new experimental and theoretical insight in to the\ncoupling between the singlet and triplet manifolds in these materials. Similar\nemission tuning can be achieved in related materials where chemical\nmodification is used to modify the charge-transfer energy.", "category": "physics_app-ph" }, { "text": "Nanoscale laser flash measurements of diffuson transport in amorphous Ge\n and Si: The thermal properties of amorphous materials have attracted significant\nattention due to their technological importance in electronic devices.\nAdditionally, the disorder-induced breakdown of the phonon gas model makes\nvibrational transport in amorphous materials a topic of fundamental interest.\nIn the past few decades, theoretical concepts such as propagons, diffusons, and\nlocons have emerged to describe different types of vibrational modes in\ndisordered solids. But experiments can struggle to accurately determine which\ntypes of vibrational states carry the majority of the heat. In the present\nstudy, we use nanoscale laser flash measurements (front/back time-domain\nthermoreflectance) to investigate thermal transport mechanisms in amorphous Ge\nand amorphous Si thin-films. We observe a nearly linear relationship between\nthe amorphous film's thermal resistance and the film's thickness. The slope of\nthe film's thermal resistance vs. thickness corresponds to a\nthickness-independent thermal conductivity of 0.4 and 0.6 W/(m-K) for a-Ge and\na-Si, respectively. This result reveals that the majority of heat currents in\namorphous Si and Ge thin films prepared via RF sputtering at room temperature\nare carried by diffusons and/or propagons with mean free paths less than a few\nnanometers.", "category": "physics_app-ph" }, { "text": "Fabry-Perot Interferometric Calibration of 2D Nanomechanical Plate\n Resonators: Displacement calibration of nanomechanical plate resonators presents a\nchallenging task. Large nanomechanical resonator thickness reduces the\namplitude of the resonator motion due to its increased spring constant and\nmass, and its unique reflectance. Here, we show that the plate thickness,\nresonator gap height, and motional amplitude of circular and elliptical drum\nresonators, can be determined in-situ by exploiting the fundamental\ninterference phenomenon in Fabry-Perot cavities. The proposed calibration\nscheme uses optical contrasts to uncover thickness and spacer height profiles,\nand reuse the results to convert the photodetector signal to the displacement\nof drumheads that are electromotively driven in their linear regime. Calibrated\nfrequency response and spatial mode maps enable extraction of the modal radius,\neffective mass, effective driving force, and Young's elastic modulus of the\ndrumhead material. This scheme is applicable to any configuration of\nFabry-Perot cavities, including plate and membrane resonators.", "category": "physics_app-ph" }, { "text": "Fiber-coupled Diamond Magnetometry with an Unshielded 30\n pT/$\\sqrt{\\textrm{Hz}}$ Sensitivity: Ensembles of nitrogen vacancy centres (NVCs) in diamond can be employed for\nsensitive magnetometry. In this work we present a fiber-coupled NVC\nmagnetometer with an unshielded sensitivity of (30 $\\pm$ 10)\npT/$\\sqrt{\\textrm{Hz}}$ in a (10 - 500)-Hz frequency range. This sensitivity is\nenabled by a relatively high green-to-red photon conversion efficiency, the use\nof a [100] bias field alignment, microwave and lock-in amplifier (LIA)\nparameter optimisation, as well as a balanced hyperfine excitation scheme.\nFurthermore, a silicon carbide (SiC) heat spreader is used for microwave\ndelivery, alongside low-strain $^{12}\\textrm{C}$ diamonds, one of which is\nplaced in a second magnetically insensitive fluorescence collecting sensor head\nfor common-mode noise cancellation. The magnetometer is capable of detecting\nsignals from sources such as a vacuum pump up to 2 m away, with some\norientation dependence but no complete dead zones, demonstrating its potential\nfor use in remote sensing applications.", "category": "physics_app-ph" }, { "text": "Moisture-Driven Degradation Mechanisms in the Viscoelastic Properties of\n TPU-Based Syntactic Foams: Syntactic foams have found widespread usage in various applications\nincluding, marine, aerospace, automotive, pipe insulation, electrical cable\nsheathing, and shoe insoles. However, syntactic foams are often exposed to\nmoisture when used in these applications that potentially alter their\nviscoelastic properties, which influences their long-term durability. Despite\ntheir significance, previous research has mainly focused on experimental\nstudies concerning mechanical property changes resulting from filler loading\nand different matrix materials, overlooking the fundamental mechanisms\nresulting from moisture exposure. The current paper aims to bridge this gap in\nknowledge by elucidating the impact of long-term moisture exposure on TPU and\nTPU-based syntactic foam through multi-scale materials characterization\napproaches. Here, we choose a flexible syntactic foam manufactured using\nthermoplastic polyurethane elastomer (TPU) reinforced with glass microballoons\n(GMB) through selective laser sintering. Specifically, the research\ninvestigates the influence of moisture exposure time and the volume fraction of\nGMB on chemical and microphase morphological changes, along with their\nassociated mechanisms. The study further examines how these microphase\nmorphological changes manifest in viscoelastic properties.", "category": "physics_app-ph" }, { "text": "High quality Al$_{0.37}$In$_{0.63}$N layers grown at low temperature\n (<300$^\\circ$C) by radio-frequency sputtering: High-quality Al0.37In0.63N layers have been grown by reactive radio-frequency\n(RF) sputtering on sapphire, glass and Si (111) at low substrate temperature\n(from room temperature to 300{\\deg}C). Their structural, chemical and optical\nproperties are investigated as a function of the growth temperature and type of\nsubstrate. X-ray diffraction measurements reveal that all samples have a\nwurtzite crystallographic structure oriented with the c-axis perpendicular to\nthe substrate surface, without parasitic orientations. The layers preserve\ntheir Al content at 37 % for the whole range of studied growth temperature. The\nsamples grown at low temperatures (RT and 100{\\deg}C) are almost fully relaxed,\nshowing a closely-packed columnar-like morphology with an RMS surface roughness\nbelow 3 nm. The optical band gap energy estimated for layers grown at RT and\n100{\\deg}C on sapphire and glass substrates is of ~2.4 eV while it red shifts\nto ~2.03 eV at 300{\\deg}C. The feasibility of growing high crystalline quality\nAlInN at low growth temperature even on amorphous substrates open new\napplication fields for this material like surface plasmon resonance sensors\ndeveloped directly on optical fibers and other applications where temperature\nis a handicap and the material cannot be heated.", "category": "physics_app-ph" }, { "text": "TE-wave propagation in a graded waveguide structure: We investigate TE-wave propagation in a hollow waveguide with a graded\ndielectric layer, described using a hyperbolic tangent function. General\nformulae for the electric field components of the TE-waves, applicable to\nhollow waveguides with arbitrary cross sectional shapes, are presented. We\nillustrate the exact analytical results for the electric field components in\nthe special case of a rectangular waveguide. Furthermore, we derive exact\nanalytical results for the reflection and transmission coefficients valid for\nwaveguides of arbitrary cross sectional shapes. Finally, we show that the\nobtained reflection and transmission coefficients are in exact asymptotic\nagreement with those obtained for a very thin homogeneous dielectric layer\nusing mode-matching and cascading. The proposed method is tractable since it\ngives analytical results that are directly applicable without the need of\nmode-matching, and it has the ability to model realistic, smooth transitions.", "category": "physics_app-ph" }, { "text": "Modeling and Characterization of Metastability in Single Flux Quantum\n (SFQ) Synchronizers: Despite the promises of low-power and high-frequency of single-flux quantum\n(SFQ) technology, scaling these circuits remains a serious challenge that\nmotivates the support of multiple SFQ clock domains. Towards this end, this\npaper analyzes the impact of setup time violations and metastability in SFQ\ncircuits comparing the derived analytical models to their CMOS counterparts. It\nthen extends this model to estimate the Mean Time Between Failure (MTBF) of\nflip-flop-based synchronizers and curve fits this model to simulations in the\nstate-of-the-art SFQ5ee process. Interestingly, we find a two-flop SFQ\nsynchronizer has an estimated MTBF of 10^6 years.", "category": "physics_app-ph" }, { "text": "High aspect ratio silicon structures by Displacement Talbot lithography\n and Bosch etching: Despite the fact that the resolution of conventional contact/proximity\nlithography can reach feature sizes down to ~0.5-0.6 micrometers, the accurate\ncontrol of the linewidth and uniformity becomes already very challenging for\ngratings with periods in the range of 1-2 {\\mu}m. This is particularly relevant\nfor the exposure of large areas and wafers thinner than 300{\\mu}m. If the wafer\nor mask surface is not fully flat due to any kind of defects, such as\nbowing/warpage or remaining topography of the surface in case of overlay\nexposures, noticeable linewidth variations or complete failure of lithography\nstep will occur. We utilized the newly developed Displacement Talbot\nlithography to pattern gratings with equal lines and spaces and periods in the\nrange of 1.0 to 2.4 {\\mu}m. The exposures in this lithography process do not\nrequire contact between the mask and the wafer, which makes it essentially\ninsensitive to surface planarity and enables exposures with very high linewidth\nuniformity on thin and even slightly deformed wafers. We demonstrated pattern\ntransfer of such exposures into Si substrates by reactive ion etching using the\nBosch process. An etching depth of 30 {\\mu}m or more for the whole range of\nperiods was achieved, which corresponds to very high aspect ratios up to 60:1.\nThe application of the fabricated gratings in phase contrast x-ray imaging is\npresented.", "category": "physics_app-ph" }, { "text": "Nonlinear analysis of a fiber-reinforced tubular conducting\n polymer-based soft actuator: This study presents the analytical modeling of a fiber-reinforced tubular\nconducting polymer (FTCP) actuator. The FTCP actuator is a low voltage-driven\nelectroactive polymer arranged in an electrochemical cell. The electrochemical\nmodel is developed following an electrical circuit analogy that predicts the\ncharge diffused inside the actuator for an applied voltage. An empirical\nrelation is applied to couple the two internal phenomena, viz., diffusion of\nthe ions and mechanical deformation. Further, the finite deformation theory is\napplied to predict the blocked force and free strain of the FTCP actuator. The\ndeveloped model is consistent with existing experimental results for an applied\nvoltage. In addition, the effect of various electrical and geometrical\nparameters on the performance of the actuator is addressed.", "category": "physics_app-ph" }, { "text": "Recycled nylon fibers as cement mortar reinforcement: We investigate engineering applications of recycled nylon fibers obtained\nfrom waste fishing nets, focusing our attention on the use of recycled nylon\nfibers as tensile reinforcement of cementitious mortars. We begin by\ncharacterizing the tensile behavior of both unconditioned and alkali-cured\nrecycled nylon fibers obtained through manual cutting of waste fishing net\nfilaments, with the aim of assessing the resistance of such materials to\nchemical attacks. Special attention is also given to evaluating the workability\nof fresh mortar and the possible impacts of contaminants released by waste\nfishing nets into the environment. Next, we deal with compression and bending\ntests on cementitious mortars reinforced with recycled nylon fibers, and\nestablish comparisons with the experimental behavior of the unreinforced\nmaterial and with results given in existing literature. In our analysis of\ndifferent weight fractions and aspect ratios of the reinforcing fibers, we\nobserve marked increases in the tensile strength (up to +35%) and toughness (up\nto 13 times greater) of the nylon reinforced mortar, as compared with the\nunreinforced material. The presented results emphasize the high environmental\nand mechanical potential of recycled nylon fibers for the reinforcement of\nsustainable cement mortars.", "category": "physics_app-ph" }, { "text": "Mode I and Mode II stress intensity factors and dislocation density\n behaviour in strain gradient plasticity: In this study, we use the mechanism-based strain gradient plasticity theory\nto evaluate both crack tip dislocation density behaviour and the coupled effect\nof the material plastic properties and the intrinsic material length on\nnon-linear amplitude factors. The two planar classical stress-strain states are\nexamined, namely, plane strain and plane stress, both under pure mode I and\npure mode II loading conditions. The constitutive relations are based on\nTaylor's dislocation model, which enables gaining insights into the role of the\nincreased dislocation density associated with large gradients in plastic strain\nnear cracks. The material model is implemented in a commercial finite element\n(FE) software package using a user subroutine, and the nonlinear stress\nintensity factors (SIF) are evaluated as a function of the intrinsic material\nlength, characterising the scale at which gradient effects become significant.\nAs a result of the FE calculations of dislocation density distributions, the\neffects of both the fracture mode and the stress-strain state are determined.\nIn pure mode I, the geometrically necessary dislocation (GND) density is\nlocated symmetrically with respect to the blunted crack tip. On the contrary,\nunder pure mode II, the GND density becomes concentrated in the blunted and\nsharp parts of the crack tip. In this case, fracture initiation is shown to be\nlikely to occur near the blunted region of the crack tip, where both the stress\ntriaxiality and the GND density are at their maximum. The relation between the\nequilibrium state of dislocation densities and the intrinsic material length as\nwell as the plastic SIF as a function of the work hardening exponent is\ndiscussed.", "category": "physics_app-ph" }, { "text": "Topological phase transition of the centered rectangular photonic\n lattice: A Cm planar photonic material (two-dimensional) including the mirror\nreflection symmetry is explored where in the Dirac cones appeared at the\nhigh-symmetry points of the Brillouin zone boundary. By implementing the\nspecific perturbation on the photonic crystal (PC), topological transition can\nmake a bridge between the trivial PC (ordinary insulator) and the topological\ninsulator including zero and non-zero spin Chern number (Cs), respectively. The\nperturbation can be realized through the rotation of the Cm photonic crystal\naround the nonzero angle to its initial position. Therefore, breaking the\nmirror symmetry of the unit cell leads to mismatch of the symmetry planes of\nthe lattice. This modification results in the directional band gap & band\ninversion which is the signature of the topological transitions. The mentioned\nPC would be suitable for examination of the unidirectional transport of light\nat the topological interfaces.", "category": "physics_app-ph" }, { "text": "Light-triggered on/off-switchable bioelectronic FET device: We report fabrication of an optically active, bio-electronic device based on\nthin film of purple membrane and single walled carbon nanotubes (SWNT). Two\ndimensional (2D) crystals of photoactive bacteriorhodopsin forms the optical\ncenter of the purple membrane where as pure SWNTs provides the necessary\nelectronic support to the complex. Electro-optically functional and stable,\nhybrid complex was prepared using surface functionalization of SWNTs with\nindigenous, batch-process synthesized purple membrane. Raman spectra of the\nhybrid complex shows significant charge transfer and surface functionalization\nof SWNTs. Optically active, field effect transistor based on the prepared thin\nfilm of bio-nano hybrid complex is fabricated using direct laser lithography\nand conventional lift off technology. Significant optical doping is observed in\nthe fabricated field effect transistor. Fabricated devices show repeatable\nstable performance with well-controlled optical and electronic gating. Device\nshows essentially n-type FET characteristics and transistor is ON for positive\ngate voltages. However, same n-type FET shows complimentary p-type\ncharacteristics under visible light illumination, with transistor being ON for\nnegative gate voltages. Significant optical doping, photo-conductivity and\noptical switching were observed.", "category": "physics_app-ph" }, { "text": "High temperature annealing enhanced diamond 13C hyperpolarization at\n room temperature: Methods of optical dynamic nuclear polarization (DNP) open the door to the\nreplenishable hyperpolarization of nuclear spins, boosting their NMR/MRI\nsignature by orders of magnitude. Nanodiamond powder rich in negatively charged\nNitrogen Vacancy (NV) defect centers has recently emerged as one such promising\nplatform, wherein 13C nuclei can be hyperpolarized through the optically pumped\ndefects completely at room temperature and at low magnetic fields. Given the\ncompelling possibility of relaying this 13C polarization to nuclei in external\nliquids, there is an urgent need for the engineered production of highly\n\"hyperpolarizable\" diamond particles. In this paper, we report on a systematic\nstudy of various material dimensions affecting optical 13C hyperpolarization in\ndiamond particles -- especially electron irradiation and annealing conditions\nthat drive NV center formation. We discover surprisingly that diamond annealing\nat elevated temperatures close to 1720C have remarkable effects on the\nhyperpolarization levels, enhancing them by upto 36-fold over materials\nannealed through conventional means. We unravel the intriguing material origins\nof these gains, and demonstrate they arise from a simultaneous improvement in\nNV electron relaxation time and coherence time, as well as the reduction of\nparamagnetic content, and an increase in 13C relaxation lifetimes. Overall this\npoints to significant recovery of the diamond lattice from radiation damage as\na result of the high-temperature annealing. Our work suggests methods for the\nguided materials production of fluorescent, 13C hyperpolarized, nanodiamonds\nand pathways for their use as multi-modal (optical and MRI) imaging and\nhyperpolarization agents.", "category": "physics_app-ph" }, { "text": "Nanoscale Cathodoluminescence Spectroscopy Probing the Nitride Quantum\n Wells in an Electron Microcope: To gain a deeper understanding of the luminescence of multiquantum wells and\nthe factors affecting it on a microscopic level, cathodoluminescence combined\nwith scanning transmission electron microscopy and spectroscopy was used to\nreveal the luminescence of In0.15Ga0.85N five-period multiquantum wells. The\ncomposition-wave-energy relationship was established in combination with\nenergy-dispersive X-ray spectroscopy , and the bandgaps of In0.15Ga0.85N and\nGaN in multiple quantum wells were extracted by electron energy loss\nspectroscopy to understand the features of cathodoluminescence luminescence\nspectra. The luminescence differences between different periods of multiquantum\nwells and the effects on the luminescence of multiple quantum wells owing to\ndefects such as composition fluctuation and dislocations were revealed. Our\nstudy establishing the direct correspondence between the atomic structure of\nInxGa1-xN multiquantum wells and photoelectric properties, provides useful\ninformation for nitride applications.", "category": "physics_app-ph" }, { "text": "Low-loss fiber-to-chip interface for lithium niobate photonic integrated\n circuits: Integrated lithium niobate (LN) photonic circuits have recently emerged as a\npromising candidate for advanced photonic functions such as high-speed\nmodulation, nonlinear frequency conversion and frequency comb generation. For\npractical applications, optical interfaces that feature low fiber-to-chip\ncoupling losses are essential. So far, the fiber-to-chip loss (commonly > 10\ndB) dominates the total insertion losses of typical LN photonic integrated\ncircuits, where on-chip propagation losses can be as low as 0.03 - 0.1 dB/cm.\nHere we experimentally demonstrate a low-loss mode size converter for coupling\nbetween a standard lensed fiber and sub-micrometer LN rib waveguides. The\ncoupler consists of two inverse tapers that convert the small optical mode of a\nrib waveguide into a symmetric guided mode of a LN nanowire, featuring a larger\nmode area matched to that of a tapered optical fiber. The measured\nfiber-to-chip coupling loss is lower than 1.7 dB/facet with high fabrication\ntolerance and repeatability. Our results open door for practical integrated LN\nphotonic circuits efficiently interfaced with optical fibers.", "category": "physics_app-ph" }, { "text": "Multi-Functional Variable Thickness Structure for Broadband and\n Omnidirectional Focusing and Collimation: Luneburg lens is a symmetric gradient-index lens with a refractive index that\nincreases from the outer surface to the center in a radial manner. It has the\nability to focus and collimate waves, which makes it useful for energy\nharvesting, waveguiding and as a component in transducers. An ideal Luneburg\nlens should be easy to fabricate, has broadband and omnidirectional\ncharacteristics, as well as a focal length that can be easily tuned. However,\nexisting structural Luneburg lenses based on phononic crystals can hardly\nachieve these requirements. Here, we propose an alternative structural Luneburg\nlens which has a refractive index that varies smoothly with its radial distance\nas a result of a changing thickness. Theoretical calculations, numerical\nsimulations and experimental measurements of flexural wave propagation through\nthe lens showed that flexural wave focusing can be obtained inside, at the edge\nand outside of the variable thickness lens for different frequencies and\npropagation directions. Flexural wave collimation was also demonstrated when a\npoint source was placed at the respective focal points for each lens.\nFurthermore, it was shown that flexural waves that were focused onto a\npiezoelectric energy harvester by the Luneburg lens can lead to a significant\nincrease in the harvested voltage compared to that obtained without focusing.", "category": "physics_app-ph" }, { "text": "Disorder-induced topological phase transition in a 1D mechanical system: We numerically investigate the topological phase transition induced purely by\ndisorder in a spring-mass chain. We employ two types of disorders - chiral and\nrandom types - to explore the interplay between topology and disorder. By\ntracking the evolution of real space topological invariants, we obtain the\ntopological phase diagrams and demonstrate the bilateral capacity of disorder\nto drive topological transitions, from topologically nontrivial to trivial and\nvice versa. The corresponding transition is accompanied by the realization of a\nmechanical Topological Anderson Insulator. The findings from this study hint\nthat the combination of disorder and topology can serve as an efficient control\nknob to manipulate the transfer of mechanical energy.", "category": "physics_app-ph" }, { "text": "Development of a computational software in Python, used to study the\n materials resistance in beams: In this research, we do a software writing in Python to calculate the\nefforts, bending moments and deformations in beams of different materials. This\ncomputational tool, that we developed, is of great help in area of\ncomputational physical, more exactly in resistance of materials, which serves\nas support for researchers and teachers especially in physics and civil\nengineering, of the part of statics, who wish to carry out the modeling of the\nfunctions, involved in the calculation of resistance in beams in a practical\nand simple way, using the software presented in this article. In order to carry\nout this software, we are going to use the following methods: the\ndouble-integration method and the conjugate-beam method, which will serve as\nthe basis of calculation to find the mathematical expressions involved in the\nanalysis of resistance in beams, then we will perform the implementation of the\naforementioned methods, using Python as the programming language. As a final\nstep in this project, the graphical interface of said calculation tool will be\nmade using the Python 3.0 Tkinter library. In this work, we show the results of\nthe graphs of the stress profiles, bending moments and deformations, for the\ncase of different types of beams, load and force distributions applied to them.\nWhere we were also able to conclude that a calculation software was\nsuccessfully built, dedicated to the analysis of efforts and deformations in\nbeams made of different materials.", "category": "physics_app-ph" }, { "text": "Reconfigurable integrated waveguide meshes for photonic signal\n processing and emerging applications: We review the recent advances reported in the field of integrated photonic\nwaveguide meshes, both from the theoretical as well as from the experimental\npoint of view. We show how these devices can be programmed to implement both\ntraditional signal processing structures, such as finite and infinite impulse\nresponse filters, delay lines, beamforming networks as well as more advanced\nlinear matrix optics functionalities. Experimental results reported both in\nSilicon and Silicon Nitride material platforms will be presented. We will also\ndiscuss the main programming algorithms to implement these structures and\ndiscuss their applications either as standalone systems or as part of more\nelaborated subsystems in microwave photonics, quantum information and machine\nlearning", "category": "physics_app-ph" }, { "text": "Quantum-mechanical effect in atomically thin MoS2 FET: Two-dimensional (2D) layered materials-based field-effect transistors (FETs)\nare promising for ultimate scaled electron device applications because of the\nimproved electrostatics to atomically thin body thickness. However, compared\nwith the typical thickness of ~5-nm for Si-on-insulator (SOI), the advantage of\nthe ultimate thickness limit of monolayer for the device performance has not\nbeen fully proved yet, especially for the on-state at the accumulation region.\nHere, we present much stronger quantum-mechanical effect at the accumulation\nregion based on the C-V analysis for top-gate MoS2 FETs. The self-consistent\ncalculation elucidated that the electrons are confined in the monolayer\nthickness, unlike in the triangle potential formed by the electric field for\nSOI, the gate-channel capacitance is ideally maximized to the gate insulator\ncapacitance since the capacitive contribution of the channel can be neglected\ndue to the negligible channel thickness. This quantum-mechanical effect agreed\nwell with the experimental results. Therefore, monolayer 2D channels are\nsuggested to be used to enhance the on-current as well as the gate modulation\nability.", "category": "physics_app-ph" }, { "text": "Spinel Cu-Mn-Cr Oxide Nanoparticle-Pigmented Solar Selective Coatings\n Maintaining >94% Efficiency at 750 degrees C: High-temperature concentrating solar power (CSP) system is capable of\nharvesting and storing solar energy as heat towards cost-effective dispatchable\nsolar electricity. Solar selective coating is a critical component to boost its\nefficiency by maximizing solar absorptance and minimizing thermal emittance\nlosses. However, maintaining a high solar-thermal conversion efficiency >90%\nfor long-term operation at >750 degrees C remains a significant challenge.\nHerein, we report spray-coated spinel Cu-Mn-Cr oxide nanoparticle-pigmented\nsolar selective coatings on Inconel tube sections maintaining >94% efficiency\nat 750 degrees C and >92.5% at 800 degrees C under 1000x solar concentration\nafter 60 simulated day-night thermal cycles in air, each cycle comprising 12h\nat 750 degrees C/800 degrees C and 12h cooling to 25 degrees C. The solar\nspectral selectivity is intrinsic to the band-to-band and d-d transitions of\nnon-stoichiometric spinel Cu-Mn-Cr oxide nanoparticles by balancing the lattice\nsite inversion of Cu2+ and Mn3+ on tetrahedral vs. octahedral sites. This\nfeature offers a large fabrication tolerance in nanoparticle volume fraction\nand coating thickness, facilitating low-cost and scalable spray-coated\nhigh-efficiency solar selective absorbers for high-temperature CSP systems.", "category": "physics_app-ph" }, { "text": "Mechanical transistors for logic-with-memory computing: As a potential revolutionary topic in future information processing,\nmechanical computing has gained tremendous attention for replacing or\nsupplementing conventional electronics vulnerable to power outages, security\nattacks, and harsh environments. Despite its potential for constructing\nintelligent matter towards nonclassical computing systems beyond the von\nNeumann architecture, most works on mechanical computing demonstrated that the\nad hoc design of simple logic gates cannot fully realize a universal mechanical\nprocessing framework involving interconnected arithmetic logic components and\nmemory. However, such a logic-with-memory computing architecture is critical\nfor complex and persistent state-dependent computations such as sequential\nlogic. Here we propose a mechanical transistor (M-Transistor), abstracting\nomnipresent temperatures as the input-output mechanical bits, which consists of\na metamaterial thermal channel as the gate terminal driving a nonlinear\nbistable soft actuator to selectively connect the output terminal to two other\nvariable thermal sources. This M-Transistor is an elementary unit to modularly\nform various combinational and sequential circuits, such as complex logic\ngates, registers (volatile memory), and long-term memories (non-volatile\nmemory) with much fewer units than the electronic counterparts. Moreover, they\ncan establish a universal processing core comprising an arithmetic circuit and\na register in a compact, reprogrammable network involving periodic read, write,\nmemory, and logic operations of the mechanical bits. Our work contributes to\nrealizing a non-electric universal mechanical computing architecture that\ncombines multidisciplinary engineering with structural mechanics, materials\nscience, thermal engineering, physical intelligence, and computational science.", "category": "physics_app-ph" }, { "text": "Yttrium Tantalum Oxynitride Multiphases as Photoanodes for Water\n Oxidation: Perovskite yttrium tantalum oxynitride is theoretically proposed as a\npromising semiconductor for solar water splitting because of the predicted\nbandgap and energy positions of band edges. In experiment, however, we show\nhere that depending on processing parameters, yttrium tantalum oxynitrides\nexist in multiphases, including the desired perovskite YTaON2, defect fluorite\nYTa(O,N,o)4, and N-doped YTaO4. These multiphases have bandgaps ranging between\n2.13 and 2.31 eV, all responsive to visible light. The N-doped YTaO4,\nperovskite main phase, and fluorite main phase derived from crystalline\nfergusonite oxide precursors exhibit interesting photoelectrochemical\nperformances for water oxidation, while the defect fluorite derived from low\ncrystallized scheelite-type oxide precursors show negligible activity.\nPreliminarily measurements show that loading IrOx cocatalyst on N-doped YTaO4\nsignificantly improves its photoelectrochemical performance encouraging further\nstudies to optimize this new material for solar fuel production.", "category": "physics_app-ph" }, { "text": "Flexibility of Ga-containing Type-II superlattice for long-wavelength\n infrared detection: In this paper, the flexibility of long-wavelength Type-II InAs/GaSb\nsuperlattice (Ga-containing SL) is explored and investigated from the growth to\nthe device performance. First, several samples with different SL period\ncomposition and thickness are grown by molecular beam epitaxy. Nearly\nstrain-compensated SLs on GaSb exhibiting an energy band gap between 105 to 169\nmeV at 77K are obtained. Second, from electronic band structure calculation,\nmaterial parameters are extracted and compared for the different grown SLs.\nFinally, two p-i-n device structures with different SL periods are grown and\ntheir electrical performance compared. Our investigation shows that an\nalternative SL design could potentially be used to improve the device\nperformance of diffusion-limited devices for long-wavelength infrared\ndetection.", "category": "physics_app-ph" }, { "text": "Direct Visualization of Perm-Selective Ion Transportation: Perm-selective ion transportation in a nanoscale structure has been\nextensively studied with aids of nanofabrication technology for a decade. While\ntheoretical and experimental advances pushed the phenomenon to seminal\ninnovative applications, its basic observation has relied only on an indirect\nanalysis such as current-voltage relation or fluorescent imaging adjacent to\nthe nanostructures. Here we experimentally, for the first time, demonstrated a\ndirect visualization of perm-selective ion transportation through the\nnanostructures using an ionic plasma generation. A micro/nanofluidic device was\nemployed for a micro bubble formation, plasma negation and penetration of the\nplasma through the nanojunction. The direct observation provided a keen\nevidence of perm-selectivity, i.e. allowing cationic species and rejecting\nanionic species. Furthermore, we can capture the plasma of Li+, which has lower\nmobility than Na+ in aqueous state, passed the nanojunction faster than Na+ due\nto the absence of hydrated shells around Li+. This simple, but essential\nvisualization technique would be effective means not only for advancing the\nfundamental nanoscale electrokinetic study but also for providing the insight\nof new innovative engineering applications.", "category": "physics_app-ph" }, { "text": "Photonic nanobeam cavities with nano-pockets for efficient integration\n of fluorescent nanoparticles: Integrating fluorescent nanoparticles with high-Q, small mode volume cavities\nis indispensable for nanophotonics and quantum technologies. To date,\nnanoparticles have largely been coupled to evanescent fields of cavity modes,\nwhich limits the strength of the interaction. Here, we developed both a cavity\ndesign and a fabrication method that enable efficient coupling between a\nfluorescent nanoparticle and a cavity optical mode. The design consists of a\nfishbone-shaped, one-dimensional photonic crystal cavity with a nano-pocket\nlocated at the electric field maximum of the fundamental optical mode.\nFurthermore, the presence of a nanoparticle inside the pocket reduces the mode\nvolume substantially and induces subwavelength light confinement. Our approach\nopens exciting pathways to achieve strong light confinement around fluorescent\nnanoparticles for applications in energy, sensing, lasing and quantum\ntechnologies.", "category": "physics_app-ph" }, { "text": "Nano-second exciton-polariton lasing in organic microcavities: Organic semiconductors are a promising platform for ambient polaritonics.\nSeveral applications, such as polariton routers, and many-body condensed matter\nphenomena are currently hindered due to the ultra-short polariton lifetimes in\norganics. Here, we employ a single-shot dispersion imaging technique, using 4\nnanosecond long non-resonant excitation pulses, to study polariton lasing in a\n$\\lambda/2$ planar organic microcavity filled with BODIPY-Br dye molecules. At\na power threshold density of $1.5 MW/cm^{2}$, we observe the transition to a\nquasi-steady state, 1.2 ns long-lived, single-mode polariton lasing and the\nconcomitant superlinear increase of photoluminescence, spectral line-narrowing,\nand energy blueshift", "category": "physics_app-ph" }, { "text": "Silicon-Organic Hybrid (SOH) Mach-Zehnder Modulators for 100 GBd PAM4\n Signaling With Sub-1 dB Phase-Shifter Loss: We report on compact and efficient silicon-organic hybrid (SOH) Mach-Zehnder\nmodulators (MZM) with low phase shifter insertion loss of 0.7 dB. The 280\n$\\mu$m-long phase shifters feature a $\\pi$-voltage-length product of 0.41 Vmm\nand a loss-efficiency product as small as $aU_{\\pi}L = 1.0\\space\\rm{VdB}$. The\ndevice performance is demonstrated in a data transmission experiment, where we\ngenerate on-off-keying (OOK) and four-level pulse-amplitude modulation (PAM4)\nsignals at symbol rates of 100 GBd, resulting in line rates of up to 200\nGbit/s. Bit error ratios are below the threshold for hard-decision forward\nerror correction (HD-FEC) with 7 % coding overhead, leading to net data rates\nof 187 Gbit/s. This is the highest PAM4 data rate ever achieved for a sub-1 mm\nsilicon photonic MZM.", "category": "physics_app-ph" }, { "text": "Ultraviolet radiation impact on the efficiency of commercial crystalline\n silicon-based photovoltaics: A theoretical thermal-electrical study in\n realistic device architectures: We investigate and evaluate the contribution of the ultraviolet radiation\nspectrum on the temperature and efficiency of commercial crystalline\nsilicon-based photovoltaics (PVs) that operate outdoors. The investigation is\nperformed by employing a comprehensive thermal-electrical modeling approach\nwhich takes into account all the major processes affected by the temperature\nvariation in the photovoltaic devices. We show that effectively reflecting the\nultraviolet radiation (i.e. up to a certain wavelength) results in a reduction\nof the overall operation temperature and enhancement of the PV cell's\nefficiency. In addition, blocking the high energy ultraviolet photons prolongs\nthe life time of the PV and its performance on the long term.", "category": "physics_app-ph" }, { "text": "Hydrogel Leclanche Cell: Construction and Characterization: A liquid-to-gel based Leclanch\\'e cell has been designed, constructed, and\ncharacterized for use in implantable medical devices and other applications\nwhere battery access is limited. This well-established chemistry will provide\nreliable electrochemical potential over a wide range of applications and the\nnovel construction provides a solution for the re-charging of electrodes in\nhard to access areas such as an internal pacemaker. The traditional Leclanch\\'e\ncell comprised of zinc (anode) and manganese dioxide (cathode), conductive\ncarbon powder (acetylene black or graphite), and aqueous electrolyte hydrogel\n(NH4Cl and ZnCl2) has been suspended in an agar hydrogel to simplify\nconstruction while maintaining electrochemical performance. Agar hydrogel,\nsaturated with electrolyte, serves as the cell support and separator allowing\nfor the discharged battery suspension to be easily replaced once exhausted.", "category": "physics_app-ph" }, { "text": "U-Slot Patch Principle and Design Methodology Using Characteristic Mode\n Analysis and Coupled Mode Theory: Patch antennas incorporating a U-shaped slot are well-known to have\nrelatively large (about 30%) impedance bandwidths. This work uses\nCharacteristic Mode Analysis to explain the impedance behavior of a classic\nU-slot patch geometry in terms of Coupled Mode Theory and shows the relevant\nmodes are in-phase and anti-phase coupled modes whose resonant frequencies are\ngoverned by Coupled Mode Theory. Additional analysis shows that one uncoupled\nresonator is the conventional TM01 patch mode and the other is a lumped LC\nresonator involving the slot and the probe. An equivalent circuit model for the\nantenna is given wherein element values are extracted from Characteristic Mode\nAnalysis data and which explicitly demonstrates coupling between these two\nresonators. The circuit model approximately reproduces the impedance locus of\nthe driven simulation. A design methodology based on Coupled Mode Theory and\nguided by Characteristic Mode Analysis is presented that allows wideband U-slot\npatch geometries to be designed quickly and efficiently. The methodology is\nillustrated through example.", "category": "physics_app-ph" }, { "text": "Angle-independent optimal adhesion in plane peeling of thin elastic\n films at large surface roughnesses: Adhesive peeling of a thin elastic film from a substrate is a classic problem\nin mechanics. However, many of the investigations on this topic to date have\nfocused on peeling from substrates with flat surfaces. In this paper, we study\nthe problem of peeling an elastic thin film from a rigid substrate that has\nperiodic surface undulations. We allow for contact between the detached part of\nthe film with the substrate. We give analytical results for computing the\nequilibrium force given the true peeling angle, which is the angle at which the\ndetached part of the film leaves the substrate. When there is no contact we\npresent explicit results for computing the true peeling angle from the\nsubstrate's profile and for determining an equilibrium state's stability solely\nfrom the substrate's surface curvature. The general results that we derive for\nthe case involving contact allow us to explore the regime of peeling at large\nsurface roughnesses. Our analysis of this regime reveals that the peel-off\nforce can be made to become independent of the peeling direction by roughening\nthe surface. This result is in stark contrast to results from peeling on flat\nsurfaces, where the peel-off force strongly depends on the peeling direction.\nOur analysis also reveals that in the large roughness regime the peel-off force\nachieves its theoretical upper bound, irrespective of the other particulars of\nthe substrate's surface profile.", "category": "physics_app-ph" }, { "text": "Au-decorated black TiO$_2$ produced via laser ablation in liquid: Rational combination of plasmonic and all-dielectric concepts within unique\nhybrid nanomaterials provides promising route toward devices with ultimate\nperformance and extended modalities. However, spectral matching of plasmonic\nand Mie-type resonances for such nanostructures can only be achieved for their\ndissimilar characteristic sizes, thus making the resulting hybrid nanostructure\ngeometry complex for practical realization and large-scale replication. Here,\nwe produced unique amorphous TiO$_2$ nanospheres simultaneously decorated and\ndoped with Au nanoclusters via single-step nanosecond-laser ablation of\ncommercially available TiO$_2$ nanopowders dispersed in aqueous HAuCl$_4$. The\nfabricated hybrids demonstrate remarkable light-absorbing properties (averaged\nvalue $\\approx$ 96%) in the visible and near-IR spectral range mediated by\nbandgap reduction of the laser-processed amorphous TiO$_2$, as well as plasmon\nresonances of the decorating Au nanoclusters, which was confirmed by combining\noptical spectroscopy, advanced electron energy loss spectroscopy, transmission\nelectron microscopy and electromagnetic modeling. Excellent light-absorbing and\nplasmonic properties of the produced hybrids were implemented to demonstrate\ncatalytically passive SERS biosensor for identification of analytes at trace\nconcentrations and solar steam generator that permitted to increase water\nevaporation rate by 2.5 times compared with that of pure water under identical\none-sun irradiation conditions.", "category": "physics_app-ph" }, { "text": "Interface controlled thermal properties of ultra-thin chalcogenide-based\n phase change memory devices: Phase change memory (PCM) is a rapidly growing technology that not only\noffers advancements in storage-class memories but also enables in-memory data\nstorage and processing towards overcoming the von Neumann bottleneck. In PCMs,\nthe primary mechanism for data storage is thermal excitation. However, there is\na limited body of research regarding the thermal properties of PCMs at length\nscales close to the memory cell dimension and, thus, the impact of interfaces\non PCM operation is unknown. Our work presents a new paradigm to manage thermal\ntransport in memory cells by manipulating the interfacial thermal resistance\nbetween the phase change unit and the electrodes without incorporating\nadditional insulating layers. Experimental measurements show a substantial\nchange in thermal boundary resistance as GST transitions from one\ncrystallographic structure (cubic) to another (hexagonal) and as the thickness\nof tungsten contacts is reduced from five to two nanometers. Simulations reveal\nthat interfacial resistance between the phase change unit and its adjacent\nlayer can reduce the reset current for 20 and 120 nm diameter devices by up to\n~40% and ~50%, respectively. The resultant phase-dependent and geometric\neffects on thermal boundary resistance dictate that the effective thermal\nconductivity of the phase change unit can be reduced by a factor of four,\npresenting a new opportunity to reduce operating currents in PCMs.", "category": "physics_app-ph" }, { "text": "Modeling based screening for optimal carrier selective material for Si\n based solar cells: Carrier selective (CS) silicon solar cells are increasingly explored using a\nvariety of different materials. However, the optimum properties of such CS\nmaterials are not well understood. In this context, through detailed analytical\nand numerical modeling, here we provide several interesting insights on the\nefficiency tradeoff with CS material properties. First, we show that perfect\nband alignment is a desirable feature only if the interface is devoid of any\ntrap states. Otherwise, a band offset of around 0.2eV-0.4eV provides sufficient\nband bending to reduce the effect of interface recombination, thus improving\nthe performance. Surprisingly, the interface passivation quality for the\nminority carrier extraction layer is found to be far less demanding than that\nfor the majority carrier extraction layer. Additionally, doping density and\ndielectric constant of CS layers have a similar effect as band offset on solar\ncell performance. Our results have obvious implications toward the selection of\nappropriate materials as carrier selective layers and hence are of broad\ninterest to the community.", "category": "physics_app-ph" }, { "text": "Single step synthesis of size-controlled carbon quantum dots using\n electrochemical etching of graphite: Carbon Quantum dots (CQD's) are nanoscale sp2 hybridized carbon particles. In\nthis work, we present a simple one-step synthesis of CQDs from the\nelectrochemical shredding method and technique to control its size during its\ngrowth process. A graphite rod extracted from commercially available pencil\nbatteries was used as electrode: source of carbon. CQDs of varying sizes were\nsynthesized through controlled current to the solution for etching and Sodium\ndodecyl sulfate (SDS) as capping agent during growth. CQD's of controlled sizes\nas formed can be used as fluorescent marker for bio-imaging and sensing\nplatform for wide range of applications.", "category": "physics_app-ph" }, { "text": "Acoustic imaging by three-dimensional acoustic Luneburg meta-lens with\n lattice columns: A three-dimensional acoustic Luneburg meta-lens has the advantage of\nrefracting sound waves for all incident angles and focusing higher sound\npressure compared to a two-dimensional lens. The lens made of plastic with a\ndiameter of 120 mm was designed with thousands of lattice column-shaped\nmeta-atoms to maintain its three-dimensional shape. The lens's\nthree-dimensional focusing performance and acoustic imaging were simulated and\nmeasured at the frequency range of 5 kHz ~ 20 kHz. The omnidirectional property\nwas confirmed by rotating the lens to change the incident angle and measuring\nthe sound pressure. The development of these spherical Luneburg meta-lenses is\nexpected to improve the performance of devices that require acoustic focusing.", "category": "physics_app-ph" }, { "text": "A Multi-frequency Magnetic Particle Spectroscopy System for the\n Characterization of Magnetic Nanoparticles: Magnetic particle spectroscopy (MPS) is one of the most versatile methods to\ncharacterize the magnetic properties of magnetic nanoparticles (MNPs). The\nexcitation magnetic field is one of the most crucial factors that affects the\nMPS signal of the MNPs. In this study, a multi-frequency MPS system is\ndeveloped to investigate the MPS signal of MNPs in different ac magnetic\nfields. The MPS system consists of a multi-channel excitation module for the\ngeneration of different-frequency ac magnetic fields and a detection module for\nthe measurement of the magnetic response of the MNPs. The MPS system allows to\ngenerate ac magnetic fields with a frequency up to 32.6 kHz and amplitude up to\n25 mT. The MPS signals of the MNPs in different ac magnetic fields are measured\nto systematically evaluate the performance of the multi-frequency MPS system,\nincluding the MNP spectra and its dynamic magnetization curve. In addition, the\nsignal-to-noise ratio (SNR) of the MPS system is quantitively assessed with\nmeasured MPS signals of a given MNP sample and DI water. Furthermore, a series\nof MNP samples with different iron concentrations are prepared and measured to\nevaluate the limit-of-detection (LOD) in terms of iron concentration. The\ninfluence of the excitation magnetic field, including frequency and amplitude,\nis discussed based on the SNRs of the measured harmonics. Experimental results\nshow that the LOD is 2.3 ng in terms of iron.", "category": "physics_app-ph" }, { "text": "The solution to an unresolved problem: newly synthesised nanocollagen\n for the preservation of leather: A widespread problem in libraries is related to the preservation of book\ncovers in leather that are often torn, powdery and abraded. The same problem is\nencountered in the conservation of leather goods. Until now a satisfactory\nsolution to contrast the leather deterioration had not been found and the\napplied conservation methods offered only temporary solutions, without\nguaranteeing a real and durable effectiveness. At the Istituto centrale\nrestauro e conservazione patrimonio archivistico e librario (Icrcpal) it was\ndecided to research more durable results and to apply nanocollagen solutions to\nthe leather. A new synthesis of nanocollagen was performed in collaboration\nwith Tor Vergata University, and Fondazione INUIT and the newly synthesised\nnanocollagen was characterised by different spectroscopic and imaging\ntechniques, then applied to laboratory samples and, at the end of the research,\nit was used in the restoration of the leather cover of a 18th book. All the\nmeasurements performed on the tested leathers did not show any colour change\nafter nanocollagen application, an increase of all mechanical characteristics\nand, of paramount importance, an increase in the shrinkage temperature of the\nleather with a partial reconstitution of its lost elasticity and flexibility.", "category": "physics_app-ph" }, { "text": "Mechanical and liquid phase exfoliation of cylindrite: a natural van der\n Waals superlattice with intrinsic magnetic interactions: We report the isolation of thin flakes of cylindrite, a naturally occurring\nvan der Waals superlattice, by means of mechanical and liquid phase\nexfoliation. We find that this material is a heavily doped p-type semiconductor\nwith a narrow gap (<0.85 eV) with intrinsic magnetic interactions that are\npreserved even in the exfoliated nanosheets. Due to its environmental stability\nand high electrical conductivity, cylindrite can be an interesting alternative\nto the existing two-dimensional magnetic materials.", "category": "physics_app-ph" }, { "text": "Collision dominated, ballistic, and viscous regimes of terahertz\n plasmonic detection by graphene: The terahertz detection performance and operating regimes of graphene\nplasmonic field-effect transistors (FETs) were investigated by a hydrodynamic\nmodel. Continuous wave detection simulations showed that the graphene response\nsensitivity is similar to that of other materials including Si, InGaAs, GaN,\nand diamond-based FETs. However, the pulse detection results indicated a very\nshort response time, which favors the rapid/high-sensitively detection. The\nanalysis on the mobility dependence of the response time revealed the same\ndetection regimes as the traditional semiconductor materials, i.e. the\nnon-resonant (collision dominated) regime, the resonant ballistic regime, and\nthe viscous regime. When the kinematic viscosity ({\\nu}) is above a certain\ncritical viscosity value, {\\nu}NR, the plasmonic FETs always operates in the\nviscous non-resonant regime regardless of channel length (L). In this regime,\nthe response time rises monotonically with the increase of L. When {\\nu} <\n{\\nu}NR, the plasmonic resonance can be reached in a certain range of L (i.e.\nthe resonant window). Within this window, the carrier transport is ballistic.\nFor a sufficiently short channel, the graphene devices would always operate in\nthe non-resonant regime regardless of the field-effect mobility, corresponding\nto another viscous regime. The above work mapped the operating regimes of\ngraphene plasmonic FETs, and demonstrated the significance of the viscous\neffects for the graphene plasmonic detection. These results could be used for\nthe extraction of the temperature dependences of viscosity in graphene.", "category": "physics_app-ph" }, { "text": "Bioinspired Nanocomposites: 2D Materials Within a 3D Lattice: Advanced composites are used in a variety of industrial applications and\ntherefore attract much scientific interest. Here we describe the formation of\nnovel carbon-based nanocomposites via incorporation of graphene oxide into the\ncrystal lattice of single crystals of calcite. Incorporation of a 2D organic\nmaterial into single-crystal lattices has never before been reported. To\ncharacterize the resulting nanocomposites we employed high-resolution\nsynchrotron powder X-ray diffraction, electron microscopy, transmission\nelectron microscopy, fluorescence microscopy, and nanoindentation tests.\nDetailed analysis revealed a layered distribution of graphene oxide sheets\nincorporated within the calcite host. Moreover, the optical and mechanical\nproperties of the calcite host were altered when a carbon-based nanomaterial\nwas introduced into its lattice. Compared to pure calcite, the composite\nGO-calcite crystals exhibited lower elastic modulus and higher hardness. The\nresults of this study show that the incorporation of a 2D material within a 3D\ncrystal lattice is not only feasible but also can lead to the formation of\nhybrid crystals exhibiting new properties.", "category": "physics_app-ph" }, { "text": "Behaviour Prediction of Closed-loop HTS coils in Non-Uniform AC fields: Field decay rate is the key characteristic of the superconducting magnets\nbased on closed-loop coils. However, in Maglev trains or rotating machines,\nclosed-loop magnets work in external AC fields and will exhibit an evidently\naccelerated field decay resulting from dynamic resistances, which are usually\nmuch larger than joint resistance. Nevertheless, there has not been a numerical\nmodel capable of systematically studying this behaviour, which is the main\ntopic of this work. The field decay curves of a closed-loop\nhigh-temperature-superconducting (HTS) coil in various AC fields are simulated\nbased on H-formulation. A non-uniform external field generated by armature\ncoils is considered. Reasonable consistence is found between experimental and\nsimulation results. In our numerical model, the impact of current relaxation,\nwhich is a historical challenge, is analysed and subsequently eliminated with\nacceptable precision. Our simulation results suggest that most proportion of\nthe field decay rate is from the innermost and outermost turns. Based on this\nobservation, a magnetic shielding pattern is designed to reduce the field decay\nrate efficiently. This work has provided magnet designers an effective method\nto predict the field decay rate of closed-loop HTS coils in external AC fields,\nand explore various shielding designs.", "category": "physics_app-ph" }, { "text": "Porosity properties of porous ceramic substrates added with zinc and\n magnesium material: Ceramic based materials covered with a mixture of mullite and zircon on the\ntop, strengthened by the addition of zinc and magnesium compounds at different\nrates (37 % and 50 %) and made by a co-precipitation method are studied. The\nthermally treated and shaped materials prepared in the shape of cylindrical\nsamples were modified to obtain different porosities. The addition of zinc to\nthe ceramic based material leads to a significant increase and control of the\ndensity of porosity compared to the addition of magnesium. The porosity of all\nthe materials was characterized. The permeability characteristics and the\nability for all the pellets to absorb water until the saturation were also\nstudied as a function of the porosity.", "category": "physics_app-ph" }, { "text": "Sodium-Ion-Conducting Polymer Nanocomposite Electrolyte of TiO2/PEO/PAN\n Complexed with NaPF6: A free standing transparent film of solid state polymer electrolyte based on\nPEO/PAN + NaPF6 with different compositions of nano sized TiO2 in weight\npercent (x = 0, 1, 2, 5, 10, 15, 20 ) is synthesized by using standard solution\ncast technique. The homogeneous surface of above polymer composition is\nexamined by FESEM. The microscopic interaction among polymer, salt and\nnanoceramic filler has been analyzed by Fourier Transformed Infra-Red (FTIR)\nspectroscopy. The reduction of ion pair formation in polymeric separator is\nclearly observed on addition of nanofiller in the polymer salt complex film.\nElectrical conductivity has been recorded of the prepared polymeric separator\nwhich is of the order of ~10-3 Scm-1 after addition of nanofiller (15% wt/wt)\nwhich support the FTIR results. Electrochemical potential window has been\nobserved of the order of ~6V by the cyclic voltammetry results. The observed\ndata of the prepared separator are at par with the desirable value for device\napplications.", "category": "physics_app-ph" }, { "text": "Plasmonic elastic capsules as colorimetric reversible pH-microsensors: There is a crucial need for effective and easily dispersible colloidal\nmicrosensors able to detect local pH changes before irreversible damages caused\nby demineralization, corrosion, or biofilms occur. One class of such\nmicrosensors is based on molecular dyes encapsulated or dispersed either in\npolymer matrices or in liquid systems exhibiting different colors upon pH\nvariations. They are efficient but often rely on sophisticated and costly\nsyntheses, and present significant risks of leakage and photobleaching damages,\nwhich is detrimental for mainstream applications. Another approach consists in\nexploiting the distance-dependent plasmonic properties of metallic\nnanoparticles. Still, assembling nanoparticles into dispersible colloidal\npH-sensitive sensors remains a challenge. Here, we show how to combine\noptically active plasmonic gold nanoparticles and pH-responsive thin shells\ninto \"plasmocapsules\". Upon pH change, plasmocapsules swell or shrink.\nConcomitantly, the distance between the gold nanoparticles embedded in the\npolymeric matrix varies, resulting in an unambiguous color change. Billions of\nmicron-size sensors can thus be easily fabricated. They are non-intrusive,\nreusable, and sense local pH changes. Each plasmocapsule is an independent\nreversible microsensor over a large pH range. Finally, we demonstrate their\npotential use for the detection of bacterial growth, thus proving that\nplasmocapsules are a new class of sensing materials.", "category": "physics_app-ph" }, { "text": "Diverse regimes of mode intensity correlation in nanofiber random lasers\n through nanoparticle doping: Random lasers are based on disordered materials with optical gain. These\ndevices can exhibit either intensity or resonant feedback, relying on diffusive\nor interference behaviour of light, respectively, which leads to either\ncoupling or independent operation of lasing modes. We study for the first time\nthese regimes in complex, solid-state nanostructured materials. The number of\nlasing modes and their intensity correlation features are found to be\ntailorable in random lasers made of light-emitting, electrospun polymer fibers\nupon nanoparticle doping. By material engineering, directional waveguiding\nalong the length of fibers is found to be relevant to enhance mode correlation\nin both intensity feedback and resonant feedback random lasing. The here\nreported findings can be used to establish new design rules for tuning the\nemission of nano-lasers and correlation properties by means of the\ncompositional and morphological properties of complex nanostructured materials.", "category": "physics_app-ph" }, { "text": "High Thermoelectric Performance of Au@Sb2Te3 Heterostructure Derived\n from the Potential Barriers: The correlated couple of electrical and thermal property is the challenge to\nrealize a substantial leap in thermoelectric materials.Synthesis of\nsemiconductor and metal composites is a significant and versatile design\nstrategy to optimize the thermoelectric performance driven by tailored\ninterface between nanoinclusions and matrix.In this study, we present the\nsimultaneous increase of electrical conductivity and Seebeck coefficient, and\nreduction of thermal conductivity in Sb2Te3-Au system.The enhanced electrical\nconductivity lies in the incorporated Au nanostructures contributing to\ninjecting carriers to Sb2Te3 matrix.The appropriate barriers originated from\nthe Au-Sb2Te3 interface, which filter low energy carriers, results in\nenhancement of Seebeck coefficient.The increased boundaries and nanodomains\nblock the transport of phonons, subsequently reducing the thermal\nconductivity.As a consequence, combination of these effects promote double of\nZT value in 1% Au@ Sb2Te3 composites with respect to the pristine Sb2Te3.", "category": "physics_app-ph" }, { "text": "Microwave-free vector magnetometry with nitrogen-vacancy centers along a\n single axis in diamond: Sensing vector magnetic fields is critical to many applications in\nfundamental physics, bioimaging, and material science. Magnetic-field sensors\nexploiting nitrogen-vacancy (NV) centers are particularly compelling as they\noffer high sensitivity and spatial resolution even at nanoscale. Achieving\nvector magnetometry has, however, often required applying microwaves\nsequentially or simultaneously, limiting the sensors' applications under\ncryogenic temperature. Here we propose and demonstrate a microwave-free vector\nmagnetometer that simultaneously measures all Cartesian components of a\nmagnetic field using NV ensembles in diamond. In particular, the present\nmagnetometer leverages the level anticrossing in the triplet ground state at\n102.4 mT, allowing the measurement of both longitudinal and transverse fields\nwith a wide bandwidth from zero to megahertz range. Full vector sensing\ncapability is proffered by modulating fields along the preferential NV axis and\nin the transverse plane and subsequent demodulation of the signal. This sensor\nexhibits a root mean square noise floor of about 300 pT/Hz^(1/2) in all\ndirections. The present technique is broadly applicable to both ensemble\nsensors and potentially also single-NV sensors, extending the vector capability\nto nanoscale measurement under ambient temperatures.", "category": "physics_app-ph" }, { "text": "Defect Physics of Pseudo-cubic Mixed Halide Lead Perovskites from First\n Principles: Owing to the increasing popularity of lead-based hybrid perovskites for\nphotovoltaic (PV) applications, it is crucial to understand their defect\nphysics and its influence on their optoelectronic properties. In this work, we\nsimulate various point defects in pseudo-cubic structures of mixed\niodide-bromide and bromide-chloride methylammonium lead perovskites with the\ngeneral formula MAPbI_{3-y}Br_{y} or MAPbBr_{3-y}Cl_{y} (where y is between 0\nand 3), and use first principles based density functional theory computations\nto study their relative formation energies and charge transition levels. We\nidentify vacancy defects and Pb on MA anti-site defect as the lowest energy\nnative defects in each perovskite. We observe that while the low energy defects\nin all MAPbI_{3-y}Br_{y} systems only create shallow transition levels, the Br\nor Cl vacancy defects in the Cl-containing pervoskites have low energy and form\ndeep levels which become deeper for higher Cl content. Further, we study\nextrinsic substitution by different elements at the Pb site in MAPbBr_{3},\nMAPbCl_{3} and the 50-50 mixed halide perovskite, MAPbBr_{1.5}Cl_{1.5}, and\nidentify some transition metals that create lower energy defects than the\ndominant intrinsic defects and also create mid-gap charge transition levels.", "category": "physics_app-ph" }, { "text": "Experimental realization of negative refraction and subwavelength\n imaging for flexural waves in phononic crystal plates: In this paper, we numerically and experimentally demonstrate negative\nrefraction of flexural waves in phononic crystal(PC) plates which is employed\nfor designing flat elastic lenses. We propose a thickness contrast-based plate\ndesign to achieve refractive index equal to -1 at the interface of the PC and\nhost plate. The thickness contrast between the PC and host plate enables\nmatching their wave numbers in the all angle negative refraction (AANR)\nfrequency regime. The PC-lens design is then numerically and experimentally\nverified to achieve the image of an omnidirectional subwavelength excitation\nsource. By changing the thickness contrast between the plate and PC, the\nPC-lens can be tuned for wave focusing and subwavelength imaging at a desired\nfrequency.", "category": "physics_app-ph" }, { "text": "Biaxial versus uniaxial strain tuning of single-layer MoS$_2$: Strain engineering has arisen as a powerful technique to tune the electronic\nand optical properties of two-dimensional semiconductors like molybdenum\ndisulfide (MoS2). Although several theoretical works predicted that biaxial\nstrain would be more effective than uniaxial strain to tune the band structure\nof MoS2, a direct experimental verification is still missing in the literature.\nHere we implemented a simple experimental setup that allows to apply biaxial\nstrain through the bending of a cruciform polymer substrate. We used the setup\nto study the effect of biaxial strain on the differential reflectance spectra\nof 12 single-layer MoS2 flakes finding a redshift of the excitonic features at\na rate between -40 meV/% and -110 meV/% of biaxial tension. We also directly\ncompare the effect of biaxial and uniaxial strain on the same single-layer MoS2\nfinding that the biaxial strain gauge factor is 2.3 times larger than the\nuniaxial strain one.", "category": "physics_app-ph" }, { "text": "Properties of Al2O3 thin films deposited on 4H-SiC by reactive ion\n sputtering: In this work, the electrical properties of Al2O3 films deposited by reactive\nion sputtering were investigated by means of morphological, chemical and\nelectrical characterizations. This insulating layer suffers of an electron\ntrapping that is mitigated after the rapid thermal annealing (RTA). The RTA\nimproved also the permittivity (up to 6{\\epsilon}0), although the negative\nfixed charge remains in the order of 1012cm-2. However, the temperature\ndependent electrical investigation of the MOS capacitors demonstrates that the\nroom temperature Fowler-Nordheim electron barrier height of 2.37 eV lies\nbetween the values expected for SiO2/4H-SiC and Al2O3/4H-SiC systems.", "category": "physics_app-ph" }, { "text": "Time of Flight Modulation of Intensity by Zero Effort on Larmor: A time of flight Modulation of IntEnsity by Zero Effort (MIEZE) spectrometer\nmode has been developed for the Larmor instrument at the ISIS pulsed neutron\nsource. The instrument utilizes resonant neutron spin flippers which employ\nelectromagnets with pole shoes, allowing the flippers to operate at frequencies\nof up to 3 MHz. Tests were conducted at modulation frequencies of 103 kHz, 413\nkHz, 826 kHz and 1.03 MHz, resulting in a Fourier time range of ~0.1 ns to 30\nns using wavelength band of 4 {\\AA}-11 {\\AA}.", "category": "physics_app-ph" }, { "text": "Generalized many-body approach for near-field radiative heat transfer\n between nonspherical particles: A generalized fluctuational electrodynamics-based many-body approach for\ncalculating near-field radiative heat transfer (NFRHT) between nonspherical\ndipoles is proposed. The geometric parameters of nonspherical dipoles are\nimplemented in the definition of the self-term of the free-space Green's\nfunction and, conversely to previous many-body models of NFRHT, dipole\npolarizability is defined a posteriori from the free-space Green's function\nsolution such that polarizability calculation is an optional post-processing\nstep rather than a required input. Both strong and weak forms of the\ngeneralized many-body approach are presented. It is shown that the approximate\nweak form is less computationally expensive but is only applicable to small\nparticles characterized by size parameters less than ~0.24. The generalized\nmany-body method is compared against an analytical solution for NFRHT between\ntwo spheroidal dipoles. Acceptable agreement is obtained, and the discrepancies\nare ascribed to differences in approximations for multiple reflections and from\nthe way in which particle orientation is implemented in each method. The\ngeneralized many-body method is then applied to analyze the near-field spectral\nconductance between two SiC ellipsoidal dipoles. Results reveal that changes in\nthe orientation of one of the ellipsoidal dipoles lead to active tuning of\nlocalized surface phonon resonance by up to three orders of magnitude. Finally,\nthe spectral radiative thermal conductivity of a metamaterial composed of 1000\nSiO2 ellipsoidal particles is studied. The metamaterial displays anisotropic\nradiative thermal conductivity, with differences in the value at resonance up\nto 2.8 times between different directions. The generalized many-body model of\nNFRHT presented in this paper may be used to develop particle-based\nmetamaterials with novel, engineered radiative thermal properties.", "category": "physics_app-ph" }, { "text": "Time-dependence of SrVO$_3$ thermionic electron emission properties: Thermionic electron emission cathodes are critical components of various high\npower and high frequency vacuum electronic devices, electron microscopes,\ne-beam lithographic devices, and thermionic energy converters, which all demand\nan efficient and long-lasting low work function cathode. Single phase,\npolycrystalline perovskite oxide SrVO$_3$, with its intrinsic low effective\nwork function and facile synthesis process, is a promising cathode candidate,\nwhere previous works have shown evidence of an effective work function as low\nas 2.3 eV. However, assessment of the stability over time under conditions\nrelevant for operation and the related interplay of evolving surface chemistry\nwith emission performance are still missing, and necessary for understanding\nhow to best prepare, process and operate SrVO$_3$ cathodes. In this work, we\nstudy the vacuum activation process of SrVO$_3$ and find it has promising\nemission stability over 15 days of continuous high temperature operation. We\nfind that SrVO$_3$ shows surface Sr and O segregation during operation, which\nwe hypothesize is needed to create a positive surface dipole, leading to low\neffective work function. Emission repeatability from cyclic heating and cooling\nsuggests the promising stability of the low effective work function surface,\nand additional observations of drift-free emission during one hour of\ncontinuous emission testing at high temperature further demonstrates its\nexcellent performance stability.", "category": "physics_app-ph" }, { "text": "Near-Field Angular Scan Enhancement of Antenna Arrays Using Metasurfaces: In this publication we continue our previous work on extending the angular\nscan range of phased arrays using metasurfaces. We consider in detail scan\nenhancement using a single metasurface lens in the near-field of a source and\nprovide analytical expressions for source excitation to obtain a desired beam.\nWe show that such a device suffers from the same directivity degradation as in\nthe case of far-field lens placement. Moreover, we discuss in detail that this\napproach has limitations, and one cannot place the lens arbitrarily close to\nthe source array. We then propose a two-lens near-field scan enhancer which is\nnot subject to the same limitations, although still subject to the same\ndirectivity degradation. Finally we propose a binary metasurface concept which\ntheoretically achieves desired scan enhancement without directivity\ndegradation. Some theoretical claims are then verified via full-field\nsimulations.", "category": "physics_app-ph" }, { "text": "Pure and Linear Frequency Converter Temporal Metasurface: Metasurfaces are ultrathin structures which are constituted by an array of\nsubwavelength scatterers with designable scattering responses. They have opened\nup unprecedented exciting opportunities for extraordinary wave engineering\nprocesses. On the other hand, frequency converters have drawn wide attention\ndue to their vital applications in telecommunication systems, health care\ndevices, radio astronomy, military radars and biological sensing systems. Here,\nwe show that a spurious-free and linear frequency converter metasurface can be\nrealized by leveraging unique properties of engineered transmissive temporal\nsupercells. Such a metasurface is formed by time-modulated supercells;\nthemselves are composed of temporal and static patch resonators and phase\nshifters. This represents the first frequency converter metasurface possessing\nlarge frequency conversion ratio with controllable frequency bands and\ntransmission magnitude. In contrast to conventional nonlinear mixers, the\nproposed temporal frequency converter offers a linear response. In addition, by\ntaking advantage of the proposed surface-interconnector-phaser-surface (SIPS)\narchitecture, a spurious-free and linear frequency conversion is achievable,\nwhere all undesired mixing products are strongly suppressed. The proposed\nmetasurface may be digitally controlled and programmed through a field\nprogrammable gate array. This makes the spurious-free and linear frequency\nconverter metasurface a prominent solution for wireless and satellite\ntelecommunication systems, as well as invisibility cloaks and radars. This\nstudy opens a way to realize more complicated and enhanced-efficiency\nspectrum-changing metasurface.", "category": "physics_app-ph" }, { "text": "Travelling Wakefield Tube: THz Source Powered by Nonrelativistic\n Electron Beam: High peak power, tunable, narrowband terahertz emitters are becoming sought\nafter given their portability, efficiency, and ability to be deployed in the\nfield for industrial, medical, and military applications. The use of\naccelerator systems producing THz frequencies via Cherenkov radiation,\ngenerated by passing an electron beam through a slow-wave wakefield structure,\nis a promising method to meet future THz requirements. To date, efforts have\nbeen dedicated to analysis and design of sources utilizing laser seeded bunched\nelectron beam drivers with relativistic energies beyond 5 MeV. Presented here\nis a wakefield THz generation scheme based on passing a long quasi-dc\nnonrelativistic beam (200 keV) through a dielectric loaded travelling wave\nstructure. Reduced energy allows for compactness and portability of the\naccelerator as the size and weight of the dielectric slow wave structure is\nvanishingly small compared to the accelerator unit. The presented scheme can\nserve as a tunable high peak power THz source operated between 0.4-1.6 THz and\nproduces power gain by a factor of five with an average efficiency of 6.8\\%.", "category": "physics_app-ph" }, { "text": "Mastering processing-microstructure complexity through the prediction of\n thin film structure zone diagrams by generative machine learning models: Thin films are ubiquitous in modern technology and highly useful in materials\ndiscovery and design. For achieving optimal extrinsic properties their\nmicrostructure needs to be controlled in a multi-parameter space, which usually\nrequires a too-high number of experiments to map. We propose to master thin\nfilm processing microstructure complexity and to reduce the cost of\nmicrostructure design by joining combinatorial experimentation with generative\ndeep learning models to extract synthesis-composition-microstructure relations.\nA generative machine learning approach comprising a variational autoencoder and\na conditional generative adversarial network predicts structure zone diagrams.\nWe demonstrate that generative models provide a so far unseen level of quality\nof generated structure zone diagrams comprising chemical and processing\ncomplexity for the optimization of chemical composition and processing\nparameters to achieve a desired microstructure.", "category": "physics_app-ph" }, { "text": "Sizing and Dynamic modeling of a Power System for the MUN Explorer\n Autonomous Underwater Vehicle using a Fuel Cell and Batteries: The combination of a fuel cell and batteries has promising potential for\npowering autonomous vehicles. The MUN Explorer Autonomous Underwater Vehicle\n(AUV) is built to do mapping-type missions of seabeds as well as survey\nmissions. These missions require a great deal of power to reach underwater\ndepths (i.e. 3000 meters). The MUN Explorer uses 11 rechargeable Lithium-ion\n(Li-ion) batteries as the main power source with a total capacity of 14.6kWh to\n17.952kWh, and the vehicle can run for 10 hours. The draw-backs of operating\nthe existing power system of the MUN Explorer, which was done by the researcher\nat the Holyrood management facility, include mobilization costs, logistics and\ntransport, and facility access, all of which should be taken into\nconsideration. Recharging the batteries for at least 8 hours is also very\nchallenging and time consuming. To overcome these challenges and run the MUN\nExplorer for a long time, it is essential to integrate a fuel cell into an\nexisting power system (i.e. battery bank). The integration of the fuel cell not\nonly will increase the system power, but it will also reduce the number of\nbatteries needed as suggested by HOMER software. In this paper, an integrated\nfuel cell is designed to be added into the MUN Explorer AUV along with a\nbattery bank system to increase its power system. The system sizing is\nperformed using HOMER software. The results from HOMER software show that a 1kW\nfuel cell and 8 Li-ion batteries can increase the power system capacity to 68\nkWh. The dynamic model is then built in MATLAB/Simulink environment to provide\na better understanding of the system behavior.The 1kW fuel cell is connected to\na DC/DC Boost Converter to increase the output voltage from 24V to 48V as\nrequired by the battery and DC motor.", "category": "physics_app-ph" }, { "text": "Radiometric propulsion: Advancing with the order-of-magnitude\n enhancement through graphene aerogel-coated vanes: Radiometer is a light-induced aerodynamic propulsive device under the\nrarefied gas environment, which holds great potential for the next-gen\nnear-space flight. However, its practical applications are hindered by the weak\npropulsion forces on the conventional radiometer vanes. Herein, this\nmaterial-aerodynamics cross-disciplinary study develops novel radiometer vanes\nwith graphene aerogel coatings, which for the first time realize an order of\nmagnitude enhancement in radiometric propulsion. The improvement is manifested\nas up to 29.7 times faster rotation speed at a low pressure of 0.2 Pa, 13.8\ntimes faster at the pressure (1.5 Pa) with maximum speeds, and 4 orders of\nmagnitude broader operating pressure range (10E-4 - 10E2 Pa). Direct Simulation\nMonte Carlo calculations reveal that the outstanding performance is ascribed to\nthe improved temperature gradient and gas-solid momentum transfer efficiency\ntailored by surface porous microstructures. Moreover, we demonstrate a stable\nand long-term levitation prototype under both 1 sun irradiation and a rarefied\ngas environment.", "category": "physics_app-ph" }, { "text": "Solid Phase Recrystallization in Arsenic Ion-Implanted\n Silicon-On-Insulator by Microsecond UV Laser Annealing: UV laser annealing (UV-LA) enables surface-localized high-temperature thermal\nprocessing to form abrupt junctions in emerging monolithically stacked devices,\nwhere the applicable thermal budget is restricted. In this work, UV-LA is\nperformed to regrow a silicon-on-insulator wafer partially amorphized by\narsenic ion implantation as well as to activate the dopants. In a microsecond\nscale ( 10^-6 s to 10^-5 s) UV-LA process, monocrystalline solid phase\nrecrystallization and dopant activation without junction deepening are\nevidenced, thus opening various applications in low thermal budget integration\nflows. However, some concerns remain. First, the surface morphology is degraded\nafter the regrowth, possibly because of the non-perfect uniformity of the used\nlaser beam and/or the formation of defects near the surface involving the\nexcess dopants. Second, many of the dopants are inactive and seem to form deep\nlevels in the Si band gap, suggesting a further optimization of the ion\nimplantation condition to manage the initial crystal damage and the heating\nprofile to better accommodate the dopants into the substitutional sites.", "category": "physics_app-ph" }, { "text": "Non-volatile memory based on PZT/FeGa thin film memtranstor: The PZT/FeGa thin film memtranstor was prepared and the modulation of the\nmagnetoelectric coefficient by external magnetic and electric fields was\nstudied. The magnetoelectric coefficient of the PZT/FeGa memtranstor can be\nreversed by flipping the direction of magnetization of FeGa or ferroelectric\npolarization of PZT. Notably, the sign of the magnetoelectric coefficient can\nbe switched repeatedly by reversing ferroelectric polarization of PZT when the\nexternal magnetic field remains constant. Moreover, the binary switching\nbehavior can still be maintained under zero DC bias magnetic field. When the\npolarization direction remains stable, the magnetoelectric coefficient also\ndoes not change. This means that the magnetoelectric coefficient of PZT/FeGa is\nnon-volatile. Furthermore, the retention and endurance characteristics of the\nPZT/FeGa thin film memtranstor have been investigated. These findings\ndemonstrate the potential of the PZT/FeGa thin film memtranstor for\nnon-volatile memory applications.", "category": "physics_app-ph" }, { "text": "Quantifying Charge Carrier Mobilities and Recombination Rates in Metal\n Halide Perovskites from Time-Resolved Microwave Photo-conductivity\n Measurements: The unprecedented rise in power conversion efficiency of solar cells based on\nmetal halide perovskites (MHPs) has led to enormous research effort to\nunderstand their photo-physical properties. In this paper, we review the\nprogress in understanding the mobility and recombination of photo-generated\ncharge carriers from nanosecond to microsecond time scales, monitored using\nelectrodeless transient photoconductivity techniques. In addition, we present a\nkinetic model to obtain rate constants from transient data recorded using a\nwide range of laser intensities. For various MHPs the temperature dependence of\nthe mobilities and recombination rates are evaluated. Furthermore, we show how\nthese rate constants can be used to predict the upper limit for the\nopen-circuit voltage Voc of the corresponding device. Finally, we discuss\nphoto-physical properties of MHPs that are not yet fully understood, and make\nrecommendations for future research directions.", "category": "physics_app-ph" }, { "text": "Modeling a Grid-Connected PV/Battery Microgrid System with MPPT\n Controller: This paper focuses on performance analyzing and dynamic modeling of the\ncurrent grid-tied fixed array 6.84kW solar photovoltaic system located at\nFlorida Atlantic University (FAU). A battery energy storage system is designed\nand applied to improve the systems stability and reliability. An overview of\nthe entire system and its PV module are presented. In sequel, the corresponding\nI-V and P-V curves are obtained using MATLAB-Simulink package. Actual data was\ncollected and utilized for the modeling and simulation of the system. In\naddition, a grid- connected PV/Battery system with Maximum Power Point Tracking\n(MPPT) controller is modeled to analyze the system performance that has been\nevaluated under two different test conditions: (1) PV power production is\nhigher than the load demand (2) PV generated power is less than required load.\nA battery system has also been sized to provide smoothing services to this\narray. The simulation results show the effective of the proposed method. This\nsystem can be implemented in developing countries with similar weather\nconditions to Florida.", "category": "physics_app-ph" }, { "text": "Properties of Nanocrystalline Silicon Probed by Optomechanics: Nanocrystalline materials exhibit properties that can differ substantially\nfrom those of their single crystal counterparts. As such, they provide ways to\nenhance and optimise their functionality for devices and applications. Here we\nreport on the optical, mechanical and thermal properties of nanocrystalline\nsilicon probed by means of optomechanical nanobeams to extract information of\nthe dynamics of optical absorption, mechanical losses, heat generation and\ndissipation. The optomechanical nanobeams are fabricated using nanocrystalline\nfilms prepared by annealing amorphous silicon layers at different temperatures.\nThe resulting crystallite sizes and the stress in the films can be controlled\nby the annealing temperature and time and, consequently, the properties of the\nfilms can be tuned relatively freely, as demonstrated here by means of electron\nmicroscopy and Raman scattering. We show that the nanocrystallite size and the\nvolume fraction of the grain boundaries play a key role in the dissipation\nrates through non-linear optical and thermal processes. Promising optical\n(13000) and mechanical (1700) quality factors were found in the optomechanical\ncavity realised in the nanocrystalline Si resulting from annealing at 950 C.\nThe enhanced absorption and recombination rates via the intra-gap states and\nthe reduced thermal conductivity boost the potential to exploit these\nnon-linear effects in applications, including NEMS, phonon lasing and\nchaos-based devices.", "category": "physics_app-ph" }, { "text": "Fluidic Shaping of Optical Components: Current methods for fabricating lenses rely on mechanical processing of the\nlens or mold, such as grinding, machining, and polishing. The complexity of\nthese fabrication processes and the required specialized equipment prohibit\nrapid prototyping of optical components. This work presents a simple method,\nbased on free-energy minimization of liquid volumes, which allows to quickly\nshape curable liquids into a wide range of spherical and aspherical optical\ncomponents, without the need for any mechanical processing. After the desired\nshape is obtained, the liquid can be cured to produce a solid object with\nnanometric surface quality. We provide a theoretical model that accurately\npredicts the shape of the optical components, and demonstrate rapid fabrication\nof all types of spherical lenses (convex, concave, meniscus), cylindrical\nlenses, bifocal lenses, toroidal lenses, doublet lenses and aspheric lenses.\nThe method is inexpensive and can be implemented using a variety of curable\nliquids with different optical and mechanical properties. In addition, the\nmethod is scale-invariant and can be used to produce even very large optical\ncomponents, without a significant increase in fabrication time. We believe that\nthe ability to easily and rapidly create high-quality optics, without the need\nfor complex and expensive infrastructure, will provide researchers with new\naffordable tools for fabricating and testing optical designs.", "category": "physics_app-ph" }, { "text": "Flexibility-assisted heat removal in thin crystalline silicon solar\n cells: Thin crystalline silicon solar photovoltaics holds great potential for\nreducing the module price by material saving and increasing the efficiency by\nreduced bulk recombination loss. However, the module efficiency decreases\nrather sensitively as the module temperature rises under sunlight. Effective,\ninexpensive approach to cooling modules would accelerate large-scale market\nadoption of thin crystalline silicon photovoltaics. For effective cooling, we\nexploit high flexibility of single-crystalline thin silicon films to create\nwavy solar cells. These wavy cells possess larger surface area than\nconventional flat cells, while occupying the same projected area. We\nexperimentally demonstrate that the temperature of thin wavy crystalline\nsilicon solar cells under the sunlight can be significantly reduced by\nincreased convective cooling due to their large surface area. The substantial\nefficiency gain, achieved by the effective heat removal, points to\nhigh-performance thin crystalline silicon photovoltaic systems that are\nradically different in configuration from conventional systems.", "category": "physics_app-ph" }, { "text": "Two-tone spectroscopy of a SQUID metamaterial in the nonlinear regime: Compact microwave resonantors made of superconducting rings containing\nJosephson junctions (SQUIDs) are attractive candidates for building frequency\ntunable metamaterials with low losses and pronounced nonlinear properties. We\nexplore the nonlinearity of a SQUID metamaterial by performing a two-tone\nresonant spectroscopy. The small-amplitude response of the metamaterial under\nstrong driving by a microwave pump tone is investigated experimentally and\ntheoretically. The transmission coefficient $S_{21}$ of a weak probe signal is\nmeasured in the presence of the pump tone. Increasing the power of the pump, we\nobserve pronounced oscillations of the SQUID's resonance frequency\n$f_{\\textrm{res}}$. The shape of these oscillations varies significantly with\nthe frequency of the pump tone $f_{\\textrm{dr}}$. The response to the probe\nsignal displays instabilities and sidebands. A state with strong second\nharmonic generation is observed. We provide a theoretical analysis of these\nobservations, which is in good agreement with the experimental results.", "category": "physics_app-ph" }, { "text": "Optimization of quantum well number of AlGaN/AlGaN deep-ultraviolet\n light-emitting diodes: In this work, performance and characteristics of AlGaN/AlGaN deep-ultraviolet\nlight-emitting diodes (DUV LEDs) with varied number of quantum-well (QW) are\ninvestigated numerically. From our simulation, 1-QW structure give the best\nperformance at low injection current. However, at higher injection current,\n2-QWs structure give the largest power output due to its higher total radiative\nrecombination rate and internal quantum efficiency (IQE) compared to other\nstructures. The 2-QWs structure also has less serious efficiency droop at high\ncurrent than 1-QW, which makes it an optimum structure for high-power LEDs.", "category": "physics_app-ph" }, { "text": "Time resolution and dynamic range of field effect transistor based\n terahertz detectors: We studied time resolution and response power dependence of three terahertz\ndetectors based on significantly different types of field effect transistors.\nWe analyzed the photoresponse of custom-made Si junctionless FETs, Si MOSFETs\nand GaAs-based high electron mobility transistors detectors. Applying\nmonochromatic radiation of high power, pulsed, line-tunable molecular THz\nlaser, which operated at frequencies in the range from 0.6-3.3 THz, we\ndemonstrated that all these detectors have at least nanosecond response time.\nWe showed that detectors yield a linear response in a wide range of radiation\npower. At high powers the response saturates varying with radiation power P as\n$U = R_0 P/(1+P/P_s)$, where $R_0$ is the low power responsivity, $P_s$ is the\nsaturation power. We demonstrated that the linear part response decreases with\nradiation frequency increase as $R_0 \\propto f^{-3}$, whereas the power at\nwhich signal saturates increases as $P_s \\propto f^3$. We discussed the\nobserved dependences in the framework of the Dyakonov-Shur mechanism and\ndetector-antenna impedance matching. Our study showed that FET transistors can\nbe used as ultrafast room temperature detectors of THz radiation and that their\ndynamic range extends over many orders of magnitude of power of incoming THz\nradiation. Therefore, when embedded with current driven read out electronics\nthey are very well adopted for operation with high power pulsed sources.", "category": "physics_app-ph" }, { "text": "Gallium nitride phononic integrated circuits for future RF front-ends: Achieving monolithic integration of passive acoustic wave devices, in\nparticular RF filters, with active devices such as RF amplifiers and switches,\nis the optimal solution to meet the challenging communication requirements of\nmobile devices, especially as we move towards the 6G era. This requires a\nsignificant ($\\approx$100x) reduction in the size of the RF passives, from\nmm$^2$ footprints in current devices to tens of ${\\mu}m^2$ in future systems.\nApplying ideas from integrated photonics, we demonstrate that high frequency\n(>3 GHz) sound can be efficiently guided in ${\\mu}$m-scale gallium nitride(GaN)\nwaveguides by exploiting the strong velocity contrast available in the GaN on\nsilicon carbide (SiC) platform. Given the established use of GaN devices in RF\namplifiers, our work opens up the possibility of building monolithically\nintegrated RF front-ends in GaN-on-SiC.", "category": "physics_app-ph" }, { "text": "Mechanism of Electric Power Generation from Ionic Droplet Motion on\n Polymer Supported Graphene: Graphene-based electric power generation that converts mechanical energy of\nflow of ionic droplets over the device surface into electricity has emerged as\npromising candidate for a blue-energy network. Yet the lack of a microscopic\nunderstanding of the underlying mechanism has prevented ability to optimize and\ncontrol the performance of such devices. This requires information on\ninterfacial structure and charging behavior at the molecular level. Here, we\nuse sum-frequency vibrational spectroscopy (SFVS) to probe the interfaces of\ndevices composed of aqueous solution, graphene and supporting polymer\nsubstrate. We discover that the surface dipole layer of the polymer is\nresponsible for ion attraction toward and adsorption at the graphene surface\nthat leads to electricity generation in graphene. Graphene itself does not\nattract ions and only acts as a conducting sheet for the induced carrier\ntransport. Replacing the polymer by an organic ferroelectric substrate could\nenhance the efficiency and allow switching of the electricity generation. Our\nmicroscopic understanding of the electricity generation process paves the way\nfor the rational design of scalable and more efficient droplet-motion-based\nenergy transducer devices.", "category": "physics_app-ph" }, { "text": "Memristor Compact Model with Oxygen-Vacancy Concentration as State\n Variable: We present a unique compact model for oxide memristors, based upon the\nconcentration of oxygen vacancies as state variables. In this model, the\nincrease (decrease) in oxygen vacancy concentration is similar in effect to the\nreduction (expansion) of the tunnel gap used as a state variable in existing\ncompact models, providing a mechanism for the electronic current to increase\n(decrease) based upon the polarity of the applied voltage. Rate equations\ndefining the dynamics of state variables are obtained from simplifications of a\nrecent manuscript in which electronic processes (i.e., electron\ncapture/emission) were combined with atomic processes (i.e., Frenkel pair\ngeneration/recombination, diffusion) stemming from the thermochemical model of\ndielectric breakdown. Central to the proposed model is the effect of the\nelectron occupancy of oxygen vacancy traps on resistive switching dynamics. The\nelectronic current is calculated considering Ohmic, band-to-band, and\nbound-to-band contributions. The model includes uniform self-heating with\nJoule-heating and conductive loss terms. The model is calibrated using\nexperimental current-voltage characteristics for HfO2 memristors with different\nelectrode materials. Though a general model is presented, a delta-shaped\ndensity of states profile for oxygen vacancies is found capable of accurately\nrepresenting experimental data while providing a minimal description of bound\nto band transitions. The model is implemented in Verilog-A and tested using\nread/write operations in a 4x4 1T1R nonvolatile memory array to evaluate its\nability to perform circuit simulations of practical interest. A particular\nbenefit is that the model does not make strong assumptions regarding filament\ngeometry of which scant experimental-evidence exists to support.", "category": "physics_app-ph" }, { "text": "Probing the adsorption/desorption of amphiphilic polymers at the\n air-water interface during large interfacial deformations: Hydrophobically modified polymers are good candidates for the stabilization\nof liquid interfaces thanks to the high anchoring energy of the hydrophobic\nparts. In this article we probe the interfacial anchoring of a series of\nhome-made hydrophobically modified polymers of controlled degree of grafting by\nstudying their behavior upon large area dilations and compressions. By\ncomparing the measured interfacial tension to the one that we expect in the\ncase of a constant number of adsorbed monomers, we are able to deduce whether\ndesorption or adsorption occurs during area variations. We find that the\npolymer chains with the longest hydrophobic grafts desorb for larger\ncompressions than the polymers with the shortest grafts, because of their\nlarger desorption energy. Furthermore, we observe more desorption for polymers\nwith the highest grafting densities. We attribute this counter intuitive result\nto the fact that for high grafting densities, the length of the polymer loops\nis shorter, hence the elastic penalty upon compression is larger for these\nlayers, leading to a faster desorption. The dilatation experiments reveal that\nthe number of adsorbed anchors remains constant in the case of chains with low\ngrafting density while chains with the highest degree of grafting seem to show\nsome degree of adsorption during the dilatation. Therefore for these highly\ngrafted chains there may be unadsorbed grafts remaining in the vicinity of the\ninterface, which may adsorb quickly to the interface upon dilatation.", "category": "physics_app-ph" }, { "text": "Optimization of light trapping micro-hole structure for high-speed\n high-efficiency silicon photodiodes: We optimized micro-holes in a thin slab for fast Si photodetectors at\nwavelength 800-950nm. Lateral modes are shown to be responsible for the\neffective light trapping. Small disorder and cone hole shapes helped achieve\nuniform quantum efficiency in a wide wavelength range.", "category": "physics_app-ph" }, { "text": "Scanning X-ray Diffraction Microscopy for Diamond Quantum Sensing: Understanding nano- and micro-scale crystal strain in CVD diamond is crucial\nto the advancement of diamond quantum technologies. In particular, the presence\nof such strain and its characterization present a challenge to diamond-based\nquantum sensing and information applications -- as well as for future dark\nmatter detectors where directional information of incoming particles is encoded\nin crystal strain. Here, we exploit nanofocused scanning X-ray diffraction\nmicroscopy to quantitatively measure crystal deformation from defects in\ndiamond with high spatial and strain resolution. Combining information from\nmultiple Bragg angles allows stereoscopic three-dimensional modeling of strain\nfeature geometry; the diffraction results are validated via comparison to\noptical measurements of the strain tensor based on spin-state-dependent\nspectroscopy of ensembles of nitrogen vacancy (NV) centers in the diamond. Our\nresults demonstrate both strain and spatial resolution sufficient for\ndirectional detection of dark matter via X-ray measurement of crystal strain,\nand provide a promising tool for diamond growth analysis and improvement of\ndefect-based sensing.", "category": "physics_app-ph" }, { "text": "Electronic states and molecular orientation of ITIC film: ITIC is the milestone of non-fullerene small molecule acceptors used in\norganic solar cells. We have studied the electronic states and molecular\norientation of ITIC film using photoelectron spectroscopy and X-ray absorption\nspectroscopy. The negative integer charge transfer energy level is determined\nto be 4.00 plus or minus 0.05 eV below the vacuum level, and the ionization\npotential is 5.75 plus or minus 0.10 eV. The molecules predominantly adopt the\nface-on orientation on inert substrates as long as the surfaces of the\nsubstrates are not too rough. These results provide physical understanding of\nthe high performance of ITIC-based solar cells, also afford implications to\ndesign more advanced photovoltaic small molecules.", "category": "physics_app-ph" }, { "text": "Extreme Asymmetry in Metasurfaces via Evanescent Fields Engineering:\n Angular-Asymmetric Absorption: On the quest towards full control over wave propagation, the development of\ncompact devices that allow asymmetric response is a challenge. In this Letter,\nwe introduce a new paradigm for the engineering of asymmetry in planar\nstructures, revealing and exploiting unilateral excitation of evanescent waves.\nWe test the idea with the design and experimental characterization of a\nmetasurface for angular-asymmetric absorption. The results show that the\ncontrast ratio of absorption (the asymmetry level) can be arbitrarily\nengineered from zero to infinity for waves coming from two oppositely tilted\nangles. We demonstrate that the revealed asymmetry effects cannot be realized\nusing conventional diffraction gratings, reflectarrays, and phase-gradient\nmetasurfaces. This Letter opens up promising possibilities for wave\nmanipulation via evanescent waves engineering with applications in one-side\ndetection and sensing, angle-encoded steganography, flat nonlinear devices and\nshaping the scattering patterns of various objects.", "category": "physics_app-ph" }, { "text": "The emergence of low-frequency dual Fano resonances in chiral twisting\n metamaterials: In the current work, through a finite element analysis, we demonstrate that a\nconfiguration of chiral cells having syndiotactic symmetry provides dual Fano\nresonances at low frequency. From the phononic dispersion and transmission\nresponse, we compare the signature provided by a composite made of chiral cells\nto the ones of homogeneous medium, isotactic nonchiral, and isotactic chiral\nbeams. The study results in an innovative design of a mechanical metamaterial\nthat induces the Fano resonance at low frequency with a relatively high quality\nfactor. This might be a significant step forward for mechanical wave filtering\nand detection. Performances have been evaluated using a sensor that will be\nimplemented as a thermometer.", "category": "physics_app-ph" }, { "text": "Giant THz surface plasmon polariton induced by high-index dielectric\n metasurface: We use computational approaches to explore the role of a\nhigh-refractive-index dielectric TiO2 grating with deep subwavelength thickness\non InSb as a tunable coupler for THz surface plasmons. We find a series of\nresonances as the grating couples a normally-incident THz wave to standing\nsurface plasmon waves on both thin and thick InSb layers. In a marked contrast\nwith previously-explored metallic gratings, we observe the emergence of a much\nstronger additional resonance. The mechanism of this giant plasmonic resonance\nis well interpreted by the dispersion of surface plasmon excited in the\nair\\TiO2\\InSb trilayer system. We demonstrate that both the frequency and the\nintensity of the giant resonance can be tuned by varying dielectric grating\nparameters, providing more flexible tunability than metallic gratings. The\nphase and amplitude of the normally-incident THz wave are spatially modulated\nby the dielectric grating to optimize the surface plasmon excitation. The giant\nsurface plasmon resonance gives rise to strong enhancement of the electric\nfield above the grating structure, which can be useful in sensing and\nspectroscopy applications.", "category": "physics_app-ph" }, { "text": "Monolithic piezoelectric control of soliton microcombs: High-speed laser frequency actuation is critical in all applications\nemploying lasers and frequency combs, and is prerequisite for phase locking,\nfrequency stabilization and stability transfer among multiple optical carriers.\nSoliton microcombs have emerged as chip-scale, broadband and\nlow-power-consumption frequency comb sources.Yet, integrated microcombs relying\non thermal heaters for on-chip actuation all exhibit only kilohertz actuation\nbandwidth. Consequently, high-speed actuation and locking of microcombs have\nbeen attained only with off-chip bulk modulators. Here, we present high-speed\nmicrocomb actuation using integrated components. By monolithically integrating\npiezoelectric AlN actuators on ultralow-loss Si3N4 photonic circuits, we\ndemonstrate voltage-controlled soliton tuning, modulation and stabilization.\nThe integrated AlN actuators feature bi-directional tuning with high linearity\nand low hysteresis, operate with 300 nW power and exhibit flat actuation\nresponse up to megahertz frequency, significantly exceeding bulk piezo tuning\nbandwidth. We use this novel capability to demonstrate a microcomb engine for\nparallel FMCW LiDAR, via synchronously tuning the laser and microresonator. By\napplying a triangular sweep at the modulation rate matching the frequency\nspacing of HBAR modes, we exploit the resonant build-up of bulk acoustic energy\nto significantly lower the required driving to a CMOS voltage of only 7 Volts.\nOur approach endows soliton microcombs with integrated,\nultralow-power-consumption, and fast actuation, significantly expanding the\nrepertoire of technological applications.", "category": "physics_app-ph" }, { "text": "MoS2 Field Effect Transistors based sensors for low concentration\n acetone detection: The measurement of acetone in human breath, a known biomarker for diabetes,\ncan act as an effective screening method for diabetes. While gas chromatography\nand mass spectroscopy based methods can detect gases in low concentration, they\nare costly, bulky, need complex sample preparation and are slow. Solid state\ndevices such as Field Effect Transistors (FETs) can perform this faster and at\na lower cost. In this work, we present the results of acetone gas sensing by\nmolybdenum disulfide (MoS2) based FETs. MoS2 channel was functionalized with\npolymethyl methacrylate (PMMA). When acetone molecules bind to PMMA, an\nelectrostatic gating effect takes place and changes the electrical\ncharacteristics of the FET. More the number of acetone molecules that bind to\nthe PMMA layer, the higher the shift in the drain current-voltage (Id-Vg) curve\nof the FET. This shift is modeled as a change in the threshold voltage of the\nFET. The Id-Vg curve was observed to shift downwards, as the acetone\nconcentration increases. The limit of detection was observed to be 0.4 parts\nper million (ppm). This is the first sub-ppm concentration acetone detection at\nroom temperature using a solid state device.", "category": "physics_app-ph" }, { "text": "Accurate high-resolution depth profiling of magnetron sputtered\n transition metal alloy films containing light species: A multi-method\n approach: We present an assessment of a multi-method approach based on ion beam\nanalysis to obtain high-resolution depth profiles of the total chemical\ncomposition of complex alloy systems. As a model system we employ an alloy\nbased on several transition metals and containing light species. Samples have\nbeen investigated by a number of different ion-beam based techniques, i.e.,\nRutherford Backscattering Spectrometry, Particle-Induced X-ray Emission,\nElastic Backscattering Spectrometry and Time-of-Flight/Energy Elastic Recoil\nDetection Analysis. Sets of spectra obtained from these different techniques\nwere analyzed both independently and following an iterative and self-consistent\napproach yielding a more accurate depth profile of the sample, including both\nmetallic heavy constituents (Cr, Fe and Ni) as well as the rather reactive\nlight species (C, O) in the alloy. A quantitative comparison in terms of\nachievable precision and accuracy is made and the limitations of the single\nmethod approach are discussed for the different techniques. The multi-method\napproach is shown to yield significantly improved and accurate information on\nstoichiometry, depth distribution, and thickness of the alloy with the\nimprovements being decisive for a detailed correlation of composition to the\nmaterial properties such as corrosion strength. The study also shows the\nincreased relative importance of experimental statistics for the achievable\naccuracy in the multi-method approach.", "category": "physics_app-ph" }, { "text": "Optimization and Neural Network-Based Modelling of Surface Passivation\n Effectiveness by Hydrogenated Amorphous Silicon for Solar Cell Applications: Intrinsic hydrogenated amorphous silicon films can provide outstanding\nsurface passivation of crystalline silicon wafer surfaces. This quality of\nIntrinsic hydrogenated amorphous silicon makes it valuable in heterojunction\nwith intrinsic thin layer (HIT) solar cell fabrication. This paper describes\nthe material characteristics and electronic properties of Intrinsic\nhydrogenated amorphous silicon that affects its passivation quality. A study of\npassivation quality of intrinsic hydrogenated amorphous silicon layer has been\ndone with respect to deposition parameters in Plasma Enhanced Chemical Vapor\nDeposition (PECVD), the most commonly used method of its deposition. It was\nfound that very good surface passivation with surface recombination velocity <\n50 cm/s can be obtained from thickness of 30 nm of Intrinsic hydrogenated\namorphous silicon (a-Si:H(i)), which is better than most other passivation\ntechniques. A mathematical model based on Artificial Neural Network (ANN) is\ndesigned to predict the carrier lifetime for a given deposition condition and\nit is shown that the prediction capability of developed ANN model varies with\nthe number of neurons in the hidden layer using Akaike Information Criterion\n(AIC), which is a widely accepted model selection method for measuring the\nvalidity of nonlinear models.", "category": "physics_app-ph" }, { "text": "MOSFET GIDL Currentby Designing a New BTBT Model Using De-Casteljaus\n Algorithm: The Band to Band tunneling probability strongly depends on the shape of the\npotential barrier. However, parabolic approximation of this shape is well\nacceptable but unfortunately significant amount of error is unavoidable by\nusing quadratic polynomial in calculation of tunneling probability. De\nCasteljaus algorithm, followed by Bezier Curve can be modeled to any arbitrary\nshape using its Geometry Invariance Property and End points geometric property.\nUsing this algorithm a new Band-to-Band tunneling model is designed and\nverified by establishing an analytic expression of Gate Induced Drain Leakage\ncurrent in MOSFET.", "category": "physics_app-ph" }, { "text": "A Numerical Approach for Modeling the Shunt Damping of Thin Panels with\n Arrays of Separately Piezoelectric Patches: Two-dimensional thin plates are widely used in many aerospace and automotive\napplications. Among many methods for the attenuation of vibration of these\nmechanical structures, piezoelectric shunt damping is a promising way. It\nenables a compact vibration damping method without adding significant mass and\nvolumetric occupancy. Analyzing the dynamics of these electromechanical systems\nrequires precise modeling tools that properly consider the coupling between the\npiezoelectric elements and the host structure. This paper presents a\nmethodology for separately shunted piezoelectric patches for achieving higher\nperformance on vibration attenuation. The Rayleigh-Ritz method is used for\nperforming the modal analysis and obtaining the frequency response functions of\nthe electro-mechanical system. The effectiveness of the method is investigated\nfor a broader range of frequencies, and it was shown that separately shunted\npiezoelectric patches are more effective.", "category": "physics_app-ph" }, { "text": "Fracturing of polycrystalline MoS$_2$ nanofilms: The possibility of tailoring the critical strain of 2D materials will be\ncrucial for the fabrication of flexible devices. In this paper, the fracture in\npolycrystalline MoS2 films with two different grain orientations is studied at\nthe micro- and nanoscale using electron microscopy. The critical uniaxial\nstrain is determined to be approximately 5% and independent of the sample\nmorphology. However, electron beam irradiation is found to enhance the\ninteraction between the MoS2 and the PDMS substrates, leading to an increased\ncritical strain that can exceed 10%. This enhancement of strain resistance was\nused to fabricate a mechanically robust array of lines 1 mm in length. Finally,\nnanoscale crack propagation studied by transmission electron microscopy showed\nthat cracks propagate along the grain boundaries as well as through the grains,\npreferentially along van der Waals bonding. These results provide insight\nregarding the fracture of polycrystalline 2D materials and a new method to\ntailor the critical strain and nanofabrication of ultra-thin MoS2 devices using\nwell-developed tools, which will be of great interest to the flexible\nelectronics industry.", "category": "physics_app-ph" }, { "text": "An Analytic Model for Eddy Current Separation: Eddy current separation (ECS) is a process used throughout the scrap\nrecycling industry for separating nonferrous metals from nonmetallic fluff. To\ndate, however, the physical theory of ECS has generally been limited to\nempirical approximations and numerical simulations. We therefore introduce a\nsimplified, two-dimensional model for ECS based on a cylindrical array of\npermanent, alternating magnets. The result is a Fourier-series expansion that\ndescribes the total magnetic field profile over all space. If the magnets are\nthen rotated with constant angular velocity, the magnetic fields vary as a\ndiscrete series of sinusoidal harmonics, thereby inducing electrical eddy\ncurrents in nearby conductive particles. Force and torque calculations can then\nbe used to predict the corresponding kinematic trajectories.", "category": "physics_app-ph" }, { "text": "Flow electrification of corona-charged polyethylene terephthalate film: Corona charging a free-standing polymer film can produce a quasi-permanent\npotential difference across the film thickness, while the absolute amplitude of\nsurface voltage may be highly sensitive to the free charges. To precisely\ncontrol the voltage distribution, we investigated the flow electrification\ntechnology, by exposing corona-charged polyethylene terephthalate films to a\nvariety of sodium salt solutions. The surface voltage and the free charge\ndensity were adjusted by the salt concentration, the anion size, and the flow\nrate. The dipolar component of electric potential remained unchanged. This\nresult has significant scientific interest and technological importance to\nsurface treatment, filtration, energy harvesting, bio-actuation and\nbio-sensing, among others.", "category": "physics_app-ph" }, { "text": "Tailored Molybdenum Carbide Properties and Graphitic Nano Layer\n Formation by Plasma and Ion Energy Control during Plasma Enhanced ALD: We demonstrate the extensive study on how film density and crystallinity of\nmolybdenum carbide ($MoC_{x}$) can be tailored during plasma-enhanced ALD\n(PEALD) by controlling either the plasma exposure time or the ion energy. We\ninvestigated $MoC_{x}$ films grown using $Mo(^tBuN)_2(NMe_2)_2$ as the\nprecursor and $H_2/Ar$ plasma as the co-reactant at temperatures between\n150{\\deg}C and 300{\\deg}C. We discover a threshold for graphitic layer\nformation at high mean ion energies during the PEALD cycle. The supplied high\nenergy dose allows for hybridised $sp^{2}$ carbon bonds formation, similar to\nhigh temperature annealing. The graphitisation of the $MoC_{x}$ surface takes\nplace at temperature of 300$^{\\circ}C$. The graphitic film show a (101) plane\ndiffraction peak with dominant intensity in XRD, and a typical $sp^{2}$ C1s\npeak along with carbidic metal in XPS measurements. Surface roughness of the\nfilm lowers significantly at the graphitisation regime of deposition. This low\ntemperature graphitisation by high energy plasma ions during PEALD shows a\ngreat promise to advancing graphene and graphite composites at low temperature\nby PEALD for future applications.", "category": "physics_app-ph" }, { "text": "Small-World Disordered Lattices: Spectral Gaps and Diffusive Transport: We investigate the dynamic behavior of lattices with disorder introduced\nthrough non-local network connections. Inspired by the Watts-Strogatz\nsmall-world model, we employ a single parameter to determine the probability of\nlocal connections being re-wired, and to induce transitions between regular and\ndisordered lattices. These connections are added as non-local springs to\nunderlying periodic one-dimensional (1D) and two-dimensional (2D) square,\ntriangular and hexagonal lattices. Eigenmode computations illustrate the\nemergence of spectral gaps in various representative lattices for increasing\ndegrees of disorder. These gaps manifest themselves as frequency ranges where\nthe modal density goes to zero, or that are populated only by localized modes.\nIn both cases, we observe low transmission levels of vibrations across the\nlattice. Overall, we find that these gaps are more pronounced for lattice\ntopologies with lower connectivity, such as the 1D lattice or the 2D hexagonal\nlattice. We then illustrate that the disordered lattices undergo transitions\nfrom ballistic to super-diffusive or diffusive transport for increasing levels\nof disorder. These properties, illustrated through numerical simulations,\nunveil the potential for disorder in the form of non-local connections to\nenable additional functionalities for metamaterials. These include the\noccurrence of disorder-induced spectral gaps, which is relevant to frequency\nfiltering devices, as well as the possibility to induce diffusive-type\ntransport which does not occur in regular periodic materials, and that may find\napplications in dynamic stress mitigation.", "category": "physics_app-ph" }, { "text": "Impact of corrosion on the emissivity of advanced-reactor structural\n alloys: Under standard operating conditions, the emissivity of structural alloys used\nfor various components of nuclear reactors may evolve, affecting the heat\ntransfer of the systems. In this study, mid-infrared emissivities of several\nreactor structural alloys were measured before and after exposure to\nenvironments relevant to next-generation reactors. We evaluated nickel-based\nalloys Haynes 230 and Inconel 617 exposed to helium gas at 1000 $^{\\circ}$C,\nnickel-based Hastelloy N and iron-based 316 stainless steel exposed to molten\nsalts at 750-850 $^{\\circ}$C, 316 stainless steel exposed to liquid sodium at\n650 $^{\\circ}$C, and 316 stainless steel and Haynes 230 exposed to\nsupercritical CO2 at 650 $^{\\circ}$C. Emissivity was measured via emissive and\nreflective techniques using a Fourier transform infrared (FTIR) spectrometer.\nLarge increases in emissivity are observed for alloys exposed to oxidizing\nenvironments, while only minor differences were observed in other exposure\nconditions.", "category": "physics_app-ph" }, { "text": "Kinetic studies on using photocatalytic coatings for removal of indoor\n volatile organic compounds: Titanium dioxide (TiO2) is a known photocatalyst with a capability of\ndecomposing organic substance. However, the photocatalysis of the pure TiO2 is\nnot effective for the indoor environment due to a lack of the ultraviolet\nirradiation inside the building. Doping TiO2 with substance such as C, N or\nmetal can extend the threshold of the absorption spectrum to the visible\nspectrum region. Thus, doped-TiO2 is able to decompose volatile organic\ncompounds (VOCs) under an indoor environment. To date, most experimental work\nreported on photocatalytic kinetics were conducted inside small-scale devices.\nThe performance of air purification function under the actual indoor\napplication scenery need to be further clarified. For this purpose, it is\ncrucial to predict the performance of autogenous air quality improvements by\nvisible light driven photocatalyst for the actual applications. This work has\ndeveloped a model to evaluate the performance of functional coating with\nphotocatalyst in removing VOCs. Factors such as the effects of coating designs\nand indoor ambient conditions on the air purification efficiency were studied.\nThis work demonstrates that doped-TiO2 photocatalytic coating is effective to\nimprove the indoor air quality.", "category": "physics_app-ph" }, { "text": "Polarization Origin of Photoconductivity in MAPbI3 Thin Films: Hybrid-halide perovskite (HHP) films exhibit exceptional photo-electric\nproperties. These materials are utilized for highly efficient solar cells and\nphotoconductive technologies. Both ion migration and polarization have been\nproposed as the source of enhanced photoelectric activity, but the exact origin\nof these advantageous device properties has remained elusive. Here, we combined\nmicroscale and device-scale characterization to demonstrate that\npolarization-assisted conductivity governs photoconductivity in thin HHP films.\nConductive atomic force microscopy under light and variable temperature\nconditions showed that the photocurrent is directional and is suppressed at the\ntetragonal-to-cubic transformation. It was revealed that polarization-based\nconductivity is enhanced by light, whereas dark conductivity is dominated by\nnon-directional ion migration, as was confirmed by large-scale device\nmeasurements. Following the non-volatile memory nature of polarization domains,\nphotoconductive memristive behavior was demonstrated. Understanding the origin\nof photoelectric activity in HHP allows designing devices with enhanced\nfunctionality and lays the grounds for photoelectric memristive devices.", "category": "physics_app-ph" }, { "text": "Linear thermal expansion coefficient (at temperatures from 130 to 800 K)\n of borosilicate glasses applicable for coupling with silicon in\n microelectronics: Processing results of measurements of linear thermal expansion coefficients\nand linear thermal expansion of two brands of borosilicate glasses --- LK5 and\nBorofloat 33 --- are presented. The linear thermal expansion of glass samples\nhave been determined in the temperature range 130 to 800 K (minus 143 to 526\n$\\deg$C) using thermomechanical analyzer TMA7100. Relative imprecision of\nindirectly measured linear thermal expansion coefficients and linear thermal\nexpansion of both glass brands is less than $\\pm$5 % and $\\pm$3 % respectively.\nPolynomial equations, approximating temperature dependence of obtained\nmeasurements, are presented. The results will facilitate the modeling of the\ncharacteristics of the devices which are used in microsystems engineering and\nfabricated by anodic bonding of silicon to glass, they can also be used to\noptimize the temperature regime of silicon to glass bonding process. Keywords:\nlinear expansion, thermal expansion coefficient, thermomechanical analysis,\nborosilicate glass.", "category": "physics_app-ph" }, { "text": "Controllable magnon frequency comb in synthetic ferrimagnets: Magnon frequency comb provides opportunities for exploring magnon nonlinear\neffects and measuring the transmission magnon frequency in magnets, whose\ncontrollability becomes vital for modulating the operating frequency and\nimproving the measurement accuracy. Nevertheless, such controllable frequency\ncomb remains to be explored. In this work, we investigate theoretically and\nnumerically the skyrmion-induced magnon frequency comb effect generated by\ninteraction between the magnon excitation mode and skyrmion breathing mode in\nsynthetic ferrimagnets. It is revealed that both the skyrmion breathing mode\nand the magnon frequency gap closely depend on the net angular momentum\n{\\delta}s, emphasizing the pivotal role of {\\delta}s as an effective control\nparameter in governing the comb teeth. With the increase of {\\delta}s, the\nskyrmion size decreases, which results in the enlargement of the breathing\nfrequency and the distance between the comb teeth. Moreover, the dependences of\nthe magnon frequency gap on {\\delta}s and the inter-layer coupling allow one to\nmodulate the comb lowest coherent frequency via structural control.\nConsequently, the coherent modes generated by the comb may range from gigahertz\nto terahertz frequencies, serving as a bridge between microwave and terahertz\nwaves. Thus, this work represents a substantial advance in understanding the\nmagnon frequency comb effect in ferrimagnets.", "category": "physics_app-ph" }, { "text": "A bulge test based methodology for characterizing ultra-thin buckled\n membranes: Buckled membranes become ever more important with further miniaturization and\ndevelopment of ultra-thin film based systems. It is well established that the\nbulge test method, generally considered the gold standard for characterizing\nfreestanding thin films, is unsuited to characterize buckled membranes, because\nof compressive residual stresses and a negligible out-of-plane bending\nstiffness. When pressurized, buckled membranes immediately start entering the\nripple regime, but they typically plastically deform or fracture before\nreaching the cylindrical regime. In this paper the bulge test method is\nextended to enable characterization of buckled freestanding ultra-thin\nmembranes in the ripple regime. In a combined experimental-numerical approach,\nthe advanced technique of digital height correlation was first extended towards\nthe sub-micron scale, to enable measurement of the highly varying local 3D\nstrain and curvature fields on top of a single ripple in a total region of\ninterest as small as approximately 25 microns. Subsequently, a finite element\n(FE) model was set up to analyze the post-buckled membrane under pressure\nloading. In the seemingly complex ripple configuration, a suitable combination\nof local region of interest and pressure range was identified for which the\nstress-strain state can be extracted from the local strain and curvature\nfields. This enables the extraction of both the Young's modulus and Poisson's\nratio from a single bulge sample, contrary to the conventional bulge test\nmethod. Virtual experiments demonstrate the feasibility of the approach, while\nreal proof of principle of the method was demonstrated for fragile specimens\nwith rather narrow ( approximately 25 microns) ripples.", "category": "physics_app-ph" }, { "text": "Amplitude-modulated pulses based phase-sensitive OTDR in distributed\n sensing: The detected frequency response range of phase-sensitive optical time domain\nreflectometry is limited by the sensing fiber length. In this paper, we\ndemonstrate an amplitude modulated pulses based phase-sensitive OTDR to detect\nvibrations with high spatial resolution and wide frequency response range. The\namplitude modulated pulses consisting of narrow pulses and background light are\ninjected into the sensing fiber as probe light. The Rayleigh backscattering\ngenerated by the background light interferes at the detection end, presenting a\nphase sensitive response to external vibrations. The Rayleigh backscattering of\nnarrow pulses are tracked to locate vibrations. The frequency information is\nobtained from the frequency domain analysis of the interference signal. The\nsystem can realize high frequency response with low repetition rate of probe\npulses by one-end detection.", "category": "physics_app-ph" }, { "text": "Thermal boundary resistance predictions with non-equilibrium Green's\n function and molecular dynamics simulations: The non-equilibrium Green's function (NEGF) method with B\\\"uttiker probe\nscattering self-energies is assessed by comparing its predictions for the\nthermal boundary resistance with molecular dynamics (MD) simulations. For\nsimplicity, the interface of Si/heavy-Si is considered, where heavy-Si differs\nfrom Si only in the mass value. With B\\\"uttiker probe scattering parameters\ntuned against MD in homogeneous Si, the NEGF-predicted thermal boundary\nresistance quantitatively agrees with MD for wide mass ratios. Artificial\nresistances that the unaltered Landauer approach yield at virtual interfaces in\nhomogeneous systems are absent in the present NEGF approach. Spectral\ninformation result from NEGF in its natural representation without further\ntransformations. The spectral results show that the scattering between\ndifferent phonon modes plays a crucial role in thermal transport across\ninterfaces. B\\\"uttiker probes provide an efficient and reliable way to include\nanharmonicity in phonon related NEGF. NEGF including the B\\\"uttiker probes can\nreliably predict phonon transport across interfaces and at finite temperatures.", "category": "physics_app-ph" }, { "text": "Multiferroic Micro-Motors with Deterministic Single Input Control: This paper describes a method for achieving continuous deterministic\n360$^{\\circ} $ magnetic moment rotations in single domain magnetoelastic discs,\nand examines the performance bounds for a mechanically lossless multiferroic\nbead-on-a-disc motor based on dipole coupling these discs to small magnetic\nnanobeads. The continuous magnetic rotations are attained by controlling the\nrelative orientation of a four-fold anisotropy (e.g., cubic magnetocrystalline\nanisotropy) with respect to the two-fold magnetoelastic anisotropy. This\napproach produces continuous rotations from the quasi-static regime up through\noperational frequencies of several GHz. Driving strains of only $\\approx$90 to\n180 ppm are required for operation of motors using existing materials. The\nlarge operational frequencies and small sizes, with lateral dimensions of\n$\\approx$100s of nanometers, produce large power densities for the rotary\nbead-on-a-disc motor, and a newly proposed linear variant, in a size range\nwhere power dense alternative technologies do not currently exist.", "category": "physics_app-ph" }, { "text": "Antiphase boundary in CH$_3$NH$_3$PbI$_3$ repels charge carriers while\n promotes fast ion migrations: Defects in organic-inorganic hybrid perovskites (OIHPs) greatly influence\ntheir optoelectronic properties. Identification and better understanding of\ndefects existing in OIHPs is an essential step towards fabricating\nhigh-performance perovskite solar cells. However, direct visualizing the\ndefects is still a challenge for OIHPs due to their sensitivity during electron\nmicroscopy characterizations. Here, by using low dose scanning transmission\nelectron microscopy techniques, we observe the common existence of antiphase\nboundary (APB) in CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$), resolve its atomic\nstructure, and correlate it to the electrical/ionic activities and structural\ninstabilities. Such an APB is caused by the half-unit-cell shift of\n[PbI$_6$]$_4$-octahedron along the [100]/[010] direction, leading to the\ntransformation from corner-sharing [PbI$_6$]$_4$-octahedron in bulk MAPbI$_3$\ninto edge-sharing ones at the APB. Based on the identified atomic-scale\nconfiguration, we further carry out density functional theory calculations and\nreveal that the APB in MAPbI$_3$ repels both electrons and holes while serves\nas a fast ion-migration channel, causing a rapid decomposition into PbI$_2$\nthat is detrimental to optoelectronic performance. These findings provide\nvaluable insights into the relationships between structures and optoelectronic\nproperties of OIHPs and suggest that controlling the APB is essential for their\nstability.", "category": "physics_app-ph" }, { "text": "Stealth and equiluminous materials for scattering cancellation and wave\n diffusion: We report a procedure to design 2-dimensional acoustic structures with\nprescribed scattering properties. The structures are designed from targeted\nproperties in the reciprocal space so that their structure factors, i.e., their\nscattering patterns under the Born approximation, exactly follow the desired\nscattering properties for a set of wavelengths. The structures are made of a\ndistribution of rigid circular cross-sectional cylinders embedded in air. We\ndemonstrate the efficiency of the procedure by designing 2-dimensional stealth\nacoustic materials with broadband backscattering suppression independent of the\nangle of incidence and equiluminous acoustic materials exhibiting broadband\nscattering of equal intensity also independent of the angle of incidence. The\nscattering intensities are described in terms of both single and multiple\nscattering formalisms, showing excellent agreement with each other, thus\nvalidating the scattering properties of each material.", "category": "physics_app-ph" }, { "text": "Picosecond Multilevel Resistive Switching in Tantalum Oxide Thin Films: The increasing demand for high-density data storage leads to an increasing\ninterest in novel memory concepts with high scalability and the opportunity of\nstoring multiple bits in one cell. A promising candidate is the redox-based\nresistive switch repositing the information in form of different resistance\nstates. For reliable programming, the underlying physical parameters need to be\nunderstood. We reveal that the programmable resistance states are linked to\ninternal series resistances and the fundamental nonlinear switching kinetics.\nThe switching kinetics of Ta$_{2}$O$_{5}$-based cells was investigated in a\nwide range over 15 orders of magnitude from 250 ps to 10$^{5}$ s. We found\nstrong evidence for a switching speed of 10 ps which is consistent with analog\nelectronic circuit simulations. On all time scales, multi-bit data storage\ncapabilities were demonstrated. The elucidated link between fundamental\nmaterial properties and multi-bit data storage paves the way for designing\nresistive switches for memory and neuromorphic applications.", "category": "physics_app-ph" }, { "text": "Interplay of thermal and non-thermal effects in x-ray-induced ultrafast\n melting: X-ray laser-induced structural changes in silicon undergoing femtosecond\nmelting have been investigated by using an x-ray pump-x-ray probe technique.\nThe experimental results for different initial sample temperatures reveal that\nthe onset time and the speed of the atomic disordering are independent of the\ninitial temperature, suggesting that equilibrium atomic motion in the initial\nstate does not play a pivotal role in the x-ray-induced ultrafast melting. By\ncomparing the observed time-dependence of the atomic disordering and the\ndedicated theoretical simulations, we interpret that the energy transfer from\nthe excited electrons to ions via electron-ion coupling (thermal effect) as\nwell as a strong modification of the interatomic potential due to electron\nexcitations (non-thermal effect) trigger the ultrafast atomic disordering. Our\nfinding of the interplay of thermal and non-thermal effects in the\nx-ray-induced melting demonstrates that accurate modeling of intense x-ray\ninteractions with matter is essential to ensure a correct interpretation of\nexperiments using intense x-ray laser pulses.", "category": "physics_app-ph" }, { "text": "Wavelength conversion of data at gigabit rates via nonlinear optics in\n an integrated micro-ring resonator: We present the first system penalty measurements for all-optical wavelength\nconversion in an integrated ring resonator. We achieve wavelength conversion\nover a range of 27.7nm in the C-band at 2.5 Gb/s by exploiting four wave mixing\nin a CMOS compatible, high index glass ring resonator at ~22 dBm average pump\npower, obtaining < 0.3 dB system penalty.", "category": "physics_app-ph" }, { "text": "Multilayer InSe-Te van der Waals heterostructures with ultrahigh\n rectification ratio and ultrasensitive photoresponse: Multilayer van der Waals (vdWs) semiconductors have great promising\napplication in high-performance optoelectronic devices. However, the\nphotoconductive photodetectors based on layered semiconductors often suffer\nfrom large dark current and high external driven bias voltage. Here, we report\na vertical van der Waals heterostructures (vdWHs) consisting of multilayer\nindium selenide (InSe) and tellurium (Te). The multilayer InSe-Te vdWHs device\nshows a record high forward rectification ratio greater than 107 at room\ntemperature. Furthermore, an ultrasensitive and broadband photoresponse\nphotodetector is achieved by the vdWHs device with an ultrahigh photo/dark\ncurrent ratio over 104, a high detectivity of 1013, and a comparable\nresponsivity of 0.45 A/W under visible light illumination with weak incident\npower. Moreover, the vdWHs device has a photovoltaic effect and can function as\na self-powered photodetector (SPPD). The SPPD is also ultrasensitive to the\nbroadband spectra ranging from 300 nm to 1000 nm and is capable of detecting\nweak light signals. This work offers an opportunity to develop next-generation\nelectronic and optoelectronic devices based on multilayer vdWs structures.", "category": "physics_app-ph" }, { "text": "Axis-dependent carrier polarity in polycrystalline NaSn$_2$As$_2$: Transverse thermoelectric devices consist of only one thermoelectric\nmaterial, unlike conventional longitudinal thermoelectric devices that require\ntwo types of thermoelectric materials with p- and n-type polarities. However,\nscalable synthesis of materials that demonstrate axis-dependent carrier\npolarity, which is a prospective component to demonstrate the transverse\nthermoelectric device, is challenging. This paper reports that polycrystalline\nNaSn$_2$As$_2$, which was prepared by using uniaxial hot pressing, displayed\naxis-dependent carrier polarity. The preferred orientation of the sample was\nconfirmed through X-ray diffraction measurements. Seebeck coefficient\nmeasurements indicate that carrier polarity depends on the measurement\ndirection, which is consistent with recently reported results on single\ncrystals of NaSn$_2$As$_2$. Given that our sample preparation procedure is\nreadily scalable, the present work shows the possibility for preparing\ntransverse thermoelectric devices using polycrystalline NaSn$_2$As$_2$ with a\npreferred orientation.", "category": "physics_app-ph" }, { "text": "Damage identification on spatial Timoshenko arches by means of genetic\n algorithms: In this paper a procedure for the dynamic identification of damage in spatial\nTimoshenko arches is presented. The proposed approach is based on the\ncalculation of an arbitrary number of exact eigen-properties of a damaged\nspatial arch by means of the Wittrick and Williams algorithm. The proposed\ndamage model considers a reduction of the volume in a part of the arch, and is\ntherefore suitable, differently than what is commonly proposed in the main part\nof the dedicated literature, not only for concentrated cracks but also for\ndiffused damaged zones which may involve a loss of mass. Different damage\nscenarios can be taken into account with variable location, intensity and\nextension of the damage as well as number of damaged segments. An optimization\nprocedure, aiming at identifying which damage configuration minimizes the\ndifference between its eigen-properties and a set of measured modal quantities\nfor the structure, is implemented making use of genetic algorithms. In this\ncontext, an initial random population of chromosomes, representing different\ndamage distributions along the arch, is forced to evolve towards the fittest\nsolution. Several applications with different, single or multiple, damaged\nzones and boundary conditions confirm the validity and the applicability of the\nproposed procedure even in presence of instrumental errors on the measured\ndata.", "category": "physics_app-ph" }, { "text": "Controlling the motional quality factor of a diamagnetically levitated\n graphite plate: Researchers seek methods to levitate matter for a wide variety of purposes,\nranging from exploring fundamental problems in science, through to developing\nnew sensors and mechanical actuators. Many levitation techniques require active\ndriving and most can only be applied to objects smaller than a few micrometers.\nDiamagnetic levitation has the strong advantage of being the only form of\nlevitation which is passive, requiring no energy input, while also supporting\nmassive objects. Known diamagnetic materials which are electrical insulators\nare only weakly diamagnetic, and require large magnetic field gradients to\nlevitate. Strong diamagnetic materials which are electrical conductors, such as\ngraphite, exhibit eddy damping, restricting motional freedom and reducing their\npotential for sensing applications. In this work we describe a method to\nengineer the eddy damping while retaining the force characteristics provided by\nthe diamagnetic material. We study, both experimentally and theoretically, the\nmotional damping of a magnetically levitated graphite plate in high vacuum and\ndemonstrate that one can control the eddy damping by patterning the plate with\nthrough-slots which interrupt the eddy currents. We find we can control the\nmotional quality factor over a wide range with excellent agreement between the\nexperiment and numerical simulations.", "category": "physics_app-ph" }, { "text": "Insights into muscle metabolic energetics: Modelling muscle-tendon\n mechanics and metabolic rates during walking across speeds: Prior studies have produced models to predict metabolic rates based on\nexperimental observations of isolated muscle contraction from various species.\nSuch models can provide reliable predictions of metabolic rates in humans if\nmuscle properties and control are accurately modeled. This study aimed to\nexamine how muscle-tendon model calibration and metabolic energy models\ninfluenced estimation of muscle-tendon states and time-series metabolic rates,\nto evaluate the agreement with empirical data, and to provide predictions of\nthe metabolic rate of muscle groups and gait phases across walking speeds.\nThree-dimensional musculoskeletal simulations with prescribed kinematics and\ndynamics were performed. An optimal control formulation was used to compute\nmuscle-tendon states with four levels of individualization, ranging from a\nscaled generic model and muscle controls based on minimal activations, to\ncalibration of passive muscle forces, personalization of Achilles and\nquadriceps tendon stiffnesses, to finally informing muscle controls with\nelectromyography. We computed metabolic rates based on existing models.\nSimulations with calibrated passive forces and personalized tendon stiffness\nmost accurately estimate muscle excitations and fiber lengths. Interestingly,\nthe inclusion of electromyography did not improve our estimates. The whole-body\naverage metabolic cost was better estimated using Bhargava et al. 2004 and\nUmberger 2010 models. We estimated metabolic rate peaks near early stance,\npre-swing, and initial swing at all walking speeds. Plantarflexors accounted\nfor the highest cost among muscle groups at the preferred speed and was similar\nto the cost of hip adductors and abductors combined. Also, the swing phase\naccounted for slightly more than one-quarter of the total cost in a gait cycle,\nand its relative cost decreased with walking speed.", "category": "physics_app-ph" }, { "text": "Memories in the Photoluminescence Intermittency of Single Cesium Lead\n Bromide Nanocrystals: Single cesium lead bromide (CsPbBr3) nanocrystals show strong\nphotoluminescence blinking, with on- and off- dwelling times following\npower-law distributions. We investigate the memory effect in the\nphotoluminescence blinking of single CsPbBr3 nanocrystals and find positive\ncorrelations for successive on-times and successive off-times. This memory\neffect is not sensitive to the nature of the surface capping ligand and the\nembedding polymer. These observations suggest that photoluminescence\nintermittency and its memory are mainly controlled by intrinsic traps in the\nnanocrystals. These findings will help optimizing light-emitting devices based\non inorganic perovskite nanocrystals.", "category": "physics_app-ph" }, { "text": "Effect of shielding gas composition and welding speed on autogenous\n welds of unalloyed tungsten plates: Tungsten usually exhibits poor weldability and marked brittleness at room\ntemperature. This cause tungsten welds to be affected by the evolution of\ncracks along the weld bead, which can be eliminated by using a pre-heating step\nto reduce thermal straining. In this study, based on the tungsten inert gas\nwelding process, a working envelope, focussed on varying welding speed and five\ndifferent shielding gas mixtures of argon and helium, has been defined with the\nview of producing crack-free autogenous welds. The bead appearance and the\nmicrostructure of the different welds were correlated to the welding\nparameters, whose main effects have been analysed. Welding defects such as\nhumping occurred when using gas mixtures with relatively low content of helium,\nand when using relatively high welding speeds. Crack-free autogenous welds have\nbeen produced without pre-heating when using a high content of helium and\nrelatively low welding speeds. Thus, this study has demonstrated that a\nhelium-rich shielding gas is required for welding thick tungsten plates.\nMoreover, the low thermal shock induced by the process, coupled with the purity\nof the tungsten plates used, strongly contributed to avoid the occurrence of\nany crack.", "category": "physics_app-ph" }, { "text": "Measuring micro-displacements of specular surfaces using speckle\n interferometry: The displacement field of an object surface can be measured by using speckle\ninterferometry. This technique is based on the phenomenon of laser speckle and\nconsists in correlating speckle interferograms taken after and before the\ndeformation of the surface. The main requirement is that the surface under\nstudy must be optically rough to generate the speckle patterns to be\ncorrelated. In this paper, we present a very simple and intuitive method based\non speckle interferometry to measure out-of-plane displacements on specular\nreflecting surfaces that generate no speckle patterns. The method consists in a\nmodified digital speckle pattern interferometer which requires no special\nequipment other than that used in conventional speckle interferometers. The\nproposed method could find useful application in the measurement of thermal\ndeformation of mirrors.", "category": "physics_app-ph" }, { "text": "Solving an old puzzle: fine structure of diffraction spots from an\n azo-polymer surface relief grating: We report on the experimental and theoretical interpretation of the\ndiffraction of a probe beam during inscription of a surface relief grating with\nan interference pattern into a photo-responsive polymer film. For this we\ndeveloped a set-up allowing for the simultaneous recording of the diffraction\nefficiency (DE), the fine structure of the diffraction spot and the\ntopographical changes, in situ and in real time while the film is irradiated.\nThe time dependence of the DE, as the surface relief deepens, follows a Bessel\nfunction exhibiting maxima and minima. The size of the probe beam relative to\nthe inscribed grating (i.e., to the size of the writing beams) matters and has\nto be considered for the interpretation of the DE signal. It is also at the\norigin of a fine structure within the diffraction spot where ring-shaped\nfeatures appear once an irradiation time corresponding to the first maximum of\nthe DE has been exceeded.", "category": "physics_app-ph" }, { "text": "Implementing Non-Universal Features with a Random Matrix Theory\n Approach: Application to Space-to-Configuration Multiplexing: We consider the efficiency of multiplexing spatially encoded information\nacross random configurations of a metasurface-programmable chaotic cavity in\nthe microwave domain. The distribution of the effective rank of the channel\nmatrix is studied to quantify the channel diversity and to assess a specific\nsystem's performance. System-specific features such as unstirred field\ncomponents give rise to nontrivial inter-channel correlations and need to be\nproperly accounted for in modelling based on random matrix theory. To address\nthis challenge, we propose a two-step hybrid approach. Based on an ensemble of\nexperimentally measured scattering matrices for different random metasurface\nconfigurations, we first learn a system-specific pair of coupling matrix and\nunstirred contribution to the Hamiltonian, and then add an appropriately\nweighted stirred contribution. We verify that our method is capable of\nreproducing the experimentally found distribution of the effective rank with\ngood accuracy. The approach can also be applied to other wave phenomena in\ncomplex media.", "category": "physics_app-ph" }, { "text": "Study of Surface Damage in Silicon by Irradiation with Focused Rubidium\n Ions: Cold atom ion sources have been developed and commercialized as alternative\nsources for focused ion beams (FIB). So far, applications and related research\nhave not been widely reported. In this paper, a prototype rubidium FIB is used\nto study the irradiation damage of 8.5 keV beam energy Rb$^+$ ions on silicon\nto examine the suitability of rubidium for nanomachining applications.\nTransmission electron microscopy combined with energy dispersive X-ray\nspectroscopy is applied to silicon samples irradiated by different doses of\nrubidium ions. The experimental results show a duplex damage layer consisting\nof an outer layer of oxidation without Rb and an inner layer containing Rb\nmostly at the interface to the underlying Si substrate. The steady-state damage\nlayer is measured to be $23.2(\\pm 0.3)$ nm thick with a rubidium staining level\nof $7(\\pm1)$ atomic percentage.", "category": "physics_app-ph" }, { "text": "A Flap-Type Seabed-Mounted Wave Energy Converter With Hydraulic PTO:\n Analytical Investigation & Experimental Analysis: This paper provides a study of a flap-type wave energy converter with a\nhydraulic power-take-off (PTO) system. This study includes the derivation of\nits equation of motion along with an analysis of natural frequencies of the\ndevice. A prototype was built using fillable cylinders and a series of\nexperiments were performed in a wave flume. In these experiments, the pressure\nvalues of the hydraulic circuit were changed to investigate the optimal value\nfor the system's pressure for a range of wave periods. The average\nwave-to-fluid efficiency (of about 15%) was achieved for a broad range of wave\nperiods. It was also found that a 26% wave-to-fluid efficiency can be reached\nfor waves with a period of 6.71 s. Based on the results of this analytical\nstudy, this device can be further optimized by filling its compartments with\nseawater.", "category": "physics_app-ph" }, { "text": "SiC-YiG X band quantum sensor for sensitive surface paramagnetic\n resonance applied to chemistry, biology, physics: Here I present the SiC-YiG Quantum Sensor, allowing electron paramagnetic\nresonance (EPR) studies of monolayer or few nanometers thick chemical,\nbiological or physical samples located on the sensor surface. It contains two\nparts, a 4H-SiC substrate with many paramagnetic silicon vacancies (V2) located\nbelow its surface, and YIG ferrimagnetic nanostripes. Spins sensing properties\nare based on optically detected double electron-electron spin resonance under\nthe strong magnetic field gradient of nanostripes. Here I describe fabrication,\nmagnetic, optical and spins sensing properties of this sensor. I show that the\ntarget spins sensitivity is at least five orders of magnitude larger than the\none of standard X band EPR spectrometer, for which it constitutes, combined\nwith a fiber bundle, a powerful upgrade for sensitive surface EPR. This sensor\ncan determine the target spins planes EPR spectrum, their positions with a\nnanoscale precision of +/- 1 nm, and their 2D concentration down to\n1/(20nm.20nm).", "category": "physics_app-ph" }, { "text": "On the thermal rectification factor in steady heat conduction: Thermal rectification in heat conduction problems has been extensively\nstudied in planar slabs. Here we consider the rectification problem in planar,\ncylindrical and spherical geometries involving two layers one of which has a\ntemperature variable heat conductivity. The rectification factor is\nanalytically calculated. It is shown that a maximum theoretical value of 1.618\nis obtained.", "category": "physics_app-ph" }, { "text": "Compact Broadband Low-Loss Taper for Coupling to a Silicon Nitride\n Photonic Wire: We demonstrate an ultra-compact waveguide taper in Silicon Nitride platform.\nThe proposed taper provides a coupling-efficiency of 95% at a length of 19.5 um\nin comparison to the standard linear taper of length 50 um that connects a 10\num wide waveguide to a 1 um wide photonic wire. The taper has a spectral\nresponse > 75% spanning over 800 nm and resilience to fabrication variations;\n>200 nm change in taper and end waveguide width varies transmission by <5%. We\nexperimentally demonstrate taper insertion loss of <0.1 dB/transition for a\ntaper as short as 19.5 um, and reduces the footprint of the photonic device by\n50.8% compared to the standard adiabatic taper. To the best of our knowledge,\nthe proposed taper is the shortest waveguide taper ever reported in Silicon\nNitride.", "category": "physics_app-ph" }, { "text": "Broadband photonic RF channelizer with a Kerr soliton crystal micro-comb: We report a 92 channel RF channelizer based on a 48.9 GHz integrated\nmicro-comb that operates via soliton crystals, together with a passive high-Q\nring resonator that acts as a periodic filter with an optical 3dB bandwidth of\n121.4 MHz. We obtain an instant RF bandwidth of 8.08 GHz and 17.55 GHz achieved\nthrough temperature tuning. These results represent a major advance to\nachieving fully integrated photonic RF spectrum channelizers with reduced low\ncomplexity, size, and high performance for digital-compatible signal detection\nand broadband analog signal processing.", "category": "physics_app-ph" }, { "text": "On the depth of cylindrical indentation of an elastic half-space for two\n types of displacement constraints: For cylindrical indentation of elastic half-space the relationship between\nthe depth of indentation delta and the applied force F is nonlinear, in\ncontrast to the linear relationship between the height of the contact zone\ndelta_0 and the force F. While the latter is independent of the boundary\nconditions used to specify the rigid-body translation, the former depends on a\nselected datum for vertical displacement. The depth of the indentation is\ndetermined for any permissible value of the length b, which specifies the\npoints of the free surface where the vertical displacement is required to be\nzero, w(b)=0. From the condition that the work of the indentation force is\nequal to the work of the contact pressure, it follows that the indentation is\ngeometrically and physically possible under imposed boundary conditions w(b)=0\nprovided that b>=b_min. The numerical value of b_min is found to be about 10\ntimes greater than the semi-width of the contact zone a, based on the numerical\nprecision in fulfilling the work condition W_F=W_p. If a datum is taken to be\nat a point at some distance h below the load, there is an alternative\nclosed-form expression for delta in terms of F, which involves the Poisson\nratio nu. For nu=1/3, it is found that h_min is about 21a. A simple expression\nrelating the permissible values of h and b is derived, which is linear for\nlarge values of h and b.", "category": "physics_app-ph" }, { "text": "Analysis of the Patent of a Protective Cover for Vertical-Axis Wind\n Turbines (VAWTs): Simulations of Wind Flow: This paper presents a numerical and experimental analysis of the patent of a\ndevice to be used in vertical-axis wind turbines (VAWTs) under extreme wind\nconditions. The device consists of two hemispheres interconnected by a set of\nconveniently implemented variable section ducts through which the wind\ncirculates to the blades. Furthermore, the design of the cross-section of the\nducts allows the control of the wind speed inside the device. These ducts are\nintended to work as diffusers or nozzles, depending on the needs of the\ninstallation site. Simulations were performed for the case of high-speed\nexternal wind, for which the ducts act as diffusers to reduce wind speed and\nmaintain a well-functioning internal turbine. Four different patent designs\nwere analyzed, focusing on turbine performance and generated power. The results\nindicate that the patent allows the generation of electric power for a greater\nrange of wind speeds than with a normal wind turbine. The results support that\nthis patent may be a good alternative for wind power generation in geographic\nareas with extreme weather conditions or with maintained or strong gusty wind.\nExperimental tests were carried out on the movement of the blades using the\navailable model. Finally, the power curve of the model of this wind turbine was\nobtained.", "category": "physics_app-ph" }, { "text": "A new artificial photosynthetic system coupling photovoltaic\n electrocatalysis with photothermal catalysis: In this work, we present a novel artificial photosynthetic paradigm with\nsquare meter (m2) level scalable production by integrating photovoltaic\nelectrolytic water splitting device and solar heating CO2 hydrogenation device,\nsuccessfully achieving the synergy of 1 sun driven 19.4% solar to chemical\nenergy efficiency (STC) for CO production (2.7 times higher than state of the\nart of large-sized artificial photosynthetic systems) with a low cost\n(equivalent to 1/7 of reported artificial photosynthetic systems). Furthermore,\nthe outdoor artificial photosynthetic demonstration with 1.268 m2 of scale\nexhibits the CO generation amount of 258.4 L per day, the STC of ~15.5% for CO\nproduction in winter, which could recover the cost within 833 suuny days of\noperation by selling CO.", "category": "physics_app-ph" }, { "text": "Graphene-based spinmechatronic valve: Interlayer twist between van der Waals graphene crystals led to the discovery\nof superconducting and insulating states near the magic angle. In this work, we\nexploit this mechanical degree of freedom by twisting the graphene middle layer\nin a trilayer graphene spacer between two metallic lead (Magnetic and\nnonmagnetic). A large difference in conductance is found depending on the angle\nof twist between the middle layer graphene and the ones at the interface this\ndifference, called twisting resistance, reach more than 1000% in the\nnon-magnetic Cu case. For the magnetic Ni case, the magneto-resistance\ndecreases and the difference in conductance between twisted and not twisted\ndepends strongly on the relative magnetization configuration. For the parallel\nconfiguration, the twisting resistance is about -40%, while for the\nanti-parallel configuration it can reach up to 130%. Furthermore, we show that\nthe twisting resistance can be enhanced by inserting a thin Cu layer at the\ninterface of Ni/graphene where it reaches a value of 200% and 1600% for\nparallel and antiparallel configurations, respectively. These finding could\npave the way toward the integration of 2D materials on novel spinmechatronics\nbased devices.", "category": "physics_app-ph" }, { "text": "Atomic scale modeling of water and ice behavior on vibrating surfaces:\n towards design of Surface Acoustic Wave anti-icing and de-icing systems: Within these studies, atomic scale molecular dynamics simulations have been\nperformed to analyze the behavior of water droplets and ice clusters on\nhydrophilic and hydrophobic surfaces subjected to high-frequency vibrations.\nThe methodology applied herewith aimed at understanding the phenomena governing\nthe anti-icing and de-icing process enabled by Surface Acoustic Waves (SAWs).\nThe complex wave propagation was simplified by in-plane and out-of-plane\nsubstrate vibrations, which are relevant to individual longitudinal and\ntransverse components of SAWs. Since the efficiency of such an active system\ndepends on the energy transfer from the vibrating substrate to water or ice,\nthe agents influencing such transfer as well as the accompanied phenomena were\nstudied in detail. Apart from the polarization of the substrate vibrations\n(in-plane/out-of-plane), the amplitude and frequency of these vibrations were\nanalyzed through atomic scale modeling. Further, the surface wettability effect\nwas introduced as a critical factor within the simulation of water or ice\nsitting on the vibrating substrate. The results of these studies allow\nidentifying the different phenomena responsible for water and ice removal from\nvibrating surfaces depending on the wave amplitude and frequency. The\nimportance of substrate wetting for the ant-icing and de-icing has also been\nanalyzed and discussed concerning the future design and optimization of\nSAW-based systems.", "category": "physics_app-ph" }, { "text": "Influence of Environmentally Affected Hole Transport Layers on Spatial\n Homogeneity and Charge Transport Dynamics of Organic Solar Cells: After the efficiency of organic photovoltaic (OPV) cells achieved more than\n10%, the control of stability and degradation mechanisms of solar cells became\na prominent task. The improvement of device efficiency due to incorporation of\na hole-transport layer (HTL) in bulk-heterojunction solar cells has been\nextensively reported. However, the most widely used HTL material, PEDOT:PSS is\nfrequently suspected to be the dominating source for devices instability under\nenvironmental conditions. Thereby effects like photooxidation and electrode\ncorrosion are often reported to shorten device lifetime. However, often in\nenvironmental device studies, the source of degradation, whether being from the\nHTL, the active layer or the metal cathode are rather difficult to distinguish,\nbecause the external diffusion of oxygen and water affects all components. In\nthis study, different HTLs, namely prepared from traditional PEDOT:PSS and also\ntwo types of molybdenum trioxide (MoO3), are exposed to different environments\nsuch as oxygen, light or humidity, prior to device finalization under inert\nconditions. This allows investigating any effects within the HTL and from\nreactions at its interface to the indium-tin-oxide electrode or the active\nlayer. The surface and bulk chemistry of the exposed HTL has been monitored and\ndiscussed in context to the observed device physics, dynamic charge transport\nand spatial performance homogeneity of the according OPV device. The results\nshow that merely humidity-exposure of the HTL leads to decreased device\nperformance for PEDOT:PSS, but also for one type of the tested MoO3. The losses\nare related to the amount of absorbed water in the HTL, inducing loss of active\narea in terms of interfacial contact. The device with PEDOT:PSS HTL after humid\nair exposure showed seriously decreased photocurrent by micro-delamination of\nswelling/shrinkage of the hygroscopic layer.", "category": "physics_app-ph" }, { "text": "Mechanical characterization of stress softening in double network\n hydrogels: In this paper, a micro-mechanical model is introduce to characterize the\nstress softening phenomenon in double network hydrogels. Damage in polymer\nmatrices under deformation, which appears as the rupture of cross-linking, is\nassumed to result in stress softening. The evolution of a polymer matrix is\ndescribed with the network evolution method by Dargazany and Itskov [Dargazany\nand Itskov, International Journal of Solids and Structures, 2009, 46, 2967].\nThe model includes a number of physically-motivated material parameters and\nobtains good agreement against different sets of experimental data of uniaxial\ncyclic tension tests.", "category": "physics_app-ph" }, { "text": "Micro/nanoliter droplet extraction by controlling acoustic vortex with\n miniwatt: Micro/nanoliter droplet is capable of achieving versatile applications with\ntiny volume and substantial surface energy, which is a big plus over bulk\nliquid. Yet, the contradiction of elaborate manipulation and enough power is\nstill a challenge. Here, we unleash the potential of our miniwatt aspirators\npumping up liquid and creating droplets with the help of acoustic vortex beams,\ninspired by the power mechanism that spirals are significant for most mollusks\nthat live in water. These droplet aspirators produce very large interface\ndeformations by small radiation pressures with orbit angular momentum from\nspiral-electrode transducers. The precisely contactless manipulation of\nphysical, chemical and biological objects at micrometric down to nanometric\nscales, promises tremendous development in fields as diverse as microrobotics,\nnanoreactors, or nanoassemblies.", "category": "physics_app-ph" }, { "text": "Micro- and Nanostructured Diamond in Electrochemistry: Fabrication and\n Application: The fabrication method of diamond nanostructures can be divided into two\ncategories: top-down etching and bottom-growth. The early work on 3D\nmicro-structured diamond dates back to mid-1990s, using chemical vapor\ninfiltration (CVI) techniques. In this technology, carbon or carbide fibers\nwere typically used as the growth template. Almost in parallel, reactive ion\netching (RIE) was applied to achieve diamond surface nanostructuring. After\nthat the diamond surface nanostructures, typically vertically aligned diamond\nnanowires (or nanorods) has been mainly fabricated using top-down plasma\netching techniques. In recent year, the templated diamond growth has gained\nincreasing attention due to the wide choice of template, mask-free production,\nand unlimited surface enlargement. In this chapter, the development and main\ntechniques used in these two approaches will be elaborated. Nevertheless, other\nless common methods, such as catalytic etching by metal particles, steam\nactivation and selective materials removal will also be discussed. As indicated\nby the title, this chapter will mainly deal with the application of micro- and\nnanostructured diamond in electrochemistry. In these applications, the\nadvantage of nanostructured diamond can be divided into three aspects: 1)\nproviding enlarged surface area for charge storage and catalyst deposition; 2)\ntip-enhanced electrochemical reactions used in sensing applications; 3) diamond\nmembranes with micro- or nanopores can be applied in the electrochemistry\nseparation and purification applications. Examples and explanations on these\napplications will be given in this chapter.", "category": "physics_app-ph" }, { "text": "Abrupt degenerately-doped silicon nanowire tunnel junctions: We have confirmed the presence of narrow, degenerately-doped axial silicon\nnanowire (SiNW) $p$-$n$ junctions via off-axis electron holography (EH). SiNWs\nwere grown via the vapor-solid-liquid (VLS) mechanism using gold (Au) as the\ncatalyst, silane (SiH$_{4}$), diborane (B$_{2}$H$_{6}$) and phosphine\n(PH$_{3}$) as the precursors, and hydrochloric acid (HCl) to stabilize the\ngrowth. Two types of growth were carried out, and in each case we explored\ngrowth with both $n$/$p$ and $p$/$n$ sequences. In the first type, we abruptly\nswitched the dopant precursors at the desired junction location, and in the\nsecond type we slowed the growth rate at the junction to allow the dopants to\nreadily leave the Au catalyst. We demonstrate degenerately-doped $p$/$n$ and\n$n$/$p$ nanowire segments with abrupt potential profiles of $1.02\\pm0.02$ and\n$0.86\\pm0.3$ V, and depletion region widths as narrow as $10\\pm1$ nm via EH.\nLow temperature current-voltage measurements show an asymmetric curvature in\nthe forward direction that resemble planar gold-doped tunnel junctions, where\nthe tunneling current is hidden by a large excess current. The results\npresented herein show that the direct VLS growth of degenerately-doped axial\nSiNW $p$-$n$ junctions is feasible, an essential step in the fabrication of\nmore complex SiNW-based devices for electronics and solar energy.", "category": "physics_app-ph" }, { "text": "Phonon condensation and cooling via nonlinear feedback: We show that in multimode mechanical systems, the amplification of the lowest\nmode and the damping of all the other modes can be realized simultaneously via\nnonlinear feedback. The feedback-induced dynamics of the multimode system is\nrelated to the formation of phonon condensation. The phonon statistics of the\nlowest mode are similar to those of a phonon laser. Finally, we show the\ncoherence of the lowest mode can be improved by an order of magnitude.", "category": "physics_app-ph" }, { "text": "Static negative susceptibility in ferromagnetic material induced by\n domain wall motion: an aspect of superconductor state: Domain wall motion in magnetic materiel induces the negative susceptibility\nleading to a perfect diamagnetism state. The local susceptibility is calculated\nby the derivative of magnetization ($\\vec{M}$) vector w.r.t. magnetic field\nstrength ($\\vec{H}$) vector. In the transient region from the upward domain to\nthe downward domain (domain wall width), local $\\vec{M}$ and $\\vec{H}$ vectors\nexhibit opposite slopes, which leads to a negative susceptibility value. A\nnegative susceptibility value induces the diamagnetism effect leading to a\nrelative permeability value $<$ 1 $\\left(\\mu _r < 1\\right)$. This diamagnetism\nsate originates due to the domain wall motion, which is an entirely different\nmechanism from the electron motion's induced diamagnetism. Furthermore, the\nstrength of the diamagnetism state can be enhanced by tuning the gradient\nenergy of a domain that may correspond to a perfect diamagnetism state\n$\\left(\\chi _v \\approx -1 \\Rightarrow \\mu _r \\rightarrow 0\\right)$. Besides, we\nbelieve that there may be a possibility of sustaining such a diamagnetic state\n(domain wall induced) in a ferromagnetic material that is utterly contradictory\nto the conventional theory.", "category": "physics_app-ph" }, { "text": "Nonvolatile bistable memory and Ising machine based on\n Micro-Electro-Mechanical Systems: We propose an Ising machine made of microelectromechanical systems (MEMS),\nwhere the annealing process is automatically executed by a dissipation\nmechanism. The core structure is a series of buckled plates. Two stable\npositions of each plate (left and right) represent its binary state acting as a\nbit so that a plate works as a mechanical memory. The electrostatic interaction\nbetween adjacent plates is introduced by applying voltage. Plates continue to\nflip between two stable buckled positions until the series of plates reaches a\nlocal minimum due to the damping of the mechanical motion. \\red{First, we\ndesign Ising machines simulating a ferromagnetic (FM) interaction and an\nantiferromagnetic (AF) interaction separately. Then, we propose a\nfully-connected MEMS\\ network representing a coexistence system of FM and AF\ninteractions in an arbitrary way, by way of which an arbitrary combinatorial\nproblem described by the Ising model can be solved.} The present mechanism\nworks at room temperature without external magnetic field, which is very\ndifferent from the standard classical or quantum annealing mechanism.", "category": "physics_app-ph" }, { "text": "All-electrical monitoring of bacterial antibiotic susceptibility in a\n microfluidic device: The lack of rapid antibiotic susceptibility tests adversely affects the\ntreatment of bacterial infections and contributes to increased prevalence of\nmultidrug resistant bacteria. Here, we describe an all-electrical approach that\nallows for ultra-sensitive measurement of growth signals from only tens of\nbacteria in a microfluidic device. Our device is essentially a set of\nmicrofluidic channels, each with a nano-constriction at one end and\ncross-sectional dimensions close to that of a single bacterium. Flowing a\nliquid bacteria sample (e.g., urine) through the microchannels rapidly traps\nthe bacteria in the device, allowing for subsequent incubation in drugs. We\nmeasure the electrical resistance of the microchannels, which increases (or\ndecreases) in proportion to the number of bacteria in the microchannels. The\nmethod and device allow for rapid antibiotic susceptibility tests in about two\nhours. Further, the short-time fluctuations in the electrical resistance during\nan antibiotic susceptibility test are correlated with the morphological changes\nof bacteria caused by the antibiotic. In contrast to other electrical\napproaches, the underlying geometric blockage effect provides a robust and\nsensitive signal, which is straightforward to interpret without electrical\nmodels. The approach also obviates the need for a high-resolution microscope\nand other complex equipment, making it potentially usable in resource-limited\nsettings.", "category": "physics_app-ph" }, { "text": "Thermo-elasto-plastic simulations of femtosecond laser-induced\n structural modifications: application to cavity formation in fused silica: The absorbed laser energy of a femtosecond laser pulse in a transparent\nmaterial induces a warm dense matter region which relaxation may lead to\nstructural modifications in the surrounding cold matter. The modeling of the\nthermo-elasto-plastic material response is addressed to predict such\nmodifications. It has been developed in a 2D plane geometry and implemented in\na hydrodynamic lagrangian code. The particular case of a tightly focused laser\nbeam in the bulk of fused silica is considered as a first application of the\nproposed general model. It is shown that the warm dense matter relaxation,\ninfluenced by the elasto-plastic behavior of the surrounding cold matter,\ngenerates both a strong shock and rarefaction waves. Permanent deformations\nappear in the surrounding solid matter if the induced stress becomes larger\nthan the yield strength. This interaction results in the formation of a\nsub-micrometric cavity surrounded by an overdense area. This approach also\nallows one to predict regions where cracks may form. The present modeling can\nbe used to design nano-structures induced by short laser pulses.", "category": "physics_app-ph" }, { "text": "BPZT HBARs for bias-tunable, stress generation at GHz frequencies: The high frequency performance of strong piezoelectric materials like PZT\nremains relatively less explored due to the assumption of large\ndielectric/ferroelectric losses at GHz frequencies. Recently, the advent of\nmagnetoelectric technology as an on-chip route to excite magnetization dynamics\nhas provided the impetus to evaluate the electromechanical performance of PZT\nat microwave frequencies. In this work, we demonstrate that HBARs fabricated\nusing Barium-doped PZT (BPZT) films can efficiently generate acoustic waves up\nto 15 GHz. The ferroelectricity of BPZT endows added functionality to the\nresonator in the form of voltage tunability of the electromechanical\nperformance. We extract the piezoelectric coefficient by numerically comparing\nthe performance of BPZT with the Mason model. The extracted piezoelectric\ncoefficient ~60 pm/V agrees well with reported values on thin film PZT measured\nat low frequencies (<100 MHz). Our results suggest that with further\nimprovement in device design and material processing, BPZT resonators could\noperate as large amplitude, tunable stress transducers at GHz frequencies.", "category": "physics_app-ph" }, { "text": "On the wave dispersion and non-reciprocal power flow in space-time\n traveling acoustic metamaterials: This note analytically investigates non-reciprocal wave dispersion in locally\nresonant acoustic metamaterials. Dispersion relations associated with\nspace-time varying modulations of inertial and stiffness parameters of the base\nmaterial and the resonant components are derived. It is shown that the\nresultant dispersion bias onsets intriguing features culminating in a break-up\nof both acoustic and optic propagation modes and one-way local resonance band\ngaps. The derived band structures are validated using the full transient\ndisplacement response of a finite metamaterial. A mathematical framework is\npresented to characterize power flow in the modulated acoustic metamaterials to\nquantify energy transmission patterns associated with the non-reciprocal\nresponse. Since local resonance band gaps are size-independent and frequency\ntunable, the outcome enables the synthesis of a new class of sub-wavelength\nlow-frequency one-way wave guides.", "category": "physics_app-ph" }, { "text": "Effect of polymeric additives on ignition, combustion and flame\n characteristics and soot deposits of crude oil droplets: Many oil fires have resulted from the crude oil train derailments in recent\nyears. Given the importance of crude oil shipping by rail to the energy\nsecurity of the US, it is important to consider various methods that will\ndecrease the likelihood of crude oil catching fire in case of a crude oil\nderailment. Present study examines the effect of polybutadiene polymer on the\ncombustion properties and soot deposits of Bakken and Pennsylvania crudes.\nTreating these crudes as multicomponent liquid fuels and polybutadiene as an\nadditive, droplet combustion experiments were conducted with sub-millimeter\nsized spherical droplets suspended on very fine support fibers. Polybutadiene\npolymer additive of two different chain lengths has been investigated. Results\nshow that both polymer chain length and origin of crude oil have a significant\neffect on various combustion properties like combustion rate, ignition delay,\ntotal combustion time, and flame stand-off ratio. Polymeric additives also\nchange the soot deposit structure and particle size compared to the base fuel.\nPresent research is envisioned to aid in theoretical combustion modeling of\ncomplex multicomponent liquid fuels, as well as generate interest in\ninvestigating more polymeric additives for liquid fuels.", "category": "physics_app-ph" }, { "text": "3D core@multishell piezoelectric nanogenerators: The thin film configuration presents obvious practical advantages over the 1D\nimplementation in energy harvesting systems such as easily manufacturing and\nprocessing and long lasting and stable devices. However, most of the ZnO-based\npiezoelectric nanogenerators (PENGs) reported so far relay in the exploitation\nof single-crystalline ZnO nanowires because their self-orientation in the\nc-axis and ability to accommodate long deformations resulting in a high\npiezoelectric performance. Herein, we show an innovative approach aiming to\nproduce PENGs by combining polycrystalline ZnO layers fabricated at room\ntemperature by plasma assisted deposition with supported small-molecule organic\nnanowires (ONWs) acting as 1D scaffold. The resulting hybrid nanostructure is\nformed by a single-crystalline organic nanowire conformally surrounded by a\nthree dimensional (3D) ZnO shell that combines the mechanical properties of the\norganic core with the piezoelectric response of the ZnO layer. In a loop\nforward towards the integration of multiple functions within a single wire, we\nhave also developed ONW@Au@ZnO nanowires including a gold shell acting as inner\nnanoscopic electrode. Thus, we have built and compare thin films and 3D\ncore@shell ONW@ZnO and ONW@Au@ZnO PENGs showing output piezo-voltages up to 170\nmV. The synergistic combination of functionalities in the ONW@Au@ZnO devices\npromotes an enhanced performance generating piezo-currents almost twenty times\nlarger than the ONW@ZnO nanowires and superior to the thin film nanogenerators\nfor equivalent and higher thicknesses.", "category": "physics_app-ph" }, { "text": "Multi-kV class $\u03b2$-Ga$_2$O$_3$ MESFETs with a Lateral Figure of\n Merit up to 355 MW/cm$^2$: We demonstrate over 3 kV gate-pad-connected field plated (GPFP)\n$\\beta$-Ga$_2$O$_3$ lateral MESFETs with high lateral figure of merit (LFOM)\nusing metalorganic vapor phase epitaxy (MOVPE) grown channel layers and regrown\nohmic contact layers. Using an improved low-temperature MOVPE selective area\nepitaxy process, we show that a total contact resistance to the channel as low\nas 1.4 $\\Omega$.mm can be achieved.The GPFP design adopted here using PECVD\n(plasma-enhanced chemical vapor deposition) deposited SiN$_x$ dielectric and\nSiN$_x$/SiO$_2$ wrap-around passivation exhibits up to ~14% improved R$_{ON}$,\nup to ~70% improved breakdown voltage (V$_{BR}$ = V$_{DS}$ - V$_{GS}$)\nresulting in up to $\\sim$3$\\times$ higher LFOM compared to non-FP\n$\\beta$-Ga$_2$O$_3$ lateral MESFETs. The V$_{BR}$ (~2.5 kV) and LFOM (355\nMW/cm$^2$) measured simultaneously in our GPFP $\\beta$-Ga$_2$O$_3$ lateral\nMESFET (with L$_{GD}$ = 10 $\\mu$m) is the highest value achieved in any\ndepletion-mode $\\beta$-Ga$_2$O$_3$ lateral device.", "category": "physics_app-ph" }, { "text": "Quality control of eggs using multivariate analysis of micro-Raman\n spectroscopy: Considering the pivotal role of eggs in the food industry and their\nnutritional significance, this study employed micro-Raman spectroscopy of eggs,\nexamining both shells and yolks to assess the quality and freshness of eggs.\nRaman spectra were collected at different temperatures and time intervals to\ninvestigate temperature and time effects, potentially indicating Raman peak\nreduction due to Maillard reaction and oxidation of proteins and lipids and\ncarotenoid depletion, respectively. By calculating the ratio of Raman peaks,\nlipids, fatty acids, and choline methyl were introduced as biomarkers of\ntemperature and time. Notable correlations were identified between Raman peaks\nand egg quality coefficients, including egg coefficient and peak 1002 cm$^{-1}$\n(protein), total weight and 1301 cm$^{-1}$ (Lipids), yolk weight and 2934 and\n3057 cm$^{-1}$, total weight with peak 710 cm$^{-1}$, and egg shape index and\npeak 3057 cm$^{-1}$. Analysis of eggshells at different time intervals revealed\nRaman peak reduction during time, demonstrating Raman's effectiveness in\nassessing egg quality from its shell. Using the PLS-DA method, the\nclassification of eggs at different temperatures and storage times using egg\nyolk Raman spectra was performed with 80% accuracy, predominantly influenced by\ncarotenoid peaks, showing Raman a practical, and non-destructive method for egg\nquality and freshness control.", "category": "physics_app-ph" }, { "text": "Borehole acoustic full-waveform inversion: Full-waveform inversion (FWI) is a technique having the potential for\nbuilding high-resolution elastic velocity models. We proposed to apply this\ntechnique to wireline monopole acoustic logging data to obtain the near\nwellbore formation velocity structures, which can be used in wellbore damage or\nfluid intrusion evaluation. A 2D FWI using monopole acoustic logging data is\npresented. The FWI is established in cylindrical coordinates instead of\nCartesian coordinates in order to adapt to the borehole geometry. A\npreconditioner is designed for suppressing the influence of the strong borehole\nguided waves in the inversion. Synthetic tests demonstrate that high-resoultion\nelastic velocity profile around borehole can be inverted from monopole acoustic\nlogging data by using the proposed method.", "category": "physics_app-ph" }, { "text": "Thermal radiation dominated heat transfer in nanomechanical silicon\n nitride drum resonators: Nanomechanical silicon nitride (SiN) drum resonators are currently employed\nin various fields of applications that arise from their unprecedented frequency\nresponse to physical quantities. In the present study, we investigate the\nthermal transport in nanomechanical SiN drum resonators by analytical\nmodelling, computational simulations, and experiments for a better\nunderstanding of the underlying heat transfer mechanism causing the thermal\nfrequency response. Our analysis indicates that radiative heat loss is a\nnon-negligible heat transfer mechanism in nanomechanical SiN resonators\nlimiting their thermal responsivity and response time. This finding is\nimportant for optimal resonator designs for thermal sensing applications as\nwell as cavity optomechanics.", "category": "physics_app-ph" }, { "text": "Adiabatic conversion between gigahertz quasi-Rayleigh and quasi-Love\n modes for phononic integrated circuits: Unsuspended phononic integrated circuits have been proposed for on-chip\nacoustic information processing. Limited by the operation mechanism of a\nconventional interdigital transducer, the excitation of the quasi-Love mode in\nGaN-on-Sapphire is inefficient and thus a high-efficiency Rayleigh-to-Love mode\nconverter is of great significance for future integrated phononic devices.\nHere, we propose a high-efficiency and robust phononic mode converter based on\nan adiabatic conversion mechanism. Utilizing the anisotropic elastic property\nof the substrate, the adiabatic mode converter is realized by a simple tapered\nphononic waveguide. A conversion efficiency exceeds $98\\%$ with a\n$3\\,\\mathrm{dB}$ bandwidth of $1.7\\,\\mathrm{GHz}$ can be realized for phononic\nwaveguides working at GHz frequency band, and excellent tolerance to the\nfabrication errors is also numerically validated. The device that we proposed\ncan be useful in both classical and quantum phononic information processing,\nand the adiabatic mechanism could be generalized to other phononic device\ndesigns.", "category": "physics_app-ph" }, { "text": "Efficient color coatings for single junction and multijunction colored\n solar cells: Colored solar cells suffer from lower efficiency due to reflection and\nabsorption losses by coatings. By studying different types of coatings on solar\ncells, the spectrum parameters impacting the solar cell efficiency were\nidentified. A collection of color coatings was fabricated and characterized\nusing spectrophotometry and colorimetric photography. The coatings include\ncommercial absorption filters, commercial distributed bragg reflectors,\nlab-made interference coatings, and cellulose nanocrystal coatings. Commercial\nsingle junction and multijunction solar cells were used to measure the impact\nof the color coatings on solar cell performance. Structural colors were found\nto result in the highest brightness to color loss ratio. Structural colors do\nnot fade provided that the structure is not compromised. Color loss in single\njunction solar cells is a result of the proportion of reflected light in the\nabsorption range of the material. Multijunction solar cells were strongly\naffected by current mismatch losses, where narrow reflection peaks resulted in\nhigh efficiency losses. Structural color coatings made using cellulose\nnanocrystals exhibited low and broad reflection peaks that produced bright\ncolors and maintained high performance of single junction and multijunction\nsolar cells, retaining up to 83 % of the reference power obtained in the\nabsence of a color coating.", "category": "physics_app-ph" }, { "text": "Analysis of hydrogen distribution and migration in fired passivating\n contacts (FPC): In this work, the hydrogenation mechanism of fired passivating contacts (FPC)\nbased on c-Si/SiO$_{x}$/nc-SiC$_{x}$(p) stacks was investigated, by correlating\nthe passivation and local re-distribution of hydrogen. Secondary ion mass\nspectroscopy (SIMS) depth profiling was used to assess the hydrogen\n(/deuterium) content. The SIMS profiles show that hydrogen almost completely\neffuses out of the SiC$_{x}$(p) during firing, but can be re-introduced by\nhydrogenation via forming gas anneal (FGA) or by release from a hydrogen\ncontaining layer such as SiN$_{x}$:H. A pile-up of H at the c-Si/SiO$_{x}$\ninterface was observed and identified as a key element in the FPC's passivation\nmechanism. Moreover, the samples hydrogenated with SiN$_{x}$:H exhibited higher\nH content compared to those treated by FGA, resulting in higher iV$_{OC}$\nvalues. Further investigations revealed that the doping of the SiC$_{x}$ layer\ndoes not affect the amount of interfacial defects passivated by the\nhydrogenation process presented in this work. Eventually, an effect of the\noxide's nature on passivation quality is evidenced. iV$_{OC}$ values of up to\n706 mV and 720 mV were reached with FPC test structures using chemical and\nUV-O$_{3}$ tunneling oxides, respectively, and up to 739 mV using a reference\npassivation sample featuring a ~25 nm thick thermal oxide.", "category": "physics_app-ph" }, { "text": "Diamond Nitrogen-Vacancy Center Magnetometry: Advances and Challenges: Diamond nitrogen-vacancy (NV) center magnetometry has recently received\nconsiderable interest from researchers in the fields of applied physics and\nsensors. The purpose of this review is to analyze the principle, sensitivity,\ntechnical development potential, and application prospect of the diamond NV\ncenter magnetometry. This review briefly introduces the physical\ncharacteristics of NV centers, summarizes basic principles of the NV center\nmagnetometer, analyzes the theoretical sensitivity, and discusses the impact of\ntechnical noise on the NV center magnetometer. Furthermore, the most critical\ntechnologies that affect the performance of the NV center magnetometer are\ndescribed: diamond sample preparation, microwave manipulation, fluorescence\ncollection, and laser excitation. The theoretical and technical crucial\nproblems, potential solutions and research technical route are discussed. In\naddition, this review discusses the influence of technical noise under the\nconventional technical conditions and the actual sensitivity which is\ndetermined by the theoretical sensitivity and the technical noise. It is\nenvisaged that the sensitivity that can be achieved through an optimized design\nis in the order of 10 fT/Hz^1/2. Finally, the roadmap of applications of the\ndiamond NV center magnetometer are presented.", "category": "physics_app-ph" }, { "text": "Growth and Characterization of Multi-Walled Carbon Nanotubes using\n Chemical Vapor Deposition: In this study, the synthesis of multi-walled carbon nanotubes (MWCNTs) was\ncarried out by chemical vapor deposition (CVD) using propane as the carbon\nsource and Si as the catalyst support. The effect of CVD process variables such\nas temperature, choice of catalyst, etc on the growth behavior of nanotubes has\nbeen examined to understand the catalytic growth of CNTs. The transition metal\ncatalysts, Fe and Ni, were used in both elemental metal form and in a metal\ncomplex form. In the case of elemental metal catalysts, the respective metals\nwere deposited over the Si substrate using thermal evaporation following which\nnanotubes were synthesized by means of CVD. Subsequent studies of the\nsynthesized carbon nanostructures employing elemental metal catalysts revealed\na significant influence of the temperature and the catalyst material on the\nstructure of CNTs. The CNTs synthesized using Ni catalyst were bamboo-like\nwhereas the CNTs developed employing Fe catalyst were straight tubes with\npartial metal filling. Consequently, growth models for the different growth\nmechanisms have been proposed. Certain limitations of the above process have\nbeen overcome by employing spin-coating of a metal complex catalyst material on\nthe Si substrate. The CVD synthesis of nanotubes using metal complex catalysts\nalways resulted in partially catalyst filled CNTs. More importantly, the metal\ncomplex catalyst could be easily patterned on the Si substrate using\nspin-coating and photolithography, which resulted in site selective growth of\npartially catalyst filled MWCNTs. Since the entire process of site selective\ngrowth is suitable for conventional device fabrication, this method is a\npromising and practical pathway for large-scale fabrication of several magnetic\nmaterial filled CNT-based devices.", "category": "physics_app-ph" }, { "text": "Joint Identification through Hybrid Models Improved by Correlations: In mechanical systems coupled with joints, accurate prediction of the joint\ncharacteristics is extremely important. Despite years of research, a lot is yet\nto be learnt about the joints' interface dynamics. The problem becomes even\nmore difficult when the interface Degrees-of-Freedom (DoF) are inaccessible for\nFrequency Response Function (FRF) measurements. This is, for example, the case\nof bladed-disk systems with dove-tail or fir-tree type joints. Therefore, an\nFRF based expansion method called System Equivalent Model Mixing (SEMM) is used\nto obtain expanded interface dynamics. The method uses numerical and\nexperimental sub-models of each component and their assembly to produce the\nrespective expanded or hybrid sub-models. By applying substructure decoupling\nto these sub-models, the joint can be identified. However, the joint can be\nnoisy due to expansion and measurement errors which propagate to the hybrid\nsub-models. In this paper, a correlation based approach is proposed in the SEMM\nmethod wherein the quality of the expanded sub-models is improved. In this new\napproach, several expanded models are generated systematically using different\ncombinations of the experimental FRFs and computing a parameter, Frequency\nResponse Assurance Criteria (FRAC), to evaluate quality of the contribution of\nthe different measurements. The lowest correlated channels or FRFs can be\nfiltered out based on a certain threshold value of FRAC. Using the improved\nhybrid sub-models, the joint identification also shows a remarkable\nimprovement. The test object for the method is an assembly of disk and one\nblade with a dove-tail joint.", "category": "physics_app-ph" }, { "text": "Project 1000 x 1000: Centrifugal melt spinning for distributed\n manufacturing of N95 filtering facepiece respirators: The COVID-19 pandemic has caused a global shortage of personal protective\nequipment. While existing supply chains are struggling to meet the surge in\ndemand, the limited supply of N95 filtering facepiece respirators (FFRs) has\nplaced healthcare workers at risk. This paper presents a method for scalable\nand distributed manufacturing of FFR filter material based on a combination of\ncentrifugal melt spinning utilizing readily available cotton candy machines as\nan example. The proposed method produces nonwoven polypropylene fabric material\nwith filtering efficiency of up to 96% for particles 0.30-0.49 {\\mu}m in\ndiameter. We additionally demonstrate a scalable means to test for filtration\nefficiency and pressure drop to ensure a standardized degree of quality in the\noutput material. We perform preliminary optimization of relevant parameters for\nscale-up and propose that this is a viable method to rapidly produce up to one\nmillion N95 FFRs per day in distributed manner with just six machines per site\noperating across 200 locations. We share this work as a starting point for\nothers to rapidly construct, replicate and develop their own affordable modular\nprocesses aimed at producing high quality filtration material to address the\ncurrent FFR shortage globally.", "category": "physics_app-ph" }, { "text": "Thermal-null medium (TNM): a novel material to achieve feasible\n thermodynamics devices beyond conventional challenges: Recently, heat manipulation has gained the attention of scientific community\ndue to its several applications. In this letter, based on transformation\nthermodynamic (TT) methodology, a novel material, which is called thermal-null\nmedium (TNM), is proposed that enables us to design various thermal\nfunctionalities such as thermal bending devices, arbitrary shape heat\nconcentrators and omnidirectional thermal cloaks. In contrary to the\nconventional TT-based conductivities, which are inhomogeneous and anisotropic,\nTNMs are homogeneous and easy to realize. In addition, the attained TNMs are\nindependent of the device shape. That is if the geometry of the desired device\nis changed, there is no need to recalculate the necessitating conductivities.\nThis feature of TNM will make it suitable for scenarios where\nre-configurability is of utmost importance. Several numerical simulations are\ncarried out to demonstrate the TNM capability and its applications in\ndirectional bending devices, heat concentrators and thermal cloaks. The\nproposed TNM could open a new avenue for potential applications in solar\nthermal panels and thermal-electric devices.", "category": "physics_app-ph" }, { "text": "Dynamical Negative Differential Resistance in Antiferromagnetically\n Coupled Few-Atom Spin-Chains: We present the appearance of negative differential resistance (NDR) in\nspin-dependent electron transport through a few-atom spin-chain. A chain of\nthree antiferromagnetically coupled Fe atoms(Fe trimer) was positioned on a\nCu2N/Cu(100) surface and contacted with the spin-polarized tip of a scanning\ntunneling microscope, thus coupling the Fe trimer to one non-magnetic and one\nmagnetic lead. Pronounced NDR appears at the low bias of 7 mV where inelastic\nelectron tunneling dynamically locks the atomic spin in a long-lived excited\nstate. This causes a rapid increase of the magnetoresistance between\nspin-polarized tip and Fe trimer and quenches elastic tunneling. By varying the\ncoupling strength between tip and Fe trimer we find that in this transport\nregime the dynamic locking of the Fe trimer competes with magnetic exchange\ninteraction, which statically forces the Fe trimer into the\nhigh-magnetoresistance state and removes the NDR.", "category": "physics_app-ph" }, { "text": "Efficient calculation of the self magnetic field, self-force, and\n self-inductance for electromagnetic coils: The design of electromagnetic coils may require evaluation of several\nquantities that are challenging to compute numerically. These quantities\ninclude Lorentz forces, which may be a limiting factor due to stresses; the\ninternal magnetic field, which is relevant for determining stress as well as a\nsuperconducting coil's proximity to its quench limit; and the inductance, which\ndetermines stored magnetic energy and dynamics. When computing the effect on\none coil due to the current in another, these quantities can often be\napproximated quickly by treating the coils as infinitesimally thin. When\ncomputing the effect on a coil due to its own current (e.g., self-force or\nself-inductance), evaluation is difficult due to the presence of a singularity;\ncoils cannot be treated as infinitesimally thin as each quantity diverges at\nzero conductor width. Here, we present novel and well-behaved methods for\nevaluating these quantities using non-singular integral formulae of reduced\ndimensions. These formulae are determined rigorously by dividing the domain of\nintegration of the magnetic vector potential into two regions, exploiting\nappropriate approximations in each region, and expanding in high aspect ratio.\nOur formulae show good agreement to full finite-thickness calculations even at\nlow aspect ratio, both analytically for a torus and numerically for a\nnon-planar coil of a stellarator fusion device, the Helically Symmetric\neXperiment (HSX). Because the integrands of these formulae develop fine\nstructure as the minor radius becomes infinitely thin, we also develop a method\nof evaluating the self-force and self-inductance with even greater efficiency\nby integrating this sharp feature analytically. We demonstrate with this method\nthat the self-force can be accurately computed for the HSX coil with as few as\n12 grid points.", "category": "physics_app-ph" }, { "text": "Nanomechanical single-photon routing: The merger between integrated photonics and quantum optics promises new\nopportunities within photonic quantum technology with the very significant\nprogress on excellent photon-emitter interfaces and advanced optical circuits.\nA key missing functionality is rapid circuitry reconfigurability that\nultimately does not introduce loss or emitter decoherence, and operating at a\nspeed matching the photon generation and quantum memory storage time of the\non-chip quantum emitter. This ambitious goal requires entirely new active\nquantum-photonic devices by extending the traditional approaches to\nreconfigurability. Here, by merging nano-optomechanics and deterministic\nphoton-emitter interfaces we demonstrate on-chip single-photon routing with low\nloss, small device footprint, and an intrinsic time response approaching the\nspin coherence time of solid-state quantum emitters. The device is an essential\nbuilding block for constructing advanced quantum photonic architectures\non-chip, towards, e.g., coherent multi-photon sources, deterministic\nphoton-photon quantum gates, quantum repeater nodes, or scalable quantum\nnetworks.", "category": "physics_app-ph" }, { "text": "Flash microwave pressing of zirconia: Microwave Pressing is a promising way to reduce microwave sintering\ntemperatures and stabilize microwave powder materials processing. A\nmulti-physics simulation was conducted of the regulated pressure-assisted\nmicrowave cavity. This simulation took into consideration resonance phenomena\nand the nonlinear temperature-dependent material parameters of zirconia. The\nintrinsic behaviors of microwave systems and zirconia make the regulation of\nthe microwave pressing difficult. However, the same phenomena can be used to\nactivate flash sintering. Flash microwave sintering uses high electric fields\nof the resonant microwave profile, the Negative Temperature Behavior (NTC) of\nzirconia resistivity, and the mechanical pressure applied to the powder via a\ndie compaction configuration. The resulting flash microwave pressing still\nneeds improvement in terms of the processed material structure homogeneity, but\nit has the capacity to become the fastest sintering treatment as it allows room\ntemperature activation where the total process time only takes a few seconds.\nIn addition, this 10-20s processing technique has shown good potential for\nimproving the transparency of alumina pre-sintered specimens.", "category": "physics_app-ph" }, { "text": "Multi-bit MRAM storage cells utilizing serially connected perpendicular\n magnetic tunnel junctions: Serial connection of multiple memory cells using perpendicular magnetic\ntunnel junctions (pMTJ) is proposed as a way to increase magnetic random access\nmemory (MRAM) storage density. Multi-bit storage element is designed using\npMTJs fabricated on a single wafer stack, with a serial connections realized\nusing top-to-bottom vias. Tunneling magnetoreistance effect above 130%, current\ninduced magnetization switching in zero external magnetic field and stability\ndiagram analysis of single, two-bit and three-bit cells are presented together\nwith thermal stability. The proposed design is easy to manufacture and can lead\nto increase capacity of future MRAM devices.", "category": "physics_app-ph" }, { "text": "Magnetic anisotropy and critical behavior of the quaternary van der\n Waals ferromagnetic material $\\bf CrGe_\u03b4Si_{1-\u03b4}Te_3$: Recently, two-dimensional ferromagnetism in the family of Chromium compounds\n$\\rm CrXTe_3 (X=Si, Ge)$ has attracted a broad research interest. Despite the\nstructural similarity in $\\rm CrTe_6$ octahedra, the size effect of inserted Ge\nor Si dimer contributes to significant differences in magnetism. Here, we\nreport a new quaternary van der Waals ferromagnetic material $\\rm\nCrGe_{\\delta}Si_{1-\\delta}Te_3$ synthesized by flux method. Ge substitution in\nSi site results in the lattice expansion, further increasing the Curie\ntemperature and reducing the magnetic anisotropy. The critical behavior of $\\rm\nCr_{0.96}Ge_{0.17}Si_{0.82}Te_3$ has been studied by specific heat as well as\nmagnetization measurements. And the extracted critical exponents are\nself-consistent and well-obeying the scaling laws, which are closer to the 2D\nIsing model with interaction decaying as $J(r)\\approx r^{-3.44}$.", "category": "physics_app-ph" }, { "text": "In-situ analysis of small microplastics in coastal surface water samples\n of the subtropical island of Okinawa, Japan: Marine plastic debris is widely recognized as a global environmental issue.\nSun-micron plastic particles, with an upper size limit of 20 um, have been\nidentified as having the highest potential for causing damage to marine\necosystems. Having accurate methods for quantifying the abundance of such\nparticles in a natural environment is essential for defining the extent of the\nproblem they pose. Using an optical micro-Raman tweezers setup, we have\nidentified the composition of particles trapped in marine aggregates collected\nfrom the coastal surface waters around the subtropical island of Okinawa.\nChemical composition analysis at the single-particle level indicates dominance\nby low-density polyethylene, which accounted for 75% of the total sub-micron\nplastics analyzed. Our results show the occurrence of plastics at all test\nsites, with the highest concentration in areas with high human activities. The\naverage, smallest sub-micron plastics size is (2.53 +/- 0.85)um for\npolystyrene. We also observed additional Raman peaks on the plastics spectrum\nwith decreasing debris size which could be related to structural modification\ndue to weathering or embedding in organic matter. By single-particle level\nsub-micron plastics identification, we can begin to understand their dispersion\nin the ocean and define their toxicity and impacts on marine biodiversity and\nfood chain.", "category": "physics_app-ph" }, { "text": "Generation of Coherent Phonons via a Cavity Enhanced Photonic Lambda\n Scheme: We demonstrate the generation of coherent phonons in a quartz Bulk Acoustic\nWave (BAW) resonator through the photoelastic properties of the crystal, via\nthe coupling to a microwave cavity enhanced by a photonic lambda scheme. This\nis achieved by imbedding a single crystal BAW resonator between the post and\nthe adjacent wall of a microwave reentrant cavity resonator. This 3D photonic\nlumped LC resonator at the same time acts as the electrodes of a BAW phonon\nresonator, and allows the direct readout of coherent phonons via the linear\npiezoelectric response of the quartz. A microwave pump, $\\omega_p$ is tuned to\nthe cavity resonance $\\omega_0$, while a probe frequency, $\\omega_{probe}$, is\ndetuned and varied around the red and blue detuned values with respect to the\nBAW phonon frequency, $\\Omega_m$. The pump and probe power dependence of the\ngenerated phonons unequivocally determines the process to be electrostrictive,\nwith the phonons produced at the difference frequency between pump and probe,\nwith no back action effects involved. Thus, the phonons are created without\nthreshold and can be considered analogous to a Coherent Population Trapped\n(CPT) maser scheme.", "category": "physics_app-ph" }, { "text": "Changes in the near edge X-ray absorption fine structure of hybrid\n organic-inorganic resists upon exposure: We report on the near edge X-ray absorption fine structure (NEXAFS)\nspectroscopy of hybrid organic-inorganic resists. These materials are\nnonchemically amplified systems based on Si, Zr, and Ti oxides, synthesized\nfrom organically modified precursors and transition metal alkoxides by a\nsol-gel route and designed for ultraviolet, extreme ultraviolet and electron\nbeam lithography. The experiments were conducted using a scanning transmission\nX-ray microscope (STXM) which combines high spatial-resolution microscopy and\nNEXAFS spectroscopy. The absorption spectra were collected in the proximity of\nthe carbon edge (~ 290 eV) before and after in situ exposure, enabling the\nmeasurement of a significant photo-induced degradation of the organic group\n(phenyl or methyl methacrylate, respectively), the degree of which depends on\nthe configuration of the ligand. Photo-induced degradation was more efficient\nin the resist synthesized with pendant phenyl substituents than it was in the\ncase of systems based on bridging phenyl groups. The degradation of the methyl\nmethacrylate group was relatively efficient, with about half of the initial\nligands dissociated upon exposure. Our data reveal that the such dissociation\ncan produce different outcomes, depending on the structural configuration.\nWhile all the organic groups were expected to detach and desorb from the resist\nin their entirety, a sizeable amount of them remain and form undesired\nbyproducts such as alkene chains. In the framework of the materials synthesis\nand engineering through specific building blocks, these results provide a\ndeeper insight into the photochemistry of resists, in particular for extreme\nultraviolet lithography.", "category": "physics_app-ph" }, { "text": "Ultrahigh flexoelectric effect of 3D interconnected porous polymers:\n modelling and verification: Non-conductive materials like rubbers, plastics, ceramics, and even\nsemiconductors have the property of flexoelectricity, which means that they can\ngenerate electricity when bent and twisted. However, an irregular shape or a\npeculiar load has been the necessary condition to realize flexoelectricity, and\nthe weight and deformability specific ratios of flexoelectricity of solids are\nlimited. In this work, we develop a theoretical model of flexoelectricity of\nthree-dimensional interconnected porous materials. Compared to the solid\nmaterials, porous materials can exhibit flexoelectricity under arbitrary\nloading forms due to their complex microstructures, and the weight and\ndeformability specific flexoelectric output is much higher than that of the\nsolids. Then, we verify the model by measuring the flexoelectric response of\npolydimethylsiloxane (PDMS) and porous polyvinylidene fluoride (PVDF). The\nporous PDMS with 3D micron-scale interconnected structures exhibits two orders\nof magnitude higher weight and deformability specific flexoelectric output than\nthat of the solid truncated pyramid PDMS. The flexoelectric signal is found to\nbe linearly proportional to the applied strain, the microstructural size and\nthe frequency. Finally, we apply the theory to a more practical bending sensor,\nand demonstrate its stable functioning and accurate response. Our model can be\napplied to other porous materials, and the results highlight the new potential\nof porous micro-structured materials with a significant flexoelectric effect in\nthe fields of mechanical sensing, actuating, energy harvesting, and biomimetics\nas light-weight materials.", "category": "physics_app-ph" }, { "text": "Cross-sectional scanning tunneling microscopy of InAs/GaAs(001)\n submonolayer quantum dots: Cross-sectional scanning tunneling microscopy (X-STM) was employed to\ncharacterize the InAs submonolayer quantum dots (SMLQDs) grown on top of a\nSi-doped GaAs(001) substrate in the presence of (2X4) and c(4X4) surface\nreconstructions. Multiple layers were grown under different conditions to study\ntheir effects on the formation, morphology and local composition of the SMLQDs.\nThe morphological and compositional variations in SMLQDs were observed by both\nfilled and emptystate imaging. A detailed analysis of indium segregation in the\nSMLQDs layers was described by fitting local indium concentration profile with\na standard segregation model. A strong influence of arsenic flux over the\nformation of the SMLQDs and indium incorporation was observed and reported. We\ninvestigated the well-width fluctuations of the InGaAs quantum well (QW) in\nwhich SMLQDs were formed . The monolayer fluctuations of the well width were\nnegligible compared to the more pronounced compositional fluctuations in all\nthe layers. Keywords: Submonolayer quantum dots, Surface reconstruction, X-STM,\nIndium segregation", "category": "physics_app-ph" }, { "text": "Bending Energy-Driven Cooperative Patterning of 2D Colloids in Elastic\n 2D Fluids: Suspensions of colloidal microplates in contoured 2D elastic fluids sheets\nare dominated by the bending mechanics and shear rigidity of the plates and the\ncontrasting in-plane shear flow of the 2D fluid. Using the phase separated\nphospholipid membranes of individual giant unilamellar vesicles as models of\ncontoured 2D suspensions, where solid domains act as colloids in a fluid\nmembrane, we explore bending elasticity-driven assembly. The plate-shaped\ndomains are varied between 1-10 {\\mu}m in diameter, with 4-100 plates per\nvesicle depending on size, contributing a solid area of 17 plus minus 3%. Three\nclasses of reversible plate arrangements evidence inter-plate attractions and\nrepulsions: persistent hexagonal vesicle-encompassing quasi-lattices,\npersistent closely associated configurations (chains or concentrated lattices),\nand a dynamic disordered state. The vesicle-encompassing quasi-lattice is\nstable to vesicle dehydration by 30% relative to an inflated sphere. Excess\narea or membrane slack, for a fixed composition, dominates the preferred\nconfiguration while domain size and number contribute pattern intricacy.\nDifferent from the gradual variations in domain interactions and tunable\npositions in two-colloid systems, multibody interactions vary sharply within a\nparticular range of excess area, producing cooperative assembly reminiscent of\na phase transition.", "category": "physics_app-ph" }, { "text": "Multilayered Recoverable Sandwich Composite Structures with Architected\n Core: In this paper, we propose a novel design and fabrication strategy to produce\narchitected core structures for use as the core in composite sandwich\nstructures. A traditional foam core or honeycomb structure is lightweight and\nstiff, but susceptible to permanent deformation when subjected to excessive\nloading. Here we propose the use of an architected structure composed of arrays\nof hollow truncated cone unit cells that dissipate energy and exhibit\nstructural recovery. These structures printed with a viscoelastic material rely\non buckling of their sidewalls to dissipate energy and snap-back to prevent\npermanent deformation. We explore the mechanical response of these conical unit\ncells in terms of their buckling strength and post-buckling stability\ncondition, and develop design maps for the same, by relating them to\nnon-dimensional geometric parameters $\\alpha$, $\\beta$, $\\gamma$, where\n$\\alpha$ represents the slenderness of the curved sidewalls, $\\beta$ is the\nangle of the sidewall to the base, and $\\gamma$ represents the curvature of the\nsidewall. A validated finite element model is developed and used to investigate\nthe effect of these parameters. We see that the peak buckling load is directly\nproportional to both $\\alpha$ & $\\beta$ and is not dependent on $\\gamma$ when\nthe load is normalized by the volume of material in the curved sidewall.\nInterestingly, the post-buckling stability is influenced by $\\gamma$, or the\ninitial curvature of the sidewall, where a larger radius of curvature makes the\nstructure less susceptible to exhibit structural bistability. The structures\npresented here are printed using a viscoelastic material, that causes them to\nexhibit pseudo-bistability, or a time-delayed recovery. This allows the\nstructures to buckle and dissipate energy, and then recover to their original\nconfigurations without the need for external stimuli or energy.", "category": "physics_app-ph" }, { "text": "Picoscale control of quantum plasmonic photoluminescence enhancement at\n 2D lateral heterojunction: Two-dimensional (2D) materials and heterostructures have recently gained wide\nattention due to potential applications in optoelectronic devices. However, the\noptical properties of the heterojunction have not been properly characterized\ndue to the limited spatial resolution, requiring nano-optical characterization\nbeyond the diffraction limit. Here, we investigate the lateral monolayer\nMoS2-WS2 heterostructure using tip-enhanced photoluminescence (TEPL)\nspectroscopy on a non-metallic substrate with picoscale tip-sample distance\ncontrol. By placing a plasmonic Au-coated Ag tip at the heterojunction, we\nobserved more than three orders of magnitude photoluminescence (PL) enhancement\ndue to the classical near-field mechanism and charge transfer across the\njunction. The picoscale precision of the distance-dependent TEPL measurements\nallowed for investigating the classical and quantum tunneling regimes above and\nbelow the ~320 pm tip-sample distance, respectively. Quantum plasmonic effects\nusually limit the maximum signal enhancement due to the near-field depletion at\nthe tip. We demonstrate a more complex behavior at the 2D lateral\nheterojunction, where hot electron tunneling leads to the quenching of the PL\nof MoS2, while simultaneously increasing the PL of WS2. Our simulations show\nagreement with the experiments, revealing the range of parameters and\nenhancement factors corresponding to various regimes. The controllable\nphotoresponse of the lateral junction can be used in novel nanodevices.", "category": "physics_app-ph" }, { "text": "All-dielectric high-Q dynamically tunable transmissive metasurfaces: Active metasurfaces, which are arrays of actively tunable resonant elements,\ncan dynamically control the wavefront of the scattered light at a subwavelength\nscale. To date, most active metasurfaces that enable dynamic wavefront shaping\noperate in reflection. On the other hand, active metasurfaces operating in\ntransmission are of considerable interest as they can readily be integrated\nwith chip-scale light sources, yielding ultra-compact wavefront shaping\ndevices. Here, we report designs for all-dielectric low-loss active\nmetasurfaces which can dynamically manipulate the transmitted light wavefront\nin the near-infrared wavelength range. Our active metasurfaces feature an array\nof amorphous silicon (a-Si) pillars on a silica substate, which support\nresonances with quality factors (Q-factors) as high as 9800, as well as other\nlower-Q resonances. First, we demonstrate that high-Q resonance dips observed\nin transmission can be transformed into a transmission resonance peak by\npositioning a-Si pillar resonators at a prescribed distance from a crystalline\nSi substrate, defined by a silica spacer layer. Next, we report the design of\nmetasurface geometry with realistic interconnect architectures that enable\nthermo-optic dynamic beam switching with switching times as low as 7.3 {\\mu}s.\nBeam switching is observed for refractive index differences between neighboring\nmetasurface elements as low as 0.0026. Finally, we demonstrate that metasurface\nstructures with both high-Q and lower-Q modes and realistic interconnect\narchitectures can be used for dynamic beam steering.", "category": "physics_app-ph" }, { "text": "Low-loss composite photonic platform based on 2D semiconductor\n monolayers: Two dimensional materials such as graphene and transition metal\ndichalcogenides (TMDs) are promising for optical modulation, detection, and\nlight emission since their material properties can be tuned on-demand via\nelectrostatic doping. The optical properties of TMDs have been shown to change\ndrastically with doping in the wavelength range near the excitonic resonances.\nHowever, little is known about the effect of doping on the optical properties\nof TMDs away from these resonances, where the material is transparent and\ntherefore could be leveraged in photonic circuits. Here, we probe the\nelectro-optic response of monolayer TMDs at near infrared (NIR) wavelengths\n(i.e. deep in the transparency regime), by integrating them on silicon nitride\n(SiN) photonic structures to induce strong light$-$matter interaction with the\nmonolayer. We dope the monolayer to carrier densities of ($7.2 \\pm 0.8$)\n$\\times$ $10^{13} \\textrm{cm}^{-2}$, by electrically gating the TMD using an\nionic liquid. We show strong electro-refractive response in monolayer tungsten\ndisulphide (WS$_2$) at NIR wavelengths by measuring a large change in the real\npart of refractive index $\\Delta$n = $0.53$, with only a minimal change in the\nimaginary part $\\Delta$k = $0.004$. The doping induced phase change\n($\\Delta$n), compared to the induced absorption ($\\Delta$k) measured for WS$_2$\n($\\Delta$n/$\\Delta$k $\\sim 125$), a key metric for photonics, is an order of\nmagnitude higher than the $\\Delta$n/$\\Delta$k for bulk materials like silicon\n($\\Delta$n/$\\Delta$k $\\sim 10$), making it ideal for various photonic\napplications. We further utilize this strong tunable effect to demonstrate an\nelectrostatically gated SiN-WS$_2$ phase modulator using a WS$_2$-HfO$_2$\n(Hafnia)-ITO (Indium Tin Oxide) capacitive configuration, that achieves a phase\nmodulation efficiency (V$_\\pi$L) of 0.8 V $\\cdot$ cm with a RC limited\nbandwidth of 0.3 GHz.", "category": "physics_app-ph" }, { "text": "An efficient procedure to predict the acoustophoresis of axisymmetric\n irregular particles above ultrasound transducer array: Acoustic radiation force and torque arising from wave scattering are able to\ntranslate and rotate matter without contact. However, the existing research\nmainly focused on manipulating simple symmetrical geometries, neglecting the\nsignificance of geometric features. For the non-spherical geometries, the shape\nof the object strongly affects its scattering properties, and thus the\nradiation force and torque as well as the acoustophoretic process. Here, we\ndevelop a semi-analytical framework to calculate the radiation force and torque\nexerted on the axisymmetric particles excited by a user-customized transducer\narray based on a conformal transformation approach, capturing the significance\nof the geometric features. The derivation framework is established under the\ncomputation coordinate system (CCS), whereas the particle is assumed to be\nstatic. For the dynamic processes, the rotation of particle is converted as the\nopposite rotation of transducer array, achieved by employing a rotation\ntransformation to tune the incident driving field in the CCS. Later, the\nobtained radiation force and torque in the CCS should be transformed back to\nthe observation coordinate system (OCS) for force and torque analysis. The\nradiation force and torque exerted on particles with different orientations are\nvalidated by comparing the full three-dimensional numerical solution in\ndifferent phase distributions. It is found that the proposed method presents\nsuperior computational accuracy, high geometric adaptivity, and good robustness\nto various geometric features, while the computational efficiency is more than\n100 times higher than that of the full numerical method. Furthermore, it is\nfound that the dynamic trajectories of particles with different geometric\nfeatures are completely different, indicating that the geometric features can\nbe a potential degree of freedom to tune acoustophoretic process.", "category": "physics_app-ph" }, { "text": "Hydroxide-based magneto-ionics: electric-field control of reversible\n paramagnetic-to-ferromagnetic switch in $\u03b1$-Co(OH)$_{2}$ films: Magneto-ionics has emerged as a promising approach to manipulate magnetic\nproperties, not only by drastically reducing power consumption associated with\nelectric current based devices but also by enabling novel functionalities. To\ndate, magneto-ionics have been mostly explored in oxygen-based systems, while\nthere is a surge of interests in alternative ionic systems. Here we demonstrate\nhighly effective hydroxide-based magneto-ionics in electrodeposited\n${\\alpha}$-Co(OH)$_{2}$ films. The ${\\alpha}$-Co(OH)$_{2}$, which is a room\ntemperature paramagnet, is switched to ferromagnetic after electrolyte gating\nwith a negative voltage. The system is fully, magnetically reversible upon\npositive voltage application. The origin of the reversible\nparamagnetic-to-ferromagnetic transition is attributed to the ionic diffusion\nof hydroxyl groups, promoting the formation of metallic cobalt ferromagnetic\nregions. Our findings demonstrate one of the lowest turn-on voltages reported\nfor propylene carbonate gated experiments. By tuning the voltage magnitude and\nsample area we demonstrate that the speed of the induced ionic effect can be\ndrastically enhanced.", "category": "physics_app-ph" }, { "text": "Thickness gradient promotes the performance of Si-based anode material\n for lithium-ion battery: The large volume change of the silicon (Si) during lithiation and\ndelithiation process has long been a problem impeding its application as one of\nthe most promising anode materials for LIBs. In this paper, we proposed a\nconceptually new idea to address this problem simply by varying the thickness\nof the electrode material film. The resulting thickness-gradient electrode\nexhibits considerable enhancement in the electrochemical performances including\ncapacity, capacity retention, Coulombic efficiency, and rate capability in\ncomparison to the traditional counterparts with uniform thickness. Such\nenhancement in the electrochemical performance can be attributed to the\nlessening of the stress concentration on the interface between the electrode\nfilm and the current collector upon the volume change of Si taking place in the\nlithiation and delithiation process. To make the best use of this strategy,\noptimal design of the gradient thickness is proposed based on the theory of\nstress homogenization, followed by the experimental verification. The results\nof this paper provide a facile, cost-effective, and scalable way for enhancing\nthe performance of Si-based anodes for LIBs. This strategy can be further\nextended to the other anode materials suffering from the similar\nlithiation-induced volume change problem.", "category": "physics_app-ph" }, { "text": "Operando monitoring of single-particle kinetic state-of-charge\n heterogeneities and cracking in high-rate Li-ion anodes: Recent years have seen a rapidly escalating demand for battery technologies\ncapable of storing more energy, charging more quickly and having longer usable\nlifetimes, driven largely by increased electrification of transport and by\ngrid-scale energy storage systems. This has led to the development of many\npromising new electrode materials for high-rate lithium ion batteries. In order\nto rationalise and improve upon material performance, it is crucial to\nunderstand the fundamental ion-intercalation and degradation mechanisms\noccurring during realistic battery operation, on the nano- to meso-scale. Here\nwe apply a straightforward laboratory-based operando optical scattering\nmicroscopy method to study micron-sized rods of the high-rate anode material\nNb$_{14}$W$_3$O$_{44}$ during cycling at rates of up to 30C. We directly\nvisualise an elongation of the rods, which, by comparison with ensemble X-ray\ndiffraction, allows us to determine the state of charge (SOC) of the individual\nparticle. A continuous change in scattering intensity with SOC is also seen,\nenabling observation of a non-equilibrium kinetic phase separation within\nindividual particles. Phase field modelling (informed by pulsed-field-gradient\nnuclear magnetic resonance and electrochemical experiments) is used to verify\nthe kinetic origin of this separation, which arises from a dependence of the\nLi-ion diffusion coefficient upon SOC. Finally, we witness how such\nintra-particle SOC heterogeneity can lead to particle cracking; we follow the\ncycling behaviour of the resultant fragments, and show that they may become\nelectrically disconnected from the electrode. These results demonstrate the\npower of optical scattering microscopy to track rapid non-equilibrium\nprocesses, often occurring over less than 1 minute, which would be inaccessible\nwith established characterisation techniques.", "category": "physics_app-ph" }, { "text": "Ionic Sieving Through One-Atom-Thick 2D Material Enables Analog\n Nonvolatile Memory for Neuromorphic Computing: The first report on ion transport through atomic sieves of atomically-thin 2D\nmaterial is provided to solve critical limitations of electrochemical\nrandom-access memory (ECRAM) devices.", "category": "physics_app-ph" }, { "text": "Advances in Modelling and Simulation of Halide Perovskites for Solar\n Cell Applications: Perovskite solar cells (PSCs) are attracting great attention as the most\npromising candidate for the next generation solar cells. This is due to their\nlow cost and high power conversion efficiency in spite of their relatively\nshort period of development. Key components of PSCs are a variety of halide\nperovskites with ABX3 stoichiometry used as a photoabsorber, which brought the\nfactual breakthrough in the field of photovoltaic (PV) technology with their\noutstanding optoelectronic properties. To commercialize PSCs in the near\nfuture, however, these materials need to be further improved for a better\nperformance, represented by high efficiency and high stability. As in other\nmaterials development, atomistic modelling and simulation can play a\nsignificant role in finding new functional halide perovskites as well as\nrevealing the underlying mechanisms of their material processes and properties.\nIn this sense, computational works for the halide perovskites, mostly focusing\non first-principles works, are reviewed with an eye looking for an answer how\nto improve the performance of PSCs. Specific modelling and simulation\ntechniques to quantify material properties of the halide perovskites are also\npresented. Finally, the outlook for the challenges and future research\ndirections in this field is provided.", "category": "physics_app-ph" }, { "text": "Topological and Network Analysis of Lithium Ion Battery Components: The\n Importance of Pore Space Connectivity for Cell Operation: The structure of lithium ion battery components, such as electrodes and\nseparators, are commonly characterised in terms of their porosity and\ntortuosity. The ratio of these values gives the effective transport of lithium\nions in the electrolyte-filled pore spaces, which can be used to determine the\nionic resistivity and corresponding voltage losses. Here, we show that these\nmicrostructural characteristics are not sufficient. Analysis of tomographic\ndata of commercial separators reveals that different polyolefin separators have\nsimilar porosity and through-plane tortuosity, which, in the homogenised\npicture of lithium ion cell operation, would imply that these different\nseparators exhibit similar performance. However, numerical diffusion\nsimulations indicate that this is not the case. We demonstrate that the extent\nto which lithium ion concentration gradients are induced or smoothed by the\nseparator structure is linked to pore space connectivity, a parameter that can\nbe determined by topological or network based analysis of separators. These\nfindings enable us to propose how to design separator microstructures that are\nsafer and accommodate fast charge and discharge.", "category": "physics_app-ph" }, { "text": "Multiple Monoenergetic Gamma Radiography (MMGR) with a compact\n superconducting cyclotron: Smuggling of special nuclear materials (SNM) and nuclear devices through\nborders and ports of entry constitutes a major risk to global security.\nTechnologies are needed to reliably screen the flow of commerce for the\npresence of high-$Z$ materials such as uranium and plutonium. Here we present\nan experimental proof-of-concept of a technique which uses inelastic ($p,p'$)\nnuclear reactions to generate monoenergetic photons, which provide means to\nmeasure the areal density and the effective-$Z$ ($Z_{\\text{eff}}$) of an object\nwith an accuracy which surpasses that achieved by current methods. We use an\nION-12$^{ \\text{SC}}$ superconducting 12~MeV proton cyclotron to produce 4.4,\n6.1, 6.9, and 7.1~MeV photons from a variety of nuclear reactions. Using these\nphotons in a transmission mode we show that we are able to accurately\nreconstruct the areal densities and $Z_{\\text{eff}}$ of a test object. This\nmethodology could enable mobile applications to screen commercial cargoes with\nhigh material specificity, providing a means of distinguishing common cargo\nmaterials from high-Z materials that include uranium and plutonium.", "category": "physics_app-ph" }, { "text": "Magnetically Ordered Insulators for Advanced Spintronics: Magnetically ordered, electrically insulating materials pave the way towards\nnovel spintronic devices. In these materials the flow of magnetic excitations\nsuch as magnons results in pure spin currents. These spin currents can be\ndriven by gradients of the spin chemical potential and/or temperature such that\nthey can play the same role in novel spintronic devices as charge currents in\ntraditional electronic circuits. Connecting spin current based and charge\ncurrent based devices requires spin to charge interconversion. This has been\nachieved by the spin Hall effect with an efficiency of several 10%. The recent\nprogress in materials development and understanding of pure spin current\nphysics opens up a plethora of novel device concepts and opportunities for\nfundamental studies.", "category": "physics_app-ph" }, { "text": "Radial Injection in Suspension High Velocity Oxy Fuel (S-HVOF) Thermal\n Spray of Graphene Nanoplatelets for Tribology: Friction is a major issue in energy efficiency of any apparatus composed of\nmoving mechanical parts, affecting durability and reliability. Graphene\nnanoplatelets (GNPs) are good candidates for reducing friction and wear, and\nsuspension high velocity oxy-fuel (SHVOF) thermal spray is a promising\ntechnique for their scalable and fast deposition, but it can expose them to\nexcessive heat. In this work, we explore radial injection of GNPs in SHVOF\nthermal spray as a means of reducing their interaction with the hot flame,\nwhile still allowing a high momentum transfer and effective deposition.\nFeedstock injection parameters, such as flowrate, injection angle and position,\nwere studied using high-speed imaging and particles temperature and velocity\nmonitoring at different flame powers using Accuraspray 4.0. Unlubricated\nball-on-flat sliding wear tests against an alumina counterbody ball showed a\nfriction coefficient reduction up to a factor 10 compared to the bare\nsubstrate, down to 0.07. The deposited layer of GNPs protects the underlying\nsubstrate by allowing low-friction dry sliding. A Transmission Electron\nMicroscopy study showed GNPs preserved crystallinity after spray, and became\namorphised and wrinkled upon wear. This study focused on GNPs but is relevant\nto other heat- and oxidation-sensitive materials such as polymers, nitrides and\n2D materials.", "category": "physics_app-ph" }, { "text": "Massively parallel fabrication of crack-defined gold break junctions\n featuring sub-3 nm gaps for molecular devices: Break junctions provide tip-shaped contact electrodes that are fundamental\ncomponents of nano and molecular electronics. However, the fabrication of break\njunctions remains notoriously time-consuming and difficult to parallelize. Here\nwe demonstrate true parallel fabrication of gold break junctions featuring\nsub-3 nm gaps on the wafer-scale, by relying on a novel self-breaking mechanism\nbased on controlled crack formation in notched bridge structures. We achieve\nfabrication densities as high as 7 million junctions per cm$^{2}$, with\nfabrication yields of around 7% for obtaining crack-defined break junctions\nwith sub-3 nm gaps of fixed gap width that exhibit electron tunneling. We also\nform molecular junctions using dithiol-terminated oligo(phenylene ethynylene)\n(OPE3) to demonstrate the feasibility of our approach for electrical probing of\nmolecules down to liquid helium temperatures. Our technology opens a whole new\nrange of experimental opportunities for nano and molecular electronics\napplications, by enabling very large-scale fabrication of solid-state break\njunctions.", "category": "physics_app-ph" }, { "text": "Manipulate Elastic Wave Modes by an Ultrathin Three-component Elastic\n Metasurface: We design a two-dimensional ultra-thin elastic metasurface consisting of\nsteel cores coated with elliptical rubbers embedded in epoxy matrix, capable of\nmanipulating bulk elastic wave modes for reflected waves. The energy exchanges\nbetween the longitudinal and transverse modes are completely controlled by the\ninclined angle of rubber. One elastic mode can totally convert into another by\nthe ultra-thin elastic metasurface. The conversion mechanism based on the\nnon-degenerate dipolar resonance is a general method and easily extended to\nthree-dimensional or mechanical systems. A mass-spring model is proposed and\nwell describe the conversion properties. We further demonstrate that high\nconversion rates (more than 95%) can be achieved steadily for one elastic\nmetasurface working on almost all different solid backgrounds. It will bring\nwide potential applications in elastic devices.", "category": "physics_app-ph" }, { "text": "Simultaneous Localization and Recognition of Subwavelength\n Non-Cooperative Entities Based on SISO Time Reversal and Neural Networks: The simultaneous localization and recognition of subwavelength\nnon-cooperative entities within complex multi-scattering environments using a\nsimplified system continues to pose a substantial challenge. This letter\naddresses this challenge by synergistically integrating time reversal\ntime-frequency phase prints (TRTFPPs) and neural networks. Initially, a time\nreversal (TR) single-input single-output (SISO) framework is employed to\ngenerate TRTFPPs. To enhance the models' adaptability, particularly in the\npresence of noise, data augmentation techniques are applied. Subsequently,\nneural networks are employed to comprehend the TRTFPPs. Specifically, a\ncascaded neural network structure is embraced, encompassing both a recognition\nneural network and distinct neural networks for localizing different entities.\nThrough the devised approach, two types of subwavelength entities are\nsuccessfully identified and precisely localized through numerical simulations\nand experimental verification in laboratory environment. The proposed\nmethodology holds applicability across various electromagnetic systems,\nincluding but not limited to detection, imaging, human-computer interaction,\nand the Internet of Things (IoT).", "category": "physics_app-ph" }, { "text": "Static Rashba Effect by Surface Reconstruction and Photon Recycling in\n the Dynamic Indirect Gap of APbBr3 (A = Cs, CH3NH3) Single Crystals: Recently, halide perovskites have gained significant attention from the\nperspective of efficient spintronics owing to Rashba effect. This effect occurs\nas a consequence of strong spin-orbit coupling under noncentrosymmetric\nenvironment, which can be dynamic and/or static. However, there exist intense\ndebates on the origin of broken inversion symmetry since the halide perovskites\ntypically crystallize into a centrosymmetric structure. In order to clarify the\nissue, we examine both dynamic and static effects in the all-inorganic CsPbBr3\nand organic-inorganic CH3NH3PbBr3 (MAPbBr3) perovskite single crystals by\nemploying temperature- and polarization-dependent photoluminescence excitation\nspectroscopy. The perovskite single crystals manifest the dynamic effect by\nphoton recycling in the indirect Rashba gap, causing dual peaks in the\nphotoluminescence. But the effect vanishes in CsPbBr3 at low temperatures (< 50\nK), accompanied by a striking color change of the crystal, arising presumably\nfrom lower degrees of freedom for inversion symmetry breaking associated with\nthe thermal motion of the spherical Cs cation, compared with the polar MA\ncation in MAPbBr3. We also show that static Rashba effect occurs only in\nMAPbBr3 below 90 K due to surface reconstruction via MA-cation ordering, which\nlikely extends across a few layers from the crystal surface to the interior. We\nfurther demonstrate that this static Rashba effect can be completely suppressed\nupon surface treatment with poly methyl methacrylate (PMMA) coating. We believe\nthat our results provide a rationale for the Rashba effects in halide\nperovskites.", "category": "physics_app-ph" }, { "text": "Closed-form expressions for the magnetic field of permanent magnets in\n three dimensions: We derive a closed-form expression of the magnetic field of a finite-size\ncurrent sheet and use it to calculate the field of permanent magnets, which are\nmodeled through their surface current densities. We illustrate the method by\ndetermining the multipoles and the effective length due to fringe fields of a\nfinite-length dipole constructed of magnetic cubes.", "category": "physics_app-ph" }, { "text": "Zeolitic imidazolate framework-coated acoustic sensors for room\n temperature detection of carbon dioxide and methane: Integration of nanoporous materials such as metal organic frameworks (MOFs)\nwith sensitive transducers can result robust sensing platforms for monitoring\ngases and chemical vapors for a range of applications. Here, we report on an\nintegration of the zeolitic imidazolate framework-8 (ZIF-8) MOF with surface\nacoustic wave (SAW) and thickness shear mode quartz crystal microbalance (QCM)\ndevices to monitor carbon dioxide(CO2)and methane (CH4) at ambient conditions.\nThe MOF was directly coated on the custom fabricated Y-Z LiNbO3 SAW delay lines\n(operating frequency,f0 = 436 MHz)and AT-cut Quartz TSM resonators (resonant\nfrequency, f0 = 9 MHz) and the devices were tested for various gases in N2 at\nambient condition. The devices were able to detect the changes in CO2 or CH4\nconcentrations with relatively higher sensitivity to CO2, which was due to its\nhigher adsorption potential and heavier molecular weight. The sensors showed\nfull reversibility and repeatability which were attributed to the physisorption\nof the gases into the MOF and high stability of the devices. Both types of the\nsensors showed linear responses relative to changes in the binary gas\ncompositions thereby allowing to construct calibration curves which correlated\nwell with the expected mass changes in the sorbent layer based on mixed-gas\ngravimetric adsorption isotherms measured on bulk samples.For 200 nm thick\nfilms, the SAW sensitivity to CO2 and CH4 were 1.44x10^-6/vol-%, respectivel\nyagainst the QCM sensitivities 0.24x10^-6/vol-% and 1x10^-8/vol-%,respectively\nwhich were evaluated as the fractional change in the signal. The SAW sensors\nwere also evaluated for 100 nm - 300 nm thick films, the sensitivities of which\nwere found to increase with the thickness due to the increased number of pores\nfor adsorption of larger amount of gases. Also, the SAW devices had a good\nwireless response for detecting gases remotely.", "category": "physics_app-ph" }, { "text": "A Graded Metamaterial for Broadband and High-capability Piezoelectric\n Energy Harvesting: This work studies a broadband graded metamaterial, which integrates the\npiezoelectric energy harvesting function targeting low-frequency structural\nvibrations, lying below 100 Hz. The device combines a graded metamaterial with\nbeam-like resonators, piezoelectric patches and a self-powered piezoelectric\ninterface circuit for energy harvesting. Based on the mechanical and electrical\nlumped parameters, an integrated model is proposed to investigate the power\nperformance of the proposed design. Thorough numerical simulations were\nconducted to analyse the spatial frequency separation capacity and the\nslow-wave phenomenon of the graded metamaterial for broadband and\nhigh-capability piezoelectric energy harvesting. Experiments with realistic\nvibration sources show that the harvested power of the proposed design yields a\nfive-fold increase with respect to conventional harvesting solutions based on\nsingle cantilever harvesters. Our results reveal the significant potential on\nexploitation of graded metamaterials for energy-efficient vibration-powered\ndevices.", "category": "physics_app-ph" }, { "text": "Analysis of two-terminal perovskite/silicon tandem solar cells with\n differing texture structure and tunneling junction quality: Presented here is the optimization of a planar two-terminal\nperovskite/silicon tandem solar cell with a texture structure. The developed\nsimulation model is fitted to published experimental results, and the\nimportance of current matching in the two-terminal structure is discussed. With\nthe texture structure optimized and considering current matching, the optimal\ntexture structure improves $J_{sc}$ from 17.9mA/cm^2 to 20.87 mA/cm^2 compared\nto the planar structure, as well as improving the power conversion efficiency\nfrom 25.8% to 35.9%. Furthermore, if the quality of the perovskite thin film\nand tunneling junction efficiency with a smaller voltage penalty can be\nimproved, then the efficiency can be further improved to 38.13%. This indicates\nthat this tandem solar cell still has much room for improvement.", "category": "physics_app-ph" }, { "text": "A Guideline for Silicon Carbide MOSFET Thermal Characterization based on\n Source-Drain Voltage: Thermal transient measurement based on source-drain voltage is a standard\nmethod to characterize thermal properties of silicon semiconductors but is\ndoubtful to be directly applied to silicon carbide (SiC) devices. To evaluate\nits feasibility and limitations, this paper conducts a comprehensive\ninvestigation into its accuracy, resolution, and stability towards yielding the\nstructure information of SiC MOSFET using the source-drain voltage as the\ntemperature sensitive electrical parameter. The whole characterization process\ninvolves two main procedures and associated key testing parameters, such as\ngate voltages, sensing and heating currents, etc. Their impacts on both the\nstatic and dynamic performances are also investigated with the aim of providing\na guideline for conducting a reproducible thermal transient measurement for SiC\nMOSFETs.", "category": "physics_app-ph" }, { "text": "Demonstration of negative refraction induced by synthetic gauge fields: The phenomenon of negative refraction generally requires negative refractive\nindices or phase discontinuities, which can be realized using metamaterials or\nmetasurfaces. Recent theories have proposed a novel mechanism for negative\nrefraction based on synthetic gauge fields, which affect classical waves as if\nthey were charged particles in electromagnetic fields, but this has not\nhitherto been demonstrated in experiment. Here, we report on the experimental\ndemonstration of gauge-field-induced negative refraction in a twisted bilayer\nacoustic metamaterial. The bilayer twisting produces a synthetic gauge field\nfor sound waves propagating within a projected two-dimensional geometry, with\nthe magnitude of the gauge field parameterized by the choice of wavenumber\nalong the third dimension. Waveguiding with backward propagating modes is also\ndemonstrated in a trilayer configuration that implements strong gauge fields.\nThese results provide an alternative route to achieving negative refraction in\nsynthetic materials.", "category": "physics_app-ph" }, { "text": "Mechanical Properties of Gradient Copper Nano-Gyroid Cellular\n Structures: A Molecular Dynamics Study: Advanced manufacturing (AM) technologies, such as nanoscale additive\nmanufacturing process, enable the fabrication of nanoscale architected\nmaterials which has received great attention due to their prominent properties.\nHowever, few studies delve into the functional gradient cellular architecture\non nanoscale. This work studied the gradient nano-Gyroid architected material\nmade of copper (Cu) by molecular dynamic (MD) simulations. The result reveals\nthat, unlike homogeneous architecture, gradient Gyroid not only shows novel\nlayer-by-layer deformation behavior, but also processes significantly better\nenergy absorption ability. Moreover, this deformation behavior and energy\nabsorption are predictable and designable, which demonstrates its highly\nprogrammable potential.", "category": "physics_app-ph" }, { "text": "Pt, Ni and Ti Schottky barrier contacts to \\{beta}-(Al0.19Ga0.81)2O3\n grown by Molecular Beam Epitaxy on Sn doped \\{beta}-Ga2O3 substrate: A comprehensive current-voltage (I-V) characterization is performed for three\ndifferent Schottky contacts; Pt, Ni and Ti, to unintentionally doped (UID)\n\\{beta}-(Al0.19Ga0.81)2O3 grown by molecular beam epitaxy (MBE) on\n\\{beta}-Ga2O3 for temperatures ranging between 25C -300C. Reciprocal space\nmapping shows the (Al0.19Ga0.81)2O3 films are strained and lattice matched to\nthe substrate. Schottky Barrier Height (SBH), ideality factor (n), and series\nresistance (Rs) are extracted from the I-V characteristics for the three types\nof metals and temperatures. Room temperature capacitance-voltage (C-V)\nmeasurements revealed fully depleted \\{beta}-(Al0.19Ga0.81)2O3 layer. Extracted\nroom temperature SBHs after zero field correction for Pt, Ni and Ti were 2.39\neV, 2.21 eV, and 1.22 eV respectively. Variation of SBHs with metal clearly\nindicates the dependence on work function.", "category": "physics_app-ph" }, { "text": "3D modeling of a Superconducting Dynamo-Type Flux Pump: High temperature superconducting (HTS) dynamos are promising devices that can\ninject large DC currents into the winding of superconducting machines or\nmagnets in a contactless way. Thanks to this, troublesome brushes in HTS\nmachines or bulky currents leads with high thermal losses will be no longer\nrequired. The working mechanism of HTS dynamo has been controversial during the\nrecent years and several explanations and models have been proposed to\nelucidate its performance. In this paper, we present the first\nthree-dimensional (3D) model of an HTS flux pump, which has good agreement with\nexperiments. This model can be beneficial to clarify the mechanism of the\ndynamo and pinpoint its unnoticed characteristics. Employing this model, we\ndelved into the screening current and electric field distribution across the\ntape surface in several crucial time steps. This is important, since the\novercritical screening current has been shown to be the reason for flux\npumping. In addition, we analyzed the impact of both components of electric\nfield and screening current on voltage generation, which was not possible in\nprevious 2D modeling. We also explored the necessary distance of voltage tab at\ndifferent airgaps for precise measurement of the voltage across the tape in the\ndynamo.", "category": "physics_app-ph" }, { "text": "Recycling of Perovskite Substrate: The use of water-soluble sacrificial layer of Sr$_3$Al$_2$O$_6$ has\ntremendously boosted the research on freestanding functional oxide thin films,\nespecially thanks to its ultimate capability to produce high-quality epitaxial\nperovskite thin films. However, the costly single-crystalline substrates, e.g.\nSrTiO$_3$, were generally discarded after obtaining the freestanding thin\nfilms. Here, we demonstrate that the SrTiO$_3$ substrates can be recycled to\nfabricate La$_{0.7}$Sr$_{0.3}$MnO$_3$ films with nearly identical structural\nand electrical properties. After attaining freestanding thin films, the\nresidues on SrTiO$_3$ can be removed by 80 \\degree C hot water soaking and\nrinsing treatments. Consequently, the surface of SrTiO$_3$ reverted to its\noriginal step-and-terrace structure.", "category": "physics_app-ph" }, { "text": "Halide perovskites: Is it all about the interfaces?: Design and modification of the interfaces, always a critical issue for\nsemiconductor devices, has become the primary tool to harness the full\npotential of halide perovskite (HaP)-based ones. In particular the outstanding\nimprovements in HaP solar cell performance and stability can be primarily\nascribed to a careful choice of the interfacial layout in the layer stack. In\nthis review we describe the unique challenges and opportunities of these\napproaches (section A). For this purpose, we first elucidate the basic physical\nand chemical properties of the exposed HaP thin film and crystal surface\n(section B). We then lay out the energetic alignment processes to adjacent\ntransport and buffer layers (section C) and finally elaborate on the impact of\nthe interface formation on how well/poor a device functions. Based on those\nsections we then present a road map for the next steps in interfacial design\nprinciples for HaP semiconductors (section D).", "category": "physics_app-ph" }, { "text": "Experimental realization of phonon demultiplexing in three-dimensions: Phononic metamaterials enabled the realization of many acoustic components\nanalogous to their electronic counterparts, such as transistors, logic gates\nand calculators. A key component among these is the demultiplexer, a device\nthat receives multiple signals and sorts them based on their frequencies into\nseparate channels. Previous experimental realizations of acoustic and elastic\nmultiplexers have employed plates with pillars or holes to demultiplex\nfrequencies. However, existing realizations are confined to two-dimensions,\nwhich can limit potential acoustic or elastic circuit design. Here we show the\nfirst experimental realization of a three-dimensional, four channel phononic\ndemultiplexer. Our design methodology is based on bundles of pass-bands within\na large band gap that can easily be tuned for multi-channel frequency\ndemultiplexing. The proposed design can be utilized in acoustic and elastic\ninformation processing, nondestructive evaluation and communication\napplications among others.", "category": "physics_app-ph" }, { "text": "The angular dependence of magnetization dynamics induced by a GHz range\n strain pulse: The dynamics of magnetization is important in spintronics, where the coupling\nbetween phonon and magnon attracts much attention. In this work, we study the\nangular dependence of the coupling between longitudinal-wave phonon and magnon.\nWe investigated the magnetization dynamics using the time-resolved\nmagneto-optical Kerr effect, which allows measuring spin-wave resonances and\nthe magnetic echo signal. The frequency, mode number, and amplitude of the\nspin-wave resonance change with the out-of-plane angle of the external magnetic\nfield. The amplitude of the magnetic echo signal caused by the strain pulse\nalso changes with the angle. We calculate these angular dependences based on\nthe Landau-Lifshitz-Gilbert equation and find that the angles of the external\nfield and magnetic moment are important factors for the phonon-magnon coupling\nwhen phonon propagates in the thickness direction under the out-of-plane\nmagnetic field.", "category": "physics_app-ph" }, { "text": "Estimation of self-healing effects in halide perovskite based rectifying\n device structures via deep-level transient spectroscopy: The defect-activity in halide perovskites remains a critical factor for the\napplication in optoelectronics. The imperfections (vacancies, anti-sites,\ninterstitials) formed in the lattice of the halide perovskites were considered\nas a main origin for the corrosion of the interfaces and decomposition process\nunder external stress. At the same time, the self-healing effect was reported\nas one of the features for the devices based on halide perovskites, which\nmanifests in the recovery of device performance under specific conditions. Such\nprocesses require a detailed analysis for the quantitative analysis of the\ndefect parameters. In this work, we used Admittance and Optical Deep-level\nTransient spectroscopy to determine the evolution of the defect energy levels\nin the simplified rectifying device architecture based on CH3NH3PbBr3 after\nconsecutive accumulation of the absorbed radiation dose (fast electrons, 5\nMeV). We found that electron beam irradiation induces the formation of the deep\nstates of anti-sites PbBr with activation energy of 0.83 eV. Increase of the\nabsorbed radiation dose up to 1.5 Mrad resulted in a critical raise of 0.83 eV\ndefect concentration, which can be effectively annealed during the temperature\nsweep. The changes in the defect parameters after different values of the\nabsorbed radiation dose were analyzed and discussed. The current work provides\nnew insights for the self-healing process of halide perovskite-based devices\nunder hard external stress, revealing the important specifics of the defect\nbehavior.", "category": "physics_app-ph" }, { "text": "Ultrafast reprogrammable multifunctional vanadium-dioxide-assisted\n metasurface for dynamic THz wavefront engineering: In this paper, for the first time, a new generation of ultrafast\nreprogrammable multi-mission bias encoded metasurface is proposed for dynamic\nTHz wavefront engineering by employing VO2 reversible and fast monoclinic to\ntetragonal phase transition. The multi-functionality of our designed VO2 based\ncoding metasurface (VBCM) was guaranteed by elaborately designed meta-atom\ncomprising three-patterned VO2 thin films whose operational statuses can be\ndynamically tuned among four states of \"00\"- \"11\" by merely changing the\nbiasing voltage controlled by an external FPGA platform. Capitalizing on such\nmeta-atom design and by driving VBCM with different spiral-like and\nspiral-parabola-like coding sequences, single vortex beam and focused vortex\nbeam with interchangeable OAM modes were satisfactorily generated respectively.\nAdditionally, by adopting superposition theorem and convolution operation,\nsymmetric/asymmetric multiple beams and arbitrarily-oriented multiple vortex\nbeams in pre-demined directions with different topological charges are\nrealized. The versatility of our designed VBCM also has equipped a platform to\nfocus the incident THz wavefront into a pre-determined point which can be\ndynamically altered. Several illustrative examples successfully have clarified\nthat proposed VBCM is a promising candidate for solving crucial THz challenges\nsuch as high data rate wireless communication where ultrafast switching between\nseveral missions is required.", "category": "physics_app-ph" }, { "text": "Detection of magnetic nanoparticles (MNPs) using spin current\n nano-oscillator (SCNO) biosensor: A frequency-based rapid, ultra-sensitive,\n magnetic bioassay: This Letter is a micromagnetic simulation-based study on the GHz-frequency\nferromagnetic resonances for the detection of magnetic nanoparticles (MNPs)\nusing spin current nano-oscillator (SCNO) operating in precession mode as a\nspintronic biosensor. The magnetic stray fields from the MNPs in an\nantibody-antigen-MNP complex on the SCNO surface modify the ferromagnetic\nresonance peaks and generate measurable resonance peak shifts. Moreover, our\nresults strongly indicate the position-sensitive behavior of the SCNO biosensor\nand ways to eradicate this effect to facilitate better bio-sensing performance.\nAdditionally, a study has been made on how nanoparticles with different sizes\ncan alter the SCNO device performance. This simulation-based study on the SCNO\ndevice shows a promise of frequency-based nano-biosensor with a sensitivity of\ndetecting even a single MNP, even in presence of thermal noise.", "category": "physics_app-ph" }, { "text": "Demultiplexing infrasound phonons with tunable magnetic lattices: Controlling infrasound signals is crucial to many processes ranging from\npredicting atmospheric events and seismic activities to sensing nuclear\ndetonations. These waves can be manipulated through phononic crystals and\nacoustic metamaterials. However, at such ultra-low frequencies, the size\n(usually on the order of meters) and the mass (usually on the order of many\nkilograms) of these materials can hinder its potential applications in the\ninfrasonic domain. Here, we utilize tunable lattices of repelling magnets to\nguide and sort infrasound waves into different channels based on their\nfrequencies. We construct our lattices by confining meta-atoms (free-floating\nmacroscopic disks with embedded magnets) within a magnetic boundary. By\nchanging the confining boundary, we control the meta-atoms' spacing and\ntherefore the intensity of their coupling potentials and wave propagation\ncharacteristics. As a demonstration of principle, we present the first\nexperimental realization of an infrasound phonon demultiplexer (i.e., guiding\nultra-low frequency waves into different channels based on their frequencies).\nThe realized platform can be utilized to manipulate ultra-low frequency waves,\nwithin a relatively small volume, while utilizing negligible mass. In addition,\nthe self-assembly nature of the meta-atoms can be key in creating\nre-programmable materials with exceptional nonlinear properties.", "category": "physics_app-ph" }, { "text": "Dynamic Control of Plasmonic Colors by Voltage Actuation MEMS\n Cantilevers for Optical Display Applications: Conventional optical displays using ITO (indium tin oxide) and LC (liquid\ncrystal) materials present a lot of challenges in terms of long-term\nsustainability. We show here how it is possible to generate a cost effective\nand CMOS compatible fast and full range electrically controlled RGB color\ndisplay by combining transmission based plasmonic metasurfaces with MEMS\n(Microelectromechanical systems) technology, using only two common materials:\nAluminum and silicon oxide. White light is filtered into red, green, and blue\ncomponents by plasmonic metasurfaces made of aluminum nanohole arrays, and the\ntransmission through each color filter is modulated by MEMS miniaturized\ncantilevers fabricated with aluminum and silicon oxide on top of the color\nfilters. We show that the relative transmission of a color subpixel can be\nfreely modulated from 35% to 100%. Our pixels can also operate well above\n800Hz, enabling future ultrafast displays. Our work provides a road to future\ncircular economic goals by exploiting advances in structural colors and MEMS\ntechnologies to innovate optical displays.", "category": "physics_app-ph" }, { "text": "Incorporation of macroscopic heterogeneity within a porous layer to\n enhance its acoustic absorptance: We seek the response, in particular the spectral absorptance, of a\nrigidly-backed periodically-(in one horizontal~~ direction) ~inhomogeneous\n~layer ~composed ~of ~alternating rigid and macroscopically-homogeneous porous\nportions, submitted to an airborne acoustic plane body wave. The rigorous\ntheory of this problem is given and the means by which the latter can be\nnumerically solved are outlined. At low frequencies, a suitable approximation\nderives from one linear equation in one unknown. This approximate solution is\nshown to be equivalent to that of the problem of the same wave incident on a\nhomogeneous, isotropic layer. The thickness $h$ of this layer is identical to\nthat of the inhomogeneous layer, the effective complex body wave velocity\ntherein is identical to that of the porous portion of the inhomogeneous layer,\nbut the complex effective mass density, whose expression is given in explicit\nalgebraic form, is that of the reference homogeneous macroscopically-porous\nlayer divided by the filling factor (fraction of porous material to the total\nmaterial in one grating period). This difference of density is the reason why\nit is possible for the lowest-frequency absorptance peak to be higher than that\nof a reference layer. Also, it is shown how to augment the height of this peak\nso that it attains unity (i.e., total absorption) and how to shift it to lower\nfrequencies, as is required in certain applications.", "category": "physics_app-ph" }, { "text": "Spin waves propagating through a stripe magnetic domain structure and\n their applications to reservoir computing: Spin waves propagating through a stripe domain structure and reservoir\ncomputing with their spin dynamics have been numerically studied with focusing\non the relation between physical phenomena and computing capabilities. Our\nsystem utilizes a spin-wave-based device that has a continuous magnetic garnet\nfilm and 1-input/72-output electrodes on the top. To control\nspatially-distributed spin dynamics, a stripe magnetic domain structure and\namplitude-modulated triangular input waves were used. The spatially-arranged\nelectrodes detected spin vector outputs with various nonlinear characteristics\nthat were leveraged for reservoir computing. By moderately suppressing\nnonlinear phenomena, our system achieves 100$\\%$ prediction accuracy in\ntemporal exclusive-OR (XOR) problems with a delay step up to 5. At the same\ntime, it shows perfect inference in delay tasks with a delay step more than 7\nand its memory capacity has a maximum value of 21. This study demonstrated that\nour spin-wave-based reservoir computing has a high potential for edge-computing\napplications and also can offer a rich opportunity for further understanding of\nthe underlying nonlinear physics.", "category": "physics_app-ph" }, { "text": "A Passive Circuit-Emulator for a Current-controlled Memristor: A memristor is an electrical element, which has been conjectured in 1971 to\ncomplete the lumped circuit theory. Currently, researchers use memristors\nemulators through diodes and other passive (or active) elements to study\ncircuits with possible attractors, chaos, and ways of implementing nonlinear\ntransformations for low-voltage novel computing paradigms. However, to date,\nsuch passive memristor emulators have been voltage-controlled. In this study,\nthe first circuit realization of a current-controlled passive emulator is\nestablished. The formal theory and simulations validate the proposed circuit.", "category": "physics_app-ph" }, { "text": "Optimized nanodevice fabrication using clean transfer of graphene by\n polymer mixture: Experiments and Neural Network based simulations: In this study, we investigate both experimentally and computationally the\nmolecular interactions of two distinct polymers with graphene. Our experimental\nfindings indicate that the use of a polymer mixture reduces the transfer\ninduced doping and strain in fabricated graphene devices as compared to\nconventional single polymer wet transfer. We found that such reduction is\nrelated to the decreased affinity of mixture of polymethyl methacrylate and\nangelica lactone polymer for graphene. We investigated changes in binding\nenergy (BE) of polymer mixture and graphene by considering energy decomposition\nanalysis using a pre-trained potential neural network. It was found that\nnumerical simulations accurately predicted two-fold reduction of BE and order\nof magnitude reduction of electrostatic interaction between polymers.", "category": "physics_app-ph" }, { "text": "Tip-induced strain, bandgap, and radiative decay engineering of a single\n metal halide perovskite quantum dot: Strain engineering of perovskite quantum dots (pQDs) enables widely-tunable\nphotonic device applications. However, manipulation at the single-emitter level\nhas never been attempted. Here, we present a tip-induced control approach\ncombined with tip-enhanced photoluminescence (TEPL) spectroscopy to engineer\nstrain, bandgap, and emission quantum yield of a single pQD. Single\nCsPbBr$_{x}$I$_{3-x}$ pQDs are clearly resolved through hyperspectral TEPL\nimaging with $\\sim$10 nm spatial resolution. The plasmonic tip then directly\napplies pressure to a single pQD to facilitate a bandgap shift up to $\\sim$62\nmeV with Purcell-enhanced PL quantum yield as high as $\\sim$10$^5$ for the\nstrain-induced pQD. Furthermore, by systematically modulating the tip-induced\ncompressive strain of a single pQD, we achieve dynamical bandgap engineering in\na reversible manner. In addition, we facilitate the quantum dot coupling for a\npQD ensemble with $\\sim$0.8 GPa tip pressure at the nanoscale. Our approach\npresents a new strategy to tune the nano-opto-electro-mechanical properties of\npQDs at the single-crystal level.", "category": "physics_app-ph" }, { "text": "The Design of Long-Life, High-Efficiency PEM Fuel Cell Power Supplies\n for Low Power Sensor Networks: Field sensor networks have important applications in environmental\nmonitoring, particularly climate change, air, water and soil quality, in\ndisaster monitoring and in border security. The reduced cost of electronics,\nsensors and actuators make it possible to deploy hundreds if not thousands of\nthese sensor modules. However power technology have not kept up. Current power\nsupply technologies such as batteries limit many applications due to their low\nspecific energy. Photovoltaics typically requires large bulky panels and is\ndependent on varying solar insolation and therefore requires backup power\nsources. Polymer Electrolyte Membrane (PEM) fuel cells are a promising\nalternative, because they are clean, quiet and operate at high efficiency.\nHowever challenges remain in achieving long lives due to factors such as\ncatalyst degradation and hydrogen storage. In this work, we devise a framework\nfor designing fuel cells power supplies for field sensor networks to achieve\nlong lives and utilize lithium hydride hydrogen storage technology that offers\nhigh energy density of up to 5,000 Wh/kg. Using this design framework, we\nidentify operating conditions to maximize the life of the power supply, meet\nthe required power output and minimize fuel consumption. We devise a series of\ncontrollers to achieve this capability and demonstrate it using a bench-top\nexperiment that operated for 5,000 hours. The laboratory experiments point\ntowards a pathway to design and scale these fuel cell power supplies for\nvarious field applications. Our studies show the proposed PEM fuel cell hybrid\nsystem fueled using lithium hydride offers at least a 3 fold reduction in mass\ncompared to state of the art batteries and 3-5 fold reduction in mass compared\nto current fuel cell technologies.", "category": "physics_app-ph" }, { "text": "HZO-based FerroNEMS MAC for In-Memory Computing: This paper demonstrates a hafnium zirconium oxide (HZO)-based ferroelectric\nNEMS unimorph as the fundamental building block for very low-energy capacitive\nreadout in-memory computing. The reported device consists of a 250 $\\mu$m\n$\\times$ 30 $\\mu$m unimorph cantilever with 20 nm thick ferroelectric HZO on 1\n$\\mu$m $SiO_2$.Partial ferroelectric switching in HZO achieves analog\nprogrammable control of the piezoelectric coefficient ($d_{31}$) which serves\nas the computational weight for multiply-accumulate (MAC) operations. The\ndisplacement of the piezoelectric unimorph was recorded by actuating the device\nwith different input voltages $V_{in}$. The resulting displacement was measured\nas a function of the ferroelectric programming/poling voltage $V_p$. The slopes\nof central beam displacement ($\\delta_{max}$) vs $V_{in}$ were measured to be\nbetween 182.9nm/V (for -8 $V_p$) and -90.5nm/V (for 8 $V_p$), demonstrating\nthat $V_p$ can be used to change the direction of motion of the beam. The\nresultant ($\\delta_{max}$) from AC actuation is in the range of -18 to 36 nm\nand is a scaled product of the input voltage and programmed $d_{31}$ (governed\nby the $V_p$). The multiplication function serves as the fundamental unit for\nMAC operations with the ferroelectric NEMS unimorph. The displacement from many\nsuch beams can be added by summing the capacitance changes, providing a pathway\nto implement a multi-input and multi-weight neuron. A scaling and fabrication\nanalysis suggests that this device can be CMOS compatible, achieving high\nin-memory computational throughput.", "category": "physics_app-ph" }, { "text": "High-Temperature Superconductor Quantum Flux Parametron for\n Energy-Efficient Logic: As we rapidly advance through the information age, the power consumed by\ncomputers, data centers, and networks grows exponentially. This has inspired a\nrace to develop alternative low-power computational technologies. A new\nadiabatic configuration of a decades-old superconducting digital logic device\nhas darted into the lead called quantum flux parametrons (QFP). QFP operate\nwith dissipation so low that they seemingly violate the laws of thermodynamics.\nIn just a short span of time, they have gone from simple single NOT gates to\ncomplex processors containing thousands of gates. They are fabricated from\nelemental niobium superconductors cooled to just a few degrees above absolute\nzero. However, their efficiency is so great that for large high-performance\ncomputers with several gates, the energy savings are immense. For smaller\ncomputational platforms QFPs from high-temperature superconductors (high-Tc)\nare highly desirable. In this work, we take the first steps towards this goal\nwith the demonstration of a high-T C QFP shift register. Our device is\nfabricated using focused helium ion beam lithography where the material is\nmodified with an ion beam at the nanoscale to directly pattern these circuits\ninto a high-T C thin film. We validate the correct logical operation at 25 K,\nover 6 times higher than niobium devices with an estimated bit energy of 0.1\nattoJoule at 10 GHz.", "category": "physics_app-ph" }, { "text": "The Effect of Hole Transporting Layer in Charge Accumulation Properties\n of p-i-n Perovskite Solar Cells: The charge accumulation properties of p-i-n perovskite solar cells were\ninvestigated using three representative organic and inorganic hole transporting\nlayer (HTLs): a) Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)\n(PEDOT:PSS, Al 4083), b) copper-doped nickel oxide (Cu:NiOx) and c) Copper\noxide (CuO). Through impedance spectroscopy analysis and modelling it is shown\nthat charge accumulation is decreased in the HTL/Perovskite interface, between\nPEDOT:PSS to Cu:NiOx and CuO respectively. This was indicative from the\ndecrease in double layer capacitance (Cdl) and interfacial charge accumulation\ncapacitance (Cel), resulting in an increase to recombination resistance (Rrec),\nthus decreased charge recombination events between the three HTLs. Through AFM\nmeasurements it is also shown that the reduced recombination events (followed\nby the increase in Rrec) is also a result of increased grain size between the\nthree HTLs, thus reduction in the grain boundaries area. These charge\naccumulation properties of the three HTLs have resulted in an increase to the\npower conversion efficiency between the PEDOT:PSS (8.44%), Cu:NiOx (11.45%) and\nCuO (15.3%)-based devices.", "category": "physics_app-ph" }, { "text": "Electron spin transport in a metal-oxide-semiconductor Si\n two-dimensional inversion channel: Effect of hydrogen annealing on spin\n scattering mechanism and spin lifetime: Department of Electrical Engineering and Information Systems, The University\nof Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan Center for Spintronics\nResearch Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo\n113-8656, Japan", "category": "physics_app-ph" }, { "text": "Beam-Shaping PEC Mirror Phase Corrector Design: The Perfect Electric Conductor (PEC) mirror phase corrector plays an\nimportant role in the beam-shaping mirror system design for Quasi-Optical (QO)\nmode converter (launcher) in the sub-THz high-power gyrotron. In this article,\nboth the Geometry Optical (GO) method and the phase gradient method have been\npresented for the PEC mirror phase corrector design. The advantages and\ndisadvantages are discussed for both methods. An efficient algorithm has been\nproposed for the phase gradient method.", "category": "physics_app-ph" }, { "text": "Out-of-Plane Resistance Switching of 2D Bi2O2Se at Nanoscale: 2D bismuth oxyselenide (Bi2O2Se) with high electron mobility shows great\npotential for nanoelectronics. Although in-plane properties of Bi2O2Se have\nbeen widely studied, its out-ofplane electrical transport behavior remains\nelusive, despite its importance in fabricating devices with new functionality\nand high integration density. Here, we study the out-of-plane electrical\nproperties of 2D Bi2O2Se at nanoscale by conductive atomic force microscope. We\nfind that hillocks with tunable heights and sizes are formed on Bi2O2Se after\napplying vertical electrical field. Intriguingly, such hillocks are conductive\nin vertical direction, resulting in a previously unknown out-of-plane\nresistance switching in thick Bi2O2Se flakes while ohmic conductive\ncharacteristic in thin ones. Furthermore, we observe the transformation from\nbipolar to stable unipolar conduction in thick Bi2O2Se flake possessing such\nhillocks, suggesting its potential to function as a selector in vertical\ndevices. Our work reveals unique out-of-plane transport behavior of 2D Bi2O2Se,\nproviding the basis for fabricating vertical devices based on this emerging 2D\nmaterial.", "category": "physics_app-ph" }, { "text": "Dual band, low profile and compact tunable frequency selective surface\n with wide tuning range: In this paper, a dual polarized, dual band, low profile, embedded bias\nnetwork, and compact tunable varactor band pass frequency selective surface\n(FSS) is designed with a wide tuning range. The proposed FSS is composed of two\nmetallic layers printed on both sides of the substrate, where the top side has\ntwo cross strips with different dimensions encircled with high pass grids,\nwhereas the bottom side includes a proper bias network. The loaded varactors\nbetween the grids and the cross strips with a designed bias network achieve two\nindependent tunable pass bands. Moreover, an equivalent circuit of the FSS is\nextracted, which show good agreement with the full wave simulation results. The\nproposed FSS can operate from 2.28 GHz to 4.66 GHz and from 5.44 GHz to 11.3\nGHz by proper tuning of the varactors loaded in the large and small cross\nstrips. The tunable range of the low and high pass bands are about 70% with\nrespect to the center frequency of each pass band. The electrical dimensions of\nthe proposed FSS are about $0.05\\lambda\\times0.05\\lambda$, where $\\lambda$ is\nthe free space wavelength at a lower pass band (2.28 GHz). Moreover, the\nproposed FSS works properly up to $60^\\circ$ incident angles.", "category": "physics_app-ph" }, { "text": "Understanding the role of threading dislocations on 4H-SiC MOSFET\n breakdown under high temperature reverse bias stress: The origin of dielectric breakdown was studied on 4H-SiC MOSFETs that failed\nafter three months of high temperature reverse bias (HTRB) stress. A local\ninspection of the failed devices demonstrated the presence of a threading\ndislocation (TD) at the breakdown location. The nanoscale origin of the\ndielectric breakdown was highlighted with advanced high-spatial-resolution\nscanning probe microscopy (SPM) techniques. In particular, SPM revealed the\nconductive nature of the TD and a local increase of the minority carrier\nconcentration close to the defect. Numerical simulations estimated a hole\nconcentration 13 orders of magnitude larger than in the ideal 4H-SiC crystal.\nThe hole injection in specific regions of the device explained the failure of\nthe gate oxide under stress. In this way, the key role of the TD in the\ndielectric breakdown of 4H-SiC MOSFET was unambiguously demonstrated.", "category": "physics_app-ph" }, { "text": "Angle-resolved broadband ferromagnetic resonance apparatus enabled\n through a spring-loaded sample mounting manipulator: Broadband ferromagnetic resonance is a useful technique to determine the\nmagnetic anisotropy and study the magnetization dynamics of magnetic thin\nfilms. We report a spring-loaded sample loading manipulator for reliable sample\nmounting and rotation. The manipulator enables maximum signal, enhances system\nstability and is particularly useful for fully automated in-plane-field\nangle-resolved measurements. This angle-resolved broadband ferromagnetic\nresonance apparatus provides a viable method to study anisotropic damping and\nweak magnetic anisotropies, both vital for fundamental research and\napplications.", "category": "physics_app-ph" }, { "text": "Real-space imaging of atomic-scale spin textures at nanometer distances: Spin-polarized scanning tunneling microscopy (SP-STM) experiments on\nultrathin films with non-collinear spin textures demonstrate that resonant\ntunneling allows for atomic-scale spin-sensitive imaging in real space at\ntip-sample distances of up to 8 nm. Spin-polarized resonance states evolving\nbetween the foremost atom of a magnetic probe tip and the opposed magnetic\nsurface atom are found to provide a loophole from the hitherto existing dilemma\nof losing spatial resolution when increasing the tip-sample distance in a\nscanning probe setup. Bias-dependent series of SP-STM images recorded via\nresonant tunneling reveal spin sensitivity at resonance conditions, indicating\nthat the spin-polarized resonance states act as mediators for the spin contrast\nacross the nm-spaced vacuum gap. With technically feasible distances in the nm\nregime, resonant tunneling in SP-STM qualifies for a spin-sensitive read-write\ntechnique with ultimate lateral resolution in future spintronic applications.", "category": "physics_app-ph" }, { "text": "Integration of High-Tc Superconductors with High Q Factor Oxide\n Mechanical Resonators: Micro-mechanical resonators are building blocks of a variety of applications\nin basic science and applied electronics. This device technology is mainly\nbased on well-established and reproducible silicon-based fabrication processes\nwith outstanding performances in term of mechanical Q factor and sensitivity to\nexternal perturbations. Broadening the functionalities of MEMS by the\nintegration of functional materials is a key step for both applied and\nfundamental science. However, combining functional materials and silicon-based\ncompounds is challenging. An alternative approach is fabricating MEMS based on\ncomplex heterostructures made of materials inherently showing a variety of\nphysical properties such as transition metal oxides. Here, we report on the\nintegration of a high-Tc superconductor YBa2Cu3O7 (YBCO) with high Q factor\nmicro-bridge resonator made of a single-crystal LaAlO3 (LAO) thin film. LAO\nresonators are tensile strained, with a stress of 345 MPa, show Q factor in the\nrange of tens of thousands, and have low roughness. The topmost YBCO layer\ndeposited by Pulse Laser Deposition shows a superconducting transition starting\nat 90 K with zero resistance below 78 K. This result opens new possibilities\ntowards the development of advanced transducers, such as bolometers or magnetic\nfield detectors, as well as basic science experiments in solid state physics,\nmaterial science, and quantum opto-mechanics.", "category": "physics_app-ph" }, { "text": "Stochastic spin-orbit-torque device as the STDP synapse for spiking\n neural networks: Neuromorphic hardware as a non-Von Neumann architecture has better energy\nefficiency and parallelism than the conventional computer. Here, with numerical\nmodeling spin-orbit torque (SOT) device using current-induced SOT and Joule\nheating effects, we acquire its magnetization switching probability as a\nfunction of the input current pulses and use it to mimic the\nspike-timing-dependent plasticity learning behavior like actual brain working.\nWe further demonstrate that the artificial spiking neural network (SNN) built\nby this SOT device can perform unsupervised handwritten digit recognition with\nthe accuracy of 80% and logic operation learning. Our work provides a new clue\nto achieving SNN-based neuromorphic hardware using high-energy efficiency and\nnonvolatile spintronics nanodevices", "category": "physics_app-ph" }, { "text": "Nonlinear energy loss in the oscillations of coated and uncoated\n bubbles: Role of thermal, radiation damping and encapsulating shell at\n various excitation pressures: A simple generalized model (GM) for coated bubbles accounting for the effect\nof compressibility of the liquid is presented. The GM was then coupled with\nnonlinear ODEs that account for the thermal effects. Starting with mass and\nmomentum conservation equations for a bubbly liquid and using the GM, nonlinear\npressure dependent terms were derived for energy dissipation due to thermal\ndamping (Td), radiation damping (Rd) and dissipation due to the viscosity of\nliquid (Ld) and coating (Cd). The dissipated energies were solved for uncoated\nand coated 2- 20 $\\mu m$ bubbles over a frequency range of $0.25f_r-2.5f_r$\n($f_r$ is the bubble resonance) and for various acoustic pressures\n(1kPa-300kPa). Thermal effects were examined for air and C3F8 gas cores in each\ncase. For uncoated bubbles with an air gas core and a diameter larger than 4\n$\\mu m$, thermal damping is the strongest damping factor. When pressure\nincreases, the contributions of Rd grow faster and become the dominant damping\nmechanism for pressure dependent resonance frequencies (e.g. fundamental and\nsuper harmonic resonances). For coated bubbles, Cd is the strongest damping\nmechanism. As pressure increases Rd contributes more to damping compared to Ld\nand Td. In case of air bubbles, as pressure increases, the linear thermal model\nlargely deviates from the nonlinear model and accurate modeling requires\ninclusion of the full thermal model. However, for coated C3F8 bubbles of\ndiameter 1-8 $\\mu m$, typically used in medical ultrasound, thermal effects\nmaybe neglected even at higher pressures. We show that the scattering to\ndamping ratio (STDR), a measure of the effectiveness of the bubble as contrast\nagent, is pressure dependent and can be maximized for specific frequency ranges\nand pressures.", "category": "physics_app-ph" }, { "text": "First-principles analysis of energy exchange in time-varying capacitors\n for energy trapping applications: Time-varying networks, consisting of lumped elements, such as resistors,\ncapacitors, and inductors, actively modulated in time, have introduced a host\nof novel wave phenomena and witnessed a remarkable development during recent\nyears. This paper investigates the scattering from a time varying capacitor and\nhow such a load can be fully reflectionless when the capacitance is suitably\nmodulated in time. We analytically derive the required temporal dependence of\nthe capacitance and show how in contrast to other techniques it avoids extreme\nand negative values and, as a result, can be implemented in a feasible way,\nwhen the capacitor is charged with a DC voltage source. We also derive from\nfirst principles the energy balance of such a time-varying capacitor, proving\nthat the energy of an incoming pulse is transferred to the modulation source.\nOur findings clarify scattering of waves from time-varying capacitors and open\nup a new way to matching of broadband pulses.", "category": "physics_app-ph" }, { "text": "On central focusing for contrast optimization in direct electron\n ptychography of thick samples: Ptychography provides high dose efficiency images that can reveal light\nelements next to heavy atoms. However, despite ptychography having an otherwise\nsingle signed contrast transfer function, contrast reversals can occur when the\nprojected potential becomes strong for both direct and iterative inversion\nptychography methods. It has recently been shown that these reversals can often\nbe counteracted in direct ptychography methods by adapting the focus. Here we\nprovide an explanation of why the best contrast is often found with the probe\nfocused to the middle of the sample. The phase contribution due to defocus at\neach sample slice above and below the central plane in this configuration\neffectively cancels out, which can prevent contrast reversals when dynamical\nscattering effects are not overly strong. In addition we show that the\nconvergence angle can be an important consideration for removal of contrast\nreversals in relatively thin samples.", "category": "physics_app-ph" }, { "text": "Thermal Management of Photovoltaics using Porous Nanochannels: The photoelectric conversion efficiency of a solar cell is dependent on its\ntemperature. When the solar radiation is incident on the photovoltaics (PV)\npanel, a large portion of it is absorbed by the underlying material which\nincreases its internal energy leading to the generation of heat. An overheated\nPV panel results in a decline in its performance which calls for an efficient\ncooling mechanism that can offer an optimum output of the electrical power. In\nthe present numerical work, thermal management with a porous nanochannels\ndevice capable to dissipate high heat flux is employed to regulate the\ntemperature of a commercial PV panel by integrating the device on the back face\nof the panel. The spatial and temporal variation of the PV surface temperature\nis obtained by solving the energy balance equation numerically. By evaluating\nthe steady-state PV surface temperature with and without thermal management,\nthe extent of cooling and the resulting enhancement in the electrical power\noutput is studied in detail. The nanochannels device is found to reduce the PV\nsurface temperature significantly with an average cooling of 31.5 oC.\nAdditionally, the enhancement in the electrical power output by ~33% and the\nreduction in the response time to 1/8th highlight the potential of using porous\nnanochannels as a thermal management device. Furthermore, the numerical method\nis used to develop a universal curve which can predict the extent of PV cooling\nfor any generic thermal management device.", "category": "physics_app-ph" }, { "text": "Scaling NbTiN-based ac-powered Josephson digital to 400M devices/cm$^2$: We describe a fabrication stackup for digital logic with 16 superconducting\nNbTiN layers, self-shunted a-silicon barrier Josephson Junctions (JJs), and low\nloss, high-$\\kappa$ tunable HZO capacitors. The stack enables 400 MJJ/cm$^2$\ndevice density, efficient routing, and AC power distribution on a resonant\nnetwork. The materials scale beyond 28nm lithography and are compatible with\nstandard high-temperature CMOS processes. We report initial results for\ntwo-metal layer NbTiN wires with 50nm critical dimension. A semi-ascendance\nwire-and-via process module using 193i lithography and 50nm critical dimension\nhas shown cross-section uniformity of 1%=1s across the 300mm wafer, critical\ntemperature of 12.5K, and critical current of 0.1mA at 4.2K. We also present a\nnew design of the resonant AC power network enabled by NbTiN wires and HZO MIM\ncapacitors. The design matches the device density and provides a 30 GHz clock\nwith estimated efficiency of up to 90%. Finally, magnetic imaging of patterned\nNbTiN ground planes shows low intrinsic defectivity and consistent trapping of\nvorteces in 0.5 mm holes spaced on a 20 $\\mu$m x 20 $\\mu$m grid.", "category": "physics_app-ph" }, { "text": "Enhanced capillary pumping through evaporation assisted leaf-mimicking\n micropumps: Pumping fluids without an aid of an external power source are desirable in a\nnumber of applications ranging from a cooling of microelectronic circuits to\nMicro Total Analysis Systems (micro-TAS). Although, several microfluidic pumps\nexist, yet passive micropumps demonstrate better energy efficiency while\nproviding a better control over a pumping rate and its operation. The fluid\npumping rate and their easy maneuverability are critical in some applications;\ntherefore, in the current work, we have developed a leaf-mimicking micropump\nthat demonstrated ~6 fold increase in a volumetric pumping rate as compared to\nthe micropumps having a single capillary fluid delivery system. We have\ndiscussed a simple, scalable, yet inexpensive method to design and fabricate\nthese leaf mimicking micopump. The microstructure of the micropumps were\ncharacterised through scanning electron microscopy and its pumping performance\n(volumetric pumping rate and pressure head sustainence) were assessed\nexperimentally. The working principle of the proposed micropump is attributed\nto its structural elements; where branched-shaped microchannels deliver the\nfluid acting like veins of leaves while the connected microporous support\nresembles mesophyll cells matrix that instantaneously transfers the delivered\nfluid by a capillary action to multiple pores mimicking the stomata for\nevaporation. Such design of micropumps will enable an efficient delivery of the\ndesired volume of a fluid to any 2D/3D micro/nanofluidic devices used in an\nengineering and biological applications.", "category": "physics_app-ph" }, { "text": "A model for Ni-63 source for betavoltaic application: A mathematical model of Ni-63 source for betavoltaic batteries is presented,\nbased on Monte Carlo calculation. Trajectories of beta particles are simulated\nin Ni-63 source until their escape or total energy dissipation. Analysis of the\neffect of physical and technological factors on the performance of a source is\ncarried out. Special attention is given to self-absorption and substrate\nbackscattering because of their impact on power emission. Addition of a\nprotective layer diminishes the source emission because of further absorption.\nThe model has been tested successfully for Ni-63/GaN structure.", "category": "physics_app-ph" }, { "text": "Dynamics of Multi-Domains in Ferroelectric Tunnel Junction: The Discovery of giant tunnel electroresistance (TER) in Ferroelectric Tunnel\nJunction (FTJ) paves a futuristic possibility of utilizing the FTJ as a\nbistable resistive device with an enormously high ON/OFF ratio. In the last 20\nyears, numerous studies have reported that the formation of multidomain in\nferroelectric material is an inevitable process to minimize the total system\nenergy. Recent studies based on phase-field simulations have demonstrated that\ndomain nucleation/motion substantially alters the electrostatics of a\nferroelectric material. However, the impact of domain dynamics on quantum\ntransport in FTJ remains elusive. This paper presents a comprehensive study of\nmultidomain dynamics in a ferroelectric tunnel junction. Analysis of this\narticle is twofold; firstly, we study the impact of domain dynamics on\nelectrostatics in an FTJ. Subsequently, the obtained electrostatics is used to\nstudy the variations in tunneling current, and TER originated from multidomain\ndynamics. We show that ON/OFF current density and TER vary locally in the\nferroelectric region. Furthermore, the device's electrostatics and quantum\ntransport exhibit an oscillatory nature due to periodic domain texture. ON/OFF\ncurrent density shows a sine/cosine distribution in ferroelectric, and\napproximately one-decade local variation in current density is observed. These\nlocal fluctuations in current density cause oscillations in the device's ON/OFF\nratio. Optimization techniques to achieve a uniform and maximum TER are also\ndiscussed. A 2D analytical and explicit model is derived by solving coupled 2D\nPoisson's equation and Landau-Ginzburg equation. The model incorporates the\nswitching and nucleation of domains by minimizing net ferroelectric energy\n(depolarization+free+gradient energy density). Furthermore, the impact of the\nbottom insulator layer on ferroelectric's gradient energy is also studied.", "category": "physics_app-ph" }, { "text": "Theoretical analysis of electrostatic energy harvester configured as\n Bennet's doubler based on Q-V cycles: This paper presents theoretical analysis of a MEMS electrostatic energy\nharvester configured as the Bennet's doubler. Steady-state operation of the\ndoubler circuit can be approximated by a right-angled trapezoid Q-V cycle. A\nsimilarity between voltage doubler and resistive-based charge-pump circuit is\nhighlighted. By taking electromechanical coupling into account, the analytical\nsolution of the saturation voltage is the first time derived, providing a\ngreater comprehension of the system performance and multi-parameter effects.\nThe theoretical approach is verified by results of circuit simulation for two\ncases of mathematically idealized diode and of Schottky diode. Development of\nthe doubler/multiplier circuits that can further increase the saturation\nvoltage is investigated.", "category": "physics_app-ph" }, { "text": "HgCdTe-based quantum cascade lasers operating in the GaAs phonon\n Reststrahlen band predicted by the balance equations method: HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen\nband with a target wavelength of 36 mkm are theoretically investigated using\nthe balance equations method. The optimized active region designs, which are\nbased on three and two quantum wells, exhibit a peak gain exceeding 100 cm(-1)\nat 150 K. We analyze the temperature dependences of the peak gain and predict\nthe maximum operation temperatures of 170 K and 225 K for three- and two-well\ndesigns, respectively. At high temperatures (T > 120 K), the better temperature\nperformance of the two-well design is associated with a larger spatial overlap\nof the weakly localized lasing wavefunctions as well as a higher population\ninversion.", "category": "physics_app-ph" }, { "text": "Casimir repulsive-attractive transition between liquid-separated\n dielectric metamaterial and metal: We study the repulsive-attractive transition, regarded as stable equilibrium,\nbetween gold and dielectric metamaterial based on Mie resonance immersed in\nvarious fluids due to the interplay of gravity, buoyancy and Casimir force\namong different geometries consisting of parallel plates and spheres levitated\nover substrates. A wider range of separation distance of stable equilibrium is\nobtained with Mie metamaterial than natural materials. We investigate the\nrelationship between separation distance of stable equilibrium and constructive\nparameters of Mie metamaterial and geometric parameters of the system, and\nprovide simple rules to tune the equilibrium position by modifying constructive\nparameters of Mie metamaterial. Particularly, the effect of permeability of Mie\nmetamaterial on equilibrium separation is also considered. Our work is\npromising for potential applications in frictionless suspension in\nmicro/nanofabrication technologies.", "category": "physics_app-ph" }, { "text": "Modeling and Testing Superconducting Artificial CPW Lines Suitable for\n Parametric Amplification: Achieving amplification with high gain and quantum-limited noise is a\ndifficult problem to solve. Parametric amplification using a superconducting\ntransmission line with high kinetic inductance is a promising technology not\nonly to solve this problem but also adding several benefits. When compared with\nother technologies, they have the potential of improving power saturation,\nachieving larger fractional bandwidths and operating at higher frequencies. In\nthis type of amplifiers, selecting the proper transmission line is a key\nelement in their design. Given current fabrication limitations, traditional\nlines such as coplanar waveguides (CPW), are not ideal for this purpose since\nit is difficult to make them with the proper characteristic impedance for good\nmatching and slow-enough phase velocity for making them more compact.\nCapacitively-loaded lines, also known as artificial lines, are a good solution\nto this problem. However, few design rules or models have been presented to\nguide their accurate design. This fact is even more crucial considering that\nthey are usually fabricated in the form of Floquet lines that have to be\ndesigned carefully to suppress undesired harmonics appearing in the parametric\nprocess. In this article we present, firstly, a new modelling strategy, based\non the use of electromagnetic-simulation software, and, secondly, a\nfirst-principles model that facilitate and speed the design of CPW artificial\nlines and of Floquet lines made out of them. Then, we present comparisons with\nexperimental results that demonstrate their accuracy. Finally, the theoretical\nmodel allows to predict the high-frequency behaviour of the artificial lines\nshowing that they are good candidates for implementing parametric amplifiers\nabove 100 GHz.", "category": "physics_app-ph" }, { "text": "Nanolaminated Al2O3/HfO2 dielectrics for silicon carbide based devices: Nanolaminated Al2O3/HfO2 thin films as well as single Al2O3 and HfO2 layers\nhave been grown as gate dielectrics by Plasma Enhanced Atomic Layer Deposition\n(PEALD) technique on silicon carbide (4H-SiC) substrates. All the three\ndielectric films have been deposited at temperature as low as 250{\\deg}C, with\na total thickness of about 30 nm and in particular, the nanolaminated\nAl2O3/HfO2 films have been fabricated by alternating nanometric Al2O3 and HfO2\nlayers. The structural characteristics and dielectrical properties of the\nnanolaminated Al2O3/HfO2 films have been evaluated and compared to those of the\nparent Al2O3 and HfO2 single layers. Moreover, the structural properties and\ntheir evolution upon annealing treatment at 800{\\deg}C have been investigated\nas preliminar test for their possible implementation in the device fabrication\nflow-chart. On the basis of the collected data, the nanolaminated films\ndemonstrated to possess promising dielectric behavior with respect to the\nsimple oxide layers.", "category": "physics_app-ph" }, { "text": "One-reactor vacuum and plasma synthesis of transparent conducting oxide\n nanotubes and nanotrees: from single wire conductivity to ultra-broadband\n perfect absorbers in the NIR: The eventual exploitation of one-dimensional nanomaterials yet needs the\ndevelopment of scalable, high yield, homogeneous, and environmentally friendly\nmethods able to meet the requirements for the fabrication of under design\nfunctional nanomaterials. In this article, we demonstrate a vacuum and plasma\none-reactor approach for the synthesis of the fundamental common element in\nsolar energy and optoelectronics, i.e. the transparent conducting electrode but\nin the form of nanotubes and nanotrees architectures. Although the process is\ngeneric and can be used for a variety of TCOs and wide-bandgap semiconductors,\nwe focus herein on Indium Doped Tin Oxide (ITO) as the most extended in the\nprevious applications. This protocol combines widely applied deposition\ntechniques such as thermal evaporation for the formation of organic nanowires\nserving as 1D and 3D soft templates, deposition of polycrystalline layers by\nmagnetron sputtering, and removal of the template by simply annealing under\nmild vacuum conditions. The process variables are tuned to control the\nstoichiometry, morphology, and alignment of the ITO nanotubes and nanotrees.\nFour-probe characterization reveals the improved lateral connectivity of the\nITO nanotrees and applied on individual nanotubes shows resistivities as low as\n3.5 +/- 0.9 x 10-4 {\\Omega}.cm, a value comparable to single-crystalline\ncounterparts. The assessment of diffuse reflectance and transmittance in the\nUV-VIS range confirms the viability of the supported ITO nanotubes as a random\noptical media working as strong scattering layers. Further ability to form ITO\nnanotrees opens the path for practical applications as ultra-broadband\nabsorbers in the NIR. The demonstrated low resistivity and optical properties\nof these ITO nanostructures open the way for their use in LEDs, IR shield,\nenergy harvesting, nanosensors, and photoelectrochemical applications", "category": "physics_app-ph" }, { "text": "On the Emergence of Negative Effective Density and Modulus in 2-phase\n Phononic Crystals: In this paper we report metamaterial properties including negative and\nsingular effective properties for what would traditionally be considered non\nlocally resonant 2-phase phononic unit cells. The negative effective material\nproperties reported here occur well below the homogenization limit and are,\ntherefore, acceptable descriptions of overall behavior. The material property\ncombinations which make this possible were first revealed by a novel level set\nbased topology optimization process which we describe. The optimization process\nrevealed that a 2-phase unit cell in which one of the phases is simultaneously\nlighter and stiffer than the other results in dynamic behavior which has all\nthe attendant characteristics of a locally resonant composite including\nnegative effective properties far below the homogenization limit. We\ninvestigate this further using the Craig-Bampton decomposition and clarify that\nthese properties emerge through an interplay between the fundamental internal\nmodeshape of the unit cell and a rigid body mode. Through explicit numerical\ncalculations on 1-D, 2-phase unit cells, we show that negative effective\nproperties only appear for the specific material property combination mentioned\nabove. Furthermore, we provide a proof which supports this conclusion. The\nconcept is also shown to hold for 2-D unit cells where we show that an\nappropriately designed hexagonal unit cell made of 2 material phases exhibits\nnegative effective shear modulus and density in an appropriate frequency regime\nin which it also exhibits negative refraction. An important conclusion of this\npaper is that the class of unit cells expected to result in negative properties\ncan be expanded beyond the classic unit cell (three-phase unit cells with an\nexplicit locally resonant phase) to include topologically simpler 2-phase unit\ncells as well.", "category": "physics_app-ph" }, { "text": "Extracting Dimensional Parameters of Gratings Produced with Self-Aligned\n Multiple Patterning Using GISAXS: Background: To ensure consistent and high-quality semiconductor production at\nfuture logic nodes, additional metrology tools are needed. For this purpose,\ngrazing-incidence small-angle X-ray scattering (GISAXS) is being considered\nbecause measurements are fast with a proven capability to reconstruct average\ngrating line profiles with high accuracy.\n Aim: GISAXS measurements of grating line shapes should be extended to samples\nwith pitches smaller than 50 nm and their defects. The method's performance\nshould be evaluated.\n Approach: A series of gratings with 32 nm pitch and deliberately introduced\npitchwalk is measured using GISAXS. The grating line profiles with associated\nuncertainties are reconstructed using a Maxwell solver and Markov-Chain Monte\nCarlo (MCMC) sampling combined with a simulation library approach.\n Results: The line shape and the pitchwalk are generally in agreement with\npreviously published transmission small-angle X-ray scattering (SAXS) results;\nhowever the line height and line width show deviations of (1.0 +/- 0.2) nm and\n(2.0 +/- 0.7) nm, respectively. The complex data evaluation leads to relatively\nhigh pitchwalk uncertainties between 0.5 nm and 2 nm.\n Conclusions: GISAXS shows great potential as a metrology tool for small-pitch\nline gratings with complex line profiles. Faster simulation methods would\nenable more accurate results.", "category": "physics_app-ph" }, { "text": "Design of Transmission Line and Electromagnetic Field Sensors for DC\n Partial Discharge Analysis: Accurate measurement circuit and high-frequency sensors with sufficient\nbandwidth are necessary for the analysis of individual partial discharge (PD)\npulses. In this paper, a testbed is designed and constructed for the\ninvestigation of DC PD pulses. The testbed is equipped with a 50 ohm\ntransmission line (TL) that terminate to an oscilloscope for measuring the\ncharge displacement current generated by PD pulses. Besides the oscilloscope\nmeasurements, two types of electromagnetic field sensors (D-dot and B-dot) were\ndeveloped to capture the EM fields of the PD pulses propagating through the TL.\nThe main goal of this paper is to investigate the DC PD pulses through the EM\nfields and the corresponding discharge current pulses that are considered as\ncalibrating signals for the developed D-dot and B-dot sensors. The results of\nDC cavity discharge measured by the constructed testbed and the EM field\nsensors demonstrate close agreement with the reference PD pulses measured via\noscilloscope.", "category": "physics_app-ph" }, { "text": "Multiple magneto-ionic regimes in\n Ta/Co$_{20}$Fe$_{60}$B$_{20}$/HfO$_{2}$: In Ta/CoFeB/HfO2 stacks a gate voltage drives, in a nonvolatile way, the\nsystem from an underoxidized state exhibiting in-plane anisotropy (IPA) to an\noptimum oxidation level resulting in perpendicular anisotropy (PMA) and further\ninto an overoxidized state with IPA. The IPA$\\,\\to\\,$PMA regime is found to be\nsignificantly faster than the PMA$\\,\\to\\,$IPA regime, while only the latter\nshows full reversibility under the same gate voltages. The effective damping\nparameter also shows a marked dependence with gate voltage in the\nIPA$\\,\\to\\,$PMA regime, going from 0.029 to 0.012, and only a modest increase\nto 0.014 in the PMA$\\,\\to\\,$IPA regime. The existence of two magneto-ionic\nregimes has been linked to a difference in the chemical environment of the\nanchoring points of oxygen species added to underoxidized or overoxidized\nlayers. Our results show that multiple magneto-ionic regimes can exist in a\nsingle device and that their characterization is of great importance for the\ndesign of high performance spintronics devices.", "category": "physics_app-ph" }, { "text": "Wang tiling aided statistical determination of the Representative Volume\n Element size of random heterogeneous materials: Wang tile based representation of a heterogeneous material facilitates fast\nsynthesis of non-periodic microstructure realizations. In this paper, we apply\nthe tiling approach in numerical homogenization to determine the Representative\nVolume Element size related to the user-defined significance level and the\ndiscrepancy between bounds on the apparent properties. First, the tiling\nconcept is employed to efficiently generate arbitrarily large, statistically\nconsistent realizations of investigated microstructures. Second, benefiting\nfrom the regular structure inherent to the tiling concept, the Partition\ntheorem, and statistical sampling, we construct confidence intervals of the\napparent properties related to the size of a microstructure specimen. Based on\nthe interval width and the upper and lower bounds on the apparent properties,\nwe adaptively generate additional microstructure realizations in order to\narrive at an RVE satisfying the prescribed tolerance. The methodology is\nillustrated with the homogenization of thermo-mechanical properties of three\ntwo-dimensional microstructure models: a microstructure with mono-disperse\nelliptic inclusions, foam, and sandstone.", "category": "physics_app-ph" }, { "text": "Laser-induced crystallization of copper oxide thin films: A comparison\n made between Gaussian and chevron-beam profiles provides a clue for the\n failure of Gaussian-beam profile: The use of laser with a Gaussian-beam profile is frequently adopted in\nattempts of crystallizing non-single-crystal thin films; however, it merely\nresults in the formation of poly-crystal thin films. In this paper, selective\narea crystallization of non-single-crystal copper(II) oxide (CuO) is described.\nThe crystallization is induced by laser, laser-induced crystallization, with a\nbeam profile in the shape of chevron. The crystallization is verified by the\nexhibition of a transition from a non-single-crystal phase consisting of small\n100 nm x 100 nm grains of CuO to a single-crystal phase of copper(I) oxide\n(Cu2O). The transition is identified by electron back scattering diffraction\nand Raman spectroscopy, which clearly suggests that a single-crystal domain of\nCu2O with size as large as 5 {\\mu}m x 1 mm develops. Provided these\nexperimental findings, a theoretical assessment based on a cellular automaton\nmodel, with the behaviors of localized recrystallization and stochastic\nnucleation, is developed. The theoretical assessment can qualitatively describe\nthe laser beam geometry-dependence of vital observable features (e.g., size and\ngross geometry of grains) in the laser-induced crystallization. The theoretical\nassessment predicts that differences in resulting crystallinity, either\nsingle-crystal or poly-crystal, primarily depend on a geometrical profile with\nwhich melting of non-single-crystal regions takes place along the laser scan\ndirection; concave-trailing profiles yield larger grains which lead to\nsingle-crystal while convex-trailing profiles results in smaller grains which\nlead to poly-crystal, casting light on the fundamental question Why does a\nchevron-beam profile succeed in producing single-crystal while a Gaussian-beam\nprofile fails?", "category": "physics_app-ph" }, { "text": "Acoustic Lenses Design based on the Rays Inserting Method: The ability to control and manipulate elastic waves is important for\napplications such as structural health monitoring, signal processing, and\nvibration isolations. In this paper, we investigated the feasibility of using\nthe Rays Inserting Method, an approach originally proposed for optical\nelements, to design structural components for flexural wave manipulation. The\nRIM entails a simple process that allows to design thickness variations in a\nthin plate with a desirable refractive index distribution for an intended wave\npath. Based on this method, a focusing and collimating lens and a waveguide\nthat rotates the wavefront by 45 degree were designed and studied. Frequency\ndomain simulations and time-based experimental characterizations were carried\nout. The results demonstrated that the effectiveness of the RIM for designing\nvariable thickness structures for manipulation of flexural wave propagation\nalong desired paths.", "category": "physics_app-ph" }, { "text": "Synergistic Effect of Multi-Walled Carbon Nanotubes and Ladder-Type\n Conjugated Polymers on the Performance of N-Type Organic Electrochemical\n Transistors: Organic electrochemical transistors (OECTs) have the potential to\nrevolutionize the field of organic bioelectronics. To date, most of the\nreported OECTs include p-type (semi-)conducting polymers as the channel\nmaterial, while n-type OECTs are yet at an early stage of development, with the\nbest performing electron-transporting materials still suffering from low\ntransconductance, low electron mobility, and slow response time. Here, the high\nelectrical conductivity of multi-walled carbon nanotubes (MWCNTs) and the large\nvolumetric capacitance of the ladder-type {\\pi}-conjugated redox polymer\npoly(benzimidazobenzophenanthroline) (BBL) are leveraged to develop n-type\nOECTs with record-high performance. It is demonstrated that the use of MWCNTs\nenhances the electron mobility by more than one order of magnitude, yielding\nfast transistor transient response (down to 15 ms) and high uC* (electron\nmobility x volumetric capacitance) of about 1 F/cmVs. This enables the\ndevelopment of complementary inverters with a voltage gain of > 16 and a large\nworst-case noise margin at a supply voltage of < 0.6 V, while consuming less\nthan 1 uW of power.", "category": "physics_app-ph" }, { "text": "Direct observation of site-specific dopant substitution in Si doped\n (AlxGa1-x)2O3 via Atom Probe Tomography: In this work, the interaction of n-type dopants in Si doped (AlxGa1-x)2O3\nfilms with varying Al content over the entire composition range (x = 0-100%)\nwas analyzed using atom probe tomography. An almost uniform dopant distribution\nwith dopant density in the range of 1018 cm-3 was obtained in all (AlxGa1-x)2O3\nlayers containing different Al contents. We have demonstrated that for the\nsingle phase \\b{eta}-(AlxGa1-x)2O3 films with Al content of x<0.30, dopants\nprefer to occupy on Ga sites while Al site is preferred for high Al content\n(x>0.50) (AlxGa1-x)2O3 layers. It was also observed for Al content, x =\n0.30-0.50, no specific cationic site occupancy was observed, Si occupies either\nAl or Ga sites. This can be attributed to highly inhomogeneous layers within\nthis composition range due to which dopant Si atoms are either in the Al-rich\nor Al-depleted regions.", "category": "physics_app-ph" }, { "text": "High thermoelectric power factor of poly(3-hexylthiophene) through\n in-plane alignment and doping with a molybdenum dithiolene complex: Here we report a record thermoelectric power factor of up to 160 $\\mu$ W m-1\nK-2 for the conjugated polymer poly(3-hexylthiophene) (P3HT). This result is\nachieved through the combination of high-temperature rubbing of thin films\ntogether with the use of a large molybdenum dithiolene p-dopant with a high\nelectron affinity. Comparison of the UV-vis-NIR spectra of the chemically doped\nsamples to electrochemically oxidized material reveals an oxidation level of\n10%, i.e. one polaron for every 10 repeat units. The high power factor arises\ndue to an increase in the charge-carrier mobility and hence electrical\nconductivity along the rubbing direction. We conclude that P3HT, with its\nfacile synthesis and outstanding processability, should not be ruled out as a\npotential thermoelectric material.", "category": "physics_app-ph" }, { "text": "Heterogeneously Integrated ITO Plasmonic Mach-Zehnder Interferometric\n Modulator on SOI: Densely integrated active photonics is key for next generation on-chip\nnetworks for addressing both footprint and energy budget concerns. However, the\nweak light-matter interaction in traditional active Silicon optoelectronics\nmandates rather sizable device lengths. The ideal active material choice should\navail high index modulation while being easily integrated into Silicon\nphotonics platforms. Indium tin oxide (ITO) offers such functionalities and has\nshown promising modulation capacity recently. Interestingly, the nanometer-thin\nunity-strong index modulation of ITO synergistically combines the high\ngroup-index in hybrid plasmonic with nanoscale optical modes. Following this\ndesign paradigm, here, we demonstrate a spectrally broadband, GHz-fast\nMach-Zehnder interferometric modulator, exhibiting a high efficiency signified\nby a miniscule VpL of 95 Vum, deploying an one-micrometer compact\nelectrostatically tunable plasmonic phase-shifter, based on heterogeneously\nintegrated ITO thin films into silicon photonics. Furthermore we show, that\nthis device paradigm enables spectrally broadband operation across the entire\ntelecommunication near infrared C-band. Such sub-wavelength short efficient and\nfast modulators monolithically integrated into Silicon platform open up new\npossibilities for high-density photonic circuitry, which is critical for high\ninterconnect density of photonic neural networks or applications in GHz-fast\noptical phased-arrays, for example.", "category": "physics_app-ph" }, { "text": "Design-oriented Modeling of 28 nm FDSOI CMOS Technology down to 4.2 K\n for Quantum Computing: In this paper a commercial 28-nm FDSOI CMOS technology is characterized and\nmodeled from room temperature down to 4.2 K. Here we explain the influence of\nincomplete ionization and interface traps on this technology starting from the\nfundamental device physics. We then illustrate how these phenomena can be\naccounted for in circuit device-models. We find that the design-oriented\nsimplified EKV model can accurately predict the impact of the temperature\nreduction on the transfer characteristics, back-gate sensitivity, and\ntransconductance efficiency. The presented results aim at extending\nindustry-standard compact models to cryogenic temperatures for the design of\ncryo- CMOS circuits implemented in a 28 nm FDSOI technology.", "category": "physics_app-ph" }, { "text": "Zero refractive index in space-time acoustic metamaterials: New scientific investigations of artificially structured materials and\nexperiments have exhibit wave manipulation to the extreme. In particular, zero\nrefractive index metamaterials have been on the front line of wave physics\nresearch for their unique wave manipulation properties and application\npotentials. Remarkably, in such exotic materials, time-harmonic fields have\ninfinite wavelength and do not exhibit any spatial variations in their phase\ndistribution. This unique feature can be achieved by forcing a Dirac cone to\nthe center of the Brillouin zone ( point), as previously predicted and\nexperimentally demonstrated in time-invariant metamaterials by means of\naccidental degeneracy between three different modes. In this article, we\npropose a different approach that enables true conical dispersion at with\ntwofold degeneracy, and generates zero index properties. We break time-reversal\nsymmetry and exploit a space-time modulation scheme to demonstrate a\ntime-Floquet acoustic metamaterial with zero refractive index. This behavior,\npredicted using stroboscopic analysis, is confirmed by fullwave finite elements\nsimulations. Our results establish the relevance of space-time metamaterials as\na novel reconfigurable platform for wave control.", "category": "physics_app-ph" }, { "text": "Raman Strain-Shift Measurements and Prediction from First-Principles in\n Highly-Strained Silicon: This work presents how first-principles simulations validated through\nexperimental measurements lead to a new accurate prediction of the expected\nRaman shift as a function of strain in silicon. Structural relaxation of a\nstrained primitive cell is first performed to tackle the relative displacement\nof the silicon atoms for each strain level. Density Functional Perturbation\nTheory (DFPT) is then used to compute the energy of the optical phonon modes in\nhighly-strained silicon and retrieve the strain-shift trend. The simulations\nare validated by experimental characterization, using scanning electron\nmicroscopy (SEM) coupled with backscattering Raman spectroscopy, of silicon\nmicrobeams fabricated using a top-down approach. The beams are strained up to\n2$\\%$ thanks to the internal tensile stress of silicon nitride actuators,\nallowing a validation of the perturbation theory in high-strain conditions. The\nresults are compared with the phonon deformation potentials (PDP) theory and\nthe uncertainty caused by the various parameters found in the literature is\ndiscussed. The simulated strain-shift coefficients of -175.77 cm$^{-1}$ (resp.\n-400.85 cm$^{-1}$) and the experimental one of -160.99 cm$^{-1}$ (resp. -414.97\ncm$^{-1}$) are found for the longitudinal optical LO (resp. transverse optical\nTO$_1$) mode, showing good agreement.", "category": "physics_app-ph" }, { "text": "Manipulating chiral-spin transport with ferroelectric polarization: A collective excitation of the spin structure in a magnetic insulator can\ntransmit spin-angular momentum with negligible dissipation. This quantum of a\nspin wave, introduced more than nine decades ago, has always been manipulated\nthrough magnetic dipoles, (i.e., timereversal symmetry). Here, we report the\nexperimental observation of chiral-spin transport in multiferroic BiFeO3, where\nthe spin transport is controlled by reversing the ferroelectric polarization\n(i.e., spatial inversion symmetry). The ferroelectrically controlled magnons\nproduce an unprecedented ratio of up to 18% rectification at room temperature.\nThe spin torque that the magnons in BiFeO3 carry can be used to efficiently\nswitch the magnetization of adja-cent magnets, with a spin-torque efficiency\nbeing comparable to the spin Hall effect in heavy metals. Utilizing such a\ncontrollable magnon generation and transmission in BiFeO3, an alloxide,\nenergy-scalable logic is demonstrated composed of spin-orbit injection,\ndetection, and magnetoelectric control. This observation opens a new chapter of\nmultiferroic magnons and paves an alternative pathway towards low-dissipation\nnanoelectronics.", "category": "physics_app-ph" }, { "text": "Phase field predictions of microscopic fracture and R-curve behaviour of\n fibre-reinforced composites: We present a computational framework to explore the effect of microstructure\nand constituent properties upon the fracture toughness of fibre-reinforced\npolymer composites. To capture microscopic matrix cracking and fibre-matrix\ndebonding, the framework couples the phase field fracture method and a cohesive\nzone model in the context of the finite element method. Virtual single-notched\nthree point bending tests are conducted. The actual microstructure of the\ncomposite is simulated by an embedded cell in the fracture process zone, while\nthe remaining area is homogenised to be an anisotropic elastic solid. A\ndetailed comparison of the predicted results with experimental observations\nreveals that it is possible to accurately capture the crack path, interface\ndebonding and load versus displacement response. The sensitivity of the crack\ngrowth resistance curve (R-curve) to the matrix fracture toughness and the\nfibre-matrix interface properties is determined. The influence of porosity upon\nthe R-curve of fibre-reinforced composites is also explored, revealing a\nstabler response with increasing void volume fraction. These results shed light\ninto microscopic fracture mechanisms and set the basis for efficient design of\nhigh fracture toughness composites.", "category": "physics_app-ph" }, { "text": "Revealing Fundamentals of Charge Extraction in Photovoltaic Devices\n Through Potentiostatic Photoluminescence Imaging: The photocurrent density-voltage (J(V)) curve is the fundamental\ncharacteristic to assess opto-electronic devices, in particular solar cells.\nHowever, it only yields information on the performance integrated over the\nentire active device area. Here, a method to determine a spatially resolved\nphotocurrent image by voltage-dependent photoluminescence microscopy is derived\nfrom basic principles. The opportunities and limitations of the approach are\nstudied by the investigation of III-V and perovskite solar cells. This approach\nallows the real-time assessment of the microscopically resolved local J(V)\ncurve, the steady-state Jsc, as well as transient effects. In addition, the\nmeasurement contains information on local charge extraction and interfacial\nrecombination. This facilitates the identification of regions of non-ideal\ncharge extraction in the solar cells and enables to link these to the\nprocessing conditions. The proposed technique highlights that, combined with\npotentiostatic measurements, luminescence microscopy turns out to be a powerful\ntool for the assessment of performance losses and the improvement of solar\ncells.", "category": "physics_app-ph" }, { "text": "Surface-diffusion-limited growth of atomically thin WS2 crystals from\n core-shell nuclei: Atomically thin transition metal dichalcogenides (TMDs) have recently\nattracted great attention since the unique and fascinating physical properties\nhave been found in various TMDs, implying potential applications in\nnext-generation devices. The progress towards developing new functional and\nhigh-performance devices based on TMDs, however, is limited by the difficulty\nof producing large-area monolayer TMDs due to a lack of knowledge of the growth\nprocesses of monolayer TMDs. In this work, we have investigated the growth\nprocesses of monolayer WS2 crystals using a thermal chemical vapor deposition\nmethod, in which the growth conditions were adjusted in a systematic manner. It\nwas found that, after forming WO3-WS2 core-shell nanoparticles as nucleation\nsites on a substrate, the growth of three-dimensional WS2 islands proceeds by\nripening and crystallization processes. Lateral growth of monolayer WS2\ncrystals subsequently occurs by surface diffusion process of adatoms. Our\nresults provide understanding of the growth processes of monolayer WS2 by using\nchemical vapor deposition methods.", "category": "physics_app-ph" }, { "text": "Dispersive readout of a high-Q encapsulated micromechanical resonator: Encapsulated bulk mode microresonators in the megahertz range are used in\ncommercial timekeeping and sensing applications but their performance is\nlimited by the current state of the art of readout methods. We demonstrate a\nreadout using dispersive coupling between a high-Q encapsulated bulk mode\nmicromechanical resonator and a lumped element microwave resonator that is\nimplemented with commercially available components and standard printed circuit\nboard fabrication methods and operates at room temperature and pressure. A\nfrequency domain measurement of the microwave readout system yields a\ndisplacement resolution of $522 \\, \\mathrm{fm/\\sqrt{Hz}}$, which demonstrates\nan improvement over the state of the art of displacement measurement in\nbulk-mode encapsulated microresonators. This approach can be readily\nimplemented in cryogenic measurements, allowing for future work characterizing\nthe thermomechanical noise of encapsulated bulk mode resonators at cryogenic\ntemperatures.", "category": "physics_app-ph" }, { "text": "Low-loss GHz frequency phononic integrated circuits in Gallium Nitride\n for compact radio-frequency acoustic wave devices: Guiding and manipulating GHz frequency acoustic waves in $\\mu$m-scale\nwaveguides and resonators opens up new degrees of freedom to manipulate radio\nfrequency (RF) signals in chip-scale platforms. A critical requirement for\nenabling high-performance devices is the demonstration of low acoustic\ndissipation in these highly confined geometries. In this work, we show that\ngallium nitride (GaN) on silicon carbide (SiC) supports low-loss acoustics by\ndemonstrating acoustic microring resonators with frequency-quality factor\n($fQ$) products approaching $4*10^{13}$ Hz at 3.4 GHz. The low dissipation\nmeasured exceeds the $fQ$ bound set by the simplified isotropic Akhiezer\nmaterial damping limit of GaN. We use this low-loss acoustics platform to\ndemonstrate spiral delay lines with on-chip RF delays exceeding 2.5 $\\mu$s,\ncorresponding to an equivalent electromagnetic delay of $\\approx$ 750 m. Given\nGaN is a well-established semiconductor with high electron mobility, our work\nopens up the prospect of engineering traveling wave acoustoelectric\ninteractions in $\\mu$m-scale waveguide geometries, with associated implications\nfor chip-scale RF signal processing.", "category": "physics_app-ph" }, { "text": "An Investigation On Neck Extensions For Single and Multi-Degree Of\n Freedom Acoustic Helmholtz Resonators: The effect of neck extensions in single and multi-degree of freedom Helmholtz\nresonator based acoustic liners is studied both experimentally and numerically\nand the resulting transmission coefficient and resonance frequencies are\nexamined. It has been shown that a single degree of freedom liner with\nincreasing neck extension lengths leads to the resonance frequencies being\npushed to lower frequency values, however, this shift to lower frequencies is\nnot linear with increasing length. A study on including neck extensions for the\nprimary and/or secondary neck within a double degree of freedom liner is also\npresented. It is shown that both neck extension concepts lead to an increase in\nbandwidth of sound absorption by a double degree of freedom Helmholtz\nresonator.", "category": "physics_app-ph" }, { "text": "Non-Line-of-Sight Passive Acoustic Localization Around Corners: Non-line-of-sight (NLoS) imaging is an important challenge in many fields\nranging from autonomous vehicles and smart cities to defense applications.\nSeveral recent works in optics and acoustics tackle the challenge of imaging\ntargets hidden from view (e.g. placed around a corner) by measuring\ntime-of-flight (ToF) information using active SONAR/LiDAR techniques,\neffectively mapping the Green functions (impulse responses) from several\nsources to an array of detectors. Here, leveraging passive correlations-based\nimaging techniques, we study the possibility of acoustic NLoS target\nlocalization around a corner without the use of controlled active sources. We\ndemonstrate localization and tracking of a human subject hidden around the\ncorner in a reverberating room, using Green functions retrieved from\ncorrelations of broadband noise in multiple detectors. Our results demonstrate\nthat the controlled active sources can be replaced by passive detectors as long\nas a sufficiently broadband noise is present in the scene.", "category": "physics_app-ph" }, { "text": "Integrated on chip platform with quantum emitters in layered materials: Integrated quantum photonic circuitry is an emerging topic that requires\nefficient coupling of quantum light sources to waveguides and optical\nresonators. So far, great effort has been devoted to engineering on-chip\nsystems from three-dimensional crystals such as diamond or gallium arsenide. In\nthis study, we demonstrate room temperature coupling of quantum emitters\nembedded within a layered hexagonal boron nitride to an on-chip aluminium\nnitride waveguide. We achieved 1.2% light coupling efficiency of the device and\nrealise transmission of single photons through the waveguide. Our results serve\nas a foundation for the integration of layered materials with on-chip\ncomponents and for the realisation of integrated quantum photonic circuitry.", "category": "physics_app-ph" }, { "text": "Design and fabrication of robust broadband extreme ultraviolet\n multilayers: The random layer thickness variations can induce a great deformation of the\nexperimental reflection of broadband extreme ultraviolet multilayer. In order\nto reduce this influence of random layer thickness fluctuations, the\nmultiobjective genetic algorithm has been improved and used in the robust\ndesign of multilayer with a broad angular bandpass. The robust multilayer with\na lower sensitivity to random thickness errors have been obtained and the\ncorresponding multilayer mirrors were fabricated. The experimental results of\nrobust Mo/Si multilayer with a wide angular band were presented and analyzed,\nand the advantage of robust multilayer design was demonstrated.", "category": "physics_app-ph" }, { "text": "Inverse Doppler Effects in Pipe Instruments: Music is older than language, and for most of human history music holds our\nculture together. The pipe instrument is one of the most popular musical\ninstruments of all time. Built on the foundation of previous flute and\nflute-like acoustic metamaterial models, we herein report the experimental\nresults of the inverse Doppler effects discovered in two common pipe\ninstruments - recorder and clarinet. Our study shows that the inverse Doppler\neffects can be detected at all seven pitches of an ascending musical scale when\nthere is a relative motion between a microphone (observer) and abovementioned\ntwo pipe instruments (source). The calculated effective refractive indices of\nthese two pipe instruments are negative and varying across a set of pitches,\nexhibiting a desired characteristic of broadband acoustic metamaterials. This\nstudy suggests that recorder and clarinet may be the earliest man-made acoustic\nmetamaterials known so far, offering a new explanation why pipe instruments\nhave enjoyed wide popularity in Europe and Asia over the past hundreds and\nthousands years. This newly discovered phenomenon would also offer a clue into\ndesigning next-generation smart broadband double-negative acoustic\nmetamaterials with varying refractive index.", "category": "physics_app-ph" }, { "text": "Tiling large areas with luminescent solar concentrators: geometry\n effects: Luminescence solar concentrators act as semi-transparent photovoltaic cells\nand can be applied to large surface areas in modern urban environment. In this\npaper their optical efficiencies were analytically derived for different unit\nshapes as simple, integral-free expressions. Perimeter length increase for the\nsame enclosed area requires more photodetectors, yet reduces optical losses per\nunit. An exact interplay between these two parameters is presented, which can\nbe directly applied to the analysis of tiling for large areas. An explicit\nexpression for the critical size of an LSC unit, above which its inner part\nbecomes inactive, has been obtained. Fabrication of devices larger than\nspecified by this limit should be discouraged from efficiency considerations.", "category": "physics_app-ph" }, { "text": "Electrochemical Degradation of Methylene Blue Using Ce(IV) Ionic\n Mediator in the Presence of Ag(I) Ion Catalyst for Environmental Remediation: Methylene blue (MB) is often used in textile industries and is actively\npresent in the wastewater runs-off. Recently, mediated electrochemical\noxidation (MEO) offers a fast, reliable and promising results for environmental\nremediation. Thus, we aimed to evaluate the electro-degradation potential of MB\nby MEO using Ce(IV) ionic mediator. Furthermore, we also observed the influence\nof addition Ag(I) ion catalyst in MEO for degradation of MB. The\nelectro-degradation of MB was evaluated by cyclic voltammetry technique and was\nconfirmed by UV-Vis spectrophotometry, high performance liquid chromatography\n(HPLC) analysis and back-titration analysis. The results showed that in the\nabsence of Ag(I) ion catalyst, about 89 % of MB was decolorized within 30\nminutes. When 2 mM of Ag(I) ion catalyst was applied, the electro-degradation\nof MB was increased to maximum value of 100%. The UV-Vis spectrum confirmed the\nelectro-degradation of MB as suggested by decreased maximum absorbance value at\n{\\lambda} 668 nm from 2.125 to 0.059. The HPLC analysis showed the formation of\nfive new peaks at retention time of 1.331, 1.495, 1.757, 1.908 and 2.017\nminutes, confirming the electro-degradation of MB. The back-titration analysis\nshowed about 52.9% of CO2 was produced during electro-degradation of MB by MEO.\nMore importantly, more than 97% of Ce(IV) ionic mediator were recovered in our\ninvestigation. Our results reveal the potential of MEO using Ce(IV) ionic\nmediator to improve the wastewater runs-off quality from textile as well as\nother industries containing methylene blue.", "category": "physics_app-ph" }, { "text": "Dipole Scattering at the Interface: The Origin of Low Mobility observed\n in SiC MOSFETs: In this work, the origin of the low free electron mobility in SiC MOSFETs is\ninvestigated using the scattering theory of two-dimensional electron gases. We\nfirst establish that neither phonon scattering nor Coulomb scattering can be\nthe cause of the low observed mobility in SiC MOSFETs; we establish this fact\nby comparing the theoretically calculated mobility considering these effects\nwith experimental observations. By considering the threshold voltages and the\neffective field dependence of the mobility in SiC MOSFETs, it is concluded that\nthe scattering centers of the dominant mechanism are electrically neutral and\nexhibit a short-range scattering potential. By considering charge distribution\naround a neutral defect at the interface, it is established that an electric\ndipole induced by the defect can act as a short-range scattering potential. We\nthen calculate the mobility in SiC MOSFETs assuming that there exist a high\ndensity of dipoles at the interface. The calculated dipole-scattering-limited\nmobility shows a similar dependence on the effective field dependence to that\nobserved in experimental results. Thus, we conclude that scattering induced by\na high density of electric dipoles at the interface is dominant cause of the\nlow mobility in SiC MOSFETs.", "category": "physics_app-ph" }, { "text": "Spot Focusing Coma Correction by Linearly Polarized Dual-Transmitarray\n Antenna in the Terahertz Region: Focus scanning is critically important in many terahertz (THz) imaging and\nsensing applications. A traditional single focusing transmitarray can achieve a\ngood focus when the source is on-axis but moving the source off-axis produces a\nsignificant aberration. This paper presents a novel approach to reducing coma\nin off-axis scanning in the THz region. Here, a dual transmitarray solution is\nproposed, in which a transmitarray with an optimized phase profile is placed\nbehind a regular phase profile transmitarray. A linearly polarized,\ndual-transmitarray antenna was fabricated for validation, and the focusing\nperformances were experimentally characterized. The measured results are in\ngood agreement with the theoretical ones. The generated spot of the\ndual-transmitarray antenna remains focused on an angle up to 50deg, with a -3\ndB spot size of less than 4 mm at 290 GHz. The measured near-field sidelobes\nare all below -10 dB within the whole scanning range.", "category": "physics_app-ph" }, { "text": "Sesame: a 2-dimensional solar cell modeling tool: This work introduces a new software package `Sesame' for the numerical\ncomputation of classical semiconductor equations. It supports 1 and\n2-dimensional systems and provides tools to easily implement extended defects\nsuch as grain boundaries or sample surfaces. Sesame has been designed to\nfacilitate fast exploration of the system parameter space and to visualize\nlocal charge transport properties. Sesame is distributed as a Python package or\nas a standalone GUI application, and is available at\nhttps://pages.nist.gov/sesame/ .", "category": "physics_app-ph" }, { "text": "Selectively biased tri-terminal vertically-integrated memristor\n configuration: Memristors, when utilized as electronic components in circuits, can offer\nopportunities for the implementation of novel reconfigurable electronics. While\nthey have been used in large arrays, studies in ensembles of devices are\ncomparatively limited. Here we propose a vertically stacked memristor\nconfiguration with a shared middle electrode. We study the compound resistive\nstates presented by the combined in-series devices and we alter them either by\ncontrolling each device separately, or by altering the full configuration,\nwhich depends on selective usage of the middle floating electrode. The shared\nmiddle electrode enables a rare look into the combined system, which is not\nnormally available in vertically stacked devices. In the course of this study\nit was found that separate switching of individual devices carries over its\neffects to the complete device (albeit non-linearly), enabling increased\nresistive state range, which leads to a larger number of distinguishable states\n(above SNR variance limits) and hence enhanced device memory. Additionally, by\napplying a switching stimulus to the external electrodes it is possible to\nswitch both devices simultaneously, making the entire configuration a voltage\ndivider with individual memristive components. Through usage of this type of\nconfiguration and by taking advantage of the voltage division, it is possible\nto surge-protect fragile devices, while it was also found that simultaneous\nreset of stacked devices is possible, significantly reducing the required reset\ntime in larger arrays.", "category": "physics_app-ph" }, { "text": "Kinetic Suppression of Photoinduced Halide Migration in Wide Bandgap\n Perovskites via Surface Passivation: In this work, we study the kinetics of photoinduced halide migration in\nFA$_{0.8}$Cs$_{0.2}$Pb(I$_{0.8}$Br$_{0.2}$)$_3$ wide (~1.69 eV) bandgap\nperovskites and show halide migration slows down following surface passivation\nwith (3-aminopropyl) trimethoxysilane (APTMS). We use scanning Kelvin probe\nmicroscopy (SKPM) to probe the contact potential difference (CPD) shift under\nillumination, and the kinetics of surface potential relaxation in the dark. Our\nresults show APTMS-passivated perovskites exhibit a smaller CPD shift under\nillumination, and a slower surface potential relaxation in the dark. We compare\nthe evolution of the photoluminescence spectra of APTMS-passivated and\nunpassivated perovskites under illumination. We find that APTMS-passivated\nperovskites exhibit more than 5 times slower photoluminescence redshift,\nconsistent with the slower surface potential relaxation as observed by SKPM.\nThese observations provide evidence for kinetic suppression of photoinduced\nhalide migration in APTMS-passivated samples, likely due to reduced halide\nvacancy densities, opening avenues to more efficient and stable devices.", "category": "physics_app-ph" }, { "text": "Size Effect and Scaling in Quasi-static and Fatigue Fracture of Graphene\n Polymer Nanocomposites: This work investigated how the structure size affects the quasi-static and\nfatigue behaviors of graphene polymer nanocomposites, a topic that has been\noften overlooked. The results showed that both quasi-static and fatigue failure\nof these materials scale nonlinearly with the structure size due to the\npresence of a significant Fracture Process Zone (FPZ) ahead of the crack tip\ninduced by graphene nanomodification. Such a complicated size effect and\nscaling in either quasi-static or fatigue scenario cannot be described by the\nLinear Elastic Fracture Mechanics (LEFM), but can be well captured by the Size\nEffect Law (SEL) which considers the FPZ.\n Thanks to the SEL, the enhanced quasi-static and fatigue fracture properties\nwere properly characterized and shown to be independent of the structure size.\nIn addition, the differences on the morphological and mechanical behaviors\nbetween quasi-static fracture and fatigue fracture were also identified and\nclarified in this work.\n The experimental data and analytical analyses reported in this paper are\nimportant to deeply understand the mechanics of polymer-based nanocomposite\nmaterials and even other quasi-brittle materials (e.g., fiber-reinforced\npolymers or its hybrid with nanoparticles, etc.), and further advance the\ndevelopment of computational models capable of capturing size-dependent\nfracture of materials in various loading conditions.", "category": "physics_app-ph" }, { "text": "Beyond 100 nm Resolution in 3D Laser Lithography: Post Processing\n Solutions: Laser polymerization has emerged as a direct writing technique allowing the\nfabrication of complex 3D structures with microscale resolution. The technique\nprovides rapid prototyping capabilities for a broad range of applications, but\nto meet the growing interest in 3D nanoscale structures the resolution limits\nneed to be pushed beyond the 100 nm benchmark, which is challenging in\npractical implementations. As a possible path towards this goal, a post\nprocessing of laser polymerized structures is presented. Precise control of the\ncross-sectional dimensions of structural elements as well as tuning of an\noverall size of the entire 3D structure was achieved by combining isotropic\nplasma etching and pyrolysis. The smallest obtainable feature sizes are mostly\nlimited by the mechanical properties of the polymerized resist and the geometry\nof 3D structure. Thus the demonstrated post processing steps open new avenues\nto explore free form 3D structures at the nanoscale.", "category": "physics_app-ph" }, { "text": "Precision manufacturing of a lightweight mirror body made by selective\n laser melting: This article presents a new and individual way to generate opto-mechanical\ncomponents by Additive Manufacturing, embedded in an established process chain\nfor the fabrication of metal optics. The freedom of design offered by additive\ntechniques gives the opportunity to produce more lightweight parts with\nimproved mechanical stability. The latter is demonstrated by simulations of\nseveral models of metal mirrors with a constant outer shape but varying mass\nreduction factors. The optimized lightweight mirror exhibits $63.5 \\%$ of mass\nreduction and a higher stiffness compared to conventional designs, but it is\nnot manufacturable by cutting techniques. Utilizing Selective Laser Melting\ninstead, a demonstrator of the mentioned topological non-trivial design is\nmanufactured out of AlSi12 alloy powder. It is further shown that -- like in\ncase of a traditional manufactured mirror substrate -- optical quality can be\nachieved by diamond turning, electroless nickel plating, and polishing\ntechniques, which finally results in $< 150$~nm peak-to-valley shape deviation\nand a roughness of $< 1$~nm rms in a measurement area of $140 \\times 110$\n$\\mu$m${}^2$. Negative implications from the additive manufacturing are shown\nto be negligible. Further it is shown that surface form is maintained over a\ntwo year storage period under ambient conditions.", "category": "physics_app-ph" }, { "text": "Conductive filament evolution dynamics revealed by cryogenic (1.5 K)\n multilevel switching of CMOS-compatible Al2O3/TiO2 resistive memories: This study demonstrates multilevel switching at 1.5 K of Al2O3/TiO2-x\nresistive memory devices fabricated with CMOS-compatible processes and\nmaterials. The I-V characteristics exhibit a negative differential resistance\n(NDR) effect due to a Joule-heating-induced metal-insulator transition of the\nTi4O7 conductive filament. Carrier transport analysis of all multilevel\nswitching I-V curves show that while the insulating regime follows the space\ncharge limited current (SCLC) model for all resistance states, the conduction\nin the metallic regime is dominated by SCLC and trap-assisted tunneling (TAT)\nfor low- and high-resistance states respectively. A non-monotonic conductance\nevolution is observed in the insulating regime, as opposed to the continuous\nand gradual conductance increase and decrease obtained in the metallic regime\nduring the multilevel SET and RESET operations. Cryogenic transport analysis\ncoupled to an analytical model accounting for the\nmetal-insulator-transition-induced NDR effects and the resistance states of the\ndevice provide new insights on the conductive filament evolution dynamics and\nresistive switching mechanisms. Our findings suggest that the non-monotonic\nconductance evolution in the insulating regime is due to the combined effects\nof longitudinal and radial variations of the Ti4O7 conductive filament during\nthe switching. This behavior results from the interplay between temperature-\nand field-dependent geometrical and physical characteristics of the filament.", "category": "physics_app-ph" }, { "text": "Spin-torque memristors based on perpendicular magnetic tunnel junctions\n with a hybrid chiral texture: Spin-torque memristors were proposed in 2009, which could provide fast,\nlow-power and infinite memristive behavior for large-density non-volatile\nmemory and neuromorphic computing. However, the strict requirements of\ncombining high magnetoresistance, stable intermediate states and spin-polarized\ncurrent switching in a single device pose difficulties in physical\nimplementation. Here, we experimentally demonstrate a nanoscale spin-torque\nmemristor based on a perpendicular-anisotropy magnetic tunnel junction with a\nCoFeB/W/CoFeB composite free layer structure. Its tunneling magnetoresistance\nis higher than 200%, and memristive behavior can be realized by spin-transfer\ntorque switching. Memristive states are maintained by robust domain wall\npinning around clusters of W atoms, where nanoscale vertical chiral spin\ntextures could be formed through the competition between opposing\nDzyaloshinskii-Moriya interactions and the fluctuating interlayer coupling\ncaused by the Ruderman-Kittel-Kasuya-Yosida interaction between the two CoFeB\nfree layers. Spike-timing-dependent plasticity is also demonstrated in this\ndevice.", "category": "physics_app-ph" }, { "text": "Wireless powering efficiency of deep-body implantable devices: The wireless power transfer efficiency to implanted bioelectronic devices is\nconstrained by several frequency-dependent physical mechanisms. Recent works\nhave developed several mathematical formulations to understand these mechanisms\nand predict the optimal operating conditions. However, existing approaches rely\non simplified body models, which are unable to capture important aspects of\nwireless power transfer. Therefore, this paper proposes the efficiency analysis\napproach in anatomical models that can provide insightful information on\nachieving the optimum operation conditions. First, this approach is validated\nwith a theoretical spherical wave expansion analysis, and the results for a\nsimplified spherical model and a human pectoral model are compared. The results\nshow that although a magnetic receiver outperforms an electric one for\nnear-field operation and both sources could be equally employed in far-field\nrange, it is in mid-field that the maximum efficiency is achieved with an\noptimum frequency between 1-5 GHz depending on the implantation depth. The\nreceiver orientation is another factor that affects the efficiency, with a\nmaximum difference between the best and worst-case scenarios around five times\nfor the electric source and over 13 times for the magnetic one. This approach\nis used to analyze the case of a deep-implanted pacemaker wirelessly powered by\nan on-body transmitter and subjected to stochastic misalignments. We evaluate\nthe efficiency and exposure, and we demonstrate how a buffered transmitter can\nbe tailored to achieve maximum powering efficiency. Finally, design guidelines\nthat lead to optimal implantable wireless power transfer systems are\nestablished from the results obtained with the proposed approach.", "category": "physics_app-ph" }, { "text": "Single Photon Source Driver Designed in ASIC: The single photon source is an important part of the quantum key distribution\n(QKD) system. At present, the single photon source is large in size and complex\nin structure for a lot of discrete components which are used. The\nminiaturization of the photon source is the tendency of the QKD system. We\nintegrate all laser driver electronic module into one single ASIC chip, which\ncan be used to drive the 1550nm DFB laser in random pulse mode and it can\ngreatly reduce the volume of the single photon source. We present the design of\nthe chip named LSD2018 and simulation results before the tape-out. The LSD2018\nis fabricated with a 130 nm CMOS process and consists of a discriminator, an\nadjustable pulse generator, a bandgap reference, an SPI bus, and an\namplitude-adjustable current pulse driver. The electronic random pulse from the\ndriver can go 20mA to 120mA in amplitude and 400ps to 4ns in pulse width. The\nparameters can be set by an SPI bus.", "category": "physics_app-ph" }, { "text": "Mixing enhancement induced by viscoelastic micromotors in microfluidic\n platform: Fine manipulation of fluid flows at the microscale has a tremendous impact on\nmass transport phenomena of chemical and biological processes inside\nmicrofluidic platforms. Fluid mixing in the laminar flow regime at low Reynolds\nis poorly effective due to the inherently slow diffusive mechanism. As a\nstrategy to enhance mixing and prompt mass transport, here, we focus on\npolyelectrolyte multilayer capsules (PMCs) embodying a catalytic\npolyoxometalate as microobjects to create elastic turbulence and as micromotors\nto generate chaotic flows by fuel-fed propulsions. The effects of the elastic\nturbolence and of the artificial propulsion on some basic flow parameters, such\nas pressure and volumetric flow rate are studied by a microfluidic set-up\nincluding pressure and flow sensors. Numerical-handling and physical models of\nthe experimental data are presented and discussed to explain the measured\ndependence of the pressure drop on the flow rate in presence of the PMCs. As a\npractical outcome of the study, a strong decrease of the mixing time in a\nserpentine microreactor is demonstrated. Unlike our previous reports dealing\nwith capillarity flow studies, the present paper relies on hydrodynamic pumping\nexperiments, that allows us to both develop a theoretical model for the\nunderstanding of the involved phenomena and demonstrate a successfully\nmicrofluidic mixing application. All of this is relevant in the perspective of\ndeveloping microobject based methods to overcome microscale processes purely\ndominated by diffusion with potential improvements of mass trasport in\nmicrofluidic platforms.", "category": "physics_app-ph" }, { "text": "Revealing the Mechanism of Electrochemical Lithiation of Carbon Nanotube\n Fibers: Fabrics of continuous fibers of carbon nanotubes (CNTFs) are attractive\nmaterials for multifunctional energy storage devices, either as current\ncollector, or as active material. Despite a similar chemical composition,\nlithiation/delithiation in CNTFs is substantially different from traditional\ngraphite electrodes. In CNTFs this process is dominated by surface processes,\ninsertion in the bundles interstices, electrochemical doping and\noften-overlooked partial degradation of the sp2 lattice upon cycling. Through\nextensive electrochemical analysis, together with in situ Raman spectroscopy\nmeasurements, we analyzed the complex lithiation behavior of highly crystalline\nfibers of CNTs. CNTF can store lithium reversibly with high specific capacity\nand rate capability, thanks to a large capacitive contribution. Upon\nlithiation, they undergo electrochemical doping, with longitudinal conductivity\nincreasing by as much as 100 %, concomitant with large downshifts in Raman\nspectra. However, CNTF are also affected by high first-cycle irreversible\ncapacity, voltage hysteresis and amorphization upon cycling. Electrochemical\nanalysis confirms that SEI formation is responsible for the first-cycle\nirreversible capacity. Voltage hysteresis is attributed primarily to the\ntrapping of lithium ions in the interstices between stacked nanotubes. Another\ndominant feature is pre-existing defects, which promote capacitive storage but\nlead to progressive amorphization of the CNTFs. Indeed, it is evidenced that\nundesired amorphization is hindered in ultra-pure CNTF without pre-existing\ndefects.", "category": "physics_app-ph" }, { "text": "A frequency-tunable nanomembrane mechanical oscillator with embedded\n quantum dots: Hybrid systems consisting of a quantum emitter coupled to a mechanical\noscillator are receiving increasing attention for fundamental science and\npotential applications in quantum technologies. In contrast to most of the\npresented works, in which the oscillator eigenfrequencies are irreversibly\ndetermined by the fabrication process, we present here a simple approach to\nobtain frequency-tunable mechanical resonators based on suspended\nnanomembranes. The method relies on a micromachined piezoelectric actuator,\nwhich we use both to drive resonant oscillations of a suspended Ga(Al)As\nmembrane with embedded quantum dots and to fine tune their mechanical\neigenfrequencies. Specifically, we excite oscillations with frequencies of at\nleast 60 MHz by applying an AC voltage to the actuator and tune the\neigenfrequencies by at least 25 times their linewidth by continuously varying\nthe elastic stress state in the membranes through a DC voltage. The light\nemitted by optically excited quantum dots is used as sensitive local strain\ngauge to monitor the oscillation frequency and amplitude. We expect that our\nmethod has the potential to be applicable to other optomechanical systems based\non dielectric and semiconductor membranes possibly operating in the quantum\nregime.", "category": "physics_app-ph" }, { "text": "Investigating the dispersion state of alumina suspensions: contribution\n of Cryo-FEGSEM characterizations: We illustrate in this paper the interest of cryo scanning electron microscopy\n(cryo-FEGSEM) to investigate the stability of alumina suspensions. The\nstability is investigated through viscosity, zeta potential, total organic\ncarbon measurements and cryo-FEGSEM observations. We focus on two examples: the\neffect of the quantity of ammonium polyacrylate as dispersant and the effect of\nits chain length on alumina particles dispersion with a solid content of\n32vol%. In the first example for some suspensions we measure values of\nviscosity or zeta potential too similar to discriminate the best state of\ndispersion. To overcome this problem we directly observe the suspensions with\nCryo-FEGSEM. We take advantage of the recent developments of the technique,\nwhich provide now extremely high cooling rates and ensure that the freezing\nstep does not induce observations artifacts related to the formation of ice.\nThis technique provides an accurate vision of particles dispersion,\nagglomeration in ceramic suspensions and it is possible to visualize the excess\nof dispersant. In the second example the longer dispersant appears to be the\nmore effective to obtain the best state of dispersion. Through both examples,\nwe demonstrate that to have the best interpretation of results it is useful to\ncombine direct observations by Cryo-FEGSEM and the usual properties\nmeasurements.", "category": "physics_app-ph" }, { "text": "Bidirectional elastic diode with frequency-preserved nonreciprocity: The study of nonreciprocal wave propagation is of great interests for both\nfundamental research and engineering applications. Here we demonstrate\ntheoretically and experimentally a bidirectional, nonreciprocal, and\nhigh-quality diode that can rectify elastic waves in both forward and backward\ndirections in an elastic metamaterial designed to exhibit enhanced nonlinearity\nof resonances. This diode can preserve or vary frequency, rectify low-frequency\nlong wave with small system size, offer high-quality insulation, can be\nmodulated by amplitude, and break reciprocity of both the total energy and\nfundamental wave. We report three mechanisms to break reciprocity: the\namplitude-dependent bandgap combining interface reflection, chaotic response\ncombining linear bandgap, amplitude-dependent attenuation rate in damping\ndiode. The bidirectional diode paves ways for mutually controlling\ninformation/energy transport between two sources, which can be used as new wave\ninsulators.", "category": "physics_app-ph" }, { "text": "Level set methods for gradient-free optimization of metasurface arrays: Global optimization techniques are increasingly preferred over human-driven\nmethods in the design of electromagnetic structures such as metasurfaces, and\ncareful construction and parameterization of the physical structure is critical\nin ensuring computational efficiency and convergence of the optimization\nalgorithm to a globally optimal solution. While many design variables in\nphysical systems take discrete values, optimization algorithms often benefit\nfrom a continuous design space. This work demonstrates the use of level set\nfunctions as a continuous basis for designing material distributions for\nmetasurface arrays and introduces an improved parameterization which is termed\nthe periodic level set function. We explore the use of alternate norms in the\ndefinition of the level set function and define a new pseudo-inverse technique\nfor upsampling basis coefficients with these norms. The level set method is\ncompared to the fragmented parameterization and shows improved electromagnetic\nresponses for two dissimilar cost functions: a narrowband objective and a\nbroadband objective. Finally, we manufacture an optimized level set metasurface\nand measure its scattering parameters to demonstrate real-world performance.", "category": "physics_app-ph" }, { "text": "Stumbling Through the Research Wilderness, Standard Methods to Shine\n Light on Electrically Conductive Nanocomposites for Future Health-Care\n Monitoring: Electrically conductive nanocomposites are an exciting ever expanding area of\nresearch that has yielded many new technologies for wearable health devices.\nActing as strain sensing materials, they have paved the way towards real time\nmedical diagnostic tools that may very well lead to a golden age of healthcare.\nCurrently, the goal in research is to create a material that simultaneously has\nboth a large gauge factor G and sensing range. However, a weakness in the area\nof electromechanical research is the lack of standardisation in the reporting\nof the figure of merit, i.e. G, and the need for new metrics to give\nresearchers a more complete view of the research landscape of resistive type\nsensors. A paradigm shift in the way in which data is reported is required, to\npush research in the right direction and to facilitate achieving research\ngoals. Here, we report a standardised method for reporting strain sensing\nperformance and the introduction of the working factor W and the Young's\nmodulus Y of a material as two new material criteria. Using this new method, we\ncan now for the first time define the benchmarks for an optimum sensing\nmaterial, G > 7, W > 1, Y < 300 kPa, using limits set by standard commercial\nmaterials and the human body. Using extrapolated data from 200 publications\nnormalised to this standard method, we can review what composite types meet\nthese benchmark limits, what governs composite performances, the literary\ntrends in composites and individual nanomaterial performance and the future\nprospects of research.", "category": "physics_app-ph" }, { "text": "Room-temperature quasi-continuous-wave pentacene maser pumped by an\n invasive Ce:YAG luminescent concentrator: We present in this work a quasi-continuous-wave (CW) pentacene maser\noperating at 1.45 GHz in the Earth's magnetic field at room temperature with a\nduration of $\\sim$4 ms and an output power of up to -25 dBm. The maser is\noptically pumped by a cerium-doped YAG (Ce:YAG) luminescent concentrator (LC)\nwhose wedge-shaped output is embedded inside a 0.1% pentacene-doped\npara-terphenyl (Pc:Ptp) crystal. The pumped crystal is located inside a ring of\nstrontium titanate (STO) that supports a TE$_{01\\delta}$ mode of high magnetic\nPurcell factor. Combined with simulations, our results indicate that CW\noperation of pentacene masers at room-temperature is perfectly feasible so long\nas excessive heating of the crystal is avoided.", "category": "physics_app-ph" }, { "text": "Large Transverse Thermopower in Shape-Engineered Tilted Leg Thermopile: We demonstrate that a novel device design, where a shape-engineered\ntilted-leg thermopile structure is employed, significantly enhances the output\nvoltage in the transverse direction. Owing to the shape engineering of the leg\ngeometry, an additional temperature gradient develops along the long direction\nof the leg, which is perpendicular to the direction of the applied temperature\ngradient, thereby generating an additional Seebeck voltage V_SE that adds to\nthe Anomalous Nernst effect (ANE) voltage V_ANE. We further show that a simple\nadjustment of electrode position within the device can further increase V_SE.\nThe tilted leg device with electrode adjustment demonstrates a 990% enhanced\ntransverse output voltage compared to that of conventional rectangular leg\nthermopile-structured devices, wherein only the ANE occurs. This combined\noutput voltage from both the Seebeck effect and ANE is equivalent to the value\nthat surpasses the state-of-the-art ANE materials and devices currently\navailable. The numerical analysis shows the tendencies of the electrical and\nthermal outputs of the tilted-leg device, which guides a way to further improve\nthe output voltage. Our study paves the way to develop highly efficient\ntransverse TE devices that can overcome intrinsic materials challenges by\nutilizing the degree of freedom of device design.", "category": "physics_app-ph" }, { "text": "Rainbow reflection and trapping for energy harvesting: Important distinctions are made between two related wave control mechanisms\nthat act to spatially separate frequency components; these so-called rainbow\nmechanisms either slow or reverse guided waves propagating along a graded line\narray. We demonstrate an important nuance distinguishing rainbow reflection\nfrom genuine rainbow trapping and show the implications of this distinction for\nenergy harvesting designs. The difference between these related mechanisms is\nhighlighted using a design methodology, applied to flexural waves on mass\nloaded thin Kirchhoff-Love elastic plates, and emphasised through simulations\nfor energy harvesting in the setting of elasticity, by elastic metasurfaces of\ngraded line arrays of resonant rods atop a beam. The delineation of these two\neffects, reflection and trapping, allows us to characterise the behaviour of\nforced line array systems and predict their capabilities for trapping,\nconversion and focusing of energy.", "category": "physics_app-ph" }, { "text": "A Nanocryotron Ripple Counter Integrated with a Superconducting Nanowire\n Single-Photon Detector for Megapixel Arrays: Decreasing the number of cables that bring heat into the cryocooler is a\ncritical issue for all cryoelectronic devices. Especially, arrays of\nsuperconducting nanowire single-photon detectors (SNSPDs) could require more\nthan $10^6$ readout lines. Performing signal processing operations at low\ntemperatures could be a solution. Nanocryotrons, superconducting nanowire\nthree-terminal devices, are good candidates for integrating sensing and\nelectronics on the same technological platform as SNSPDs in photon-counting\napplications. In this work, we demonstrated that it is possible to read out,\nprocess, encode, and store the output of SNSPDs using exclusively\nsuperconducting nanowires. In particular, we present the design and development\nof a nanocryotron ripple counter that detects input voltage spikes and converts\nthe number of pulses to an $N$-digit value. The counting base can be tuned from\n2 to higher values, enabling higher maximum counts without enlarging the\ncircuit. As a proof-of-principle, we first experimentally demonstrated the\nbuilding block of the counter, an integer-$N$ frequency divider with $N$\nranging from 2 to 5. Then, we demonstrated photon-counting operations at\n405\\,nm and 1550\\,nm by coupling an SNSPD with a 2-digit nanocryotron counter\npartially integrated on-chip. The 2-digit counter operated in either base 2 or\nbase 3 with a bit error rate lower than $2 \\times 10^{-4}$ and a maximum count\nrate of $45 \\times 10^6\\,$s$^{-1}$. We simulated circuit architectures for\nintegrated readout of the counter state, and we evaluated the capabilities of\nreading out an SNSPD megapixel array that would collect up to $10^{12}$ counts\nper second. The results of this work, combined with our recent publications on\na nanocryotron shift register and logic gates, pave the way for the development\nof nanocryotron processors, from which multiple superconducting platforms may\nbenefit.", "category": "physics_app-ph" }, { "text": "Real-time-controlled artificial quiet channel for acoustic cloaking\n under varying detection conditions: We consider the problem of hiding non-stationary objects from acoustic\ndetection in a two-dimensional environment, where both the object's impedance\nand the properties of the detection signal may vary during operation. The\ndetection signal is assumed to be an acoustic beam created by an array of\nemitters, which scans the area at different angles and different frequencies.\nWe propose an active control-based solution that creates an effective moving\ndead zone around the object, and results in an artificial quiet channel for the\nobject to pass through undetected. The control principle is based on mid-domain\ngeneration of near uni-directional beams using only monopole actuators. Based\non real-time response prediction, these beams open and close the dead zone with\na minimal perturbation backwards, which is crucial due to detector observers\nbeing located on both sides of the object's route. The back action wave\ndetermines the cloak efficiency, and is traded-off with the control effort; the\nhigher is the effort the quieter is the cloaking channel. We validate our\ncontrol algorithm via numerical experiments in a two-dimensional acoustic\nwaveguide, testing variation in frequency and incidence angle of the detection\nsource. Our cloak successfully intercepts the source by steering the control\nbeams and adjusting their wavelength accordingly.", "category": "physics_app-ph" }, { "text": "Nanofluidic trapping and enhanced Raman detection of single biomolecules\n in plasmonic bowl-shaped nanopore: Solid-state nanopores are emerging platforms for single-molecule protein\nsequencing due to their tolerance to hash physiology environment and\ncompatibility with different electrical and optical detection methods. However,\nthey suffer from poor molecular manipulations that were twisted with and thus\nlimited by the detection methods. Here, we report a bowl-shaped plasmonic gold\nnanopore on silicon nitride with hydrogel to demonstrate near-field nanofluidic\nmanipulation of DNA translocation for plasmon-enhanced Raman spectroscopic\ndetection. The hydrogel linearized the DNA, and the linear DNA was trapped in\nthe nanopore for tens of seconds due assumably to bipolar effect of the\nnanopore that generate electroosmotic sheath flow and bipolar surface charge\ndistribution. Their combination led to a near-field confinement of the DNA in\nthe nanopore hot spot to allow stable Raman detection. We envision that a\ncombination of Raman spectroscopy with the bowl-shaped nanopores can succeed in\nsingle-molecule protein sequencing in a label-free way", "category": "physics_app-ph" }, { "text": "Tunable telecom to mid-infrared optical parametric oscillation via\n microring-based $\u03c7^{(3)}$ nonlinearities: Optical parametric oscillation (OPO) with far-shifted frequency sidebands has\nattracted significant interests in precision spectroscopy and quantum\ninformation processing. Microresonator based OPO sources hold the advantages of\nminiaturized footprint and versatile dispersion engineering. Here we\ndemonstrate large-frequency-shifted $\\chi^{(3)}$-based OPO from crystalline\naluminum nitride microrings pumped at $\\sim$2 $\\mu$m in the normal dispersion\nregime. OPO in the telecom and mid-infrared bands with a frequency separation\nof 65.5 THz is achieved. The OPO frequency can be agilely tuned in the ranges\nof 10, 1 and 0.1 THz respectively by tailoring the microring dimensions,\nshifting the pump wavelength, and controlling the chip temperature. At high\nintracavity pump powers, the OPO sidebands further evolve into localized\nfrequency comb lines. Such telecom to mid-infrared OPO with flexible wavelength\ntunability will lead to enhanced chip-scale light sources.", "category": "physics_app-ph" }, { "text": "Mechanical Properties of a Diamond Schwarzite: From Atomistic Models to\n 3D-Printed Structures: Triply Periodic Minimal Surfaces (TPMS) possess locally minimized surface\narea under the constraint of periodic boundary conditions. Different families\nof surfaces were obtained with different topologies satisfying such conditions.\nExamples of such families include Primitive (P), Gyroid (G) and Diamond (D)\nsurfaces. From a purely mathematical subject, TPMS have been recently found in\nmaterials science as optimal geometries for structural applications. Proposed\nby Mackay and Terrones in 1991, schwarzites are 3D crystalline porous carbon\nnanocrystals exhibiting the shape of TPMS. Although their complex topology\nposes serious limitations on their synthesis with conventional nanoscale\nfabrication methods, such as Chemical Vapour Deposition (CVD), TPMS can be\nfabricated by Additive Manufacturing (AM) techniques, such as 3D Printing. In\nthis work, we used an optimized atomic model of a schwarzite structure from the\nD family (D8bal) to generate a surface mesh that was subsequently used for\n3D-printing through Fused Deposition Modelling (FDM). This D schwarzite was\n3D-printed with thermoplastic PolyLactic Acid (PLA) polymer filaments.\nMechanical properties under uniaxial compression were investigated for both the\natomic model and the 3D-printed one. Fully atomistic Molecular Dynamics (MD)\nsimulations were also carried out to investigate the uniaxial compression\nbehavior of the D8bal atomic model. Mechanical testings were performed on the\n3D-printed schwarzite where the deformation mechanisms were found to be similar\nto those observed in MD simulations. These results are suggestive of a\nscale-independent mechanical behavior that is dominated by structural topology.", "category": "physics_app-ph" }, { "text": "Realization of the all-optical phase modulator, filter, splitter, and\n self-consistent logic gates based on assembled magneto-optical\n heterostructures: All-optical computing has recently emerged as a vibrant research field in\nresponse to the energy crisis and the growing demand for information\nprocessing. However, the efficiency of subwavelength-scale all-optical devices\nremains relatively low due to challenges such as back-scattering reflections\nand strict surface roughness. Furthermore, achieving multifunctionality through\nthe reassembly of all-optical structures has thus far been rarely accomplished.\nOne promising approach to address these issues is the utilization of one-way\nedge modes. In this study, we propose four types of deep-subwavelength ($\\sim\n10^{-2} \\lambda_0$, where $\\lambda_0$ is the wavelength in vacuum) all-optical\nfunctional devices: a phase modulator, a filter, a splitter, and logic gates.\nThese devices are based on robust one-way modes but do not require an external\nmagnetic field, which can allow for flexible assembly. In particular, we\ninvestigate a phase modulation range spanning from $-\\pi$ to $\\pi$, a perfect\nfilter that divides the input port's one-way region into two output one-way\nregions with equal bandwidth, a multi-frequency splitter with an equal\nsplitting ratio (e.g., 50/50), and self-consistent logic gates. We validate\nthese theoretical findings through comprehensive full-wave numerical\nsimulations. Our findings may find applications in minimal optical calculations\nand integrated optical circuits.", "category": "physics_app-ph" }, { "text": "Observation of roton-like dispersion relations in acoustic metamaterials: Roton dispersion relations, displaying a pronounced \"roton\" minimum at finite\nmomentum, were firstly predicted by Landau and have been extensively explored\nin correlated quantum systems at low temperatures. Recently, the roton-like\ndispersion relations were theoretically extended to classical acoustics, which,\nhowever, have remained elusive in reality. Here, we report the experimental\nobservation of roton-like dispersions in acoustic metamaterials with\nbeyond-nearest-neighbour interactions at ambient temperatures. The resulting\nmetamaterial supports multiple coexisting modes with different wavevectors and\ngroup velocities at the same frequency and broadband backward waves, analogous\nto the \"return flow\" termed by Feynman in the context of rotons. Moreover, by\nincreasing the order of long-range interaction, we observe multiple rotons on a\nsingle dispersion band, which have never appeared in Landau's prediction or any\nother condensed matter study. The realization of roton-like dispersions in\nmetamaterials could pave the way to explore novel physics and applications on\nquantum-inspired phenomena in classical systems.", "category": "physics_app-ph" }, { "text": "Dark current in monolithic extended-SWIR GeSn PIN photodetectors: The monolithic integration of extended short-wave infrared (e-SWIR)\nphotodetectors (PDs) on silicon is highly sought-after to implement\nmanufacturable, cost-effective sensing and imaging technologies. With this\nperspective, GeSn PIN PDs have been the subject of extensive investigations\nbecause of their bandgap tunability and silicon compatibility. However, due to\ngrowth defects, these PDs suffer a relatively high dark current density as\ncompared to commercial III-V PDs. Herein, we elucidate the mechanisms governing\nthe dark current in $2.6 \\, \\mu$m GeSn PDs at a Sn content of $10$ at.%. It was\nfound that in the temperature range of $293 \\, $K -- $363 \\,$K and at low bias,\nthe diffusion and Shockley-Read-Hall (SRH) leakage mechanisms dominate the dark\ncurrent in small diameter ($20 \\, \\mu$m) devices, while combined SRH and trap\nassisted tunneling (TAT) leakage mechanisms are prominent in larger diameter\n($160 \\, \\mu$m) devices. However, at high reverse bias, TAT leakage mechanism\nbecomes dominant regardless of the operating temperature and device size. The\neffective non-radiative carrier lifetime in these devices was found to reach\n$\\sim 300$ -- $400$ ps at low bias. Owing to TAT leakage current, however, this\nlifetime reduces progressively as the bias increases.", "category": "physics_app-ph" }, { "text": "An experimental design for the control and assembly of magnetic\n microwheels: Superparamagnetic colloidal particles can be reversibly assembled into\nwheel-like structures called microwheels ($\\mu$wheels) which roll on surfaces\ndue to friction and can be driven at user-controlled speeds and directions\nusing rotating magnetic fields. Here, we describe the hardware and software to\ncreate and control the magnetic fields that assemble and direct wheel motion\nand the optics to visualize them. Motivated by portability, adaptability and\nlow-cost, an extruded aluminum heat dissipating frame incorporating open optics\nand audio speaker coils outfitted with high magnetic permeability cores was\nconstructed. Open-source software was developed to define the magnitude,\nfrequency, and orientation of the magnetic field, allowing for real time\njoystick control of $\\mu$wheels through two-dimensional (2D) and\nthree-dimensional (3D) fluidic environments. With this combination of hardware\nand software, $\\mu$wheels translate at speeds up to 50 $\\mu$m/s through sample\nsizes up to 5 cm x 5 cm x 5 cm using 0.75-2.5 mT magnetic fields with rotation\nfrequencies of 5-40 Hz. Heat dissipation by aluminum coil clamps maintained\nsample temperatures within 3 C of ambient temperature, a range conducive for\nbiological applications. With this design, $\\mu$wheels can be manipulated and\nimaged in 2D and 3D networks at length scales of micrometers to centimeters", "category": "physics_app-ph" }, { "text": "Transient Dynamics of a Miura-Origami Tube during Free Deployment: With excellent folding-induced deformability and shape reconfigurability,\norigami-based designs have shown great potentials in developing deployable\nstructures. Noting that origami deployment is essentially a dynamic process,\nwhile its dynamical behaviors remain largely unexplored owing to the challenges\nin modeling. This research aims at advancing the state of the art of origami\ndeployable structures by exploring the transient dynamics under free\ndeployment, with the Miura-origami tube being selected as the object of study\nbecause it possesses relatively simple geometry, exceptional kinematic\nproperties, and wide applications. In detail, a preliminary free deployment\ntest is performed, which indicates that the transient oscillation in the\ntransverse direction is nonnegligible and the tube deployment is no longer a\nsingle-degree-of-freedom (SDOF) mechanism. Based on experimental observations,\nfour assumptions are made for modeling purposes, and a 2N-DOF dynamic model is\nestablished for an N-cell Miura-origami tube to predict the transient\noscillations in both the deploying and the transverse directions. Employing the\nsettling times and the overshoot values as the transient dynamic indexes, a\ncomprehensive parameter study is then carried out. It reveals that both the\nphysical and geometrical parameters will significantly affect the transient\ndeploying dynamics, with some of the parameter dependence relationships being\ncounter-intuitive. The results show that the relationships between the\ntransient dynamic behaviors and the examined parameters are sometimes\ncontradictory in the deploying and the transverse directions, suggesting the\nnecessity of a compromise in design.", "category": "physics_app-ph" }, { "text": "Development of highly nonlinear polarization maintaining fibers with\n normal dispersion across entire transmission window: Determined polarization state of light is required in nonlinear optics\napplications related to ultrashort and single-cycle light pulse generation.\nSuch short time scales require up to full octave of spectral width of light.\nFiber-based, pulse-preserving and linearly polarized supercontinuum can meet\nthese requirements. We report on the development - from linear simulations of\nthe fiber structure, through fabrication of physical fibers to their versatile\ncharacterization - of polarization maintaining, highly nonlinear photonic\ncrystal fibers, intended for femtosecond pumping at a wavelength of 1560 nm.\nFull octave of linearly polarized light around this wavelength would enable to\ncover amplification bandwidths of the three major fiber amplifiers from\nytterbium doped systems up to thulium and holmium doped fiber amplifiers, with\na coherent, linearly polarized seed signal. At the same time, an all-normal\nchromatic dispersion profile over an entire transmission window, and small\ndispersion of nonlinearity in the developed fibers, would facilitate use of\ncommercially available femtosecond fiber lasers as pump sources for the\ndeveloped fibers.", "category": "physics_app-ph" }, { "text": "Van der Waals device integration beyond the limits of van der Waals\n forces via adhesive matrix transfer: Pristine van der Waals (vdW) interfaces between two-dimensional (2D) and\nother materials are core to emerging optical and electronic devices. Their\ndirect fabrication is, however, challenged as the vdW forces are weak and\ncannot be tuned to accommodate integration of arbitrary layers without\nsolvents, sacrificial-layers or high-temperatures, steps that can introduce\ndamage. To address these limitations, we introduce a single-step 2D\nmaterial-to-device integration approach in which forces promoting transfer are\ndecoupled from the vdW forces at the interface of interest. We use this\nadhesive matrix transfer to demonstrate conventionally-forbidden direct\nintegration of diverse 2D materials (MoS2, WSe2, PtS2, GaS) with dielectrics\n(SiO2, Al2O3), and scalable, aligned heterostructure formation, both\nfoundational to device development. We then demonstrate a single-step\nintegration of monolayer-MoS2 into arrays of transistors. With no exposure to\npolymers or solvents, clean interfaces and pristine surfaces are preserved,\nwhich can be further engineered to demonstrate both n- and p-type behavior.\nBeyond serving as a platform to probe the intrinsic properties of sensitive\nnanomaterials without the influence of processing steps, our technique allows\nefficient formation of unconventional device form-factors, with an example of\nflexible transistors demonstrated.", "category": "physics_app-ph" }, { "text": "Going Beyond the Debye Length: Overcoming Charge Screening Limitations\n in Next-Generation Bioelectronic Sensors: Electronic biosensors are a natural fit for field-deployable diagnostic\ndevices, because they can be miniaturized, mass produced, and integrated with\ncircuitry. Unfortunately, progress in the development of such platforms has\nbeen hindered by the fact that mobile ions present in biological samples screen\ncharges from the target molecule, greatly reducing sensor sensitivity. Under\nphysiological conditions, the thickness of the resulting electric double layer\nis less than 1 nm, and it has generally been assumed that electronic detection\nbeyond this distance is virtually impossible. However, a few recently-described\nsensor design strategies seem to defy this conventional wisdom, exploiting the\nphysics of electrical double layers in ways that traditional models do not\ncapture. In the first strategy, charge screening is decreased by constraining\nthe space in which double layers can form. The second strategy uses external\nstimuli to prevent double layers from reaching equilibrium, thereby effectively\nreducing charge screening. The goal of this article is to describe these\nrelatively new concepts, and to offer theoretical insights into mechanisms that\nmay enable electronic biosensing beyond the double-layer. If these concepts can\nbe further developed and translated into practical electronic biosensors, we\nforesee exciting opportunities for the next generation of diagnostic\ntechnologies.", "category": "physics_app-ph" }, { "text": "Tapered ultra-high Numerical Aperture optical fiber tip for Nitrogen\n Vacancy ensembles based endoscope in a fluidic environment: Fixing a diamond containing a high density of Nitrogen-Vacancy (NV) center\nensembles on the apex of a multimode optical fiber (MMF) extends the\napplications of NV-based endoscope sensors. Replacing the normal MMF with a\ntapered MMF (MMF-taper) has enhanced the fluorescence (FL) collection\nefficiency from the diamond and achieved a high spatial resolution NV-based\nendoscope. The MMF-taper's high FL collection efficiency is the direct result\nof multiple internal reflections in the tapered region caused by silica, which\nhas a higher refractive index (RI) than the surrounding air. However, for\napplications involving fluidic environments whose RI is close to or higher than\nthat of the silica, the MMF-taper loses its FL collection significantly. Here,\nto overcome this challenge, we replaced the MMF-taper with an ultra-high\nnumerical aperture (NA) microstructured optical fiber (MOF) which is tapered\nand sealed its air capillaries at the tapered end. Since the end-sealed air\ncapillaries along the tapered MOF (MOF-taper) have isolated the MOF core from\nthe surrounding medium, the core retains its high FL collection and NV\nexcitation efficiency in liquids regardless of their RI values. Such a\nversatile NV-based endoscope could potentially find broad applications in\nfluidic environments where many biological processes and chemical reactions\noccur.", "category": "physics_app-ph" }, { "text": "Loss Compensation in Time-Dependent Elastic Metamaterials: Materials with properties that are modulated in time are known to display\nwave phenomena showing energy increasing with time, with the rate mediated by\nthe modulation. Until now there has been no accounting for material\ndissipation, which clearly counteracts energy growth. This paper provides an\nexact expression for the amplitude of elastic or acoustic waves propagating in\nlossy materials with properties that are periodically modulated in time. It is\nfound that these materials can support a special propagation regime in which\nwaves travel at constant amplitude, with temporal modulation compensating for\nthe normal energy dissipation. We derive a general condition under which\namplification due to time-dependent properties offsets the material\ndissipation. This identity relates band-gap properties associated with the\ntemporal modulation and the average of the viscosity coefficient, thereby\nproviding a simple recipe for the design of loss-compensated mechanical\nmetamaterials.", "category": "physics_app-ph" }, { "text": "Tunable and Transferable Diamond Membranes for Integrated Quantum\n Technologies: Color centers in diamond are widely explored as qubits in quantum\ntechnologies. However, challenges remain in the effective and efficient\nintegration of these diamond-hosted qubits in device heterostructures. Here,\nnanoscale-thick uniform diamond membranes are synthesized via \"smart-cut\" and\nisotopically (12C) purified overgrowth. These membranes have tunable\nthicknesses (demonstrated 50 nm to 250 nm), are deterministically transferable,\nhave bilaterally atomically flat surfaces (Rq <= 0.3 nm), and bulk-diamond-like\ncrystallinity. Color centers are synthesized via both implantation and in-situ\novergrowth incorporation. Within 110 nm thick membranes, individual\ngermanium-vacancy (GeV-) centers exhibit stable photoluminescence at 5.4 K and\naverage optical transition linewidths as low as 125 MHz. The room temperature\nspin coherence of individual nitrogen-vacancy (NV-) centers shows Ramsey spin\ndephasing times (T2*) and Hahn echo times (T2) as long as 150 us and 400 us,\nrespectively. This platform enables the straightforward integration of diamond\nmembranes that host coherent color centers into quantum technologies.", "category": "physics_app-ph" }, { "text": "Direct polariton-to-electron tunneling in quantum cascade detectors\n operating in the strong light-matter coupling regime: We demonstrate mid-infrared quantum cascade detectors (QCD) operating in the\nstrong light-matter coupling regime. They operate around $\\lambda = 10~\\mu m$\nwith a minimum Rabi splitting of 9.3 meV. A simple model based on the usual\ndescription of transport in QCDs does not reproduce the polaritonic features in\nthe photo-current spectra. On the contrary, a more refined approach, based on\nthe semi-classical coupled modes theory, is capable to reproduce both optical\nand electrical spectra with excellent agreement. By correlating\nabsorption/photo-response with the simulations, we demonstrate that - in this\nsystem - resonant tunneling from the polaritonic states is the main extraction\nmechanism. The dark intersubband states are not involved in the process,\ncontrary to what happens in electrically injected polaritonic emitters.", "category": "physics_app-ph" }, { "text": "Super Damping of Mechanical Vibrations: We report the phenomenon of coherent super decay, where a linear sum of\nseveral damped oscillators can collectively decay much faster than the\nindividual ones in the first stage, followed by stagnating ones after more than\n90 percent of the energy has already been dissipated. The parameters of the\ndamped oscillators for CSD are determined by the process of response function\ndecomposition, which is to use several slow decay response functions to\napproximate the response function of a fast decay reference resonator. Evidence\nestablished in experiments and in finite element simulations not only strongly\nsupported the numerical investigations, but also uncovered an unexplored region\nof the tuned mass damper parameter space where TMDs with total mass less than\n0.2 percent of a primary free body can damp its first resonance up to a damping\nratio of 4.6 percent. Our findings also shed light onto the intriguing\nunderline connections between complex functions with different singular points.", "category": "physics_app-ph" }, { "text": "Material and Process Tolerant High Efficiency Solar Cells with Dynamic\n Recovery of Performance: Low cost, highly efficient, and stable solar cells demand low temperature\nprocessing, less stringent criteria on materials, and possibility of dynamic\nrecovery from long term degradation: a combination of features unachievable\nfrom the perspectives of current cSi technology. To this end, here we propose a\nnovel solar cell architecture with an additional control gate. Our simulation\nresults indicate that the proposed device can achieve excellent efficiency even\nif the back-surface passivation is sub-optimal; thus allowing exploration of a\nwide variety of materials and low temperature fabrication processes.\nImportantly, such solar cells can dynamically offset efficiency loss due to\nelevated temperature and interface degradation associated with long term field\noperation and hence could be of broad interest to the PV community.", "category": "physics_app-ph" }, { "text": "Generalized dissipation dilution in strained mechanical resonators: Mechanical resonators with high quality factors are of relevance in precision\nexperiments, ranging from gravitational wave detection and force sensing to\nquantum optomechanics. Beams and membranes are well known to exhibit flexural\nmodes with enhanced quality factors when subjected to tensile stress. The\nmechanism for this enhancement has been a subject of debate, but is typically\nattributed to elastic energy being \"diluted\" by a lossless potential. Here we\nclarify the origin of the lossless potential to be the combination of tension\nand geometric nonlinearity of strain. We present a general theory of\ndissipation dilution that is applicable to arbitrary resonator geometries and\ndiscuss why this effect is particularly strong for flexural modes of\nnanomechanical structures with high aspect ratios. Applying the theory to a\nnon-uniform doubly clamped beam, we show analytically how dissipation dilution\ncan be enhanced by modifying the beam shape to implement \"soft clamping\", thin\nclamping and geometric strain engineering, and derive the ultimate limit for\ndissipation dilution.", "category": "physics_app-ph" }, { "text": "Minimising the Levelised Cost of Electricity for Bifacial Solar Panel\n Arrays using Bayesian Optimisation: Bifacial solar module technology is a quickly growing market in the\nphotovoltaics (PV) sector. By utilising light impinging on both, front and back\nsides of the module, actual limitations of conventional monofacial solar\nmodules can be overcome at almost no additional costs. Optimising large-scale\nbifacial solar power plants with regard to minimum levelised cost of\nelectricity (LCOE), however, is challenging due to the vast amount of free\nparameters such as module inclination angle and distance, module and land\ncosts, character of the surroundings, weather conditions and geographic\nposition. We present a detailed illumination model for bifacial PV modules in a\nlarge PV field and calculate the annual energy yield exemplary for two\nlocations with different climates. By applying the Bayesian optimisation\nalgorithm we determine the global minimum of the LCOE for bifacial and\nmonofacial PV fields at these two exemplary locations considering land costs in\nthe model. We find that currently established design guidelines for mono- and\nbifacial solar farms often do not yield the minimum LCOE. Our algorithm finds\nsolar panel configurations yielding up to 23 % lower LCOE compared to the\nestablished configuration with the module tilt angle equal to the latitude and\nthe module distance chosen such that no mutual shading of neighboring solar\npanels occurs at winter solstice. Our algorithm enables the user to extract\nclear design guidelines for mono- and bifacial large-scale solar power plants\nfor most regions on Earth and further accelerates the development of\ncompetitively viable photovoltaic systems.", "category": "physics_app-ph" }, { "text": "Permittivity of waste-activated sludge by an open-ended coaxial line: The complex permittivity of thickened waste activated sludge (WAS) was\nmeasured from 3 MHz to 40 GHz. The solid content of the thickened WAS sample\nwas varied from 4.5% to 18% by weight. The permittivity spectra exhibit\nfeatures typical of biological tissues that have a high water content. At high\nfrequencies, a Debye-type dispersion is observed with a relaxation rate of 19\nGHz characteristic of the bulk water in the sample ($\\gamma$-dispersion). At\nlower frequencies, the solid content of the samples determines the properties\nof the permittivity. The onset of the so-called $\\beta$-dispersion, attributed\nto the charging of cell membranes, occurs between 10-100 MHz. For samples with\nhigher solid concentrations, a weak dispersion of the real part of the\npermittivity, characteristic of bound water, was observed at intermediate\nfrequencies ($\\delta$-dispersion).", "category": "physics_app-ph" }, { "text": "Going Beyond Perfect Absorption: Reconfigurable Super-directive\n Absorbers: In the context of electromagnetic absorption, it is obvious that for an\ninfinite planar periodic structure illuminated by a plane wave, the maximum\nattainable absorptance, i.e., perfect absorption, is theoretically limited to\n100% of the incident power. Here we show that an intriguing possibility of\novercoming this limit arises in finite-size resonant absorbing arrays. We\npresent a comprehensive analysis of a simple two-dimensional strip array over\nan infinite perfectly conducting plane, where the strips are loaded by\nreconfigurable impedance loads. The absorptance is defined as the ratio of the\ndissipated power per unit length of the strips to the incident power on the\nunit length of the array width. The results show that even regular arrays of\nimpedance strips can slightly overcome the limit of 100% absorptance, while\nusing aperiodic arrays with optimized loads, absorptance can be significantly\nincreased as compared with the scenario where the strips are identical. In\nprinciple, by tuning the reconfigurable loads, high super-unity absorptance can\nbe realized for all angles of illumination.", "category": "physics_app-ph" }, { "text": "Chiral sensing with achiral isotropic metasurfaces: Metasurfaces, the two-dimensional analogues of metamaterials, are ideal\nplatforms for sensing molecular chirality at the nanoscale, e.g. of inclusions\nof natural optically active molecules, as they offer large accessible areas\n(they are essentially surfaces) and can accommodate the necessary strong\nresonances for coupling the probing radiation with the chiral inclusions. Here,\nwe examine theoretically achiral isotropic metasurfaces, and we treat them as\npolarizable surfaces that support resonant electric and magnetic currents,\nwhich are coupled via the chiral inclusions. We derive analytically, and verify\nnumerically, expressions that provide insight to the enhancement mechanism of\nthe magneto-electric coupling and explain why circular dichroism signals\n(difference in absorption between left- and right- circularly polarized waves)\ncan arise from both the real and the imaginary part of the chirality parameter\n$\\kappa$. Our analysis demonstrates distinct chiroptical signals where the\ncontributions from both the real and imaginary part of $\\kappa$ can be\nindependently observed and, based on such measurements, we propose a scheme for\nthe unambiguous determination of an unknown chirality.", "category": "physics_app-ph" }, { "text": "One-transmitter Multiple-receiver Wireless Power Transfer System Using\n an Exceptional Point of Degeneracy: Robust transfer efficiency against the various operating conditions in a\nwireless power transfer system remains a fundamentally important challenge.\nThis challenge becomes even more critical when transferring power to groups of\ninductively coupled receivers. We propose a method for efficient wireless power\ntransfer to multiple receivers exploiting the concept of exceptional points of\ndegeneracy (EPD). In previous studies based on PT symmetry, a receiver's\noperation has been divided into two strong and weak coupling regimes, and the\npower transfer efficiency is constant in the strong coupling regime when\nvarying the coupling factor.Here the concept of strong and weak coupling and\nconstant power efficiency is extended to a system of multiple receivers that do\nnot follow PT symmetry. We show that the important feature to have a roughly\nconstant power efficiency, independently of the positions of the receivers, is\nthe existence of an EPD that separates the weak and strong regimes. Our\nproposed method demonstrates a system with less sensitivity to the coupling\nchange than a conventional system without EPD when the receivers and their\ncouplings to the transmitter are not necessarily identical.", "category": "physics_app-ph" }, { "text": "Realization of the unidirectional amplification in a cavity magnonic\n system: We experimentally demonstrate the nonreciprocal microwave amplification using\na cavity magnonic system, consisting of a passive cavity (i.e., the split-ring\nresonator), an active feedback circuit integrated with an amplifier, and a\nferromagnetic spin ensemble (i.e., a yttrium-iron-garnet sphere). Combining the\namplification provided by the active circuit and the nonreciprocity supported\nby the cavity magnonics, we implement a nonreciprocal amplifier with the\nfunctions of both unidirectional amplification and reverse isolation. The\nmicrowave signal is amplified by 11.5 dB in the forward propagating direction\nand attenuated in the reverse direction by -34.7 dB, giving an isolation ratio\nof 46.2 dB. Such a unidirectional amplifier can be readily employed in quantum\ntechnologies, where the device can simultaneously amplify the weak signal\noutput by the quantum system and isolate the sensitive quantum system from the\nbackscattered external noise. Also, it is promising to explore more functions\nand applications using a cavity magnonic system with real gain.", "category": "physics_app-ph" }, { "text": "High sensitivity refractive index sensor based on the semicircular bent\n fiber: A refractive index sensor based on a semicircular bent fiber is presented.\nThe interference occurs between the cladding mode excited in the bending region\nand the core mode. Both the theoretical and experimental results show that the\nresonant dip wavelength decreases linearly with the increase of the refractive\nindex of the surrounding environment. A high sensitivity of 1031 nm per\nrefractive index unit is obtained over the refractive index range of 1.3324 to\n1.3435 by using a bent fiber with a bending radius of 500 {\\mu}m.", "category": "physics_app-ph" }, { "text": "Microwave AC voltage induced phase change in Sb$_2$Te$_3$ nanowires: Scaling information bits to ever smaller dimensions is a dominant drive for\ninformation technology (IT). Nanostructured phase change material emerges as a\nkey player in the current green-IT endeavor with low power consumption,\nfunctional modularity and promising scalability. In this work, we present the\ndemonstration of microwave AC voltage induced phase change phenomenon at 3 GHz\nin single Sb$_2$Te$_3$ nanowires. The resistance change by a total of 6 - 7\norders of magnitude is evidenced by a transition from the crystalline metallic\nto the amorphous semiconducting phase, which is cross-examined by temperature\ndependent transport measurement and high-resolution electron microscopy\nanalysis. This discovery could potentially tailor multi-state information bit\nencoding and discrimination along a single nanowire, rendering technology\nadvancement for neuro-inspired computing devices.", "category": "physics_app-ph" }, { "text": "Characterisation of carbon fibre-reinforced polymer composites through\n complex Radon-transform analysis of eddy-current data: Maintaining the correct fibre orientations and stacking sequence in\ncarbon-fibre reinforced polymers (CFRP) during manufacture is essential for\nachieving the required mechanical properties of a component. This paper\npresents and evaluates a method for the rapid characterisation of the fibre\norientations present in CFRP structures, and the differentiation of different\nstacking sequences, through the Radon-transform analysis of complex-valued\neddy-current testing (ECT) inspection data. A high-frequency (20 MHz)\neddy-current inspection system was used to obtain 2D scans of a range of CFRP\nsamples of differing ply stacking sequences. The complex electrical impedance\nscan data was analysed using Radon-transform techniques to quickly and simply\ndetermine the dominant fibre orientations present in the structure. This method\nis compared to 2D-fast Fourier transform (2D-FFT) analysis of the same data and\nshown to give superior quantitative results with comparatively fewer\ncomputational steps and corrections. Further analysis is presented\ndemonstrating and examining a method for preserving the complex information\ninherent within the eddy-current scan data during Radon-transform analysis.\nThis investigation shows that the real and imaginary components of the ECT data\nencode information about the sacking sequence allowing the distinction between\ncomposites with different stacking structures. This new analysis technique\ncould be used for in-process analysis of CFRP structures as a more accurate\ncharacterisation method, reducing the chance of costly manufacturing errors.", "category": "physics_app-ph" }, { "text": "Limits to Electrical Mobility in Lead-Halide Perovskite Semiconductors: Semiconducting polycrystalline thin films are cheap to produce and can be\ndeposited on flexible substrates, yet high-performance electronic devices\nusually utilize single-crystal semiconductors, owing to their superior\nelectrical mobilities and longer diffusion lengths. Here we show that the\nelectrical performance of polycrystalline films of metal-halide perovskites\n(MHPs) approaches that of single crystals at room temperature. Combining\ntemperature-dependent terahertz conductivity measurements and ab initio\ncalculations we uncover a complete picture of the origins of charge scattering\nin single crystals and polycrystalline films of CH$_3$NH$_3$PbI$_3$. We show\nthat Fr\\\"ohlich scattering of charge carriers with multiple phonon modes is the\ndominant mechanism limiting mobility, with grain-boundary scattering further\nreducing mobility in polycrystalline films. We reconcile the large discrepancy\nin charge diffusion lengths between single crystals and films by considering\nphoton reabsorption. Thus, polycrystalline films of MHPs offer great promise\nfor devices beyond solar cells, including transistors and modulators.", "category": "physics_app-ph" }, { "text": "Schottky diode temperature sensor for pressure sensor: The small silicon chip of Schottky diode (0.8x0.8x0.4 mm3) with planar\narrangement of electrodes (chip PSD) as temperature sensor, which functions\nunder the operating conditions of pressure sensor, was developed. The forward\nI-V characteristic of chip PSD is determined by potential barrier between Mo\nand n-Si (ND = 3x1015 cm-3). Forward voltage UF = 208 mV and temperature\ncoefficient TC = -1.635 mV/C (with linearity kT <0.4% for temperature range of\n-65 to +85 C) at supply current IF = 1 mA is achieved. The reverse I-V\ncharacteristic has high breakdown voltage UBR > 85 V and low leakage current IL\n< 5 {\\mu}A at 25 C and IL < 130 {\\mu}A at 85 C (UR = 20 V) because chip PSD\ncontains the structure of two p-type guard rings along the anode perimeter. The\napplication of PSD chip for wider temperature range from -65 to +115 C is\nproved. The separate chip PSD of temperature sensor located at a distance of\nless than 1.5 mm from the pressure sensor chip. The PSD chip transmits input\ndata for temperature compensation of pressure sensor errors by ASIC and for\ndirect temperature measurement.", "category": "physics_app-ph" }, { "text": "Fabrication, characterization, and simulation of glass devices with\n AlN-thin-film-transducers for excitation of ultrasound resonances: We present fabrication of 570-um-thick, millimeter-sized soda-lime-silicate\nfloat glass blocks with a 1-um-thick AlN-thin-film piezoelectric transducer\nsandwiched between thin metallic electrodes and deposited on the top surface.\nThe electro-mechanical properties are characterized by electrical impedance\nmeasurements in the frequency range from 0.1 to 10 MHz with a peak-to-peak\nvoltage of 0.5 V applied to the electrodes. We measured the electrical\nimpedance spectra of 35 devices, all of width 2 mm, but with 9 different\nlengths ranging from 2 to 6 mm and with 2-7 copies of each individual geometry.\nEach impedance spectrum exhibits many resonance peaks, of which we carefully\nmeasured the 5 most prominent ones in each spectrum. We compare the resulting\n173 experimental resonance frequencies with the simulation result of a\nfinite-element-method model that we have developed. When using material\nparameters from the manufacturer, we obtain an average relative deviation of\nthe 173 simulated resonance frequencies from the experimental ones of (-4.2\n+/-0.04)%. When optimizing the values of the Young's modulus and the Poisson\nratio of the float glass in the simulation, this relative deviation decreased\nto (-0.03 +/- 0.04)%. Our results suggest a method for an accurate in-situ\ndetermination of the acoustic parameters at ultrasound frequencies of any\nelastic solid onto which a thin-film transducer can be attached", "category": "physics_app-ph" }, { "text": "Electric Switching of the Charge-Density-Wave and Normal Metallic Phases\n in Tantalum Disulfide Thin-Film Devices: We report on switching among three charge-density-wave phases - commensurate,\nnearly commensurate, incommensurate - and the high-temperature normal metallic\nphase in thin-film 1T-TaS2 devices induced by application of an in-plane\nelectric field. The electric switching among all phases has been achieved over\na wide temperature range, from 77 K to 400 K. The low-frequency electronic\nnoise spectroscopy has been used as an effective tool for monitoring the\ntransitions, particularly the switching from the incommensurate\ncharge-density-wave phase to the normal metal phase. The noise spectral density\nexhibits sharp increases at the phase transition points, which correspond to\nthe step-like changes in resistivity. Assignment of the phases is consistent\nwith low-field resistivity measurements over the temperature range from 77 K to\n600 K. Analysis of the experimental data and calculations of heat dissipation\nsuggest that Joule heating plays a dominant role in the electric-field induced\ntransitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The\npossibility of electrical switching among four different phases of 1T-TaS2 is a\npromising step toward nanoscale device applications. The results also\ndemonstrate the potential of noise spectroscopy for investigating and\nidentifying phase transitions in materials.", "category": "physics_app-ph" }, { "text": "Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon\n sources for quantum acoustodynamics: Solid-state quantum acoustodynamic (QAD) systems provide a compact platform\nfor quantum information storage and processing by coupling acoustic phonon\nsources with superconducting or spin qubits. The multi-mode composite\nhigh-overtone bulk acoustic wave resonator (HBAR) is a popular phonon source\nwell suited for QAD. However, scattering from defects, grain boundaries, and\ninterfacial/surface roughness in the composite transducer severely limits the\nphonon relaxation time in sputter-deposited devices. Here, we grow an\nepitaxial-HBAR, consisting of a metallic NbN bottom electrode and a\npiezoelectric GaN film on a SiC substrate. The acoustic impedance-matched\nepi-HBAR has a power injection efficiency > 99% from transducer to phonon\ncavity. The smooth interfaces and low defect density reduce phonon losses,\nyielding fxQ products and phonon lifetimes up to 1.36 x 10^17 Hz and 500\nmicroseconds respectively. The GaN/NbN/SiC epi-HBAR is an electrically\nactuated, multi-mode phonon source that can be directly interfaced with\nNbN-based superconducting qubits or SiC-based spin qubits.", "category": "physics_app-ph" }, { "text": "Terahertz emission from anomalous Hall effect in a single-layer\n ferromagnet: We report on terahertz emission from a single layer ferromagnet which\ninvolves the generation of backflow nonthermal charge current from the\nferromagnet/dielectric interface by femtosecond laser excitation and subsequent\nconversion of the charge current to a transverse transient charge current via\nthe anomalous Hall effect, thereby generating the THz radiation. The THz\nemission can be either enhanced or suppressed, or even the polarity can be\nreversed, by introducing a magnetization gradient in the thickness direction of\nthe ferromagnet. Unlike spintronic THz emitters reported previously, it does\nnot require additional non-magnetic layer or Rashba interface.", "category": "physics_app-ph" }, { "text": "Current density distribution in resistive fault current limiters and its\n effect on device stability: The increase of current uniformity along of a resistive type superconductor\nfault current limiter (R-SFCL) in the design of this type of limiters is well\nperceived as an important issue. The non-uniform distribution of current in\nR-SFCL only increases the current in some superconducting regions, as a result,\nin the fault conditions, only certain parts of the superconductor undergo a\nphase change that increases the heat pressure in those areas and causes the\nbreakdown and destruction of the device. In this paper, the current density\ndistributions in common patterns used in R-SFCs constructions have been\nsimulated and investigated. To this end, an effective model is proposed for\nR-SFCL to achieve the highest uniformity of current and harmonic phase change\nover superconductors compared to other patterns. The simulation results in the\nAnsys Maxwell Software advocate the appropriate and satisfying performance of\nthe proposed model.", "category": "physics_app-ph" }, { "text": "Terahertz Frequency Domain Sensing for Fast Porosity Measurement of\n Pharmaceutical Tablets: Porosity is an important property of pharmaceutical tablets since it may\naffect tablet disintegration, dissolution, and bio-availability. It is,\ntherefore, essential to establish non-destructive, fast, and compact techniques\nto assess porosity, in-situ, during the manufacturing process. In this paper,\nthe terahertz frequency-domain (THz-FD) technique was explored as a fast,\nnon-destructive, and sensitive technique for porosity measurement of\npharmaceutical tablets. We studied a sample set of 69 tablets with different\ndesign factors, such as particle size of the active pharmaceutical ingredient\n(API), Ibuprofen, particle size of the filler, Mannitol, API concentration, and\ncompaction force. The signal transmitted through each tablet was measured\nacross the frequency range 500-750 GHz using a vector network analyzer combined\nwith a quasi-optical set-up consisting of four off-axis parabolic mirrors to\nguide and focus the beam. We first extracted the effective refractive index of\neach tablet from the measured complex transmission coefficients and then\ntranslated it to porosity, using an empirical linear relation between effective\nrefractive index and tablet density. The results show that the THz-FD technique\nwas highly sensitive to the variations of the design factors, showing that\nfiller particle size and compaction force had a significant impact on the\neffective refractive index of the tablets and, consequently, porosity.\nMoreover, the fragmentation behaviour of particles was observed by THz porosity\nmeasurements and was verified with scanning electron microscopy of the\ncross-section of tablets. In conclusion, the THz-FD technique, based on\nelectronic solutions, allows for fast, sensitive, and non-destructive porosity\nmeasurement that opens for compact instrument systems capable of in-situ\nsensing in tablet manufacturing.", "category": "physics_app-ph" }, { "text": "Argon Cluster-Ion Sputter Yield: Molecular Dynamics Simulations on\n Silicon and an Equation for Estimating Total Sputter Yield: Argon Gas Cluster-Ion Beam sources have become widely-used on x-ray\nphotoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS)\ninstruments in recent years, but there is little reference data on sputter\nyields in the literature as yet. Total sputter yield reference data is needed\nin order to plan, and later calibrate the depth scale, of XPS or SIMS depth\nprofiles. We previously published a semi-empirical Threshold equation for\nestimating cluster total sputter yield from the energy-per-atom of the cluster\nand the effective monatomic sputter threshold of the material. This has already\nbeen shown to agree extremely well with sputter yield measurements on a range\nof organic and inorganic materials for clusters of around a thousand atoms.\nHere we use the molecular dynamics (MD) approach to explore a wider range of\nenergy and cluster size than is easy to do experimentally to high precision. We\nhave performed MD simulations using the Large-scale Atomic/Molecular Massively\nParallel Simulator (LAMMPS) parallel MD code on high-performance computer (HPC)\nsystems at Cincinnati and Newcastle. We performed 1,150 simulations of\nindividual collisions with a silicon (100) surface as an archetypal inorganic\nsubstrate, for cluster sizes between 30 and 3,000 argon atoms and energies in\nthe range 5 to 40eV per atom. This corresponds to the most important regime for\nexperimental cluster depth-profiling in SIMS and XPS. Our MD results show a\ndependence on cluster size as well as energy-per-atom. Using the exponent\npreviously suggested by Paruch et al, we modified the Threshold model equation\npublished previously to take this into account. The modified Threshold equation\nfits all our MD results extremely well, building on its success in fitting\nexperimental sputter yield measurements.", "category": "physics_app-ph" }, { "text": "Multilayer GZ/YSZ Thermal Barrier Coating from Suspension and Solution\n Precursor Plasma Spray: Gas turbines rely on thermal barrier coating (TBC) to thermally insulate the\nnickel-based superalloys underneath during operation; however, current TBCs,\nyttria stabilised zirconia (YSZ), limit the operating temperature and hence\nefficiency. At an operating temperature above 1200{\\deg}C, YSZ is susceptible\nto failure due to phase instabilities and CMAS (Calcia-Magnesia-Alumina-Silica)\nattack. Gadolinium zirconates (GZ) could overcome the drawback of YSZ,\ncomplementing each other with the multi-layer approach. This study introduces a\nnovel approach utilising axial suspension plasma spray (ASPS) and axial\nsolution precursor plasma spray (ASPPS) to produce a double-layer and a\ntriple-layer TBCs with improved CMAS resistance. The former comprised\nsuspension plasma sprayed GZ and YSZ layers while the latter had an additional\ndense layer deposited through a solution precursor to minimise the columnar\ngaps that pre-existed in the SPS GZ layer, thus resisting CMAS infiltration.\nBoth coatings performed similarly in furnace cycling test (FCT) and burner rig\ntesting (BRT). In the CMAS test, triple-layer coating showed better CMAS\nresistivity, as evidenced by the limited CMAS infiltration observed on the\nsurface.", "category": "physics_app-ph" }, { "text": "Making Graphene Nano Inductor Using Table Top Laser Engraver: There is great interest in so-called nano-electronic devices due to the\nfurious rate of device miniaturization. Fabrication of micro and nano scale\nresistors and capacitors have already been achieved steadily, but so far, there\nhas been little development in the way of nano-scale coil inductors. This is\nbecause of the physical limitations in miniaturization of the design of a\nsolenoid with wires coiled around a metallic core. So, while transistors get\nsteadily smaller, basic inductors in electronics remained relatively bulky. Few\nmethods exist for creating conductive polymer coils and graphene-based kinetic\nnano-inductors, but their large-scale fabrication process is complex and mostly\nbeyond the current commercial technology available. So, a simpler, scalable,\nand robust fabrication technique is needed to overcome this bottleneck. In this\nwork we demonstrate a new technique consisting of the laser lithography using a\nlaser engraver of a (poly)vinyl alcohol (PVA)/graphene oxide film composite\nwhich results in a large inductive effect. We attribute this behavior to the\nformation of high curvature twisted screw dislocation type conductive pathways\ncomposed of polyacetylene chains linked by pi-pi interactions to reduced\ngraphene oxide flakes resulting in inductive effect.", "category": "physics_app-ph" }, { "text": "Ultrahigh electrostrain in Pb-free piezoceramics: Effect of bending: Recently several reports showing ultra-high electrostrain (> 1 %) have\nappeared in Pb-free piezoceramics. However, there is lack of clarity on the\nnature of the ultrahigh strain. Here, we demonsrate that the ultrahigh strain\nis a consequence of bending of the disc. We show that the propensity for\nbending arises from the difference in the response magnitude of the grains at\nthe positive and negative surfaces of the piezoceramic when the field is\napplied.", "category": "physics_app-ph" }, { "text": "3D Printed PVDF: In this paper we report on the 3D printing and testing of the piezoelectric\npolymer polyvinylidene difluoride (PVDF). Samples of PVDF were fabricated using\na fused deposition modeling (FDM) 3D printer and then activated using a corona\npoling process. The d33 piezoelectric coefficient, which is related to the\noverall piezoelectric performance, was experimentally measured using a d33\nmeter to be 6 pC/N. While less than commercially available PVDF fabricated\nusing traditional techniques (which can have a d33 between 10 and 40 pC/N), the\nvalue of 6 pC/N achieved in this work is several orders of magnitude larger\nthan comparable previously published results for 3D printed PVDF, and as a\nresult represents a significant step in the 3D printing of piezoelectric\npolymers.", "category": "physics_app-ph" }, { "text": "Quasi-deterministic Localization of Er Emitters in Thin Film TiO$_2$\n through Submicron-scale Crystalline Phase Control: With their shielded 4f orbitals, rare-earth ions (REIs) offer optical and\nelectron spin transitions with good coherence properties even when embedded in\na host crystal matrix, highlighting their utility as promising quantum emitters\nand memories for quantum information processing. Among REIs, trivalent erbium\n(Er$^{3+}$) uniquely has an optical transition in the telecom C-band, ideal for\ntransmission over optical fibers, and making it well-suited for applications in\nquantum communication. The deployment of Er$^{3+}$ emitters into a thin film\nTiO$_2$ platform has been a promising step towards scalable integration;\nhowever, like many solid-state systems, the deterministic spatial placement of\nquantum emitters remains an open challenge. We investigate laser annealing as a\nmeans to locally tune the optical resonance of Er$^{3+}$ emitters in TiO$_2$\nthin films on Si. Using both nanoscale X-ray diffraction measurements and\ncryogenic photoluminescence spectroscopy, we show that tightly focused\nbelow-gap laser annealing can induce anatase to rutile phase transitions in a\nnearly diffraction-limited area of the films and improve local crystallinity\nthrough grain growth. As a percentage of the Er:TiO$_2$ is converted to rutile,\nthe Er$^{3+}$ optical transition blueshifts by 13 nm. We explore the effects of\nchanging laser annealing time and show that the amount of optically active\nEr:rutile increases linearly with laser power. We additionally demonstrate\nlocal phase conversion on microfabricated Si structures, which holds\nsignificance for quantum photonics.", "category": "physics_app-ph" }, { "text": "Vector magneto-optical magnetometer based on the resonant all-dielectric\n gratings with highly anisotropic iron-garnet films: A sensitive vector magnetometry with high spatial resolution is important for\nvarious practical applications, such as magnetocardiography,\nmagnetoencephalography, explosive materials detection and many others. We\npropose a magnetometer based on the magnetic iron-garnet film possessing a very\nhigh magnetic anisotropy, placed in the rotating external magnetic field. Each\nof the measured magnetic field spatial components produces different temporal\nharmonics in the out-of-plane magnetization dependence. The dielectric resonant\ngrating placed on the top of an ultrathin film enhanced the magneto-optical\nresponse 10 times which makes it possible to achieve 10 times higher spatial\nresolution in the perpendicular to the film direction. The reported\nmagneto-optical magnetometer allows one to measure simultaneously all three\nspatial components of the magnetic field with high spatial resolution and\nsensitivity up to 100 pT/Hz$^{1/2}$.", "category": "physics_app-ph" }, { "text": "Hybrid optical fiber for light-induced superconductivity: We exploit the recent proposals for the light-induced superconductivity\nmediated by a Bose-Einstein condensate of exciton-polaritons to design a\nsuperconducting fiber that would enable long-distance transport of a\nsupercurrent at elevated temperatures. The proposed fiber consists of a\nconventional core made of a silica glass with the first cladding layer formed\nby a material sustaining dipole-polarised excitons with a binding energy\nexceeding 25 meV. To be specific, we consider a perovskite cladding layer of 20\nnm width. The second cladding layer is made of a conventional superconductor\nsuch as aluminium. The fiber is covered by a conventional coating buffer and by\na plastic outer jacket. We argue that the critical temperature for a\nsuperconducting phase transition in the second cladding layer may be strongly\nenhanced due to the coupling of the superconductor to a bosonic condensate of\nexciton-polaritons optically induced by the evanescent part of the guiding mode\nconfined in the core. The guided light mode would penetrate to the first\ncladding layer and provide the strong exciton-photon coupling regime. We run\nsimulations that confirm the validity of the proposed concept. The fabrication\nof superconducting fibers where a high-temperature superconductivity could be\ncontrolled by light would enable passing superconducting currents over\nextremely long distances.", "category": "physics_app-ph" }, { "text": "An Ultrasensitive 3D Printed Tactile Sensor for Soft Robotics: A new method is presented to manufacture piezoresistive tactile sensors using\nfused deposition modelling (FDM)printing technology with two different\nfilaments made of thermoplastic polyurethane (TPU) and polylactic acid-graphene\n(PLA-G) composite. The sensor shows very high sensitivity (gauge factor~550)\nand excellent recovery to bending-induced strain and can detect a wide range of\npressures. This new technology opens the door for 3D printing soft robotic\nparts capable of tactile communications.", "category": "physics_app-ph" }, { "text": "Tests of cryogenic Fabry-Perot cavity with mirrors on different\n substrates: Experiments were performed with Fabry-Perot optical resonators in vacuum at\nlow temperatures. Mirrors were applied on substrates of various optical\nmaterials. The infrared laser with a wavelength of 1.064 microns was used. The\npump power at the maximum could reach 450 mW. The evolution of the optical\nproperties of the FP cavity was traced in the temperature range (300 - 10)K.\nThe main parameters measured were the integral characteristics of the FP\nresonances: sharpness (finesse) and contrast of interference. Three types of\nsubstrates were tested: a sitall -- the optical glass with ultra low thermal\nexpansion (ULE), sapphire and calcium fluoride. During cooling, the degradation\nof the integral characteristics of the FP cavity was observed for the sitall\nmirrors due to the loss of the properties of (ULE), for sapphire mirrors due to\nthe birefringence effect. The satisfactory constancy of the integral\ncharacteristics of the FP resonator on calcium fluoride was demonstrated in the\nentire temperature range studied 1", "category": "physics_app-ph" }, { "text": "Efficient Identifying the Orientation of Single NV Centers in Diamond\n and Using them to Detect Near Field Microwave: Arrays of NV centers in the diamond have the potential in the fields of\nchip-scale quantum information processing and nanoscale quantum sensing.\nHowever, determining their orientations one by one is resource intensive and\ntime consuming. Here, in this paper, by combining scanning confocal\nfluorescence images and optical detected magnetic resonance, we realized a\nmethod of identifying single NV centers with the same orientation, which is\npracticable and high efficiency. In the proof of principle experiment, five\nsingle NV centers with the same orientation in a NV center array were\nidentified. After that, using the five single NV centers, microwave near field\ngenerated by a 20 {\\mu}m-diameter Cu antenna was also measured by reading the\nfluourescence intensity change and Rabi frequency at different microwave source\npower. The gradient of near field microwave at sub-microscale can be resoluted\nby using arry of NV centers in our work. This work promotes the quantum sensing\nusing arrays of NV centers.", "category": "physics_app-ph" }, { "text": "Fully superconducting machine for electric aircraft propulsion: study of\n AC loss for HTS stator: Fully superconducting machines provide the high power density required for\nfuture electric aircraft propulsion. However, superconducting windings generate\nAC losses in AC electrical machine environments. These AC losses are difficult\nto remove at low temperatures and they add an extra burden to the aircraft\ncooling system. Due to heavy cooling penalty, AC losses in the HTS stator, is\none of the key topics in HTS machine design. In order to evaluate the AC loss\nof superconducting stator windings in a rotational machine environment, we\ndesigned and built a novel axial-flux high temperature superconducting (HTS)\nmachine platform. The AC loss measurement is based on calorimetrically\nboiling-off liquid nitrogen. Both total AC loss and magnetisation loss in HTS\nstator are measured in a rotational magnetic field condition. This platform is\nessential to study ways to minimise AC losses in HTS stator, in order to\nmaximum the efficiency of fully HTS machines.", "category": "physics_app-ph" }, { "text": "The Effects of Rolling Deformation and Annealing Treatment on Damping\n Capacity of 1200 Aluminium Alloy: Annealing treatment is an important step of rolling deformation that\ncontributes to microstructural evolution and leads to the significant changes\nin damping capacity. Damping capacities were analyzed in the parallel to\nrolling direction at 1 and 10 Hz respectively. It was found that severe plastic\ndeformation at 40 percent reduction has lower damping capacity compared to that\nof 30 percent and 20 percent reductions respectively. The microstructural\nresults show that the grains of as rolled alloys were changed to almost\nequiaxed structures after a rolling reduction at 40 percent reduction.", "category": "physics_app-ph" }, { "text": "Enhancement of photovoltaic efficiency by insertion of a polyoxometalate\n layer at the anode of an organic solar cell: In this article the Wells-Dawson polyoxometalate K6[P2W18O62] is grown as an\ninterfacial layer between indium tin oxide and bulk heterojunction of\npoly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester\n(PCBM). The structure of the POM layers depends on the thickness and shows a\nhighly anisotropic surface organization. The films have been characterized by\natomic force microscopy and X-ray photoelectron spectroscopy (XPS) to gain\ninsight into their macroscopic organization and better understand their\nelectronic properties. Then, they were put at the anodic interface of a\nP3HT:PCBM organic solar cell and characterized on an optical bench. The\nphotovoltaic efficiency is discussed in terms of the benefit of the\npolyoxometalate at the anodic interface of an organic photovoltaic cell.", "category": "physics_app-ph" }, { "text": "Growing Phenotype-controlled Phononic Materials from Plant Cells\n Scaffolds: Biological composites offer self-healing properties, biocompatibility, high\nresponsivity to external stimuli, and multifunctionality, due, in part, to\ntheir complex, hierarchical microstructure. Such materials can be inexpensively\ngrown, and self-assembled from the bottom up, enabling democratized,\nsustainable manufacturing routes for micro- and nano-devices. While biological\ncomposites have been shown to incorporate rich photonic structures, their\nphononic properties have hitherto remained unexplored. In this study, we\ndemonstrate that biological composites in the form of micron-thick\ndecellularized onion cell scaffolds behave as an organic phononic material,\nwith the presence of band gaps forbidding the propagation of elastic waves in\nselect frequency ranges. We show that the onion cells' phononic properties can\nbe phenotypically tuned, and anticipate these findings will yield new\nbiologically-derived, \"green\", and genetically tailorable phononic materials.", "category": "physics_app-ph" }, { "text": "The e_LiBANS facility: a new compact thermal neutron source based on a\n medical electron LINAC: A new photonuclear thermal neutron facility has been developed at the Physics\nDepartment of University of Torino. The facility is based on a medical electron\nLINAC coupled to a compact converter and moderator assembly. A homogenous\nthermal neutron field of the order of 10$^6$ cm$^{-2}$s$^{-1}$ is achievable in\nthe enclosed irradiation cavity with low gamma and fast neutron contaminations.\nIts intensity can be tuned varying the LINAC current. These characteristics\nmake the source appropriate for several applications like detectors\ndevelopment, material studies and BNCT preclinical research. This work\ndescribes the project and the experimental characterization of the facility.\nThis includes the measurement of the thermal neutron fluence rate, the\ndetermination of the neutron energy spectrum and of the thermal neutron field\nuniformity and the evaluation of the gamma contamination.", "category": "physics_app-ph" }, { "text": "Dynamics of a Superconducting Linear Slider: In this paper, the dynamic behavior of a one degree-of-freedom (DOF)\ncontactless linear slider based on superconducting magnetic levitation is\nexperimentally analyzed. The device is intended for precision positioning of an\noptic mirror in cryogenic environments. Different prototypes of this device\nhave been tested at cryogenic temperatures (77 K), and their mechanical\nbehavior characterized in the sliding direction for forced and unforced\noscillations. Experimental results reveal that the slider is self-stable at the\ninitial equilibrium position and the dynamic behavior fits well an underdamped\nharmonic oscillator. Finally, the device showed great potential for horizontal\nvibration isolation, acting as a low-pass filter with a resonance at about 0.9\nHz", "category": "physics_app-ph" }, { "text": "An UWB Hemispherical Vivaldi Array: We report the first conformal ultra-wide band (UWB) array on a doubly curved\nsurface for wide angle electronic scanning. We use a quadrilateral mesh as the\nbasis for systematically arraying UWB radiators on arbitrary surfaces. A\nprototype consisting of a 52 element, dual-polarized Vivaldi array arranged\nover a 181 mm diameter hemisphere is developed. The antennas and SMP connectors\nare 3D printed out of titanium to allow for simple fabrication and assembly. We\nderive the theoretical gain of a hemispherical array based on the antenna size\nand number of elements. The measured realized gain of the prototype array is\nwithin 2 dB of the theoretical value from 2-18 GHz and scan angles out to\n120{\\deg} from the z-axis. This field of view is twice that of a planar array\nwith the same diameter in agreement with theory. This work provides a baseline\nperformance for larger conformal arrays that have more uniform meshes.\nFurthermore, the basic concept can be extended to other UWB radiating elements.", "category": "physics_app-ph" }, { "text": "Interlaced wire medium with quasicrystal lattice: We propose a design of interlaced wire medium with quasicrystalline lattice\nbased on five-fold rotation symmetry Penrose tiling. The transport properties\nof this structure are studied. We distinguish two transport regimes, namely,\npropagation regime related to the low-frequency interval and localization\nregime in the high-frequency interval. While the former is observed in\nstructures both with and without translation symmetry property, the latter is\nexclusive for aperiodic structures only. We show that the localization regime\nis promising for many applications including engineering of effective\nmulti-channel devices for telecommunication and imaging systems.", "category": "physics_app-ph" }, { "text": "Substrate-Versatile Direct-Write Printing of Carbon Nanotube-Based\n Flexible Conductors, Circuits, and Sensors: Printed electronics rely on the deposition of conductive liquid inks,\ntypically onto polymeric or paper substrates. Among available conductive\nfillers for use in electronic inks, carbon nanotubes (CNTs) have high\nconductivity, low density, processability at low temperatures, and intrinsic\nmechanical flexibility. However, the electrical conductivity of printed CNT\nstructures has been limited by CNT quality and concentration, and by the need\nfor nonconductive modifiers to make the ink stable and extrudable. This study\nintroduces a polymer-free, printable aqueous CNT ink, and presents the\nrelationships between printing resolution, ink rheology, and ink-substrate\ninteractions. A model is constructed to predict printed feature sizes on\nimpermeable substrates based on Wenzel wetting. Printed lines have conductivity\nup to 10,000 S/m. The lines are flexible, with < 5% change in DC resistance\nafter 1,000 bending cycles, and <3% change in DC resistance with a bending\nradius down to 1 mm. Demonstrations focus on (i) conformality, via printing\nCNTs onto stickers that can be applied to curved surfaces, (ii) interactivity\nusing a CNT-based button printed onto folded paper structure, and (iii)\ncapacitive sensing of liquid wicking into the substrate itself. Facile\nintegration of surface mount components on printed circuits is enabled by the\nintrinsic adhesion of the wet ink.", "category": "physics_app-ph" }, { "text": "Tuning the dynamics of magnetic droplet solitons using dipolar\n interactions: Magnetic droplets are dissipative magnetodynamical solitons that can form\nunder current driven nanocontacts in magnetic layers with large perpendicular\nmagnetic anisotropy. Here, we extend the original droplet theory by studying\nthe impact of the dipolar interactions on the dynamics of droplet solitons. By\nvarying the thickness of the free layer of a spin torque nano-oscillator, we\nsystematically tune the internal field of the free layer to investigate the\ndynamics of droplet solitons. Our numerical results show that increasing the\nfree layer thickness increases the droplet threshold current, decreases the\ndroplet frequency and diameter, enlarges the current hysteresis and also\nmodifies the structure of the droplet. The Oersted field of the current breaks\nthe phase coherency and deteriorates the stability of the droplet in free\nlayers with larger thicknesses. Moreover, our findings show a simple relation\nto determine the impact of the free layer thickness on the droplet nucleation\nboundaries. Our study presents the missing brick on the physics behind magnetic\ndroplet solitons, and further illustrates that magnetic droplets in thinner\nlayers possess more promising characteristics for spintronic applications and\nenable devices with higher speed of operation.", "category": "physics_app-ph" }, { "text": "Theory of Truncation Resonances in Continuum Rod-based Phononic Crystals\n with Generally Asymmetric Unit Cells: Phononic crystals exhibit Bragg bandgaps, frequency regions within which wave\npropagation is forbidden. In solid continua, bandgaps are the outcome of\ndestructive interferences resulting from periodically alternating layers. Under\ncertain conditions, natural frequencies emerge within these bandgaps in the\nform of high-amplitude localized vibrations near a structural boundary,\nreferred to as truncation resonances. In this paper, we investigate the\nvibrational spectrum of finite phononic crystals which take the form of a\none-dimensional rod, and explain the factors that contribute to the origination\nof truncation resonances. By identifying a unit cell symmetry parameter, we\ndefine a family of finite phononic rods which share the same dispersion\nrelation, yet distinct truncated forms. A transfer matrix method is utilized to\nderive closed-form expressions of the characteristic equations governing the\nnatural frequencies of the finite system and decipher the truncation resonances\nemerging across different boundary conditions. The analysis establishes\nconcrete connections between the localized vibrations associated with a\ntruncation resonance, boundary conditions, and the overall configuration of the\ntruncated chain as dictated by unit cell choice. The study provides tools to\npredict, tune, and selectively design truncation resonances, to meet the\ndemands of various applications that require and uniquely benefit from such\ntruncation resonances.", "category": "physics_app-ph" }, { "text": "Electrical transport and optical band gap of\n NiFe$_\\textrm{2}$O$_\\textrm{x}$ thin films: We fabricated NiFe$_\\textrm{2}$O$_\\textrm{x}$ thin films on\nMgAl$_2$O$_4$(001) substrates by reactive dc magnetron co-sputtering varying\nthe oxygen partial pressure during deposition. The fabrication of a variable\nmaterial with oxygen deficiency leads to controllable electrical and optical\nproperties which would be beneficial for the investigations of the transport\nphenomena and would, therefore, promote the use of such materials in spintronic\nand spin caloritronic applications. We used several characterization techniques\nin order to investigate the film properties, focusing on their structural,\nmagnetic, electrical, and optical properties. From the electrical resistivity\nmeasurements we obtained the conduction mechanisms that govern the systems in\nhigh and low temperature regimes, extracting low thermal activation energies\nwhich unveil extrinsic transport mechanisms. The thermal activation energy\ndecreases in the less oxidized samples revealing the pronounced contribution of\na large amount of electronic states localized in the band gap to the electrical\nconductivity. Hall effect measurements showed the mixed-type semiconducting\ncharacter of our films. The optical band gaps were determined via\nultraviolet-visible spectroscopy. They follow a similar trend as the thermal\nactivation energy, with lower band gap values in the less oxidized samples.", "category": "physics_app-ph" }, { "text": "Coherent Magneto-Optomechanical Signal Transduction and Long-Distance\n Phase-Shift Keying: A transducer capable of converting quantum information stored as microwaves\ninto telecom-wavelength signals is a critical piece of future quantum\ntechnology as it promises to enable the networking of quantum processors.\nCavity optomechanical devices that are simultaneously coupled to microwave\nfields and optical resonances are being pursued in this regard. Yet even in the\nclassical regime, developing optical modulators based on cavity optomechanics\ncould provide lower power or higher bandwidth alternatives to current\ntechnology. Here we demonstrate a magnetically-mediated wavelength conversion\ntechnique, based on mixing high frequency tones with an optomechanical\ntorsional resonator. This process can act either as an optical phase or\namplitude modulator depending on the experimental configuration, and the\ncarrier modulation is always coherent with the input tone. Such coherence\nallows classical information transduction and transmission via the technique of\nphase-shift keying. We demonstrate that we can encode up to eight bins of\ninformation, corresponding to three bits, simultaneously and demonstrate the\ntransmission of an 52,500 pixel image over 6 km of optical fiber with just\n0.67% error. Furthermore, we show that magneto-optomechanical transduction can\nbe described in a fully quantum manner, implying that this is a viable approach\nto signal transduction at the single quantum level.", "category": "physics_app-ph" }, { "text": "High-efficiency thermophotovoltaic system that employs an emitter based\n on a silicon rod-type photonic crystal: Thermophotovoltaic systems in principle enable utilization of heat that is\nusually regarded as wasted energy. However, the wavelength selectivity of the\nthermal emitter required for high efficiencies is rather difficult to control\nwith conventional designs. Here, we design a thermophotovoltaic system\ncomprising silicon rods as thermal emitter with a relatively narrow emission\nspectrum and a photovoltaic cell with a band gap corresponding to 1.76 $\\mu$m,\nand verify efficient power generation. By accurately measuring the heat flux\nthat enters the emitter, the emitter temperature, and the electrical output\npower of the photovoltaic cell, we find that the actual system efficiency\n(ratio of ingoing heat flux to output power) is 11.2% at an emitter temperature\nof 1338 K, and that the output power density footprint is 0.368 W/cm2. The\nobtained efficiency is relatively high, i.e., 1.65 times that of the previously\nreported record value (6.8%). Further efficiency improvements in the future may\nlead to development of distributed energy supplies using combustion heat.", "category": "physics_app-ph" }, { "text": "An innovative, fast and facile soft-template approach for the\n fabrication of porous PDMS for oil-water separation: Oil wastewater and spilled oil caused serious environmental pollution and\ndamage to public health in the last years. Therefore, considerable efforts are\nmade to develop sorbent materials able to separate oil from water with high\nselectivity and sorption capacity. However most of them are low reusable, with\nlow volume absorption capacity and poor mechanical properties. Moreover, the\nsynthesis is time-consuming, complex and expensive limiting its practical\napplication in case of emergency. Here we propose an innovative approach for\nthe fabrication of porous PDMS starting from an inverse water-in-silicone\nprocedure able to selectively collect oil from water in few seconds. The\nsynthesis is dramatically faster than previous approaches, permitting the\nfabrication of the material in few minutes independently from the dimension of\nthe sponges. The porous material evidenced a higher volume sorption capacity\nwith respect to other materials already proposed for oil sorption from water\nand excellent mechanical and reusability properties.This innovative fast and\nsimple approach can be successful in case of emergency, as oil spill accidents,\npermitting in situ fabrication of porous absorbents.", "category": "physics_app-ph" }, { "text": "Transfer Learning for Inverse Design of Tunable Graphene-Based\n Metasurfaces: This paper outlines a new approach to designing tunable electromagnetic (EM)\ngraphene-based metasurfaces using convolutional neural networks (CNNs). EM\nmetasurfaces have previously been used to manipulate EM waves by adjusting the\nlocal phase of subwavelength elements within the wavelength scale, resulting in\na variety of intriguing devices. However, the majority of these devices have\nonly been capable of performing a single function, making it difficult to\nachieve multiple functionalities in a single design. Graphene, as an active\nmaterial, offers unique properties, such as tunability, making it an excellent\ncandidate for achieving tunable metasurfaces. The proposed procedure involves\nusing two CNNs to design the passive structure of the graphene metasurfaces and\npredict the chemical potentials required for tunable responses. The CNNs are\ntrained using transfer learning, which significantly reduced the time required\nto collect the training dataset. The proposed inverse design methodology\ndemonstrates excellent performance in designing reconfigurable EM metasurfaces,\nwhich can be tuned to produce multiple functions, making it highly valuable for\nvarious applications. The results indicate that the proposed approach is\nefficient and accurate and provides a promising method for designing\nreconfigurable intelligent surfaces for future wireless communication systems.", "category": "physics_app-ph" }, { "text": "Stress-transfer from polymer substrates to monolayer and few-layer\n graphenes: In the present study the stress transfer mechanism in graphene-polymer\nsystems under tension is examined experimentally using the technique of laser\nRaman microscopy. We discuss in detail the effect of graphene edge geometry,\nlateral size and thickness which need to be taken under consideration when\nusing graphene as a protective layer. The systems examined comprised of\ngraphene flakes with large length (over ~50 microns) and thickness of one to\nthree layers simply deposited onto PMMA substrates which were then loaded to\ntension up to ca. 1.60% strain. The stress transfer profiles were found to be\nlinear while the results show that large lateral sizes of over twenty microns\nare needed in order to provide effective reinforcement at levels of strain\nhigher than 1%. Moreover, the stress-built up has been found to be quite\nsensitive to both edge shape and geometry of the loaded flake. Finally, the\ntransfer lengths were found to increase with the increase of graphene layers.\nThe outcomes of the present study provide crucial insight on the issue of\nstress transfer from polymer to nano-inclusions as a function of edge geometry,\nlateral size and thickness in a number of applications.", "category": "physics_app-ph" }, { "text": "Analysis of Performance Limits in Current-Matched Tandem Solar Cells: Our work estimates the performance limits of an N-layer current-matched (CM)\ntandem solar cell with and without subcells/modules in each layer, accounting\nfor radiative coupling between the layers. Current matching constraints are\nalleviated with the help of adding additional modules at each layer\nappropriately. The optimal number of subcells to achieve maximum efficiency is\nalso determined. This model serves as a general framework for the analysis of\nefficiency limits and provides design insights into the number of\nsubcells/modules of any number of layers and can be extended to voltage-matched\n(VM) devices and bifacial devices as well.", "category": "physics_app-ph" }, { "text": "Temperature Dependent Low-Frequency Noise Characteristics of\n NiO$_x$/Ga$_2$O$_3$ p-n Heterojunction Diodes: We report on the temperature dependence of the low-frequency electronic noise\nin NiO$_x$/Ga$_2$O$_3$ p-n heterojunction diodes. The noise spectral density is\nof the 1/f-type near room temperature but shows signatures of Lorentzian\ncomponents at elevated temperatures and at higher current levels (f is the\nfrequency). We observed an intriguing non-monotonic dependence of the noise on\ntemperature near T = 380$^\\circ$ K. The Raman spectroscopy of the device\nstructure suggests material changes, which results in reduced noise above this\ntemperature. The normalized noise spectral density in such diodes was\ndetermined to be on the order of 10$^{-14}$ cm$^2$/Hz (f = 10 Hz) at 0.1\nA/cm$^2$ current density. In terms of the noise level, NiO$_x$/Ga$_2$O$_3$ p-n\ndiodes occupy an intermediate position among devices of various designs\nimplemented with different ultra-wide-band-gap (UWBG) semiconductors. The\nobtained results are important for understanding the electronic properties of\nthe UWBG heterojunctions and contribute to the development of noise\nspectroscopy as the quality assessment tool for new electronic materials and\ndevice technologies.", "category": "physics_app-ph" }, { "text": "Threshold Voltage Improvement and Leakage Reduction of AlGaN/GaN HEMTs\n Using Dual-Layer SiNx Stressors: In this work, AlGaN/GaN HEMTs with dual-layer SiNx stressors (composed of a\nlow-stress layer and a high-stress layer) were investigated. The low-stress\npadding layer solved the surface damage problem caused during the deposition of\nthe high-stress SiNx, and provided a good passivated interface. The HEMTs with\ndual-layer stressors showed a 1 V increase in the threshold voltage (Vth) with\ncomparable on-current and RF current gain to those without stressors. Moreover,\nthe off-current (I_off) was shown to be reduced by one to three orders of\nmagnitude in the strained devices as a result of the lower electric field in\nAlGaN, which suppressed the gate injection current. The dual-layer stressor\nscheme supports strain engineering as an effective approach in the pursuit of\nthe normally-off operation of AlGaN/GaN HEMTs.", "category": "physics_app-ph" }, { "text": "Current-induced deterministic switching of van der Waals ferromagnet at\n room temperature: Recent discovery of emergent magnetism in van der Waals magnetic materials\n(vdWMM) has broadened the material space for developing spintronic devices for\nenergy-efficient computation. While there has been appreciable progress in\nvdWMM discovery, with strong perpendicular magnetic anisotropy (PMA) and Curie\ntemperatures exceeding room temperature, a solution for non-volatile,\ndeterministic switching of vdWMMs at room temperature has been missing,\nlimiting the prospects of their adoption into commercial spintronic devices.\nHere, we report the first demonstration of current-controlled non-volatile,\ndeterministic magnetization switching in a vdW magnetic material at room\ntemperature. We have achieved spin-orbit torque (SOT) switching of the PMA vdW\nmagnet Fe3GaTe2 using a Pt spin-Hall layer up to 320 K, with a threshold\nswitching current density as low as $J_{sw} = 1.69\\times10^6 A/cm^2$ at room\ntemperature. We have also quantitatively estimated the anti-damping-like SOT\nefficiency of our Fe3GaTe2/Pt bilayer system to be $\\xi_{DL}$ = 0.093, using\nsecond harmonic Hall voltage measurement technique. These results mark a\ncrucial step in making vdW magnetic materials a viable choice for the\ndevelopment of scalable, future spintronic devices.", "category": "physics_app-ph" }, { "text": "Optical probing of the intrinsic spin Hall effect in a high mobility\n GaAs p-doped quantum well: We report on the detection of the intrinsic spin Hall effect in a modulation\ndoped Al-GaAs/GaAs/AlGaAs heterostructure bounded by a self-aligned\npn-junction, fabricated by the cleaved edge overgrowth method. Light emission\ndue to the recombination of electrons and spin-polarized holes was generated\nand mapped with a spatial resolution of one micrometer. An edge accumulated\nspin polarization of up to 11% was measured, induced solely by application of\nan electric Field perpendicular to the pn-junction. Using a quantum dot\nstructure as light source, a linear dependence of the effective spin\npolarization, and with that the dominance of the spin Hall effect, with the\nelectric field is seen. Spatially resolved spectroscopy from an epitaxially\nfabricated LED is demonstrated to be a valuable tool to probe the edge states\nof electron and hole gases in reduced dimensions.", "category": "physics_app-ph" }, { "text": "MilliKelvin microwave impedance microscopy in a dry dilution\n refrigerator: Microwave impedance microscopy (MIM) is a near-field imaging technique that\nhas been used to visualize the local conductivity of materials with nanoscale\nresolution across the GHz regime. In recent years, MIM has shown great promise\nfor the investigation of topological states of matter, correlated electronic\nstates and emergent phenomena in quantum materials. To explore these low-energy\nphenomena, many of which are only detectable in the milliKelvin regime, we have\ndeveloped a novel low-temperature MIM incorporated into a dilution\nrefrigerator. This setup which consists of a tuning-fork-based atomic force\nmicroscope with microwave reflectometry capabilities, is capable of reaching\ntemperatures down to 70 mK during imaging and magnetic fields up to 9 T. To\ntest the performance of this microscope, we demonstrate microwave imaging of\nthe conductivity contrast between graphite and silicon dioxide at cryogenic\ntemperatures and discuss the resolution and noise observed in these results. We\nextend this methodology to visualize edge conduction in Dirac semimetal cadmium\narsenide in the quantum Hall regime", "category": "physics_app-ph" }, { "text": "All-solid flexible fiber-shaped lithium ion batteries: We propose fabrication of the fiber-shaped lithium ion batteries assembled by\ntwisting a cathode filament together with an anode filament. The cathode\nfilament is fabricated by depositing a LiFePO4 (LFP)-composite layer onto a\nsteel-filled polyester conductive thread (SPCT). As anode filaments, we propose\nseveral scenarios including a Li4Ti5O12 (LTO)-composite coated SPCT\n(dip-and-dry deposition), a tin-coated SPCT (PVD deposition) as well as a bare\ntin wire. An electrolyte composite layer consisting of LiPF6 and polyethylene\noxide (PEO) is then deposited onto both the anode and cathode filament before\nthe battery assembly. By twisting the cathode filament and anode filament\ntogether using a customized jig, the batteries are then assembled. The\nopen-circuit voltage is found to be ~ 2.3 V for the battery using the LTO@SPCT\nanode, and ~3.3 V for the battery using the tin@SPCT anode and the tin wire\nanode. Charge-discharge tests are carried out at different C rates for each\nbattery sample. Experimental results suggest that the LIBs using the LTO@SPCT\nanode, the tin@SPCT anode and the bare tin wire anode could achieve a specific\ncapacity of ~64, ~67, and ~96 mAh/g, respectively, when charge-discharged at\n0.5-C rate. The battery could retain well its capacity after 80\ncharge-discharge cycles. During operation of all the batteries reported in this\npaper, their coulombic efficiency remained above 80%. Among the advantages of\nthe proposed LIB are light weight, ease of fabrication, high specific\ncapacitance, high energy density, and good durability. Finally, employing cheap\nand commercially-available steel-filled polyester threads as a base material in\nour batteries, makes them potentially suitable for integration into wearables\nusing various standard textile manufacturing techniques.", "category": "physics_app-ph" }, { "text": "Analysis of a capped carbon nanotube (CNT) with linear-scaling\n density-functional theory: The apex region of a capped (5,5) carbon nanotube (CNT) has been modelled\nwith the DFT package ONETEP, using boundary conditions provided by a classical\ncalculation with a conducting surface in place of the CNT. Results from the DFT\nsolution include the Fermi level and the physical distribution and energies of\nindividual Kohn-Sham orbitals for the CNT tip. Application of an external\nelectric field changes the orbital number of the highest occupied molecular\norbital (the HOMO) and consequently changes the distribution of the HOMO on the\nCNT.", "category": "physics_app-ph" }, { "text": "Modified Steinberg-Guinan elasticity model to describe\n softening-hardening dual anomaly in vanadium: Constitutive models are essential for describing the mechanical behavior of\nmaterials under high temperatures and pressures, among which the\nSteinberg-Guinan (SG) model is widely adopted. Recent work has discovered a\npeculiar dual anomaly of compression-induced softening and heating-induced\nhardening in the elasticity of compressed vanadium [Phys. Rev. B 104, 134102\n(2021)], which is beyond the capability of the SG model to describe. In this\nwork, a modified SG constitutive model is proposed to embody such an anomalous\nbehavior. Elemental vanadium is considered as an example to demonstrate the\neffectiveness of this improved model in describing the dual anomalies of\nmechanical elasticity. This new variant of the SG model can also be applied to\nother materials that present an irregular variation in the mechanical\nelasticity, and is important to faithfully model and simulate the mechanical\nresponse of materials under extreme conditions.", "category": "physics_app-ph" }, { "text": "An evaluation strategy of the thermal conductance of semiconductor\n interfaces using ultraviolet light: In the previous studies, the ultraviolet light thermoreflectance (UV-TDTR)\nsignal from bulk semiconducting samples cannot be well explained by a thermal\nmodels based on the assumption that the heat is both absorbed and probed near\nthe surface. A thermoreflectance (TDTR) technique was developed to directly\nexcite semiconductors using UV-TDTR. At {\\lambda} = 400nm, the photon energy is\nmuch greater than most semiconducting bandgaps, potentially allowing\nsemiconducting transducers to absorb light within about 10 nm of the surface,\npotentially enabling direct measurements of semiconductor-semiconductor\ninterfaces. The thermoreflectance coefficient for some direct-bandgap\nsemiconducting materials was measured. Thermal transport models were fitted to\nthermorefectance data collected from the system. The differences in the signal\nfor semiconductors with different doping and nanostructure features were also\nstudied, which should change the recombination rate. No significant changes to\nthe signal were observed.", "category": "physics_app-ph" }, { "text": "Dual-band electro-optically steerable antenna: The ability to obtain dynamic control over an antenna radiation pattern is\none of the main functions, desired in a vast range of applications, including\nwireless communications, radars, and many others. Widely used approaches\ninclude mechanical scanning with antenna apertures and phase switching in\narrays. Both of those realizations have severe limitations, related to scanning\nspeeds and implementation costs. Here we demonstrate a solution, where the\nantenna pattern is switched with optical signals. The system encompasses an\nactive element, surrounded by a set of cylindrically arranged passive dipolar\ndirectors, functionalized with tunable impedances. The control circuit is\nrealized as a bipolar transistor, driven by a photodiode. Light illumination in\nthis case serves as a trigger, capable of either closing or opening the\ntransistor, switching the impedance between two values. Following this\napproach, a compact half-a-wavelength footprint antenna, capable to switch\nbetween 6 dBi directional patterns within a few milliseconds latency was\ndemonstrated. The developed light activation approach allows constructing\ndevices with multiple almost non-interacting degrees of freedom, as brunched\nfeeding network is not required. The capability of MHz and faster switching\nbetween multiple electromagnetic degrees of freedom open pathways to new\nwireless applications, where fast beam steering and beamforming performances\nare required.", "category": "physics_app-ph" }, { "text": "Analytical Modeling of k33 Mode Partial Electrode Configuration for Loss\n Characterization: Accurate determination of three types of losses (dielectric, elastic and\npiezoelectric) in piezoelectric materials is critical, since they are closely\nrelated to the performance of high-power piezoelectric devices. The Standard\nk33 mode has a number of serious deficits that hinders researchers from\ndetermining accurate physical parameters and losses. In order to overcome such\ndeficits, partial electrode has been devised and proposed. This study provides\nanalytical derivation process and proposes parameter determination method by\nutilizing analytical solutions. Compared to finite element analysis, analytical\nsolutions show 0.1 % difference in resonance frequencies and 2 % difference in\nmechanical quality factors, proving them as valid modeling. The analytical\nsolutions are fitted to experimental data to determine physical parameters and\nlosses. The k33 (electromechanical coupling factor) values were calculated with\ndetermined values from curve fitting in two different ways and show good\nagreement to each other.", "category": "physics_app-ph" }, { "text": "Universal Battery Performance and Degradation Model for Electric\n Aircraft: Development of Urban Air Mobility (UAM) concepts has been primarily focused\non electric vertical takeoff and landing aircraft (eVTOLs), small aircraft\nwhich can land and takeoff vertically, and which are powered by rechargeable\n(typically lithium-ion) batteries. Design, analysis, and operation of eVTOLs\nrequires fast and accurate prediction of Li-ion battery performance throughout\nthe lifetime of the battery. eVTOL battery performance modeling must be\nparticularly accurate at high discharge rates to ensure accurate simulation of\nthe high power takeoff and landing portions of the flight. In this work, we\ngenerate a battery performance and thermal behavior dataset specific to eVTOL\nduty cycles. We use this dataset to develop a battery performance and\ndegradation model (Cellfit) which employs physics-informed machine learning in\nthe form of Universal Ordinary Differential Equations (U-ODE's) combined with\nan electrochemical cell model and degradation models which include solid\nelectrolyte interphase (SEI) growth, lithium plating, and charge loss. We show\nthat Cellfit with U-ODE's is better able to predict battery degradation than a\nmechanistic battery degradation model. We show that the improved accuracy of\nthe degradation model improves the accuracy of the performance model. We\nbelieve that Cellfit will prove to be a valuable tool for eVTOL designers.", "category": "physics_app-ph" }, { "text": "Flexible daytime radiative cooling enhanced by enabling three-phase\n composites with scattering interfaces between silica-microspheres and\n hierarchical porous coatings: Daytime radiative cooling has attracted considerable attention recently due\nto its tremendous potential for passively exploiting the coldness of deep-sky\nas clean and renewable energy. Many advanced materials with novel photonic\nmicro-nanostructures have already been developed to enable highly efficient\ndaytime radiative coolers, among which the flexible hierarchical porous\ncoatings (HPCs) are a more distinguished category. However, it is still hard to\nprecisely control the size distribution of the randomized pores within the\nHPCs, usually resulting in a deficient solar reflection at the near-infrared\noptical regime under diverse fabrication conditions of the coatings. We report\nhere a three-phase (i.e., air pore-phase, microsphere-phase and polymer-phase)\nself-assembled hybrid porous composite coating which dramatically increases the\naverage solar reflectance and yields a remarkable temperature drop of ~10 degC\nand 30 degC compared to the ambient circumstance and black paint, respectively,\naccording to the rooftop measurements. Mie theory and Monte Carlo simulations\nreveal the origin of the low reflectivity of as-prepared two-phase porous HPCs,\nand the optical cooling improvement of the three-phase porous composite\ncoatings is attributed to the newly generated interfaces possessing the high\nscattering efficiency between the hierarchical pores and silica microspheres\nhybridized with appropriate mass fractions. As a result, the hybrid porous\ncomposite approach enhances the whole performance of the coatings, which\nprovides a promising alternative to the flexible daytime radiative cooler.", "category": "physics_app-ph" }, { "text": "High yield production of ultrathin fibroid semiconducting nanowire of\n Ta$_2$Pd$_3$Se$_8$: Immediately after the demonstration of the high-quality electronic properties\nin various two dimensional (2D) van der Waals (vdW) crystals fabricated with\nmechanical exfoliation, many methods have been reported to explore and control\nlarge scale fabrications. Comparing with recent advancements in fabricating 2D\natomic layered crystals, large scale production of one dimensional (1D)\nnanowires with thickness approaching molecular or atomic level still remains\nstagnant. Here, we demonstrate the high yield production of a 1D vdW material,\nsemiconducting Ta2Pd3Se8 nanowires, by means of liquid-phase exfoliation. The\nthinnest nanowire we have readily achieved is around 1 nm, corresponding to a\nbundle of one or two molecular ribbons. Transmission electron microscopy and\ntransport measurements reveal the as-fabricated Ta2Pd3Se8 nanowires exhibit\nunexpected high crystallinity and chemical stability. Our low frequency Raman\nspectroscopy reveals clear evidence of the existing of weak inter-ribbon\nbindings. The fabricated nanowire transistors exhibit high switching\nperformance and promising applications for photodetectors.", "category": "physics_app-ph" }, { "text": "The Controlled Large-Area Synthesis of Two Dimensional Metals: The rise of nanotechnology has been propelled by low dimensional metals.\nAlbeit the long perceived importance, synthesis of freestanding metallic\nnanomembranes, or the so-called 2D metals, however has been restricted to\nsimple metals with a very limited in-plane size (< 10{\\mu}m). In this work, we\ndeveloped a low-cost method to synthesize 2D metals through polymer surface\nbuckling enabled exfoliation. The 2D metals so obtained could be as chemically\ncomplex as high entropy alloys while possessing in-plane dimensions at the\nscale of bulk metals (> 1 cm). With our approach, we successfully synthesized a\nvariety of 2D metals, such as 2D high entropy alloy and 2D metallic glass, with\ncontrollable geometries and morphologies. Moreover, our approach can be readily\nextended to non-metals and composites, thereby opening a large window to the\nfabrication of a wide range of 2D materials of technologic importance which\nhave never been reported before.", "category": "physics_app-ph" }, { "text": "Giant and bidirectionally tunable thermopower in non-aqueous ionogels\n enabled by selective ion doping: Ionic thermoelectrics show great potential in low-grade heat harvesting and\nthermal sensing owing to their ultrahigh thermopower, low cost and ease in\nproduction. However, the lack of effective n-type ionic thermoelectric\nmaterials seriously hinders their applications. Here, we report giant and\nbidirectionally tunable thermopowers within an ultrawide range from -23 to +32\nmV K-1 at 90% RH in solid ionic-liquid-based ionogels, rendering it among the\nbest n- and p-type ionic thermoelectric materials. A novel thermopower\nregulation strategy through ion doping to selectively induce ion aggregates via\nstrong ion-ion interactions is proposed. These charged aggregates are found\ndecisive in modulating the sign and enlarging the magnitude of the thermopower\nin the ionogels. A prototype wearable device integrated with 12 p-n pairs is\ndemonstrated with a total thermopower of 0.358 V K-1 in general indoor\nconditions, showing promise for ultrasensitive body heat detection.", "category": "physics_app-ph" }, { "text": "Topological magnetoelectric response in passive magnetic devices: Despite the prospect of next-generation electronic technologies has spurred\nthe investigation of the remarkable topological magnetoelectric response, it\nremains largely unexplored its potential in the application of basic electronic\ndevices. In this paper, we undertake this task at the theoretical level by\naddressing the $\\theta$-electrodynamics and examine electromagnetic properties\n(e.g. tunable inductance, operating frequency range, and power consumption) of\nthree fundamental passive magnetic devices endowed with this effect: the\nprimitive transformer, the bilayer solenoid inductor, and the solenoid\nactuator. We further exploit the methodology of magnetic circuits to obtain an\nextended Hopkinson's law that is valid for both topological and ordinary\nmagnetoelectric responses (provided it is uniform in the bulk). Under low-power\nconditions, we find out that the functionally passive part of the\ntopological-magnetoelectric transformer, solenoid inductor as well as solenoid\nactuator is indistinguishable from the conventional situation up to\nsecond-order in the magnetoelectric susceptibility; and argue that the main\nbenefit of using topological insulators essentially relies on a lower power\nconsumption. Our theoretical framework is also convenient to analyse\nmagnetoelectric inductors endowed with a relatively large magnetoelectric\nsusceptibility, they display a broad inductance tunability of over 200% up to\n100 GHz in the millimeter length scale. Conversely, our treatment predicts that\nthe operating frequency range could be restricted below the ultra low frequency\nby a significantly strong magnetoelectric response (e.g. retrieved by certain\nmultiferroic heterostructures).", "category": "physics_app-ph" }, { "text": "Identifying optimal photovoltaic technologies for underwater\n applications: Improving solar energy collection in aquatic environments would allow for\nsuperior environmental monitoring and remote sensing, but the identification of\noptimal photovoltaic technologies for such applications is challenging as\nevaluation requires either field deployment or access to large water tanks.\nHere, we present a simple bench-top characterization technique that does not\nrequire direct access to water and therefore circumvents the need for field\ntesting during initial trials of development. Employing LEDs to simulate\nunderwater solar spectra at various depths, we compare Si and CdTe solar cells,\ntwo commercially available technologies, with GaInP cells, a technology with a\nwide band gap close to ideal for underwater solar harvesting. We use this\nmethod to show that while Si cells outperform both CdTe and GaInP under\nterrestrial AM1.5G solar irradiance, both CdTe and GaInP outperform Si at\ndepths > 2 m, with GaInP cells operating with underwater efficiencies exceeding\n51%.", "category": "physics_app-ph" }, { "text": "Scalable production of high sensitivity, label-free DNA biosensors based\n on back-gated graphene field-effect transistors: Scalable production of all-electronic DNA biosensors with high sensitivity\nand selectivity is a critical enabling step for research and applications\nassociated with detection of DNA hybridization. We have developed a scalable\nand very reproducible (> 90% yield) fabrication process for label-free DNA\nbiosensors based upon graphene field effect transistors (GFETs) functionalized\nwith single-stranded probe DNA. The shift of the GFET sensor Dirac point\nvoltage varied systematically with the concentration of target DNA. The\nbiosensors demonstrated a broad analytical range and limit of detection of 1 fM\nfor 60-mer DNA oligonucleotide. In control experiments with mismatched DNA\noligomers, the impact of the mismatch position on the DNA hybridization\nstrength was confirmed. This class of highly sensitive DNA biosensors offers\nthe prospect of detection of DNA hybridization and sequencing in a rapid,\ninexpensive, and accurate way.", "category": "physics_app-ph" }, { "text": "3D Reconstruction of Bias Effects on Porosity, Alignment and Mesoscale\n Structure in Electrospun Tubular Polycaprolactone: Porosity variations in tubular scaffolds are critical to reproducible,\nsophisticated applications of electrospun fibers in biomedicine. Established\nlaser micrometry techniques produced ~14,000 datapoints enabling thickness and\nporosity plots versus both the azimuthal (Phi) and axial (Z) directions\nfollowing cylindrical mandrel deposition. These 3D datasets could then be\n\"unrolled\" into \"maps\" revealing variations in thickness and porosity versus 0,\n-5, and -15 kV collector bias. As bias increases, thinner, more \"focused\"\ndepositions occur. Simultaneous decreases in net porosity versus bias (91.1%\n0kV > 83.4% -5kV > 80.2% -15 kV) are sensible, but significant changes in the\ndistribution were unexpected. Surprisingly, at 0 kV, extensive mesoscale\nsurface roughness is evident. Optical profilometry revealed unique features\n~1600-420 mum in size, standing ~210 mum above the surrounding surface. These\nshrink to only ~440-150 mum in size and ~30 mum higher at -5 kV bias and\ndisappear entirely at -15 kV. Scanning electron microscopy (SEM) resolved these\ninto novel, localized \"domains\" containing tightly aligned fibers oriented\nparallel to the mandrel axis. Unexpectedly, we also observed substantial\norientation along the mandrel axis. By modifying classical bending instability\nmodels to incorporate cylindrical electric fields, simulation revealed that\nhorizontal components in the modified electric field alter bending loop shape,\ncausing the observed alignment. This provides a new, easily utilized tool\nenabling facile, efficient tuning of orientation.", "category": "physics_app-ph" }, { "text": "Multiple damage detection in piezoelectric ceramic sensor using point\n contact excitation and detection method: Lead Zirconate Titanate [(ZrxTi1-x)O3 ]is used to make ultrasound\ntransducers, sensors, and actuators due to its large piezoelectric coefficient.\nSeveral surfaces and subsurface micro defects develop within the Lead Zirconate\nTitanate (PZT) sensor due to delamination, corrosion, huge temperature\nfluctuation, etc., causing a decline in its performance. It is thus necessary\nto identify, locate, and quantify the defects. Non-Destructive Structural\nHealth Monitoring (SHM) is the most optimal and economical method of\nevaluation. Traditional ultrasound SHM techniques have a huge impedance\nmismatch between air and any solid material. And most of the popular signal\nprocessing methods define time-series signals in only one domain which gives\nsub-optimal results. Thus to improve the accuracy of detection point contact\nexcitation and detection methods have been implemented to determine the\ninteraction of ultrasonic waves with microscale defects in the PZT. And Haar\nDiscrete Wavelet Transformation (DWT) is applied to the time series data\nobtained from the Coulomb coupling setup. Using the above process, defect up to\n100 um in diameter could be successfully distinguished and localized.", "category": "physics_app-ph" }, { "text": "Effect of plasma formation on the double pulse laser excitation of cubic\n silicon carbide: We calculate the electron excitation in cubic silicon carbide (3C-SiC) caused\nby the intense femtosecond laser double pulses using time-dependent density\nfunctional theory (TDDFT). We assume the electron distributions in the valence\nband (VB) and the conduction band (CB) based on three different approaches to\ndetermine the dependence of the plasma that is formed on the excitation by the\nfirst pulse. First, we consider the simple double pulse irradiation, which does\nnot include the electron-electron collisions and relaxation. Second, we\nconsider the partially thermalized electronic state, in which the electron\ntemperatures and numbers in the VB and the CB are defined independently. This\nassumption corresponds to the plasma before the electron-hole collisions\nbecomes dominant. The third approach uses the fully thermalized electron\ndistribution, which corresponds to a timescale of hundreds fs. Our results\nindicate that the simple double pulse approach is the worst of the three, and\nshow that the plasma formation changes the efficiency of the excitation by the\nsecond pulse. When the electron temperature decreases, the laser excitation\nefficiency increases as a result.", "category": "physics_app-ph" }, { "text": "A Method To Characterize Metalenses For Light Collection Applications: Metalenses and metasurfaces are promising emerging technologies that could\nimprove light collection in light collection detectors, concentrating light on\nsmall area photodetectors such as silicon photomultipliers. Here we present a\ndetailed method to characterize metalenses to assess their efficiency at\nconcentrating monochromatic light coming from a wide range of incidence angles,\nnot taking into account their imaging quality.", "category": "physics_app-ph" }, { "text": "Modeling and simulation of interface failure in metal-composite hybrids: The application of hybrid composites in lightweight engineering enables the\ncombination of material-specific advantages of fiber-reinforced polymers and\nclassical metals. The interface between the connected materials is of\nparticular interest since failure often initializes in the bonding zone. In\nthis contribution the connection of an aluminum component and a glass\nfiber-reinforced epoxy is considered on the microscale. The constitutive\nmodeling accounts for adhesive failure of the local interfaces and cohesive\nfailure of the bulk material. Interface failure is represented by cohesive zone\nmodels, while the behavior of the polymer is described by an elastic-plastic\ndamage model. A gradient-enhanced formulation is applied to avoid the\nwell-known mesh dependency of local continuum damage models. The application of\nnumerical homogenization schemes allows for the prediction of effective\ntraction-separation relations. Therefore, the influence of the local interface\nstrength and geometry of random rough interfaces on the macroscopical\nproperties is investigated in a numerical study. There is a positive effect of\nan increased roughness on the effective joint behavior.", "category": "physics_app-ph" }, { "text": "Vertical Bifacial Solar Farms: Physics, Design, and Global Optimization: There have been sustained interest in bifacial solar cell technology since\n1980s, with prospects of 30-50% increase in the output power from a stand-alone\nsingle panel. Moreover, a vertical bifacial panel reduces dust accumulation and\nprovides two output peaks during the day, with the second peak aligned to the\npeak electricity demand. Recent commercialization and anticipated growth of\nbifacial panel market have encouraged a closer scrutiny of the integrated\npower-output and economic viability of bifacial solar farms, where mutual\nshading will erode some of the anticipated energy gain associated with an\nisolated, single panel. Towards that goal, in this paper we focus on\ngeography-specific optimizations of ground mounted vertical bifacial solar\nfarms for the entire world. For local irradiance, we combine the measured\nmeteorological data with the clear-sky model. In addition, we consider the\ndetailed effects of direct, diffuse, and albedo light. We assume the panel is\nconfigured into sub-strings with bypass-diodes. Based on calculated light\ncollection and panel output, we analyze the optimum farm design for maximum\nyearly output at any given location in the world. Our results predict that,\nregardless of the geographical location, a vertical bifacial farm will yield\n10-20% more energy than a traditional monofacial farm for a practical\nrow-spacing of 2m (1.2m high panels). With the prospect of additional 5-20%\nenergy gain from reduced soiling and tilt optimization, bifacial solar farm do\noffer a viable technology option for large-scale solar energy generation.", "category": "physics_app-ph" }, { "text": "Electromechanical control of polarization vortex ordering in an\n interacting ferroelectric-dielectric composite dimer: Using a free-energy based computational model, we have investigated the\nresponse of a system comprising two interacting ferroelectric nanospheres,\nembedded in a dielectric medium, to a static external electric field. The\nsystem response is hysteretic and tunable by changing the inter-particle\ndistance and the orientation of the applied field, which strongly modulates the\nfield-driven long-range elastic interactions between the particles that\npropagate through the dielectric matrix. At small separations, the sensitivity\nof the system behavior with respect to the electric field direction originates\nfrom drastically different configurations of the local vortex-like polarization\nstates in ferroelectric particles. This suggests new routes for the design of\ncomposite metamaterials whose dielectric properties can be controlled and tuned\nby selecting the mutual arrangement of their ferroelectric components.", "category": "physics_app-ph" }, { "text": "Franz-Keldysh effect in semiconductor built-in fields: Franz-Keldysh effect is expressed in the smearing of the absorption edge in\nsemiconductors under high electric fields. While Franz and Keldysh considered a\nlimited case of externally applied uniform electric field, the same effect may\nbe caused by built-in electric fields at semiconductor surfaces and interfaces.\nWhile in the first case, the bands are bent linearly, in the latter case, they\nare bent parabolically. This non-linear band bending poses an additional\ncomplexity that has not been considered previously. Here, we extend the linear\nmodel to treat the case of a non-linear band bending. We then show how this\nmodel may be used to quantitatively analyze photocurrent and photovoltage\nspectra to determine the built-in fields, the density of surface state charge,\nand the doping concentration of the material. We use the model on a GaN\\AlGaN\nheterostructure, and GaAs bulk. The results demonstrate that the same mechanism\nunderlies the band-edge response both in photocurrent and photovoltage spectra\nand demonstrate the quantitative use of the model in contactless extraction of\nimportant semiconductor material parameters.", "category": "physics_app-ph" }, { "text": "The influence of additives in the stoichiometry of hybrid lead halide\n perovskites: We investigate the employment of carefully selected solvent additives in the\nprocessing of a commercial perovskite precursor ink and analyze their impact on\nthe performance of organometal trihalide perovskite photovoltaic devices. We\nprovide evidence that the use of benzaldehyde can be used as an effective\nmethod to preserve the stoichiometry of the perovskite precursors in solution.\nBenzaldehyde based additive engineering shows to improve perovskite solid state\nfilm morphology and device performance of trihalide perovskite based solar\ncells.", "category": "physics_app-ph" }, { "text": "Epitaxial Al/GaAs/Al tri-layers fabricated using a novel wafer-bonding\n technique: Epitaxial Al/GaAs/Al structures having controlled thickness of high-quality\nGaAs and pristine interfaces have been fabricated using a wafer-bonding\ntechnique. III-V semiconductor/Al structures are grown by molecular beam\nepitaxy on III-V semiconductor substrates and bonded to silicon and sapphire.\nSelective etching is used to remove the III-V substrate followed by surface\ncleaning and superconductor regrowth, resulting in epitaxial Al/GaAs/Al\ntri-layers on sapphire or silicon substrates. Structures are characterized with\nreflection high energy electron diffraction, atomic force microscopy, X-ray\nphotoelectron spectroscopy, transmission electron microscopy, and X-ray\ndiffraction. Applications of these structures to the field of quantum\ninformation processing is discussed.", "category": "physics_app-ph" }, { "text": "Polarisation of radio-frequency magnetic fields in magnetic induction\n measurements with an atomic magnetometer: We explore properties of the radio-frequency atomic magnetometer,\nspecifically its sensitivity to the polarisation of an oscillating magnetic\nfield. This aspect can be particularly relevant to configurations where the\nsensor monitors fields created by more than one source. The discussion,\nillustrated by theoretical and experimental studies, is done in the context of\nthe signals produced by electrically conductive and magnetically permeable\nplates in magnetic induction tomography measurements. We show that different\ncomponents of the secondary magnetic fields create the object response\ndepending on the properties of the material, with the polarisation of the rf\nfield varying across the object's surface. We argue that the ability of the\nsensor to simultaneously detect different field components enables the\noptimisation of measurement strategies for different object compositions.", "category": "physics_app-ph" }, { "text": "Inverted Perovskite Photovoltaics using Flame Spray Pyrolysis Solution\n based CuAlO2/Cu-O Hole Selective Contact: We present the functionalization process of a conductive and transparent\ncopper aluminum oxide, copper oxide alloy. The copper aluminum oxide, copper\noxide powders were developed by flame spray pyrolysis and their stabilized\ndispersions were treated by sonication and centrifugation methods. We show that\nwhen the supernatant part of the treated copper aluminum oxide, copper oxide\ndispersions is used for the development of hole transporting layers the\ncorresponding inverted perovskite solar cells show improved functionality and\npower conversion efficiency with negligible hysteresis effect.", "category": "physics_app-ph" }, { "text": "New Concept in Moisture detection with Unconventional pore morphology\n Design: A break in traditional pore morphology approach, is presented here to see its\nniche merit over the conventional sensors for water vapour detection. Tubular\npores were replaced with normal cone for trace- and inverse cone for RH- level\ndetection. The normal conical pore was fabricated by sheer manipulation of\nreaction rates of electrolytes, anodic polarization rate and time; and the\nprocedure made reversed in case of inverse cone structure. Sensor with normal\ncone geometry exhibits response in ppm level with sensitivity of 13pF/ppm,\nlower detection limit(LOD)~120 ppm with excellent response/recovery time.\nLowering LOD further requires alteration of conical geometric parameters in\ntandem with kinetic theory of water vapour molecules. In contrast, sensor\ndeveloped from inverse conical structure shows response in RH level and LOD\ntouches down to even less than 20 RH% unlike 45 RH% in conventional RH sensors.\nLinear response characteristics with sensitivity of 5.14 pF/RH%; surprisingly,\nthe limitations such as nonlinear response, large response recovery time and\nhigh hysteresis as observed in conventional anodic alumina based humidity\nsensors have been removed. Sensing mechanism in both the structures have been\nsuitably demonstrated and ratified with experimental data. Trace level\ndetection is interpreted with the statistical probabilistic approach in the\nlight of kinetic theory of gases and Brownian energy. A correlation between top\nsurface pore diameter (through which water molecule enters) and the optimized\nmean free path of vapour molecule is established, and demonstrated its\neffectiveness for humidity detection in trace level. Results are encouraging\nand same concept may be tried for detection of other gaseous stimuli including\norganic vapours.", "category": "physics_app-ph" }, { "text": "Chipless Dielectric Constant Sensor for Structural Health Testing: A low-cost chipless RFID sensor tag to determine the dielectric properties of\nmaterials is presented. The sensor is based on a depolarizing dipole resonator\nloaded with printed capacitors whose capacitance depends on the permittivity of\nthe material located on contact with the tag. The permittivity is obtained from\nthe shift of the resonance frequency. The resonator is tested both individually\nas well as placed on a periodic arrangement so as to form a frequency selective\nstructure (FSS) to increase the cross- polar radar cross section, thus\nfacilitating the tag detection. The proposed structure and measurement\nprocedure is particularly suitable for the characterization of civil materials\nas a nondestructive testing (NDT).", "category": "physics_app-ph" }, { "text": "On-chip self-sensing enhancing actuation for MEMS/NEMS with large\n efficiency: The implementation of on-chip MEMS/NEMS transducers for arbitrary resonators\nis difficult due to a number of difficulties such as material choice, large\ndissipation, restriction in high frequency, low sensitivity, poor reliability,\nand poor integrability. We show a universal on-chip transduction scheme, which\ncan be adapted to any MEMS/NEMS resonator. We achieve all electrical, on-chip\nMEMS/NEMS for any resonator.", "category": "physics_app-ph" }, { "text": "Enhanced broad band photoresponse of a partially suspended horizontal\n array of Silicon microlines fabricated on Silicon-On-Insulator wafers: We report a high Responsivity broad band photo-detector working in the\nwavelength range 400 nm to 1100 nm in a horizontal array of Si microlines (line\nwidth ~1 micron) fabricated on a Silicon-on-Insulator (SOI) wafer. The array\nwas made using a combination of plasma etching, wet etching and electron beam\nlithography. It forms a partially suspended (nearly free) Silicon\nmicrostructure on SOI. The array detector under full illumination of the device\nshows a peak Responsivity of 18 A/W at 800 nm, at a bias of 1V which is more\nthan an order of magnitude of the Responsivity in a commercial Si detector. In\na broad band of 400 nm to 1000 nm the Responsivity of the detector is in excess\nof 10A/W. We found that the suspension of the microlines in the array is\nnecessary to obtain such high Responsivity. The suspension isolates the\nmicrolines from the bulk of the wafer and inhibits carrier recombination by the\nunderlying oxide layer leading to enhanced photo-response. This has been\nvalidated through simulation. By using focused illumination of selected parts\nof a single microline of the array, we could isolate the contributions of the\ndifferent parts of the microline to the photo-current.", "category": "physics_app-ph" }, { "text": "Modal interferometer sensor optimized for transverse misalignment: We study the transmission coefficient and the transmitted power through an\nSMS sensor with transverse misalignment. We use the Finite Element Method to\ncalculate the modes distribution by numerically solving the wave equation. The\nresults show that the maximum transmission can be obtained when the\nmisalignment is greater than zero due to the $n \\neq m$ LP$_{nm}$ excited\nmodes. Additionally, the transmitted power as function of the temperature shows\nthat it is significant only in the aligned case.", "category": "physics_app-ph" }, { "text": "Optimizing Polarizability Distributions for Metasurface Apertures with\n Lorentzian-Constrained Radiators: We present a design strategy for selecting the effective polarizability\ndistribution for a metasurface aperture needed to form a desired radiation\npattern. A metasurface aperture consists of an array of subwavelength\nmetamaterial elements, each of which can be conceptualized as a radiating,\npolarizable dipole. An ideal polarizability distribution can be determined by\nusing a holographic approach to first obtain the necessary aperture fields,\nwhich can then be converted to a polarizability distribution using equivalence\nprinciples. To achieve this ideal distribution, the polarizability of each\nelement would need to have unconstrained magnitude and phase; however, for a\nsingle, passive, metamaterial resonator the magnitude and phase of the\neffective polarizability are inextricably linked through the properties of the\nLorentzian resonance, with the range of phase values restricted to a span of at\nmost 180 degrees. Here, we introduce a family of mappings from the ideal to the\navailable polarizability distributions, easily visualized by plotting both\npolarizabilities in the complex plane. Using one of these mappings it is\npossible to achieve highly optimized beam patterns from a metasurface antenna,\ndespite the inherent resonator limitations. We introduce the mapping technique\nand provide several specific examples, with numerical simulations used to\nconfirm the design approach.", "category": "physics_app-ph" }, { "text": "Single Pixel MEMS Spectrometer using Electrothermal Tunable Grating: Miniaturized spectrometers are widely used for non-destructive and on-field\nspectral analysis. Here we report a tunable grating-based MEMS spectrometer for\nvisible to near-infrared (VIS-NIR) spectroscopy. The MEMS spectrometer consists\nof a spherical mirror and an electrothermally actuated tunable grating. The\nspectrometer detects the dispersed spectral signal with a single-pixel detector\nby tilting the diffraction grating. The large tilting angle from electrothermal\nactuation and highly dispersive diffraction grating improves the spectral range\nand resolution, respectively. The MEMS spectrometer was fully packaged within\n1.7 cm3 and provides a measurable spectral range up to 800 nm with an average\n1.96 nm spectral resolution. This miniaturized single-pixel spectrometer can\nprovide diverse applications for advanced mobile spectral analysis in\nagricultural, industrial, or medical fields.", "category": "physics_app-ph" }, { "text": "A UV-cured nanofibrous membrane of vinylbenzylated\n gelatin-poly(\u03b5-caprolactone) dimethacrylate co-network by scalable\n free surface electrospinning: Electrospun nanofibrous membranes of natural polymers, such as gelatin, are\nfundamental in the design of regenerative devices. Crosslinking of electrospun\nfibres from gelatin is required to prevent dissolution in water, to retain the\noriginal nanofibre morphology after immersion in water, and to improve the\nthermal and mechanical properties, although this is still challenging to\naccomplish in a controlled fashion. In this study, we have investigated the\nscalable manufacture and structural stability in aqueous environment of a\nUV-cured nanofibrous membrane fabricated by free surface electrospinning (FSES)\nof aqueous solutions containing vinylbenzylated gelatin and\npoly(epsilon-caprolactone) dimethacrylate (PCL-DMA). Vinylbenzylated gelatin\nwas obtained via chemical functionalisation with photopolymerisable\n4-vinylbenzyl chloride (4VBC) groups, so that the gelatin and PCL phase in\nelectrospun fibres were integrated in a covalent UV-cured co-network at the\nmolecular scale, rather than being simply physically mixed. UV-cured\nnanofibrous membranes did not dissolve in water and showed enhanced thermal and\nmechanical properties, with respect to as-spun samples, indicating the\neffectiveness of the photo-crosslinking reaction. In addition, UV-cured\ngelatin/PCL membranes displayed increased structural stability in water with\nrespect to PCL-free samples and were highly tolerated by G292 osteosarcoma\ncells. These results therefore support the use of PCL DMA as hydrophobic,\nbiodegradable crosslinker and provide new insight on the scalable design of\nwater insoluble, mechanical competent gelatin membranes for healthcare\napplications.", "category": "physics_app-ph" }, { "text": "Strain-engineered inverse charge-funnelling in layered semiconductors: The control of charges in a circuit due to an external electric field is\nubiquitous to the exchange, storage and manipulation of information in a wide\nrange of applications, from electronic circuits to synapses in neural cells.\nConversely, the ability to grow clean interfaces between materials has been a\nstepping stone for engineering built-in electric fields largely exploited in\nmodern photovoltaics and opto-electronics. The emergence of atomically thin\nsemiconductors is now enabling new ways to attain electric fields and unveil\nnovel charge transport mechanisms. Here, we report the first direct electrical\nobservation of the inverse charge-funnel effect enabled by deterministic and\nspatially resolved strain-induced electric fields in a thin sheet of HfS2. We\ndemonstrate that charges driven by these spatially varying electric fields in\nthe channel of a phototransistor lead to a 350% enhancement in the\nresponsivity. These findings could enable the informed design of highly\nefficient photovoltaic cells.", "category": "physics_app-ph" }, { "text": "Magnetic Field Dependent Piezoelectricity in Atomically Thin\n Co$_2$Te$_3$: Two dimensional (2D) materials have received a surge in research interest due\nto their exciting range of properties. Here we show that 2D cobalt telluride\n(Co2Te3), successfully synthesized via liquid-phase exfoliation in an organic\nsolvent, exhibits weak ferromagnetism and semiconducting behavior at room\ntemperature. The magnetic field-dependent piezoelectric properties of 2D Co2Te3\nsample show magneto-electric response of the material and a linear relationship\nbetween the output voltage and applied magnetic field. First-principles density\nfunctional theory (DFT) and ab initio molecular dynamics are used to explain\nthese experimental results. Our work could pave the way for the development of\n2D materials with coupled magnetism and piezoelectricity, leading to new\napplications in electromagnetics.", "category": "physics_app-ph" }, { "text": "Electrically inert h-BN/bilayer graphene interface in\n all-2D-heterostructure FETs: Bilayer graphene field-effect transistors (BLG-FETs), unlike conventional\nsemiconductors, are greatly sensitive to potential fluctuations due to the\ncharged impurities in high-k gate stacks since the potential difference between\ntwo layers induced by the external perpendicular electrical filed is the\nphysical origin behind the band gap opening. The assembly of BLG with layered\nh-BN insulators into van der Waals heterostructure has been widely recognized\nto achieve the superior electrical transport properties. However, the carrier\nresponse properties at the h-BN/BLG heterointerface, which control the device\nperformance, have not yet been revealed due to the inevitably large parasitic\ncapacitance. In this study, the significant reduction of potential fluctuations\nto ~1 meV is achieved in all-2-dimensional heterostructure BLG-FET on a quartz\nsubstrate, which results in the suppression of the off-current to the\nmeasurement limit at a small band gap of ~90 meV at 20 K. By capacitance\nmeasurement, we demonstrate that the electron trap/detrap response at such\nheterointerface is suppressed to undetectable level in the measurement\nfrequency range. The electrically inert van der Waals heterointerface paves the\nway for the realization of future BLG electronics applications.", "category": "physics_app-ph" }, { "text": "Direct loading of nanoparticles under high vacuum into a Paul trap for\n levitodynamical experiments: Mechanical oscillators based on levitated particles are promising candidates\nfor sensitive detectors and platforms for testing fundamental physics. The\ntargeted quality factors for such oscillators correspond to extremely low\ndamping rates of the center-of-mass motion, which can only be obtained if the\nparticles are trapped in ultrahigh vacuum (UHV). In order to reach such low\npressures, a noncontaminating method of loading particles in a UHV environment\nis necessary. However, loading particle traps at pressures below the viscous\nflow regime is challenging due to the conservative nature of trapping forces\nand reduced gas damping. We demonstrate a technique that allows us to overcome\nthese limitations and load particles into a Paul trap at pressures as low as\n4x10^-7 mbar. The method is based on laser-induced acoustic desorption of\nnanoparticles from a metallic foil and temporal control of the Paul trap\npotential. We show that the method is highly efficient: More than half of the\ntrapping attempts are successful. Moreover, since trapping attempts can be as\nshort as a few milliseconds, the technique provides high throughput of loaded\nparticles. Finally, the efficiency of the method does not depend on pressure,\nindicating that the method should be extensible to UHV.", "category": "physics_app-ph" }, { "text": "Dependence of chaotic behavior on optical properties and electrostatic\n effects in double beam torsional Casimir actuation: We investigate the influence of Casimir and electrostatic torques on double\nbeam torsional microelectromechanical systems with materials covering a broad\nrange of conductivities of more than three orders of magnitude. For the\nfrictionless autonomous systems, bifurcation and phase space analysis shows\nthat there is a significant difference between stable and unstable operating\nregimes for equal and unequal applied voltages on both sides of the double\ntorsional system giving rise to heteroclinic and homoclinic orbits,\nrespectively. For equal applied voltages, only the position of a symmetric\nunstable saddle equilibrium point is dependent on the material optical\nproperties and electrostatic effects, while in any other case there are stable\nand unstable equilibrium points are dependent on both factors. For the\nperiodically driven system, a Melnikov function approach is used to show the\npresence of chaotic motion rendering predictions of whether stiction or stable\nactuation will take place over long times impossible. Chaotic behavior\nintroduces significant risk for stiction, and it is more prominent to occur for\nthe more conductive systems that experience stronger Casimir forces and\ntorques. Indeed, when unequal voltages are applied, the sensitive dependence of\nchaotic motion on electrostatics is more pronounced for the highest\nconductivity systems.", "category": "physics_app-ph" }, { "text": "Real-space imaging of acoustic plasmons in large-area CVD graphene: An acoustic plasmonic mode in a graphene-dielectric-metal heterostructure has\nrecently been spotlighted as a superior platform for strong light-matter\ninteraction. It originates from the coupling of graphene plasmon with its\nmirror image and exhibits the largest field confinement in the limit of a\nnm-thick dielectric. Although recently detected in the far-field regime,\noptical near-fields of this mode are yet to be observed and characterized.\nDirect optical probing of the plasmonic fields reflected by the edges of\ngraphene via near-field scattering microscope reveals a relatively small\ndamping rate of the mid-IR acoustic plasmons in our devices, which allows for\ntheir real-space mapping even with unprotected, chemically grown, large-area\ngraphene at ambient conditions. We show an acoustic mode that is twice as\nconfined - yet 1.4 times less damped - compared to the graphene surface plasmon\nunder similar conditions. We also image the resonant acoustic Bloch state in a\n1D array of gold nanoribbons responsible for the high efficiency of the\nfar-field coupling. Our results highlight the importance of acoustic plasmons\nas an exceptionally promising platform for large-area graphene-based\noptoelectronic devices operating in mid-IR.", "category": "physics_app-ph" }, { "text": "Thickness optimization of the output power and effective thermoelectric\n figure of merit of thin thermoelectric generator: The conventional thermoelectric figure of merit and the power factor are not\nsufficient as a measure of thin film quality of thermoelectric materials, where\nthe power conversion efficiency depends on the film dimensions. By considering\nthe film size, the effective thermoelectric figure of merit and effective\nSeebeck coefficient are introduced to guarantee that the maximum energy\nconversion efficiency increases as the effective thermoelectric figure of merit\nincreases. Similarly, the effective power factor is defined. By introducing\ntypical material properties for Bi$_2$Te$_3$ and PEDOT, we study the thickness\ndependence of the effective figure of merit and the effective power factor.", "category": "physics_app-ph" }, { "text": "Amorphous Mo-Ta oxide nanotubes for long-term stable Mo oxide based\n supercapacitors: With a large-scale usage of portable electric appliances, a high demand for\nincreasingly high density energy storage devices has emerged. MoO3 has, in\nprinciple, a large potential as negative electrode material in supercapacitive\ndevices, due to high charge densities that can be obtained from its reversible\nredox reactions. Nevertheless, the extremely poor electrochemical stability of\nMoO3 in aqueous electrolytes prevents a practical use in high capacitance\ndevices. In this work, we describe how to overcome this severe stability issue\nby forming amorphous molybdenum oxide/tantalum oxide nanotubes by anodic\noxidation of a Mo-Ta alloy. The presence of a critical amount of Ta-oxide (> 20\nat-%) prevents the electrochemical decay of the MoO3 phase and thus yields an\nextremely high stability. Due to the protection provided by tantalum oxide, no\ncapacitance losses are measureable after 10000 charg-ing/discharging cycles.", "category": "physics_app-ph" }, { "text": "Defect detection and NDE of low-modulus PMMA material using mechanical\n loading and WFT analysis: In present communication, we report our investigations undertaken towards\ndetection of defects and non-destructive evaluation of low-modulus sample of\nPoly Methyl Metha Acrylate (PMMA) material using phase measuring deflectometry\nand windowed Fourier transform (WFT). The slope of the phase provides the\ninformation regarding defects and surface variation of the object. Experimental\nresults conclusively establish the viability of the technique.", "category": "physics_app-ph" }, { "text": "Shaping contactless forces through anomalous acoustic scattering: Waves impart momentum and exert force on obstacles in their path. The\ntransfer of wave momentum is a fundamental mechanism for contactless\nmanipulation, yet the rules of conventional scattering intrinsically limit the\nradiation force based on the shape and the size of the manipulated object.\nHere, we show that this intrinsic limit can be overcome for acoustic waves with\nsubwavelength-structured metasurfaces, where the force becomes controllable by\nthe arrangement of surface features, independent of the object's overall shape\nand size. Harnessing such anomalous metasurface scattering, we demonstrate\ncomplex actuation phenomena: self-guidance, where a metasurface object is\nautonomously guided by an acoustic wave, and contactless pulling, where a\nmetasurface object is pulled by the wave. Our results show that bringing\nmetasurface physics, and its full arsenal of tools, to the domain of mechanical\nmanipulation opens the door to diverse actuation mechanisms that are beyond the\nlimits of traditional wave-matter interactions.", "category": "physics_app-ph" }, { "text": "Freeze cast porous barium titanate for enhanced piezoelectric energy\n harvesting: Energy harvesting is an important developing technology for a new generation\nof self-powered sensor networks. This paper demonstrates the significant\nimprovement in the piezoelectric energy harvesting performance of barium\ntitanate by forming highly aligned porosity using freeze casting. Firstly, a\nfinite element model demonstrating the effect of pore morphology and angle with\nrespect to poling field on the poling behaviour of porous ferroelectrics was\ndeveloped. A second model was then developed to understand the influence of\nmicrostructure-property relationships on the poling behaviour of porous freeze\ncast ferroelectric materials and their resultant piezoelectric and energy\nharvesting properties. To compare with model predictions, porous barium\ntitanate was fabricated using freeze casting to form highly aligned\nmicrostructures with excellent longitudinal piezoelectric strain coefficients,\nd 33. Both model and experimental data indicated that introducing porosity\nprovides a large reduction in the permittivity () of barium titanate, which\nleads to a substantial increase in energy harvesting figure of merit, , with a\nmaximum of 3.79 pm2 N-1 for barium titanate with 45 vol.% porosity, compared to\nonly 1.40 pm2 N-1 for dense barium titanate. Dense and porous barium titanate\nmaterials were then used to harvest energy from a mechanical excitation by\nrectification and storage of the piezoelectric charge on a capacitor. The\nporous barium titanate charged the capacitor to a voltage of 234 mV compared to\n96 mV for the dense material, indicating a 2.4-fold increase that was similar\nto that predicted by the energy harvesting figures of merit.", "category": "physics_app-ph" }, { "text": "Energy exchange between surface plasmon polaritons and CdSe/ZnS quantum\n dots: Evidence is presented for energy exchange between surface plasmon polaritons\n(SPPs) excited in waveguide-coupled Ag/Si3N4/Au structures and CdSe/ZnS quantum\ndot (QD) emitters. The QD dispersion is coated on the surface of Ag/Si3N4/Au\nnanostructure, surface plasmon resonance (SPR) is excited on surface of\nmultilayered structure and the photoluminescence (PL) emission by the QDs is\nmonitored as a function of the evanescent electric field by using\nfixed-detector pump-probe spectroscopy. We observe relatively large shift in\nthe PL emission wavelength (corresponding to 4-5 meV) with accompanying\nelectric field induced quenching (up to 50%) of the emission. Under the\ninfluence of the evanescent field, the PL emission peak splits into two\ncomponents corresponding to two frequencies (Rabi splitting). Computer\nsimulations are used to understand conditions under which Rabi splitting should\noccur.", "category": "physics_app-ph" }, { "text": "Field emission microscopy of carbon nanotube fibers: evaluating and\n interpreting spatial emission: In this work, we quantify field emission properties of cathodes made from\ncarbon nanotube (CNT) fibers. The cathodes were arranged in different\nconfigurations to determine the effect of cathode geometry on the emission\nproperties. Various geometries were investigated including: 1) flat cut fiber\ntip, 2) folded fiber, 3) looped fiber and 4) and fibers wound around a\ncylinder. We employ a custom field emission microscope to quantify I-V\ncharacteristics in combination with laterally-resolved field-dependent electron\nemission area. Additionally we look at the very early emission stages, first\nwhen a CNT fiber is turned on for the first time which is then followed by\nmultiple ramp-up/down. Upon the first turn on, all fibers demonstrated limited\nand discrete emission area. During ramping runs, all CNT fibers underwent\nmultiple (minor and/or major) breakdowns which improved emission properties in\nthat turn-on field decreased, field enhancement factor and emission area both\nincreased. It is proposed that breakdowns are responsible for removing\ninitially undesirable emission sites caused by stray fibers higher than\naverage. This initial breakdown process gives way to a larger emission area\nthat is created when the CNT fiber sub components unfold and align with the\nelectric field. Our results form the basis for careful evaluation of CNT fiber\ncathodes for dc or low frequency pulsed power systems in which large uniform\narea emission is required, or for narrow beam high frequency applications in\nwhich high brightness is a must.", "category": "physics_app-ph" }, { "text": "Abnormal Staebler-Wronski effect of amorphous silicon: Great achievements in last five years, such as record-efficient\namorphous/crystalline silicon heterojunction (SHJ) solar cells and cutting-edge\nperovskite/SHJ tandem solar cells, place hydrogenated amorphous silicon\n(a-Si:H) at the forefront of emerging photovoltaics. Due to the extremely low\ndoping efficiency of trivalent boron (B) in amorphous tetravalent silicon,\nlight harvesting of aforementioned devices are limited by their fill factors\n(FF), which is a direct metric of the charge carrier transport. It is\nchallenging but crucial to develop highly conductive doped a-Si:H for\nminimizing the FF losses. Here we report intensive light soaking can\nefficiently boost the dark conductance of B-doped a-Si:H \"thin\" films, which is\nan abnormal Staebler-Wronski effect. By implementing this abnormal effect to\nSHJ solar cells, we achieve a certificated power conversion efficiency (PCE) of\n25.18% (26.05% on designated area) with FF of 85.42% on a 244.63-cm2 wafer.\nThis PCE is one of the highest reported values for total-area \"top/rear\"\ncontact silicon solar cells. The FF reaches 98.30 per cent of its\nShockley-Queisser limit.", "category": "physics_app-ph" }, { "text": "Towards Topological Protection based millimetre wave devices: Feasibility of Topological Metawaveguides supporting helical propagation in\nthe microwave range has been recently proven. The advantages of unidirectional\npropagation supported by such waveguides however can only be exploited in real\ndevices if topological modes are endowed with the capability to interact within\nthemselves as well as with trivial modes. Here we show a modal launcher to\ninterface a topological metawaveguide with conventional circular waveguides\nwith negligible reflection and we exploit the properties of coupled topological\nmodes to show a proof of concept of a topological contra-directional coupler.", "category": "physics_app-ph" }, { "text": "Applicability of the Debye-Waller damping factor for the determination\n of the line-edge roughness of lamellar gratings: Periodic nanostructures are fundamental elements in optical instrumentation\nas well as basis structures in integrated electronic circuits. Decreasing sizes\nand increasing complexity of nanostructures have made roughness a limiting\nparameter to the performance. Grazing-incidence small-angle X-ray scattering is\na characterization method that is sensitive to three-dimensional structures and\ntheir imperfections. To quantify line-edge roughness, a Debye-Waller factor\n(DWF), which is derived for binary gratings, is usually used. In this work, we\nsystematically analyze the effect of roughness on the diffracted intensities.\nTwo different limits to applying the DWF are found depending on whether or not\nthe roughness is normally distributed.", "category": "physics_app-ph" }, { "text": "Freeze Casting: A Review of Processing, Microstructure and Properties\n via the Open Data Repository, FreezeCasting.net: Freeze-casting produces materials with complex, three-dimensional pore\nstructures which may be tuned during the solidification process. The range of\npotential applications of freeze-cast materials is vast, and includes:\nstructural materials, biomaterials, filtration membranes, pharmaceuticals, and\nfoodstuffs. Fabrication of materials with application-specific microstructures\nis possible via freeze casting, however, the templating process is highly\ncomplex and the underlying principles are only partially understood. Here, we\nreport the creation of a freeze-casting experimental data repository, which\ncontains data extracted from ~800 different freeze-casting papers (as of August\n2017). These data pertain to variables that link processing conditions to\nmicrostructural characteristics, and finally, mechanical properties. The aim of\nthis work is to facilitate broad dissemination of relevant data to\nfreeze-casting researchers, promote better informed experimental design, and\nencourage modeling efforts that relate processing conditions to microstructure\nformation and material properties. An initial, systematic analysis of these\ndata is provided and key processing-structure-property relationships posited in\nthe freeze-casting literature are discussed and tested against the database.\nTools for data visualization and exploration available through the web\ninterface are also provided.", "category": "physics_app-ph" }, { "text": "Gate-controllable electronic trap detection in dielectrics: Gate controllable electronic trap detection method has been demonstrated by\nregulating the gate potential of MIS devices. This method is based on shift of\ncapacitance voltage (CV) curve as well as flatband voltage (VFB) measure in\nless than 10 micro-seconds due to injection or ejection of electrons through\nthe metal gate. Using this method, an electronic trap energy distribution was\nmeasured in the HfO2 dielectric film and it confirms a maximum number of traps\n(Delta_NT) of 1.7x1012 cm-2 corresponding to an energy level (Delta_EIL) of\n0.45 eV above silicon conduction band (Si-ECB). In comparison, ZrO2-based MIS\ndevices showed a broader distribution of electronic traps throughout the band\ngap. However, HfO2 contained more than 60% traps in deep level compared to 50%\nin ZrO2, which establishes the effects of material variation.", "category": "physics_app-ph" }, { "text": "Coefficient of Thermal Expansion Mismatch Induced Stress Calculation for\n Field Assisted Bonding of Silicon to Glass: The residual stress induced in assembly is a common concern in electronic\npackaging. The mismatch in coefficient of thermal expansion between\nborosilicate glass and silicon, upon temperature variation, generates an\ninternal stress state. This affects important characteristics of\nmicroelectromechanical devices or constituent elements. Such as self frequence\nor stiffness. Stresses caused by thermal expansion coefficients mismatch of\nanodically bonded glass and silicon samples are studied in this paper. Stress\ncalculation based on lamination theory is presented. Usage examples of such\ncalculations are described. For bonded silicon and LK-5 glass several results\nof calculations are presented. Stress distribution in bonded silicon and glass\nof several thicknesses is evaluated. Stress distribution in bonded\nglass-silicon-glass structure is evaluated. Bonded silicon surface stress\ndependence of glass to silicon wafer thickness ratio is evaluated. Experimental\nstudy of thermal mismatch stress in glass based on birefringence phenomenon was\nconducted. It's results are presented in this paper. Keywords: anodic bonding,\nfield assisted bonding, thermal expansion, stress.", "category": "physics_app-ph" }, { "text": "Ultra-sensitive graphene membranes for microphone applications: Microphones exploit the motion of suspended membranes to detect sound waves.\nSince the microphone performance can be improved by reducing the thickness and\nmass of its sensing membrane, graphene-based microphones are expected to\noutperform state-of-the-art microelectromechanical (MEMS) microphones and allow\nfurther miniaturization of the device. Here, we present a laser vibrometry\nstudy of the acoustic response of suspended multilayer graphene membranes for\nmicrophone applications. We address performance parameters relevant for\nacoustic sensing, including mechanical sensitivity, limit of detection and\nnonlinear distortion, and discuss the trade-offs and limitations in the design\nof graphene microphones. We demonstrate superior mechanical sensitivities of\nthe graphene membranes, reaching more than 2 orders of magnitude higher\ncompliances than commercial MEMS devices, and report a limit of detection as\nlow as 15 dBSPL, which is 10 - 15 dB lower than that featured by current MEMS\nmicrophones.", "category": "physics_app-ph" }, { "text": "Reduced sensitivity to process, voltage and temperature variations in\n activated perpendicular magnetic tunnel junctions based stochastic devices: True random number generators (TRNGs) are fundamental building blocks for\nmany applications, such as cryptography, Monte Carlo simulations, neuromorphic\ncomputing, and probabilistic computing. While perpendicular magnetic tunnel\njunctions (pMTJs) based on low-barrier magnets (LBMs) are natural sources of\nTRNGs, they tend to suffer from device-to-device variability, low speed, and\ntemperature sensitivity. Instead, medium-barrier magnets (MBMs) operated with\nnanosecond pulses - denoted, stochastic magnetic actuated random transducer\n(SMART) devices - are potentially superior candidates for such applications. We\npresent a systematic analysis of spin-torque-driven switching of MBM-based\npMTJs (Eb ~ 20 - 40 kBT) as a function of pulse duration (1 ps to 1 ms), by\nnumerically solving their macrospin dynamics using a 1-D Fokker-Planck\nequation. We investigate the impact of voltage, temperature, and process\nvariations (MTJ dimensions and material parameters) on the switching\nprobability of the device. Our findings indicate SMART devices activated by\nshort-duration pulses (< 1 ns) are much less sensitive to\nprocess-voltage-temperature (PVT) variations while consuming lower energy (~\nfJ) than the same devices operated with longer pulses. Our results show a path\ntoward building fast, energy-efficient, and robust TRNG hardware units for\nsolving optimization problems.", "category": "physics_app-ph" }, { "text": "Surface modulation of metal-organic frameworks for on-demand\n photochromism in the solid state: Organic photoswitchable molecules have struggled in solid state form to\nfulfill their remarkable potential, in terms of photoswitching performance and\nlong-term stability when compared to their inorganic counterparts. We report\nthe concept of non-electron deficient host's surface with optimal porosity and\nhydrophobicity, as a priori strategy to design photoefficient organic\nsolid-state photochromic materials with outstanding mechanical robustness. When\nexposed to a light stimulus including natural sunlight, the photoswitchable\nnanocomposite changes color promptly and reversibly, in a matter of seconds\nalong with excellent photo-fatigue resistance, which are on a par with\ninorganic photochromes. Exemplars of commercially viable prototypes that are\noptically clear, comprising smart windows, complex photochromic sculptures, and\nself-erasing rewritable devices, were engineered by direct blending with\nresilient polymers; particularly, the use of high-stiffness polymer (> 2 GPa)\nis no longer an insurmountable challenge. Finally, photochromic films with\nanticounterfeiting features could be manufactured through precision inkjet\nprinting of nanocrystals.", "category": "physics_app-ph" }, { "text": "Trade-off Between Antenna Efficiency and Q-Factor: The trade-off between radiation efficiency and antenna bandwidth, expressed\nin terms of Q-factor, for small antennas is formulated as a multi-objective\noptimization problem in current distributions of predefined support. Variants\non the problem are constructed to demonstrate the consequences of requiring a\nself-resonant current as opposed to one tuned by an external reactance. The\nresulting Pareto-optimal sets reveal the relative cost of valuing low radiation\nQ-factor over high efficiency, the cost in efficiency to require a\nself-resonant current, the effects of lossy parasitic loading, and other\ninsights.", "category": "physics_app-ph" }, { "text": "Morphogenetic Design of Self-Organized Correlated Disordered\n Electromagnetic Media: The last decades witnessed the emergence of the field of correlated\ndisordered media, a great challenge offering a large panel of new perspectives\nfor applications in theoretical modelling and material fabrication. The\nefficient design of structures with a controlled level of spatial correlation\nis a central challenge in this field, in a context where existing techniques\ngenerally rely on gradient descent on non-convex functions and on the use of\nstochastic methods to explore vast design spaces more efficiently. In this\nwork, we propose a new generative technique based on Alan Turing's\nmorphogenesis theory for designing correlated disordered materials. Inspired by\nthe structuring of living organisms, this technique relies on the definition of\nsimple local interactions guiding the self-organization of a generated medium.\nThe decentralization of design constraints and the elimination of cost function\nminimization make this approach natively scalable to the design of large\ndomains with controlled levels of disorder. As a validation, the morphogenetic\ngeneration of stealthy hyperuniform disordered structures is exploited to\nreproduce an experiment of isotropic electromagnetic bandgap synthesis in the\nmicrowave range using a low refractive index contrast.", "category": "physics_app-ph" }, { "text": "Self-Aligned van der Waals Heterojunction Diodes and Transistors: A general self-aligned fabrication scheme is reported here for a diverse\nclass of electronic devices based on van der Waals materials and\nheterojunctions. In particular, self-alignment enables the fabrication of\nsource-gated transistors in monolayer MoS2 with near-ideal current saturation\ncharacteristics and channel lengths down to 135 nm. Furthermore, self-alignment\nof van der Waals p-n heterojunction diodes achieves complete electrostatic\ncontrol of both the p-type and n-type constituent semiconductors in a\ndual-gated geometry, resulting in gate-tunable mean and variance of\nanti-ambipolar Gaussian characteristics. Through finite-element device\nsimulations, the operating principles of source-gated transistors and\ndual-gated anti-ambipolar devices are elucidated, thus providing design rules\nfor additional devices that employ self-aligned geometries. For example, the\nversatility of this scheme is demonstrated via contact-doped MoS2 homojunction\ndiodes and mixed-dimensional heterojunctions based on organic semiconductors.\nThe scalability of this approach is also shown by fabricating self-aligned\nshort-channel transistors with sub-diffraction channel lengths in the range of\n150 nm to 800 nm using photolithography on large-area MoS2 films grown by\nchemical vapor deposition. Overall, this self-aligned fabrication method\nrepresents an important step towards the scalable integration of van der Waals\nheterojunction devices into more sophisticated circuits and systems.", "category": "physics_app-ph" }, { "text": "Designing Planar, Ultra-Thin, Broad-Band and Material-Versatile Solar\n Absorbers via Bound-Electron and Exciton Absorption: Ultrathin planar absorbing layers, including semiconductor and metal films,\nand 2D materials, are promising building blocks for solar energy harvesting\ndevices but poor light absorption has been a critical issue. Although\ninterference in ultrathin absorbing layers has been studied to realize near\nperfect absorption at a specific wavelength, achieving high broadband\nabsorption still remains challenging. Here, we both theoretically and\nexperimentally demonstrated a method to tune not only reflection phase shift\nbut also electromagnetic energy dissipation to design broadband solar absorber\nwith simple planar structure consisting of an ultrathin absorbing layer\nseparated from the metallic substrate by a transparent layer. We explicitly\nidentified by deriving a new formulism that the absorbing material with\nrefractive index proportional to the wavelength as well as extinction\ncoefficient independent of the wavelength, is the ideal building block to\ncreate ultrathin planar broadband absorbers. To demonstrate the general\nstrategy for naturally available absorbing materials in both high-loss\n(refractory metals) and weak-absorption (2D materials) regimes, we leveraged\nthe bound-electron interband transition with a broad Lorentz oscillator peak to\ndesign a solar thermal absorber based on a ultrathin Cr layer; and leveraged\nthe strong exciton attributed to the spin-orbit coupling for the spectrum near\nthe band edge, and the bound-electron interband transition for shorter\nwavelengths, to design a solar photovoltaic absorber based on a atomically thin\nMoS2 layer. Furthermore, our designed ultrathin broadband solar absorbers with\nplanar structures have comparable absorption properties compared to the\nabsorbers with nanopatterns. Our proposed design strategies pave the way to\nnovel nanometer thick energy harvesting and optoelectronic devices with simple\nplanar structures.", "category": "physics_app-ph" }, { "text": "Anisotropic model with truncated linear dispersion for lattice and\n interfacial thermal transport in layered materials: Recently, an anisotropic Debye model [Dames et al., Physical Review B 87, 12\n(2013)] was proposed for calculations of the interfacial thermal conductance\nand the minimum thermal conductivity of graphite-like layered materials.\nDespite successes of the model in explaining heat transport mechanisms in\nlayered materials (e.g., phonon focusing in highly anisotropic materials), the\nanisotropic Debye model assumes a phonon dispersion with unrealistic speeds of\nsounds especially for the flexural (ZA) phonons and overestimated cutoffs for\nall phonon branches. The deficiencies lead to substantially underestimated\nphonon irradiation for low-frequency phonons. Here, we develop an anisotropic\nmodel with truncated linear dispersion that resembles the real phonon\ndispersion, using speeds of sounds derived from elastic constants and cutoff\nfrequencies derived from Brillouin zone boundaries. We also employ a piecewise\nlinear function for the ZA phonons. Our model correctly calculates the phonon\nirradiation over a wide temperature range, verifying the accuracy of our\nmodel.We compare calculations of our and the Dames models to measurements of\nthermal conductivity of graphite and thermal conductance of metal/graphite\ninterfaces, and find that the two models differ significantly for heat\ntransport across the basal planes in graphite even at high temperatures. Our\nwork thus provides a convenient analytical tool to study the phonon transport\nproperties in layered materials.", "category": "physics_app-ph" }, { "text": "Modeling of Radiation-Induced Defect Recovery in 3C-SiC Under High Field\n Bias Conditions: In this work, the implications of high field bias conditions in\nradiation-induced defect recovery in 3C-SiC crystals is studied. It is well\nknown that transient heating effects (or thermal spikes) occur when energetic\nswift heavy ions (SHIs) deposit energy to the surrounding medium via\nionization. Here, we explore the dynamics of this transient event under high\nbackground electric fields in 3C-SiC, which is what occurs when an ion strike\ncoincides with field-sensitive volumes. In this study, we use the Ensemble\nMonte Carlo method to quantify how the energy deposition of the ionized regions\nchange in response to high background electric fields. Subsequently, we study\nthe relationship between the radiation-induced thermal spike and defect\nrecovery using molecular dynamics simulations. We find that field strengths\nbelow the critical breakdown of wide bandgap devices are sufficient to\nexacerbate the localized heating, which subsequently enhances the defect\nrecovery effect. This work is beneficial for 3C-SiC electronics and materials\nused in high radiation environments.", "category": "physics_app-ph" }, { "text": "Broadband Circular-to-Linear Polarization Conversion of Terahertz Waves\n Using Self-Complementary Metasurfaces: In this work, we theoretically and experimentally study the conversion from a\ncircularly polarized plane electromagnetic wave into a linearly polarized\ntransmitted one using anisotropic self-complementary metasurfaces. For this\npurpose, a metasurface design operable at sub-terahertz frequencies is proposed\nand investigated in the range of 230-540 GHz. The metasurface is composed of\nalternating complementary rectangular patches and apertures patterned in an\naluminum layer deposited on a thin polypropylene film. The term\n\\textit{self-complementary} implies that the pattern is invariant with respect\nto its inversion (with some translation). Our study shows that the\ntranslational symmetry of the metasurface results in unusual and useful\nelectromagnetic properties under illumination with circularly polarized\nradiation beams. In particular, alongside with broadband circular-to-linear\nconversion, the transmitted wave exhibits a frequency independent magnitude,\nwhile its polarization angle gradually changes with frequency that paves the\nway for new beam-splitting applications.", "category": "physics_app-ph" }, { "text": "Fully Automatic In-Situ Reconfiguration of RF Photonic Filters in a\n CMOS-Compatible Silicon Photonic Process: Automatic reconfiguration of optical filters is the key to novel flexible RF\nphotonic receivers and Software Defined Radios (SDRs). Although silicon\nphotonics (SiP) is a promising technology platform to realize such receivers,\nprocess variations and lack of in-situ tuning capability limits the adoption of\nSiP filters in widely-tunable RF photonic receivers. To address this issue,\nthis work presents a first `in-situ' automatic reconfiguration algorithm and\ndemonstrates a software configurable integrated optical filter that can be\nreconfigured on-the-fly based on user specifications. The presented\nreconfiguration scheme avoids the use of expensive and bulky equipment such as\nOptical Vector Network Analyzer (OVNA), does not use simulation data for\nreconfiguration, reduces the total number of thermo-optic tuning elements\nrequired and eliminates several time consuming configuration steps as in the\nprior art. This makes this filter ideal in a real world scenario where user\nspecifies the filter center frequency, bandwidth, required rejection & filter\ntype (Butterworth, Chebyshev, etc.) and the filter is automatically configured\nregardless of process, voltage & temperature (PVT) variations. We fabricated\nour design in AIM Photonics' Active SiP process and have demonstrated our\nreconfiguration algorithm for a second-order filter with 3dB bandwidth of 3\nGHz, 2.2 dB insertion loss and >30 dB out-of-band rejection using only two\nreference laser wavelength settings. Since the filter photonic integrated\ncircuit (PIC) is fabricated using a CMOS-compatible SiP foundry, the design is\nmanufacturable with repeatable and scalable performance suited for its\nintegration with electronics to realize complex chip-scale RF photonic systems.", "category": "physics_app-ph" }, { "text": "Suppression of Brillouin oscillation in transparent free-standing\n diamond thin films in picosecond ultrasound: Brillouin oscillation appears in picosecond ultrasonics for a transparent\nspecimen because of backward light scattering by moving strain pulse. Its\namplitude is comparable with those of other responses, such as pulse-echo\nsignals and through-thickness resonance, obscuring these\nnon-Brillouin-oscillation responses. We here find that Brillouin oscillation\ncan be suppressed in a transparent free-standing film by coating both sides\nwith metallic thin film of appropriate thickness and that this peculiar\nbehavior is caused by strain pulses generated on both sides with a slight phase\ndifference. This phenomenon allowed us to fabricate a\nBrillouin-oscillation-free diamond free-standing film, which showed high\ncapability for sensor applications.", "category": "physics_app-ph" }, { "text": "InGaAsP/InP uni-travelling-carrier photodiode at 1064nm wavelength: High-speed back-illuminated uni-traveling-carrier photodiodes at 1064nm were\ndemonstrated grown on InP with 3dB bandwidth of 17.8 GHz at -5 V bias, using\nInGaAsP as absorption layer. PDs with 40um diameter deliver RF output power\nlevels as high as 19.5 dBm at 13 GHz. This structure can achieve low dark\ncurrent density of 10 nA per cm2 at -5V bias and quantum efficiency of 45.2% at\n1064nm. An analytical model based on S-parameter fitting was built to extract\nparameter to access the bandwidth limiting factors.", "category": "physics_app-ph" }, { "text": "Reliability comparison of AlGaN/GaN HEMTs with different carbon doping\n concentration: The reliability of AlGaN/GaN HEMTs adopting Fe and C co-doping, with high and\nlow carbon doping concentration was investigated by means of different stress\ntests. Firstly, DC and pulsed I-V characterization at room temperature are\ndiscussed, then drain step stress tests at different gate voltages are\ncompared, afterwards, the constant stress at different bias points are\ndiscussed. Results show that the high C HEMTs showed reduced DIBL, smaller\nleakage current, as well as decreased electric field, leading to an improved\nrobustness during on-state stress testing, with respect to the reference ones.\nFailure modes during constant voltage stress consists in a decrease of drain\ncurrent and transconductance, accelerated by temperature and electric field.", "category": "physics_app-ph" }, { "text": "Modeling the Generic Breakthrough Curve for Adsorption Process: This work is aimed at understanding the basic principles of adsorption\nprocess in great details as adsorptive separation process has broad\napplications in the industry. To this end, a simple mathematical model has been\nused to describe transient fixed bed physical adsorption process. Governing\nequations are solved numerically to obtain breakthrough curves for single\ncomponent and multi-component monolayer adsorption. Desorption of a saturated\nbed by an inert fluid is also considered. A full parametric study is performed\nto analyze the effects of different parameters such as bed length, velocity,\ndiffusivity, particle radius and isotherm properties on the nature of the\nbreakthrough curve. Analysis of these results led to the development of the\ngeneric breakthrough curve for a single component monolayer adsorption which\nwill enable us to tell the nature of breakthrough curve for different process\nparameters without recourse to the numerical simulation or experiment. Thus\nthis study will be of great interest in the industrial separation process.", "category": "physics_app-ph" }, { "text": "Irradiation of Nanostrained Monolayer WSe$_2$ for Site-Controlled\n Single-Photon Emission up to 150 K: Quantum-dot-like WSe$_2$ single-photon emitters have become a promising\nplatform for future on-chip scalable quantum light sources with unique\nadvantages over existing technologies, notably the potential for site-specific\nengineering. However, the required cryogenic temperatures for the functionality\nof these sources have been an inhibitor of their full potential. Existing\nstrain engineering methods face fundamental challenges in extending the working\ntemperature while maintaining the emitter's fabrication yield and purity. In\nthis work, we demonstrate a novel method of designing site-specific\nsingle-photon emitters in atomically thin WSe$_2$ with near-unity yield\nutilizing independent and simultaneous strain engineering via nanoscale\nstressors and defect engineering via electron-beam irradiation. Many of these\nemitters exhibit exciton-biexciton cascaded emission, purities above 95%, and\nworking temperatures extending up to 150 K, which is the highest observed in\nvan der Waals semiconductor single-photon emitters without Purcell enhancement.\nThis methodology, coupled with possible plasmonic or optical micro-cavity\nintegration, potentially furthers the realization of future scalable,\nroom-temperature, and high-quality van der Waals quantum light sources.", "category": "physics_app-ph" }, { "text": "Reconfigurable Enhancement of Actuation Forces by Engineered Losses in\n non-Hermitian Metamaterials: While boosting signals with amplification mechanisms is a well established\napproach, attenuation mechanisms are typically considered an anathema because\nthey degrade the efficiency of the structures employed to perform useful\noperations on these signals. An emerging alternate viewpoint promotes losses as\na novel design element by utilizing the notion of exceptional point\ndegeneracies (EPDs) points in parameter space where the eigenvalues of the\nunderlying system and the associated eigenvectors simultaneously coalesce.\nHere, we demonstrate a direct consequence of such eigenbasis collapse in\nelastodynamics, an unusual enhancement of actuation force by a judiciously\ndesigned non-Hermitian metamaterial supporting an EPD that is coupled to an\nactuation source. Intriguingly, the EPD enables this enhancement while\nmaintaining a constant signal quality. Our work constitutes a\nproof-of-principle design which can promote a new class of reconfigurable\nnano-indenters and robotic-actuators. Importantly, it reveals the ramifications\nof non-Hermiticity in boosting the Purcell emissivity enhancement factor beyond\nits expected value, which can guide the design of metamaterials with enhanced\nemission that does not deteriorate signal quality for mechanical, acoustic,\noptical, and photonic applications.", "category": "physics_app-ph" }, { "text": "Limitation of simple np-n tunnel junction based LEDs grown by MOVPE: We show evidence that tunnel junctions (TJs) in GaN grown by metal-organic\nvapor phase epitaxy are dominated by trap-assisted (Poole-Frenkel) tunneling.\nThis stems from observations of the careful optimized doping for the TJs.\nEspecially the p$^{++}$ and the n$^{++}$ layers are far from ideal. The\nn$^{++}$ layer induces 3D growth, which can be seen by a rising oxygen signal\nin Secondary Ions Mass Spectroscopy (SIMS). Furthermore, Mg segregation\nobserved by SIMS indicates a depletion region of more than 10 nm. Still, we\ncould realize TJ based LEDs with a low penalty voltage of 1.1 V and a specific\ndifferential resistance of about 10$^{-2}$ $\\Omega$.cm$^2$ at 20 mA without\nusing an InGaN interlayer.", "category": "physics_app-ph" }, { "text": "Electro-opto-mechanical radio-frequency oscillator driven by guided\n acoustic waves in standard single-mode fiber: An opto-electronic radio-frequency oscillator that is based on forward\nscattering by the guided acoustic modes of a standard single-mode optical fiber\nis proposed and demonstrated. An optical pump wave is used to stimulate\nnarrowband, resonant guided acoustic modes, which introduce phase modulation to\na co-propagating optical probe wave. The phase modulation is converted to an\nintensity signal at the output of a Sagnac interferometer loop. The intensity\nwaveform is detected, amplified and driven back to modulate the optical pump.\nOscillations are achieved at a frequency of 319 MHz, which matches the\nresonance of the acoustic mode that provides the largest phase modulation of\nthe probe wave. Oscillations at the frequencies of competing acoustic modes are\nsuppressed by at least 40 dB. The linewidth of the acoustic resonance is\nsufficiently narrow to provide oscillations at a single longitudinal mode of\nthe hybrid cavity. Competing longitudinal modes are suppressed by at least 38\ndB as well. Unlike other opto-electronic oscillators, no radio-frequency\nfiltering is required within the hybrid cavity. The frequency of oscillations\nis entirely determined by the fiber opto-mechanics.", "category": "physics_app-ph" }, { "text": "Method for Extracting the Equivalent Admittance from Time-Varying\n Metasurfaces and Its Application to Self-Tuned Spatiotemporal Wave\n Manipulation: With their self-tuned time-varying responses, waveform-selective metasurfaces\nembedded with nonlinear electronics have shown fascinating applications,\nincluding distinguishing different electromagnetic waves depending on the pulse\nwidth. However, thus far they have only been realized with a spatially\nhomogeneous scattering profile. Here, by modeling a metasurface as time-varying\nadmittance sheets, we provide an analytical calculation method to predict the\nmetasurface time-domain responses. This allows derivation of design\nspecifications in the form of equivalent sheet admittance, which is useful in\nsynthesizing a metasurface with spatiotemporal control, such as to realize a\nmetasurface with prescribed time-dependent diffraction characteristics. As an\nexample, based on the proposed equivalent admittance sheet modeling, we\nsynthesize a waveform-selective Fresnel zone plate with variable focal length\ndepending on the incoming pulse width. The proposed synthesis method of\npulse-width-dependent metasurfaces may be extended to designing metasurfaces\nwith more complex spatiotemporal wave manipulation, benefiting applications\nsuch as sensing, wireless communications and signal processing.", "category": "physics_app-ph" }, { "text": "Spectrum Cascade Bloch Oscillations in Temporally Modulated Acoustics: Bloch oscillations (BOs) refer to a periodically oscillatory motion of\nparticle in lattice systems driven by a constant force. By temporally\nmodulating acoustic waveguides, BOs can be generalized from spatial to\nfrequency domain, opening new possibilities for spectrum manipulations. The\nmodulation can induce mode transitions in the waveguide band and form an\nartificial frequency lattice, with the mismatched wave vector during\ntransitions acting as a constant force that drives frequency Bloch oscillations\n(FBOs). Furthermore, the modulation phase accompanying transitions serves as a\ngauge potential that controls the initial oscillation phase, providing an\nadditional degree of freedom to tailor FBOs. We report that multiple FBOs with\njudiciously designed oscillation phases can be further cascaded to realize\nacoustic spectrum self-imaging, unidirectional transduction and bandwidth\nengineering. The study proposes the concept of FBOs in acoustic systems and\nfunctionalizes its cascade configurations for advanced control of sound\nspectrum. This paradigm may find versatile applications in underwater secure\ncommunication, voice encryption and signal processing.", "category": "physics_app-ph" }, { "text": "Enhanced tunability in ferroelectric composites through local field\n enhancement and the effect of disorder: We investigate numerically the homogenized permittivities of composites made\nof low index dielectric inclusions in a ferroelectric matrix under a static\nelectric field. A refined model is used to take into account the coupling\nbetween the electrostatic problem and the electric field dependent permittivity\nof the ferroelectric material, leading to a local field enhancement and\npermittivity change in the ferroelectric. Periodic and pseudo-random structures\nin two dimensions are investigated and we compute the effective permittivity,\nlosses, electrically induced anisotropy and tunability of those metamaterials.\nWe show that the tunability of such composites might be substantially enhanced\nin the periodic case, whereas introducing disorder in the microstructure weaken\nthe effect of enhanced local permittivity change. Our results may be useful to\nguide the synthesis of novel composite ceramics with improved characteristics\nfor controllable microwave devices.", "category": "physics_app-ph" }, { "text": "The dynamic expansion of positive leaders observed using Mach-Zehnder\n interferometry in a 1-m air gap: The leader plays an important role in long-air-gap discharges. In this paper,\nMach-Zehnder interferometry and a high-speed video camera were used to observe\nthe dynamic expansion process of positive leaders near the anode in a 1 m air\ngap. The leader diameters under lightning and switching impulse are obtained\nthrough the analysis of interference fringes. The influences of the applied\nvoltage, including the amplitude and the front time, as well as the electrode\nsizes on leader expansion are obtained and analysed. For a 0.5-cm-diameter cone\nelectrode, when the applied voltage amplitudes are 330-419 kV, the diameters of\nthe leaders are 1.5-2.5 mm at time scales of less than 195 {\\mu}s, and the\ndiameters increase as the voltage rises. The diameters of the leaders are\nlarger and the expansion rates are higher for shorter front times. The average\nexpansion rates are 72.30-9.54, 28.09-5.05, 14.38-3.02 and 5.73-1.44 m/s for\nfront times of 1.2, 40, 100 and 250 {\\mu}s for a 0.5-cm-diameter cone\nelectrode. A larger electrode size leads to a wider diameter. A numerical model\nwas employed to analyse the expansion of the leaders, and the calculated\nresults are in good agreement with the experimental data. Based on the model,\nthe mechanism underlying the leader expansion is discussed in detail.", "category": "physics_app-ph" }, { "text": "Polarization-independent reconfigurable frequency selective\n rasorber/absorber with low insertion loss: A polarization-independent reconfigurable frequency selective rasorber\n(FSR)/absorber with low insertion loss based on diodes is proposed in this\npaper. The presented structure consists of a lossy layer based on square loops\nand a bandpass frequency-selective surface. These two layers are separated by\nan air layer. Each layer has an embedded bias network that provides the bias\nvoltage to the diodes through metallic via. This configuration can avoid\nundesirable effects associated with the additional biasing wire. When the\ndiodes are in off-state, the structure is in FSR mode and exhibits a\ntransmission window at 4.28GHz with only 0.69dB insertion loss (IL) within the\nabsorption bands. While diodes are in on-state and the structure switches to\nabsorber mode, it achieves perfect absorption with absorptivity of over 90%\nranging from 2.8 to 5.2 GHz. An equivalent circuit model (ECM) is developed to\nanalyse the physical mechanism of the structure. A prototype of the proposed\narchitecture is fabricated and measured, where reasonable agreements between\nsimulations and measurements are observed, verifying the effectiveness of this\ndesign.", "category": "physics_app-ph" }, { "text": "Plasticity and damage mechanisms in Ti-6Al-4V printed with selective\n laser melting: The ability to create complex geometries with tailored material properties\nhas brought interest in using additive manufacturing (AM) techniques in various\nindustrial applications. However, the complex relationship between AM process\nparameters, microstructure, and resultant properties of metals needs to be\nfully understood for the widespread use of metal AM. In this study, selective\nlaser melting is used to print Ti-6Al-4V. In-situ tensile tests with concurrent\ndetailed microstructural analysis using electron backscatter diffraction,\nelectron channeling contrast imaging, and digital image correlation are\nperformed to understand the damage mechanism and its relation to the\nmicrostructure. Our results show that the as-printed part develops a\nhierarchical microstructures, consisting of primary, secondary, and tertiary\n{\\alpha}^' martensite. This hierarchical structure is formed as a result of\ncyclic heat treatment during the course of selective laser melting. Upon\ndeformation, strain localization within primary {\\alpha}^' martensite results\nin microscopic ductile micro-void formation and coalescence, as well as\nmacroscopic brittle fracture. In addition to localization inside primary\n{\\alpha}^', surface steps at the boundaries of these high aspect ratio grains\nare formed which reveal the contribution of interfacial plasticity to the\noverall deformation of the material.", "category": "physics_app-ph" }, { "text": "Large colloidal probes for atomic force microscopy: fabrication and\n calibration issues: Atomic force microscopy (AFM) is a powerful tool to investigate interaction\nforces at the micro and nanoscale. Cantilever stiffness, dimensions and\ngeometry of the tip can be chosen according to the requirements of the specific\napplication, in terms of spatial resolution and force sensitivity. Colloidal\nprobes (CPs), obtained by attaching a spherical particle to a tipless (TL)\ncantilever, offer several advantages for accurate force measurements: tunable\nand well-characterisable radius; higher averaging capabilities (at the expense\nof spatial resolution) and sensitivity to weak interactions; a well-defined\ninteraction geometry (sphere on flat), which allows accurate and reliable data\nfitting by means of analytical models. The dynamics of standard AFM probes has\nbeen widely investigated, and protocols have been developed for the calibration\nof the cantilever spring constant. Nevertheless the dynamics of CPs, and in\nparticular of large CPs, with radius well above 10 um and mass comparable, or\nlarger, than the cantilever mass, is at present still poorly characterised.\nHere we describe the fabrication and calibration of (large) CPs. We describe\nand discuss the peculiar dynamical behaviour of CPs, and present an alternative\nprotocol for the accurate calibration of the spring constant.", "category": "physics_app-ph" }, { "text": "Novel microfluidic strategy for the production of sodium alginate fibers\n with regular inclusions at very high throughput: Scalable technologies for the production of bio-compatible complex\nmicrofibers with controllable size and composition at competitively high\nthroughput are urgently needed in order to meet the growing demand for such\nmicrostructures in pharmaceutical or biomedical applications. Here, we\nintroduce a new in-air microfluidic strategy with throughput of > 1400 ml/h\n(corresponding to > 17000 m fiber per h). The microfibers of uniform diameter\nhave regular inclusions, which can potentially be used for encapsulating cells\ninto a protecting and nutrient environment, or for finely tuning the release of\nvarious actives at individualized doses. With the help of a newly developed\nprototype, we test seven different liquid combinations and obtain seven types\nof fibers, whose \"dry\" diameter range between 73um and 141um. The principle of\nour approach is to solidify the complex liquid structures generated by the\ncontrolled collisions of a drop stream with a continuous liquid jet, in air,\nvia ionic crosslinking. After the stream of water-based droplets, which\nconstitute the inclusions, collides in-air with the alginate-based jet (jet 1),\nthe generated \"drops-in-jet\" compound is brought in contact with a second jet\n(jet 2) containing divalent strontium or calcium cations to initiate the\nsolidification. Finally, the fibers are collected via a horizontal spinning\nplate, let to dry, i.e. to fully equilibrate under controlled conditions, and\ncharacterized by their elongation at break and Young's modulus.", "category": "physics_app-ph" }, { "text": "Aluminum lactate role in improving hydration and drying behavior of\n MgO-bonded refractory castables: Developing MgO-bonded castables is still an important subject for refractory\nproducers and end-users based on the expansive character of the in-situ Mg(OH)2\nformation. Considering that magnesia undergoes hydration when exposed to water\nand the generated hydrated phase needs to be properly accommodated in the\nresulting microstructure to inhibit the generation of cracks, it is very\nimportant to find out alternatives to control the MgO hydration reaction rate.\nThis research investigated the use of aluminum lactate (AL) as a likely\nadditive to change the hydration and drying behavior of vibratable castables\nbonded with different MgO sources (dead burnt, caustic or fumed one). Firstly,\nXRD, TG and DSC measurements of magnesia-based aqueous suspensions were\nevaluated to identify the AL effect on changing the hydration reaction products\nduring the curing and drying steps. After that, Al2O3-MgO refractories were\nprepared and their flowability, curing behavior, cold flexural strength,\napparent porosity, permeability and explosion resistance were evaluated. The\nresults indicated that, instead of Mg(OH)2, Mg6Al2(OH)16(OH)2.4.5H2O/\nMg6Al2(OH)16(CO3).4H2O was the main hydrated phase identified in the\nAL-containing compositions. Due to this change in the hydration behavior of the\nrefractories, the mixtures prepared with dead-burnt or magnesia fumes plus\norganic salt presented a longer setting time. Besides that, crack-free samples\nwith improved permeability and green mechanical strength could be obtained when\nadding 0.5 wt.% or 1.0 wt.% of aluminum lactate to the tested castable\ncompositions. Consequently, 1.0 wt.% of the selected additive favored the\ndesign of refractories with enhanced properties and greater spalling\nresistance, as no explosion could be observed even when subjecting the prepared\nsamples to severe heating conditions (20C/min).", "category": "physics_app-ph" }, { "text": "Tunable Anisotropic Thermal Transport in Super-Aligned Carbon Nanotube\n Films: Super-aligned carbon nanotube (CNT) films have intriguing anisotropic thermal\ntransport properties due to the anisotropic nature of individual nanotubes and\nthe important role of nanotube alignment. However, the relationship between the\nalignment and the anisotropic thermal conductivities was not well understood\ndue to the challenges in both the preparation of high-quality super-aligned CNT\nfilm samples and the thermal characterization of such highly anisotropic and\nporous thin films. Here, super-aligned CNT films with different alignment\nconfigurations are designed and their anisotropic thermal conductivities are\nmeasured using time-domain thermoreflectance (TDTR) with an elliptical-beam\napproach. The results suggest that the alignment configuration could tune the\ncross-plane thermal conductivity k_z from 6.4 to 1.5 W/mK and the in-plane\nanisotropic ratio from 1.2 to 13.5. This work confirms the important role of\nCNT alignment in tuning the thermal transport properties of super-aligned CNT\nfilms and provides an efficient way to design thermally anisotropic films for\nthermal management.", "category": "physics_app-ph" }, { "text": "Photochemical Upconversion Light Emitting Diode (LED): Theory of Triplet\n Annihilation Enhanced by a Cavity: Artificial lighting is a widespread technology which consumes large amounts\nof energy. Triplet-triplet annihilation photochemical upconversion is a method\nof converting light to a higher frequency. Here, we show theoretically that\nphotochemical upconversion can be applied to Watt-scale lighting, with\nperformance closely approaching the 50% quantum yield upper limit. We describe\nthe dynamic equilibrium of an efficient device consisting of an LED, an\nupconverting material, and an optical cavity from optical and thermal\nperspectives.", "category": "physics_app-ph" }, { "text": "Conductive Paintable 2D Layered MoS2 Inks: Conductive and paintable inks of 2D layered MoS2 with aspect ratio-dependent\nconductivity are demonstrated. Using ultrasonically assisted\nsolvent-exfoliation of MoS2, high concentration 2D and few-layer suspensions\nbecome inks that provide coherent films when painted. Conductivity of paintable\n2D MoS2 inks can be modulated by length and width, where the conductivity is\nlinked to the painting direction. Reducing the painted film width, increases\nconductivity for similar length, and the films conductivity is aspect\nratio-dependent. Inks of solvent-exfoliated 2D MoS2 can be painted without\npolymeric additives.", "category": "physics_app-ph" }, { "text": "Ripple formation and its effect on the multi-scale microstructure of\n Directed Energy Deposition (DED)-printed 316L components: An experimental study is presented to characterize the ripple formations in\nthe directed energy deposition (DED) process and study the influence of the\nripples on the heterogenous microstructure in the scan direction of a\nDED-printed 316L components. While considerable studies on ripple formations\nexist in the welding literature, these formations in DED process have not\nreceived much attention. Also, little prior efforts exist on the microstructure\nalong the scan direction (or the scan surface) as compared with the build\ndirection. Experiments consisted of printing 10 mm x 10 mm x 10 mm cubical\ncomponents on a Optomec LENS 500 Hybrid Machine Tool under different laser\npower, scan speed and dwell time combinations, chosen according to a Latin\nhypercube design. The surface of the scan face of the prints were finished to\nan Ra < 30 nm, and etched with Aqua regia for 90 sec. An optical microscope was\nemployed to observe the microstructure at 4 difference scales. The studies\nsuggest a significant influence of ripple formations as well as the scan width\non the solidification front, the dendritic patterns as well as the heterogenous\nmicrostructure.", "category": "physics_app-ph" }, { "text": "A Shock-Optimized SECE Integrated Circuit: This paper presents a fully integrated, self-starting shock-optimized\nSynchronous Electric Charge Extraction (SECE) interface for piezoelectric\nharvesters (PEHs). After introducing a model of the electromechanical system\nunder shocks, we prove that the SECE is the most appropriate electrical\ninterface to maximize the harvested energy from our PEH. The proposed interface\nis then presented, both at system-and transistor-levels. Thanks to a dedicated\nsequencing, its quiescent current is as low as 30nA. This makes the proposed\ninterface efficient even under time-spaced shocks occurring at sporadic and\nunpredictable rates. The circuit is for instance able to maintain its\nself-powered operation while harvesting very small shocks of 8uJ happening\nevery 100 seconds. Our chip was fabricated in CMOS 40nm technology, and\noccupies a 0.55mm^2 core area. The measured maximum electrical efficiency under\nshocks reaches 91%. Under shocks, the harvested energy by the proposed\nshock-optimized SECE interface is 4.2 times higher than using a standard energy\nharvesting circuit, leading to the best shock FoM among prior art.", "category": "physics_app-ph" }, { "text": "Stoichiometric Lithium Niobate Crystals: Towards Identifiable Wireless\n Surface Acoustic Wave Sensors Operable up to 600$^\\circ$C: Wireless surface acoustic wave (SAW) sensors constitute a promising solution\nto some unsolved industrial sensing issues taking place at high temperatures.\nCurrently, this technology enables wireless measurements up to 600-700$^\\circ$C\nat best. However, the applicability of such sensors remains incomplete since\nthey do not allow identification above 400$^\\circ$C. The latter would require\nthe use of a piezoelectric substrate providing a large electromechanical\ncoupling coefficient K 2 , while being stable at high temperature. In this\nletter, we investigate the potentiality of stoichiometric lithium niobate (sLN)\ncrystals for such purpose. Raman spectroscopy and X-ray diffraction attest that\nsLN crystals withstand high temperatures up to 800$^\\circ$C, at least for\nseveral days. In situ measurements of sLN-based SAW resonators conducted up to\n600$^\\circ$C show that the K 2 of these crystals remains high and stable\nthroughout the whole experiment, which is very promising for the future\nachievement of identifiable wireless high-temperature SAW sensors.", "category": "physics_app-ph" }, { "text": "Modeling Electrical Switching of Nonvolatile Phase-Change Integrated\n Nanophotonic Structures with Graphene Heaters: Progress in integrated nanophotonics has enabled large-scale programmable\nphotonic integrated circuits (PICs) for general-purpose electronic-photonic\nsystems on a chip. Relying on the weak, volatile thermo-optic or electro-optic\neffects, such systems usually exhibit limited reconfigurability along with high\nenergy consumption and large footprints. These challenges can be addressed by\nresorting to chalcogenide phase-change materials (PCMs) such as Ge2Sb2Te5 (GST)\nthat provide substantial optical contrast in a self-holding fashion upon phase\ntransitions. However, current PCM-based integrated photonic applications are\nlimited to single devices or simple PICs due to the poor scalability of the\noptical or electrical self-heating actuation approaches. Thermal-conduction\nheating via external electrical heaters, instead, allows large-scale\nintegration and large-area switching, but fast and energy-efficient electrical\ncontrol is yet to show. Here, we model electrical switching of GST-clad\nintegrated nanophotonic structures with graphene heaters based on the\nprogrammable GST-on-silicon platform. Thanks to the ultra-low heat capacity and\nhigh in-plane thermal conductivity of graphene, the proposed structures exhibit\na high switching speed of ~80 MHz and high energy efficiency of 19.2 aJ/nm^3\n(6.6 aJ/nm^3) for crystallization (amorphization) while achieving complete\nphase transitions to ensure strong attenuation (~6.46 dB/micron) and optical\nphase (~0.28 dB/micron at 1550 nm) modulation. Compared with indium tin oxide\nand silicon p-i-n heaters, the structures with graphene heaters display two\norders of magnitude higher figure of merits for heating and overall\nperformance. Our work facilitates the analysis and understanding of the\nthermal-conduction heating-enabled phase transitions on PICs and supports the\ndevelopment of the future large-scale PCM-based electronic-photonic systems.", "category": "physics_app-ph" }, { "text": "Eliminating the Electric Field Response in a Perovskite Heterojunction\n Solar Cell to Improve Operational Stability: Intrinsic and extrinsic ion migration is a very large threat to the\noperational stability of perovskite solar cells and is difficult to completely\neliminate due to the low activation energy of ion migration and the existence\nof internal electric field. We propose a heterojunction route to help suppress\nion migration, thus improving the operational stability of the cell from the\nperspective of eliminating the electric field response in the perovskite\nabsorber. A heavily doped p-type (p+) thin layer semiconductor is introduced\nbetween the electron transporting layer (ETL) and perovskite absorber. The\nheterojunction charge depletion and electric field are limited to the ETL and\np+ layers, while the perovskite absorber and hole transporting layer remain\nneutral. The p+ layer has a variety of candidate materials and is tolerant of\ndefect density and carrier mobility, which makes this heterojunction route\nhighly feasible and promising for use in practical applications.", "category": "physics_app-ph" }, { "text": "Transient Propagation and Scattering of Quasi-Rayleigh Waves in Plates:\n Quantitative comparison between Pulsed TV-Holography Measurements and\n FC(Gram) elastodynamic simulations: We study the scattering of transient, high-frequency, narrow-band\nquasi-Rayleigh elastic waves by through-thickness holes in aluminum plates, in\nthe framework of ultrasonic nondestructive testing (NDT) based on full-field\noptical detection. Sequences of the instantaneous two-dimensional (2-D)\nout-of-plane displacement scattering maps are measured with a self-developed\nPTVH system. The corresponding simulated sequences are obtained by means of an\nFC(Gram) elastodynamic solver introduced recently, which implements a full\nthree-dimensional (3D) vector formulation of the direct linear-elasticity\nscattering problem. A detailed quantitative comparison between these\nexperimental and numerical sequences, which is presented here for the first\ntime, shows very good agreement both in the amplitude and the phase of the\nacoustic field in the forward, lateral and backscattering areas. It is thus\nsuggested that the combination of the PTVH system and the FC(Gram)\nelastodynamic solver provides an effective ultrasonic inspection tool for\nplate-like structures, with a significant potential for ultrasonic NDT\napplications.", "category": "physics_app-ph" }, { "text": "Metal-oxide interface reactions and their effect on integrated\n resistive/threshold switching in NbOx: Reactive metal electrodes (Nb, Ti, Cr, Ta, and Hf) are shown to play an\nimportant role in controlling the volatile switching characteristics of\nmetal/Nb2O5/Pt devices. In particular, devices are shown to exhibit stable\nthreshold switching under negative bias but to have a response under positive\nbias that depends on the choice of metal. Three distinct responses are\nhighlighted: Devices with Nb and Ti top electrodes are shown to exhibit stable\nthreshold switching with symmetric characteristics for both positive and\nnegative polarities; devices with Cr top electrodes are shown to exhibit stable\nthreshold switching but with asymmetric hysteresis windows under positive and\nnegative polarities; and devices with Ta and Hf electrodes are shown to exhibit\nan integrated threshold-memory (1S1M) response. Based on thermodynamic data and\nlumped element modelling these effects are attributed to the formation of a\nmetal-oxide interlayer and its response to field-induced oxygen exchange. These\nresults provide important insight into the physical origin of the switching\nresponse and pathways for engineering devices with reliable switching\ncharacteristics.", "category": "physics_app-ph" }, { "text": "Power Module (PM) core-specific parameters for a detailed\n design-oriented inductor model: This paper obtains shape related parameters and functions of a Power Module\nferrite core which can be required in a design-oriented inductor model, which\nis a fundamental tool to design any electronic power converter and its control\npolicy. Some particular modifications have been introduced into the\nstandardized method of obtaining characteristics core areas and lengths. Also,\na novel approach is taken to obtain the air gap reluctance as a function of air\ngap length for that specific core shape.", "category": "physics_app-ph" }, { "text": "Advanced Analytics on 3D X-ray Tomography of Irradiated Silicon Carbide\n Claddings: Silicon Carbide (SiC) ceramic matrix composite (CMC) cladding is currently\nbeing pursued as one of the leading candidates for accident-tolerant fuels. To\nenable an improved understanding of SiC-SiC composite performance, the\ndevelopment of non-destructive evaluation techniques to assess critical defects\nis needed. Three-dimensional (3D) X-ray imaging, also referred to as X-ray\ncomputed tomography (CT), is a non-destructive, data-rich characterization\ntechnique that can provide surface and subsurface spatial information. This\npaper discusses the design and implementation of a fully automatic workflow to\ndetect and analyze SiC-SiC defects using image processing techniques on 3D\nX-ray images. The workflow consists of four processing blocks, including data\npreparation, void/crack detection, visualization, and analysis. In this work,\nthree SiC samples (two irradiated and one unirradiated) provided by General\nAtomics are investigated. The irradiated samples were exposed in a way that was\nexpected to induce cracking, and indeed, the automated workflow developed in\nthis work was able to successfully identify and characterize the crack\nformation in the irradiated samples while detecting no observed cracking in the\nunirradiated sample. These results demonstrate the value of automated XCT tools\nto better understand the damage and damage propagation in SiC-SiC structures\nfor nuclear applications.", "category": "physics_app-ph" }, { "text": "The role of deformability in determining the structural and mechanical\n properties of bubbles and emulsions: We perform computational studies of jammed particle packings in two\ndimensions undergoing isotropic compression using the well-characterized soft\nparticle (SP) model and the deformable particle (DP) model that we developed\nfor compressed bubbles and emulsions. In the SP model, circular particles are\nallowed to overlap, generating purely repulsive forces. In the DP model,\nparticles minimize their perimeter, while deforming at fixed area to avoid\noverlap during compression. We directly compare the structural and mechanical\nproperties of jammed particle packings generated using the SP and DP models as\na function of the true packing fraction $\\rho$, instead of the reduced number\ndensity $\\phi$. We show that near jamming onset the excess contact number\n$\\Delta z=z-z_J$ and shear modulus ${\\cal G}$ scale as $\\Delta \\rho^{0.5}$ in\nthe large system limit for both the SP and DP models, where $\\Delta \\rho =\n\\rho-\\rho_J$ and $z_J \\approx 4$ and $\\rho_J \\approx 0.842$ are the values at\njamming onset. $\\Delta z$ and ${\\cal G}$ for the SP and DP models begin to\ndiffer for $\\rho \\gtrsim 0.88$. In this regime, $\\Delta z \\sim {\\cal G}$ can be\ndescribed by a sum of two power-laws in $\\Delta \\rho$, i.e. $\\Delta z \\sim\n{\\cal G} \\sim C_0\\Delta \\rho^{0.5} +C_1\\Delta \\rho^{1.0}$ to lowest order. We\nshow that the ratio $C_1/C_0$ is much larger for the DP model compared to to\nthat for the SP model. We also characterize the void space in jammed packings\nas a function of $\\rho$. We find that, unlike the SP model, the DP model is\nable to describe the formation of Plateau borders as the system approaches\n$\\rho = 1$. We further show that the results for $z$ and the shape factor\n${\\cal A}$ versus $\\rho$ for the DP model agree with recent experimental\nstudies of compressed foams and emulsions.", "category": "physics_app-ph" }, { "text": "Corona-Enabled Electrostatic Printing for Ultra-Fast R2R Manufacturing\n of Binder-Free Multifunctional E-Skins: As essential components in intelligent systems, printed soft electronics\n(PSEs) are playing crucial roles in public health, national security, and\neconomics. Innovations in printing technologies are required to promote the\nbroad application of high-performance PSEs at a low cost. However, current\nprinting techniques are still facing long-lasting challenges in addressing the\nconflict between printing speed and performance. To overcome this challenge, we\ndeveloped a new corona-enabled electrostatic printing (CEP) technique for\nultra-fast (milliseconds) roll-to-roll (R2R) manufacturing of binder-free\nmultifunctional e-skins. The printing capability and controllability of CEP\nwere investigated through parametric studies and microstructure observation.\nThe electric field generation, material transfer, and particle amount and size\nselecting mechanisms were numerically and experimentally studied. CEP printed\ngraphene e-skins were demonstrated to possess outstanding strain sensing\nperformance. The binder-free feature of the CEP-assembled networks enables them\nto provide pressure sensitivity as low as 2.5 Pa, and capability to detect\nacoustic signals of hundreds of hertz in frequency. Furthermore, the CEP\ntechnique was utilized to pattern different types of functional materials\n(e.g., graphene and thermochromic polymers) onto different substrates (e.g.,\ntape and textile). Overall, this study demonstrated that CEP can be a novel\ncontactless and ultrafast manufacturing platform compatible with R2R process\nfor fabricating high-performance, scalable, and low-cost soft electronics.", "category": "physics_app-ph" }, { "text": "Physical factors governing the shape of the Miram curve knee in\n thermionic emission: In a current density versus temperature (J-T) (Miram) curve in thermionic\nelectron emission, experimental measurements demonstrate there is a smooth\ntransition between the exponential region and the saturated emission regions,\nwhich is sometimes referred to as the \"roll-off\" or \"Miram curve knee\". The\nshape of the Miram curve knee is an important figure of merit for thermionic\nvacuum cathodes. Specifically, cathodes with a sharp Miram curve knee at low\ntemperature with a flat saturated emission current are typically preferred. Our\nprevious work on modeling nonuniform thermionic emission revealed that the\nspace charge effect and patch field effect are key pieces of physics which\nimpact the shape of the Miram curve knee. This work provides a more complete\nunderstanding of the physical factors connecting these physical effects and\ntheir relative impact on the shape of the knee, including the smoothness, the\ntemperature, and the flatness of the saturated emission current density. For\nour analyses, we use a periodic, equal-width striped (\"zebra crossing\") work\nfunction distribution as a model system and illustrate how the space charge and\npatch field effects restrict the emission current density near the Miram curve\nknee. The results indicate there are three main physical parameters which\nsignificantly impact the shape of the Miram curve. Such physical knowledge\ndirectly connects the patch size, work function values, anode-cathode voltage,\nand anode-cathode gap distance to the shape of the Miram curve, providing new\nunderstanding and a guide to the design of thermionic cathodes used as electron\nsources in vacuum electronic devices (VEDs).", "category": "physics_app-ph" }, { "text": "Current-induced motion of twisted skyrmions: Twisted skyrmions, whose helicity angles are different from that of Bloch\nskyrmions and N\\'eel skyrmions, have already been demonstrated in experiments\nrecently. In this work, we first contrast the magnetic structure and origin of\nthe twisted skyrmion with other three types of skyrmion including Bloch\nskyrmion, N\\'eel skyrmion and antiskyrmion. Following, we investigate the\ndynamics of twisted skyrmions driven by the spin transfer toque (STT) and the\nspin Hall effect (SHE) by using micromagnetic simulations. It is found that the\nspin Hall angle of the twisted skyrmion is related to the dissipative force\ntensor and the Gilbert damping both for the motions induced by the STT and the\nSHE, especially for the SHE induced motion, the skyrmion Hall angle depends\nsubstantially on the skyrmion helicity. At last, we demonstrate that the\ntrajectory of the twisted skyrmion can be controlled in a two dimensional plane\nwith a Gilbert damping gradient. Our results provide the understanding of\ncurrent-induced motion of twisted skyrmions, which may contribute to the\napplications of skyrmion-based racetrack memories.", "category": "physics_app-ph" }, { "text": "Multiharmonic frequency-chirped transducers for surface-acoustic-wave\n optomechanics: Wide passband interdigital transducers are employed to establish a stable\nphase-lock between a train of laser pulses emitted by a mode-locked laser and a\nsurface acoustic wave generated electrically by the transducer. The transducer\ndesign is based on a multi-harmonic split-finger architecture for the\nexcitation of a fundamental surface acoustic wave and a discrete number of its\novertones. Simply by introducing a variation of the transducer's periodicity\n$p$, a frequency chirp is added. This combination results in wide frequency\nbands for each harmonic. The transducer's conversion efficiency from the\nelectrical to the acoustic domain was characterized optomechanically using\nsingle quantum dots acting as nanoscale pressure sensors. The ability to\ngenerate surface acoustic waves over a wide band of frequencies enables\nadvanced acousto-optic spectroscopy using mode-locked lasers with fixed\nrepetition rate. Stable phase-locking between the electrically generated\nacoustic wave and the train of laser pulses was confirmed by performing\nstroboscopic spectroscopy on a single quantum dot at a frequency of 320 MHz.\nFinally, the dynamic spectral modulation of the quantum dot was directly\nmonitored in the time domain combining stable phase-locked optical excitation\nand time-correlated single photon counting. The demonstrated scheme will be\nparticularly useful for the experimental implementation of surface acoustic\nwave-driven quantum gates of optically addressable qubits or collective quantum\nstates or for multi-component Fourier synthesis of tailored nanomechanical\nwaveforms.", "category": "physics_app-ph" }, { "text": "Controlled Preparation, Characterization, and Bandgap Modulation of RF\n Sputtered Antimony Vanadium Oxide (SbVO4) Thin Films: In this paper, RF sputtered antimony vanadium oxide (SbVO4) thin films and\nits characterization are reported. High purity sputtering targets were\nfabricated by sintering a mixture of Sb2O3 and V2O5 powders. Thin films were\ndeposited by reactive sputtering at various temperature and argon/oxygen\npartial pressures. Several growth parameters and surface chemistry were studied\nby applying numerous optical and electrochemical characterization technique. It\nis found that SbVO4 exhibits an indirect band gap in the range of 1.89 eV to\n2.36 eV and has desirable valence band position to drive water oxidation\nreaction under illumination. The bandgap depends heavily on stoichiometry of\nthe film and can be modulated by incorporating controlled amount of oxygen gas\nin plasma environment. Optimized SbVO4 photoanodes was designed and tested for\nphotoelectrochemical water oxidation catalysis. Preliminary studies show that\nthese electrodes possess n-type catalytic behavior in alkaline media. The\nprepared SbVO4 thin films, with typical film thickness was around 400 nm,\ncontain nanoparticles having the sizes of 10-15 nm.", "category": "physics_app-ph" }, { "text": "Impact of spectral effects on photovoltaic energy production: A case\n study in the United States: The time averaged efficiency of photovoltaic modules in the field is\ngenerally lower than the efficiency measured in the laboratory under standard\ntesting conditions due to the combined effects of temperature and spectral\nvariability, affecting the bankability of power plant projects. We report\ncorrection factors to account for spectral effects ranging from -2% to 1.3% of\nthe produced energy for silicon modules depending on location and collector\ngeometry. In high irradiance locations, the energy yield advantage of trackers\nis underestimated by 0.4% if spectral sensitivity effects are neglected. We\nfind a correlation between the locations most favourable for tracking, and\nthose most favourable for multijunctions. As the photovoltaic market grows to a\nmulti-terawatt size, these seemingly small effects are expected to have an\neconomic impact equivalent to tens of billions of dollars in the next few\ndecades, far out-weighting the cost of the required research effort.", "category": "physics_app-ph" }, { "text": "Piezoelectric composite cements: Towards the development of self-powered\n and self-diagnostic materials: Piezoresistivity is the most commonly used sensing principle in cement-based\nsmart composites for strain-monitoring applications. Nonetheless, the need for\nexternal electric power to conduct electrical resistivity measurements\nrestricts the scalability of this technology, especially when implemented in\nremote structures. To address this issue, this manuscript thoroughly analyzes\nthe piezoelectric properties of cement composites doped with reduced graphene\noxide (rGO) and evaluates their potential as self-powered strain sensors. To do\nso, a comprehensive methodology involving voltammetry measurements, open\ncircuit potential determination, and uniaxial compression testing is developed\nto determine the piezoelectric coefficients of charge $d_{33}$ and voltage\n$g_{33}$. Furthermore, a novel circuital model for signal processing of the\nelectromechanical response is developed and experimentally validated in terms\nof time series of output voltage, resistance, and the generated electric power.\nThe developed methodology is applied to laboratory samples manufactured\nfollowing two different filler dispersion methods. The presented results\nevidence that samples prepared by ultrasonic cleaner dispersion achieve optimal\nproperties, with a piezoelectric charge coefficient of\n1122.28$\\mathrm{\\pm}$246.67 pC/N, about 47 times greater than previously\nreported composites in the literature. Unlike piezoresistive cement-based\ncomposites, a remarkable nonlinear correlation between the fractional change in\nthe intrinsic resistance of the material and the applied mechanical strain has\nbeen observed. Instead, a considerable linearity ($\\mathrm{R^2}=0.96$) between\nthe externally applied mechanical strain and the generated (piezoelectric)\nelectric power has been found, which suggests the great potential of the latter\nfor conducting off-the-grid strain monitoring applications.", "category": "physics_app-ph" }, { "text": "Effect of Electron Irradiation on the Transport and Field Emission\n Properties of Few-Layer MoS2 Field Effect Transistors: Electrical characterization of few-layer MoS2 based field effect transistors\nwith Ti/Au electrodes is performed in the vacuum chamber of a scanning electron\nmicroscope in order to study the effects of electron beam irradiation on the\ntransport properties of the device. A negative threshold voltage shift and a\ncarrier mobility enhancement is observed and explained in terms of positive\ncharges trapped in the SiO2 gate oxide, during the irradiation. The transistor\nchannel current is increased up to three order of magnitudes after the exposure\nto an irradiation dose of 100e-/nm2. Finally, a complete field emission\ncharacterization of the MoS2 flake, achieving emission stability for several\nhours and a minimum turn-on field of about 20 V/um with a field enhancement\nfactor of about 500 at anode-cathode distance of 1.5um, demonstrates the\nsuitability of few-layer MoS2 as two-dimensional emitting surface for\ncold-cathode applications.", "category": "physics_app-ph" }, { "text": "Non-Negative Matrix Factorization for 2D-XAS Images of Lithium Ion\n Batteries: Lithium-ion secondary batteries have been used in a wide variety of purposes,\nsuch as for powering mobile devices and electric vehicles, but their\nperformance should be improved. One of the factors that limits their\nperformance is the non-uniformity of the chemical reaction in the process of\ncharging and discharging. Many attempts have been made to elucidate the\nmechanism behind this reaction non-uniformity. In this paper, to detect\nnon-uniformity in various physical properties from Co K-edge two-dimensional\nX-ray absorption spectroscopy (2D-XAS) images of lithium ion batteries, we\npropose a method that consists of one-sided orthogonal non-negative matrix\nfactorization in combination with removal of the reference signal. The\ndifference between X-ray absorption spectra acquired at different positions in\nthe battery is very small. However, even in such a situation, our method can\ndecompose the 2D-XAS data into different spatial domains and their\ncorresponding absorption spectra. From the spectral decomposition of the\nobtained absorption spectra, we confirmed a transition-energy shift of the main\npeak as evidence for a change in the state of charge and also found spectral\nchanges due to orbital hybridization in the decomposed spectral components.", "category": "physics_app-ph" }, { "text": "Spin Logic Devices via Electric Field Controlled Magnetization Reversal\n by Spin-Orbit Torque: We describe a spin logic device with controllable magnetization switching of\nperpendicularly magnetized ferromagnet / heavy metal structures on a\nferroelectric (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT) substrate using\ncurrent-induced spin-orbit torque. The devices were operated without an\nexternal magnetic field and controlled by voltages as low as 10 V applied\nacross the PMN-PT substrate, which is much lower compared to previous reports\n(500 V). The deterministic switching with smaller voltage was realized from the\nvirgin state of the PMN-PT. Ferroelectric simulation shows the unsaturated\nminor loop exhibits obvious asymmetries in the polarizations. Larger\npolarization can be induced from the initial ferroelectric state, while it is\ndifficult for opposite polarization. The XNOR, AND, NAND and NOT logic\nfunctions were demonstrated by the deterministic magnetization switching from\nthe interaction between the spin-orbit torque and electric field at the\nPMN-PT/Pt interface. The nonvolatile spin logic scheme in this work is simple,\nscalable, programmable, which are favorable in the logic-in-memory design with\nlow energy consumption.", "category": "physics_app-ph" }, { "text": "3D large-scale fused silica microfluidic chips enabled by hybrid laser\n microfabrication for continuous-flow UV photochemical synthesis: We demonstrate a hybrid laser microfabrication approach, which combines the\ntechnical merits of ultrafast laser-assisted chemical etching and carbon\ndioxide laser-induced in-situ melting, for centimeter-scale and bonding-free\nfabrication of 3D complex hollow microstructures in fused silica glass. With\nthe developed approach, large-scale fused silica microfluidic chips with\nintegrated 3D cascaded micromixing units can be reliably manufactured.\nHigh-performance on-chip mixing and continuous-flow photochemical synthesis\nunder UV LEDs irradiation at ~280 nm were demonstrated using the manufactured\nchip, indicating a powerful capability for versatile fabrication of highly\ntransparent all-glass microfluidic reactors for on-chip photochemical\nsynthesis.", "category": "physics_app-ph" }, { "text": "High Voltage Generation by Fiber-Coupled Pulsed Laser for a Simple\n Receiver Circuit Structure: Almost all high-voltage dc generation for low-power applications is done by\neither electrostatic machines or voltage multipliers. Electrostatic machines\nuse mechanically moving parts to transfer charge and energy from the\nlow-voltage side to the high-voltage side. Voltage multipliers use capacitive\nand inductive networks to achieve the same purpose of energy transfer.\nConsidering the pros and cons inherent in those mechanical, capacitive, and\ninductive energy transfer, a new means of energy transfer may provide a\nsuperior design of a high voltage dc generator. Here we investigate the design\nof high voltage generators based on optical power transfer. Optical power\ndelivered via fiber-optic cable allows extensive input-to-output dc insulation\nand spatial separation. These characteristics lead to advantages with respect\nto ease of insulation, ease of electromagnetic shielding, and scalability. We\nexperimentally validate the idea by building and testing a 5.5 kV dc generator\nmodule solely powered by a 20 kHz pulsed laser, and cascading three of those\nmodules to obtain 14.7 kV dc output voltage. We then discuss possible\nimprovements to the circuit design to make it useful for real-world\napplications. Finally, we demonstrate an optically powered electroadhesion\ngripper to show the practicality of the proposed high voltage generator.", "category": "physics_app-ph" }, { "text": "Optoelectronic properties of silver doped copper oxide thin films: Thin films have found a wide variety of applications because of the\nsubstantial improvement in their properties as compared to bulk metals. Metal\noxide thin films are increasingly being used in various fields and are\nespecially important in functional applications. They can be either p- or\nn-type in nature depending on the materials, dopants, and preparation route.\nCopper oxide is an example of a p-type metal oxide, which finds application in\nsolar cells, photo-electrochemical cells, gas sensors, supercapacitors, and\nthermoelectric touch detectors. Both copper (I) and copper (II) oxides can be\ngrown with the lower valence state oxide stable at low temperature and the\nhigher valence state obtained by annealing at higher temperatures. In this\nwork, we modify the optical and electrical properties of copper oxide thin\nfilms, by doping of silver through a thermal evaporation process route. Copper\nis thermally evaporated onto the substrate and silver is co-evaporated during\nthis process. The films are then annealed in ambient under various conditions\nto obtain copper oxide. Structural and functional comparison is made between\nundoped and silver doped copper oxide thin films, prepared under the same\nconditions. Thermal evaporation is a simple route for obtaining doped metal\noxides and the process can be extended to a variety of other systems as well.", "category": "physics_app-ph" }, { "text": "Structural Multi-Colour Invisible Inks with Submicron 4D Printing of\n Shape Memory Polymers: Four-dimensional (4D) printing of shape memory polymer (SMP) imparts time\nresponsive properties to 3D structures. Here, we explore 4D printing of a SMP\nin the submicron length scale, extending its applications to nanophononics. We\nreport a new SMP photoresist based on Vero Clear achieving print features at a\nresolution of ~300 nm half pitch using two-photon polymerization lithography\n(TPL). Prints consisting of grids with size-tunable multi-colours enabled the\nstudy of shape memory effects to achieve large visual shifts through nanoscale\nstructure deformation. As the nanostructures are flattened, the colours and\nprinted information become invisible. Remarkably, the shape memory effect\nrecovers the original surface morphology of the nanostructures along with its\nstructural colour within seconds of heating above its glass transition\ntemperature. The high-resolution printing and excellent reversibility in both\nmicrotopography and optical properties promises a platform for\ntemperature-sensitive labels, information hiding for anti-counterfeiting, and\ntunable photonic devices.", "category": "physics_app-ph" }, { "text": "Universal map of gas-dependent kinetic selectivity in carbon nanotube\n growth: Single-walled carbon nanotubes have been a candidate for outperforming\nsilicon in ultrascaled transistors, but the realization of nanotube-based\nintegrated circuits requires dense arrays of purely semiconducting species.\nControl over kinetics and thermodynamics in tube-catalyst systems plays a key\nrole for direct growth of such nanotube arrays, and further progress requires\nthe comprehensive understanding of seemingly contradictory reports on the\ngrowth kinetics. Here, we propose a universal kinetic model and provide its\nquantitative verification by ethanol-based isotope labeling experiments. While\nthe removal of carbon from catalysts dominates the growth kinetics under a low\nsupply of precursors, our kinetic model and experiments demonstrate that\nchirality-dependent growth rates emerge when sufficient amounts of carbon and\netching agents are co-supplied. As the model can be extended to create kinetic\nmaps as a function of gas compositions, our findings resolve discrepancies in\nliterature and offer rational strategies for chirality selective growth for\npractical applications.", "category": "physics_app-ph" }, { "text": "Nonlinear Self-Calibrated Spectrometer with Single GeSe-InSe\n Heterojunction Device: Optical spectroscopy the measurement of electromagnetic spectra is\nfundamental to various scientific domains and serves as the building block of\nnumerous technologies. Computational spectrometry is an emerging field that\nemploys an array of photodetectors with different spectral responses or a\nsingle photodetector device with tunable spectral response, in conjunction with\nnumerical algorithms, for spectroscopic measurements. Compact single\nphotodetectors made from layered materials are particularly attractive, since\nthey eliminate the need for bulky mechanical and optical components used in\ntraditional spectrometers and can easily be engineered as heterostructures to\noptimize device performance. However, compact tunable photodetectors are\ntypically nonlinear devices and this adds complexity to extracting optical\nspectra from the device response. Here, we report on the training of an\nartificial neural network (ANN) to recover the full nonlinear spectral\nphotoresponse of a nonlinear problem of high dimensionality of a single\nGeSe-InSe p-n heterojunction device. We demonstrate the functionality of a\ncalibrated spectrometer in the spectral range of 400-1100 nm, with a small\ndevice footprint of ~25X25 micrometers, and we achieve a mean reconstruction\nerror of 0.0002 for the power-spectrum at a spectral resolution of 0.35 nm.\nUsing our device, we demonstrate a solution to metamerism, an apparent matching\nof colors with different power spectral distributions, which is a fundamental\nproblem in optical imaging.", "category": "physics_app-ph" }, { "text": "Analysis of Phase Formations and Mechanical Properties in Complex\n Concentrated Alloys by Machine Learning Approach: The mechanical properties of complex concentrated alloys (CCAs) depend on\ntheir forming phases and corresponding structures, the prediction of the phase\nformation for a given CCA is essential to its discovery and applications. 541\nsample were collected from previous studies, comprising 61 amorphous, 164\nsingle-phase crystalline, and 361 multi-phases crystalline CCAs. We proposed\nthree classification models to category and understand the phase selection of\nCCAS. Also, a two-objective regression model was constructed to predict the\nhardness and compressive yield stress of CCAs. All three classification models\nhave accuracies higher than 85%, and correlation coefficient of random forest\nregression model is greater than 0.9 for both of two objectives. In addition,\nwe proposed four descriptors via multi-task SISSO method to predict the\nmechanical properties of CCAs, the average correlation coefficient of SISSO\nmodels is higher than 0.85. The present work demonstrates the great potential\nof machine learning approach in the prediction of target properties in CCAs.", "category": "physics_app-ph" }, { "text": "Giant and explosive plasmonic bubbles by delayed nucleation: When illuminated by a laser, nano particles immersed in water can very\nquickly and strongly heat up, leading to the nucleation of so called vapor\nbubbles, which have huge application potential in e.g. solar light-harvesting,\ncatalysis, and for medical applications.Whilst the long-time behavior of such\nbubbles has been well-studied, here, by employing ultra-high-speed imaging, we\nreveal the nucleation and early life phase of these bubbles. After some delay\ntime after beginning of the illumination, a giant bubble explosively grows, up\nto a maximal radius of 80 um, and collapses again within 200 us (bubble life\nphase 1). The maximal bubble volume remarkably increases with decreasing laser\npower P. To explain this behavior, we measure the delay time from the beginning\nof the illumination up to nucleation,which drastically increases with\ndecreasing laser power, leading to less total dumped energy . This dumped\nenergy E shows a universal linear scaling relation. This finding supports that\nthe initial giant bubble is a pure vapor bubble. In contrast, the delay time\ndoes depend on the gas concentration of the water, as gas pockets in the water\nfacilitate an earlier vapor bubble nucleation, which leads to smaller delay\ntimes and lower bubble nucleation temperatures. After the collapse of the\ninitial giant bubbles, first much smaller oscillating bubbles form out of the\nremaining gas nuclei (bubble life phase 2, up to typically 10 ms). Subsequently\nthe known vaporization dominated growth phase takes over and the bubble\nstabilizes (life phase 3). In the final life phase 4 the bubble slowly grows by\ngas expelling due to heating of the surrounding. Our findings on the explosive\ngrowth and collapse during the early life phase of a vapor bubble have strong\nbearings on possible applications of such bubbles, affecting their risk\nassessment.", "category": "physics_app-ph" }, { "text": "Programming nonreciprocity and reversibility in multistable mechanical\n metamaterials: Nonreciprocity can be passively achieved by harnessing material\nnonlinearities. In particular, networks of nonlinear bistable elements with\nasymmetric energy landscapes have recently been shown to support unidirectional\ntransition waves. However, in these systems energy can be transferred only when\nthe elements switch from the higher to the lower energy well, allowing for a\none-time signal transmission. Here, we show that in a mechanical metamaterial\ncomprising a 1D array of bistable arches nonreciprocity and reversability can\nbe independently programmed and are not mutually exclusive. By connecting\nshallow arches with symmetric energy wells and decreasing energy barriers, we\ndesign a reversible mechanical diode that can sustain multiple signal\ntransmissions. Further, by alternating arches with symmetric and asymmetric\nenergy landscapes we realize a nonreciprocal chain that enables propagation of\ndifferent transition waves in opposite directions.", "category": "physics_app-ph" }, { "text": "Calibration and electric characterization of p-MNOS RADFETs at different\n dose rates and temperatures: This paper describes the radiation response and I-V characteristics of the\nstacked p-MNOS based RADFETs measured at different dose rates and irradiation\ntemperatures. It is shown that the enhanced charge trapping takes place at the\ninterface of the thick gate dielectrics in the MNOS transistors at low dose\nrates (ELDRS). The sensitivity of the radiation effect to irradiation\ntemperature has also experimentally revealed. We associate both effects with\nthe temperature and dose rate dependence of the effective charge yield in the\nthick oxides described within the framework of the previously proposed model.\nWe have also simulated the I-V characteristics of the transistors for different\ntotal doses and irradiation conditions. It has been found the used electric and\nradiation models consistently describe the observed dependencies of the RADFETs\nsensitivity on dose rates and irradiation temperatures for the devices with\ndifferent thickness of insulators.", "category": "physics_app-ph" }, { "text": "A Review on Environmental Barrier Coatings: History, Current State of\n the Art and Future Developments: The increasing demand for more efficient and environmental-friendly gas\nturbines has driven the development of new strategies for material development.\nSiC/SiC ceramic matrix composites (CMCs) can fulfil the stringent requirements;\nhowever, they require protection from the operating environment and debris\ningested during operation. Environmental barrier coatings (EBCs) are a\nprotective measure to enable the CMCs to operate under harsh conditions.\nEBC-coated CMCs will enable an increased efficiency and reduced pollutant and\nCO2 emissions. In this review, the fundamentals of SiC/SiC ceramic matrix\ncomposites degradation in steam environments and under the presence of molten\nalkali salts, namely CaO-MgO-Al2O3-SiO2 (CMAS), are first presented. Then, a\nsummary of EBCs along with a comprehensive summary of the current compositions\nand their interactions with steam and molten salts is presented. Finally, an\noverview of the latest research directions for the potential next generation of\nEBCs are outlined", "category": "physics_app-ph" }, { "text": "Inverted GaInP/GaAs Three-Terminal Heterojunction Bipolar Transistor\n Solar Cell: Here we present the experimental results of an inverted three-terminal\nheterojunction bipolar transistor solar cell (HBTSC) made of GaInP/GaAs. The\ninverted growth and processing enable contacting the intermediate layer (base)\nfrom the bottom, which improves the cell performance by reducing shadow factor\nand series resistance at the same time. With this prototype we show that an\ninverted processing of a three-terminal solar cell is feasible and pave the way\nfor the application of epitaxial lift-off, substrate reuse and mechanical\nstacking to the HBTSC which can eventually lead to a low-cost high-efficiency\nIII-V-on-Si HBTSC technology.", "category": "physics_app-ph" }, { "text": "Novel one-step electrophoretic deposition of membrane-electrode assembly\n for flexible-batteries application: Wearable electronic devices and gadgets raise the need for flexible, thin and\nlightweight batteries. In this article we present for the first time, a unique,\nsingle-step method for the preparation of a membrane-electrode assembly for\nflexible-batteries application. Concurrent electrophoretic deposition (EPD) of\npositive and negative battery electrodes (LFP and LTO) on opposite sides of a\ncommercial nanoporous membrane (Celgard 2325) results in the formation of a\nthree-layer-battery structure. The cell comprising this electrophoretically\ndeposited structure ran for more than 150 cycles with 125-140mAh/g capacity,\nwhich approaches the theoretical value of lithium iron phosphate. The\nelectrodes can be deposited either cathodically or anodically by replacing the\ninterchangeable charging agents, like polyethyleneimine and polyacrylic acid.\nThese polyelectrolytes, when adsorbed on the particles of the active material,\nserve also as the binders. The simultaneous EPD, which we developed, can be\nused for the simple and low-cost manufacturing of a variety of cathode and\nanode materials on nanoporous polymer- and ceramic ion-conducting membranes for\nenergy storage devices.", "category": "physics_app-ph" }, { "text": "Transition between radial and toroidal orders in a trimer-based magnetic\n metasurface: The change in the arrangement of magnetic dipole moments in a magnetic\nmetasurface, due to the influence of an external static magnetic field, is\ndiscussed. Each meta-atom of the metasurface is composed of three identical\ndisk-shaped resonators (trimer) made of magnetically saturated ferrite. To\nprovide physical insight, full-wave numerical simulations of the near-fields\nand transmission characteristics of the metasurface are complemented by the\ntheoretical description based on the multipole decomposition method. With these\nmethods, the study of eigenmodes and scattering conditions of a single magnetic\nresonator, trimer, and their array forming the metasurface is performed. It is\nfound that the magnetic dipole-based collective hybrid mode of the trimer can\nbe gradually transformed from the radial (pseudomonopole) to azimuthal\n(toroidal) order and vice versa by varying the bias magnetic field strength.\nThis is because the magnetic dipole moment of each individual disk constituting\nthe trimer undergoes rotation as the bias magnetic field strength changes. This\ntransition between two orders is accompanied by various patterns of\nlocalization of the electric field inside the meta-atoms. Due to the unique\nfield configuration of these modes, the proposed metasurface can be considered\nfor designing magnetic field sensors and nonreciprocal devices.", "category": "physics_app-ph" }, { "text": "Ultra-Efficient Conversion of Microwave into Ultrasound Wave through a\n Split Ring Resonator: Thermo-elastic conversion of electromagnetic wave into ultrasound wave has\nenabled diverse biomedical applications such as photoacoustic imaging.\nMicrowave, which has ~10 cm long wavelength, can penetrate deeper into tissue\nthan photons, heralding exciting applications such as deep tissue imaging via\nthermo-acoustic tomography. However, the thermo-acoustic conversion efficiency\nis very low even with an exogenous contrast agent such as carbon nanotube.\nHere, we break this low conversion limit through using a split ring resonator\n(SRR) to effectively collect and concentrate the microwave energy into a\nsub-millimeter hot spot and subsequently convert the energy into ultrasound\nwave. Our SRR achieves over three orders of magnitude higher thermo-acoustic\nconversion efficiency than commonly used thermo-acoustic contrast agents. We\nfurther harness the SRR as a wireless, battery-free ultrasound emitter placed\nunder a breast phantom. These results promise exciting potential of SRR for\nprecise thermo-acoustic localization and modulation of subjects in deep tissue.", "category": "physics_app-ph" }, { "text": "130 mA/mm $\u03b2$-Ga$_2$O$_3$ MESFET with Low-Temperature MOVPE-Regrown\n Ohmic Contacts: We report on the demonstration of metalorganic vapor phase epitaxy-regrown\n(MOVPE) ohmic contacts in an all MOVPE-grown $\\beta$-Ga$_2$O$_3$\nmetal-semiconductor field effect transistor (MESFET). The low-temperature\n(600$^{\\circ}$C) heavy (n$^{+}$) Si-doped regrown layers exhibit extremely high\nconductivity with sheet resistance of 73 $\\Omega$/$\\square$ and record low\nmetal/n$^{+}$-Ga$_2$O$_3$ contact resistance of 80 m$\\Omega$.mm and specific\ncontact resistivity of 8.3$\\times$10$^{-7}$ $\\Omega$.cm$^{2}$ were achieved.\nThe fabricated MESFETs exhibit a maximum drain-to-source current of 130 mA/mm,\na high I$_{ON}$/I$_{OFF}$ of $>$10$^{10}$ with a high power FOM of 25\nMW/cm$^{2}$ were achieved without any field plates. Nanoparticle-assisted Raman\nthermometry, thermal modeling, and infrared thermography were performed to\nassess the device self-heating under the high current and power conditions.\nThis demonstration shows the promise of MOVPE technique for the realization of\nhigh-performance lateral $\\beta$-Ga$_2$O$_3$ devices and also highlights the\nneed for device-level thermal management.", "category": "physics_app-ph" }, { "text": "Uniformly Distributed Fe$_2$O$_3$ Nanoparticles Thin Films Synthesized\n by Spray Pyrolysis: Thin films of uniformly distributed Fe2O3 nanoparticles have been prepared on\nsingle crystal silicon and glass substrates by a spray pyrolysis technique in a\nsingle step using a mixture of water and ferrocene dissolved in xylene. The\nsize distribution of nanoparticles is found to be in the range of 20 nm to 30\nnm. The films have been characterized by X-ray diffraction, scanning electron\nmicroscopy and Raman spectroscopy techniques. The uniformity of the grown film\nwas evident from the electron microscopic images on both the substrates. The\ncrystallinity and band gap were investigated using X-ray diffraction and\nabsorption spectroscopy respectively. Raman measurements of the prepared films\nhave been carried out using two excitation wavelengths of 633 nm and 785 nm to\ninvestigate the depth of homogeneity of the films. The wavelength dependent\nRaman measurements reveal that the film is uniform across the thickness of the\nfilm on both the substrates.", "category": "physics_app-ph" }, { "text": "Topological acoustic fields protected by real-space topology of acoustic\n cavities: Most properties of acoustic structures derive from their material and\ngeometry. Few are explicitly related to the real-space topology of the\nstructures. Here, we discover a fundamental connection between the real-space\ntopology of acoustic structures and the topological properties of acoustic\nfields. We find that the genus of acoustic cavities can protect the birth of\nacoustic polarization singularities and give rise to chiral velocity fields\nwith nonzero spin density. These polarization singularities are characterized\nby an integer or half-integer topological index. For a cavity with smooth and\nhard boundaries, the total index of the surface singularities must be equal to\nthe Euler characteristic of the cavity and is decided solely by the number of\n\"holes\" in the cavity surface, guaranteed by the Poincare-Hopf theorem. This\nintriguing property is irrelevant to the specific material, geometric details,\nor excitation properties. Besides, the polarization singularities can give rise\nto nontrivial polarization Mobius strips and skyrmion textures of velocity\nfield with rich spatial and temporal properties. The study uncovers the\nintrinsic effects of real-space topology on acoustic field properties and\nenables sound manipulation via a new degree of freedom, i.e., structural\ntopology. The results can find applications in chiral sound-matter interactions\nand acoustic manipulation of small particles.", "category": "physics_app-ph" }, { "text": "Surface Reconstruction Limited Conductivity in Block-Copolymer Li\n Battery Electrolytes: Solid polymer electrolytes for lithium batteries promise improvements in\nsafety and energy density if their conductivity can be increased.\nNanostructured block copolymer electrolytes specifically have the potential to\nprovide both good ionic conductivity and good mechanical properties. This study\nshows that the previously neglected nanoscale composition of the polymer\nelectrolyte close to the electrode surface has an important effect on impedance\nmeasurements, despite its negligible extent compared to the bulk electrolyte.\nUsing standard stainless steel blocking electrodes, the impedance of lithium\nsalt-doped poly(isoprene-b-styrene-b-ethylene oxide) (ISO) exhibited a marked\ndecrease upon thermal processing of the electrolyte. In contrast, covering the\nelectrode surface with a low molecular weight poly(ethylene oxide) (PEO) brush\nresulted in higher and more reproducible conductivity values, which were\ninsensitive to the thermal history of the device. A qualitative model of this\neffect is based on the hypothesis that ISO surface reconstruction at the\ndifferent electrode surfaces leads to a change in the electrostatic double\nlayer, affecting electrochemical impedance spectroscopy measurements. As a main\nresult, PEO-brush modification of electrode surfaces is beneficial for the\nrobust electrolyte performance of PEO-containing block-copolymers and may be\ncrucial for their accurate characterization and use in Li-ion batteries.", "category": "physics_app-ph" }, { "text": "Comment on 'Table-like magnetocaloric effect and enhanced refrigerant\n capacity in Eu8Ga16Ge30-EuO composite materials' [Appl. Phys. Lett. 99,\n 162513 (2011)]: This is a comment on 'Table-like magnetocaloric effect and enhanced\nrefrigerant capacity in Eu8Ga16Ge30-EuO composite materials', published few\nyears ago. Refrigerant Capacity (RC) and Relative Cooling Power (RCP) are\nproperties that characterize the magnetocaloric effect. RCP and mainly RC are\nalso important to characterize other i-caloric effects (electrocaloric and\nmechanocaloric effects). This comment intends to point out mistakes in a\nspecific paper and to be helpful to prevent inappropriate comparisons between\nRC and RCP.", "category": "physics_app-ph" }, { "text": "Cavitation bubble dynamics and sonochemiluminescence activity inside\n sonicated submerged flow tubes: Bubble dynamics and luminol emissions of cavitation in sub-millimeter-sized\nPFA flow tubes, submerged in an ultrasonic bath reactor, are studied at 27 kHz\ndriving frequency. Nucleation of cavitation inside the tubes only takes place\nvia a free interface, realized here in form of an alternating water-air slug\nflow. High-speed recordings show that cavitation bubbles in the water slugs\noften develop localized structures in form of clusters or bubble plugs, and\nthat such structures can be seeded via a single pinch-off from the free\ninterface. Within the structures, bubbles strongly interact and frequently\nundergo merging or splitting events. Due to the mutual interaction and\nresulting motion, bubbles often collapse with a fast displacement, suggesting\njetting dynamics. Bubble compression ratios are estimated on basis of observed\nindividual bubble dynamics and numerical fitting by a single bubble model. The\nresulting peak temperatures around 3000 K allow for dissociation of water\nvapor. This is in accordance with observed sonochemiluminescence from luminol,\noriginating from active bubble zones in the tubes.", "category": "physics_app-ph" }, { "text": "Characterization of Broadband Focusing Microwave Metasurfaces at Oblique\n Incidence: We report the characterization of an achromatic focusing metasurface at\noblique incident angles. We show that in addition to the inherent off-axis\naberrations that occurs due to the hyperbolic phase profile of the metasurface,\nthe focusing performance is significantly degraded due to the meta-atoms'\nangular dispersion. To obtain insights into how the angular and spectral\nbandwidth of meta-atoms relate to the metasurface focusing performance,\npoint-dipole models are used which incorporate different aspect's of the\nmeta-atoms' angular response. It is emphasized that despite the meta-atoms\nbeing designed under the assumption that they support a single dipolar\nresonance, other resonances exist within the meta-atom geometry and become\nstronger at oblique incidence. These resonances disturb the designed phase and\namplitude responses, resulting in lower focusing efficiency at higher incident\nangles. The modelling of higher order modes leads to good agreement with the\nexperimental measurements, confirming that angular dispersion of the meta-atoms\nis the dominant mechanism in determining off-axis aberrations.", "category": "physics_app-ph" }, { "text": "Strongly adhesive dry transfer technique for van der Waals\n heterostructure: That one can stack van der Waals materials with atomically sharp interfaces\nhas provided a new material platform of constructing heterostructures. The\ntechnical challenge of mechanical stacking is picking up the exfoliated\natomically thin materials after mechanical exfoliation without chemical and\nmechanical degradation. Chemically inert hexagonal boron nitride (hBN) has been\nwidely used for encapsulating and picking up vdW materials. However, due to the\nrelatively weak adhesion of hBN, assembling vdW heterostructures based on hBN\nhas been limited. We report a new dry transfer technique. We used two vdW\nsemiconductors (ZnPS3 and CrPS4) to pick up and encapsulate layers for vdW\nheterostructures, which otherwise are known to be hard to fabricate. By\ncombining with optimized polycaprolactone (PCL) providing strong adhesion, we\ndemonstrated various vertical heterostructure devices, including quasi-2D\nsuperconducting NbSe2 Josephson junctions with atomically clean interface. The\nversatility of the PCL-based vdW stacking method provides a new route for\nassembling complex 2D vdW materials without interfacial degradation.", "category": "physics_app-ph" }, { "text": "The automation of robust interatomic-force measurements: Interatomic-force measurements are regularly performed using\nfrequency-modulation atomic force microscopy. This requires conversion of the\nobserved shift in the resonant frequency of a force-sensing cantilever, to the\nactual force experienced by its tip. Recently, Sader et al. Nature\nNanotechnology 13, 1088 (2018) showed that this force conversion can be\nunreliable and proposed the inflection point test to identify valid and robust\nforce data. Efficient and user-friendly algorithms are required for its routine\npractical implementation, which currently do not exist. Here, we (1) advance\nthe theoretical framework of the inflection point test, (2) develop the\nrequired efficient algorithms for its complete automation, and (3) demonstrate\nthe utility of this automation by studying two experimental datasets. The\nprincipal outcome of this report is the development of user-friendly software\nthat integrates this automation with a standard force conversion methodology.\nThis software provides the enabling technology for practitioners to now\nseamlessly perform robust nanoscale and interatomic-force measurements.", "category": "physics_app-ph" }, { "text": "A review of the degradation mechanisms of NCM cathodes and corresponding\n mitigation strategies: Li-ion batteries (LIBs) are the most widely used form of energy storage in\nmobile electronic devices and electric vehicles. Li-ion battery cathodes with\nthe composition LiNixMnyCozO2 (NCMs) currently display some of the most\npromising electrochemical characteristics for high performance LIBs. NCM\ncompositions with high nickel content (x > 0.8) exhibit the largest specific\ncapacity while undergoing fast degradation and presenting safety issues. As the\nmain degradation mechanisms of NCM materials and the mitigation of their\ndegradation, are still subjects of many ongoing studies, this work summarizes\nthe current knowledge on the subject. Here, the existing literature is reviewed\nto present the structural and electrochemical degradation of NCM with varying\nNi stoichiometries (NCM111, NCM622, NCM811, and beyond). Routes for hindering\nthe degradation of NCM are discussed as a function of Ni content in NCM and\ninclude doping, application of protective coatings, and engineering of the\nmicrostructure. A comprehensive understanding of the main degradation pathways\nof NCM is key to applying the most appropriate mitigation strategies and keep\nadvancing towards higher energy NCM materials with longer cycle-life.", "category": "physics_app-ph" }, { "text": "The Potential of Combining Thermal Scanning Probes and Phase-Change\n Materials for Tunable Metasurfaces: Metasurfaces allow for the spatiotemporal variation of amplitude, phase, and\npolarization of optical wavefronts. Implementation of active tunability of\nmetasurfaces promises compact flat optics capable of reconfigurable wavefront\nshaping. Phase-change materials (PCMs), such as germanium telluride or\ngermanium antimony telluride, are a prominent material class enabling\nreconfigurable metasurfaces due to their large refractive index change upon\nstructural transition. However, commonly employed laser-induced switching of\nPCMs limits the achievable feature sizes and thus, restricts device\nminiaturization. Here, we propose thermal scanning-probe-induced local\nswitching of germanium telluride to realize near-infrared metasurfaces with\nfeature sizes far below what is achievable with diffraction-limited optical\nswitching. Our design is based on a planar multilayer stack and does not\nrequire fabrication of protruding dielectric or metallic resonators as commonly\napplied in the literature. Instead, we numerically demonstrate that a\nbroad-band tuning of perfect absorption could be realized by the localized and\ncontrolled tip-induced crystallization of the PCM layer. The spectral response\nof the metasurface is explained using simple resonance mode analysis and\nnumerical simulations. To facilitate experimental realization, we provide a\ndetailed theoretical description of the tip-induced crystallization employing\nmultiphysics simulations to demonstrate the great potential for fabricating\ncompact reconfigurable metasurfaces. Our concept allows for tunable perfect\nabsorption and can be applied not only for thermal imaging or sensing, but also\nfor spatial frequency filtering.", "category": "physics_app-ph" }, { "text": "Low-loss, high-bandwidth fiber-to-chip coupling using capped adiabatic\n tapered fibers: We demonstrate adiabatically tapered fibers terminating in sub-micron tips\nthat are clad with a higher-index material for coupling to an on-chip\nwaveguide. This cladding enables coupling to a high-index waveguide without\nlosing light to the buried oxide. A technique to clad the tip of the tapered\nfiber with a higher-index polymer is introduced. Conventional tapered\nwaveguides and forked tapered waveguide structures are investigated for\ncoupling from the clad fiber to the on-chip waveguide. We find the forked\nwaveguide facilitates alignment and packaging, while the conventional taper\nleads to higher bandwidth. The insertion loss from a fiber through a forked\ncoupler to a sub-micron silicon nitride waveguide is 1.1 dB and the 3\ndB-bandwidth is 90 nm. The coupling loss in the packaged device is 1.3 dB. With\na fiber coupled to a conventional tapered waveguide, the loss is 1.4 dB with a\n3 dB bandwidth extending beyond the range of the measurement apparatus,\nestimated to exceed 250 nm.", "category": "physics_app-ph" }, { "text": "Origin of Robust Rectification in Geometric Diodes: Geometric diodes, which take advantage of geometric asymmetry to achieve\ncurrent flow preference, are promising for THz current rectification. Previous\nstudies relate geometric diodes' rectification to quantum coherent or ballistic\ntransport, which is fragile and critical of the high-quality transport system.\nHere we propose a different physical picture and demonstrate a robust current\nrectification originating from the asymmetric bias induced barrier lowering,\nwhich generally applies to common semiconductors in normal environments. Key\nfactors to the diode's performance are carefully analyzed, and an intrinsic\nrectification ability at up to 1.1 THz is demonstrated.", "category": "physics_app-ph" }, { "text": "Space-coiling Acoustic Metasurface with Independent Modulations of Phase\n and Amplitude: In this work, we propose a design of acoustic meta-surfaces in sub-wavelength\nscale enabling independent modulations of phase and amplitude. Each unit cell\nof the acoustic meta-surface consists of simple conventional space-coiling\nstructure added with an air layer, which can be analyzed as two equivalent\nslabs with non-dispersion effective parameters. The amplitude depends on the\nspace-coiling structure regardless of the air layer, and the phase can be\nfurther adjusted by the air layer independent to the amplitude. The acoustic\nmeta-surface covers an entire phase change of 2-pi and amplitude change of one.\nWe demonstrate an acoustic illusion effect by using the acoustic meta-surface\nscreen, which works well as a full-control discontinuous boundary to support\nphase and amplitude differences between the original and illusion patterns. The\nincident field of a point source is transformed into a target field of the\npoint source scattered by an object with shadow area behind it.", "category": "physics_app-ph" }, { "text": "The Synthescope: A Vision for Combining Synthesis with Atomic\n Fabrication: The scanning transmission electron microscope, a workhorse instrument in\nmaterials characterization, is being transformed into an atomic-scale material\nmanipulation platform. With an eye on the trajectory of recent developments and\nthe obstacles toward progress in this field, we provide a vision for a path\ntoward an expanded set of capabilities and applications. We reconceptualize the\nmicroscope as an instrument for fabrication and synthesis with the capability\nto image and characterize atomic-scale structural formation as it occurs.\nFurther development and refinement of this approach may have substantial impact\non research in microelectronics, quantum information science, and catalysis\nwhere precise control over atomic scale structure and chemistry of a few\n\"active sites\" can have a dramatic impact on larger scale functionality and\nwhere developing a better understanding of atomic scale processes can help\npoint the way to larger scale synthesis approaches.", "category": "physics_app-ph" }, { "text": "Segmented ion-trap fabrication using high precision stacked wafers: We describe the use of laser-enhanced etching of fused silica in order to\nbuild multi-layer ion traps. This technique offers high precision of both\nmachining and alignment of adjacent wafers. As examples of designs taking\nadvantage of this possibility, we describe traps for realizing two key elements\nof scaling trapped ion systems. The first is a trap for a cavity-QED interface\nbetween single ions and photons, in which the fabrication allows shapes that\nprovide good electro-static shielding of the ion from charge build-up on the\nmirror surfaces. The second incorporates two X-junctions allowing\ntwo-dimensional shuttling of ions. Here we are able to investigate designs\nwhich explore a trade-off between pseudo-potential barriers and confinement at\nthe junction center. In both cases we illustrate the design constraints arising\nfrom the fabrication.", "category": "physics_app-ph" }, { "text": "Electrically Induced Photonic and Acoustic Quantum Effect From Liquid\n Metal Droplets in Aqueous Solution: So far, several macroscopic quantum phenomena have been discovered in the\nJosephson junction. Through introducing such a structure with a liquid membrane\nsandwiched between two liquid metal electrodes, we had ever observed a lighting\nand sound phenomenon which was explained before as discharge plasma. In fact,\nsuch an effect also belongs to a quantum process. It is based on this\nconceiving, we proposed here that an electrically controllable method can thus\nbe established to generate and manipulate as much photonic quantum as desired.\nWe attributed such electrically induced lighting among liquid metal droplets\nimmersed inside aqueous solution as photonic quantum effect. Our experiments\nclarified that a small electrical voltage would be strong enough to trigger\nblue-violet light and sound inside the aqueous solution system. Meanwhile,\nthermal heat is released, and chemical reaction occurs over the solution. From\nan alternative way which differs from former effort in interpreting such effect\nas discharge plasma, we treated this process as a quantum one and derived new\nconceptual equations to theoretically quantify this phenomenon in light of\nquantum mechanics principle. It can be anticipated that given specific\ndesigning, such spontaneously generated tremendous quantum can be manipulated\nto entangle together which would possibly help mold functional elements for\ndeveloping future quantum computing or communication system. With superior\nadaptability than that of the conventional rigid junction, the present\nelectro-photonic quantum generation system made of liquid metal droplets\nstructure could work in solution, room temperature situation and is easy to be\nadjusted. It suggests a macroscopic way to innovate the classical strategies\nand technologies in generating quantum as frequently adopted in classical\nquantum engineering area.", "category": "physics_app-ph" }, { "text": "High-Q photonic crystal cavities in all-semiconductor photonic-crystal\n heterostructures: Photonic crystal cavities enable the realization of high Q-factor and low\nmode-volume resonators, with typical architectures consisting of a thin\nsuspended periodically-patterned layer to maximize confinement of light by\nstrong index guiding. We investigate a heterostructure-based approach\ncomprising a high refractive index core and lower refractive index cladding\nlayers. Whilst confinement typically decreases with decreasing index contrast\nbetween the core and cladding layers, we show that, counter-intuitively, due to\nthe confinement provided by the photonic band structure in the cladding layers,\nit becomes possible to achieve Q-factors $>10^4$ with only a small refractive\nindex contrast. This opens up new opportunities for implementing high Q-factor\ncavities in conventional semiconductor heterostructures, with direct\napplications to the design of electrically-pumped nano-cavity lasers using\nconventional fabrication approaches.", "category": "physics_app-ph" }, { "text": "Sound Absorption and Transmission Loss Properties of Open-Celled\n Aluminum Foams with Stepwise Relative Density Gradients: We investigate the acoustical properties of uncompressed and compressed\nopen-celled aluminum metal foams fabricated using a directional solidification\nfoaming process. We compressed the fabricated foams using a hydraulic press to\ndifferent compression ratios and characterized the effect of compression on the\ncellular microstructure using microtomography and scanning electron microscopy.\nThe static airflow resistances of the samples are measured and related to the\nobserved microstructural changes. We measured the normal incidence acoustical\nproperties using two- and four-microphone impedance tube methods and show that\nthe compression substantially improves their sound absorption and transmission\nloss performance. We then stack individual disks with different compression\nratios to create various stepwise relative density gradient configurations and\nshow that stepwise gradients provide a significant improvement in properties as\ncompared to the uncompressed sample. The effect of increasing and decreasing\nrelative density gradients on the overall absorption and transmission loss\nbehavior is characterized. Finally, we use an experimentally informed and\nvalidated transfer matrix method to predict the effect of various layer\nthicknesses and stacking sequences on the global acoustical properties. Our\nresults show that open-celled metal foams with stepwise relative density\ngradients can be designed to provide tailored acoustic absorption performance\nwhile reducing the overall weight of the noise reduction package.", "category": "physics_app-ph" }, { "text": "Enhanced radiative efficiency in GaN nanowires grown on sputtered\n TiN$_{\\boldsymbol{x}}$: effects of surface electric fields: GaN nanowires grown by molecular beam epitaxy generally suffer from dominant\nnonradiative recombination, which is believed to originate from point defects.\nTo suppress the formation of these defects, we explore the synthesis of GaN\nnanowires at temperatures up to 915 ${\\deg}C$ enabled by the use of thermally\nstable TiN$_x$/Al$_2$O$_3$ substrates. These samples exhibit indeed bound\nexciton decay times approaching those measured for state-of-the-art bulk GaN.\nHowever, the decay time is not correlated with the growth temperature, but\nrather with the nanowire diameter. The inverse dependence of the decay time on\ndiameter suggests that the nonradiative process in GaN nanowires is not\ncontrolled by the defect density, but by the field ionization of excitons in\nthe radial electric field caused by surface band bending. We propose a unified\nmechanism accounting for nonradiative recombination in GaN nanowires of\narbitrary diameter.", "category": "physics_app-ph" }, { "text": "Experimental Demonstration of a Rowland Spectrometer for Spin Waves: We experimentally demonstrate the operation of a spin-wave Rowland\nspectrometer. In the proposed device geometry, spin waves are coherently\nexcited on a diffraction grating and form an interference pattern that\nspatially separates spectral components of the incoming signal. The diffraction\ngrating was created by focused-ion-beam irradiation, which was found to locally\neliminate the ferrimagnetic properties of YIG, without removing the material.\nWe found that in our experiments spin waves were created by an indirect\nmechanism, by exploiting nonlinear resonance between the grating and the\ncoplanar waveguide. Our work paves the way for complex spin-wave optic devices\n-- chips that replicate the functionality of integrated optical devices on a\nchip-scale.", "category": "physics_app-ph" }, { "text": "A simple transcendental travelling wave solution and stability study for\n the thermophoretic motion with variable heat transmission factors on\n substrate-supported grapheme sheet: Manually tailored wrinkled graphene sheets hold great promise in fabricating\nsmart solid-state devices. In this paper, we employ an energy method to\ntransform the original third-order partial differential equation (pde), i.e.\nEq. (1) into the first-order pde, i.e. Eq. (8) for the thermophoretic motion of\nsubstrate-supported graphene sheets, which can be solved in terms of semi-group\nand transcendental solutions. Unlike soliton solutions derived using other more\nsophisticated techniques [9, 23], the present transcendental solution can be\neasily solved numerically and provides physical insights. Most importantly, we\nverify that the formation of various forms for wrinkling wave solutions can be\ndetermined by the evolution of equilibrium points for Eq. (1). This sheds a\nlight on modifying the heat sources in order to control the configuration of\nwrinkle waves that has not been previously addressed.", "category": "physics_app-ph" }, { "text": "THz Acoustic Attenuations of Glycerol by Pump Probe Technique: The coherent acoustic waves can be created by InGaN double quantum wells. We\nmeasured the signals information of the coherent acoustic waves at the\ninterface of GaN/glycerol to obtain the attenuations of glycerol at 295 K and\n120 K by the femto-sec laser pump probe technique in THz regime. The\nattenuations of glycerol are calculated by using the acoustic mismatch model\n(AMM) through the complex acoustic impedance. We compared pump probe results\nwith inelastic neutron scattering (INS) and inelastic X ray scattering (IXS),\nfound they are matched within 0.5 THz at room temperature. The glycerol\nattenuations are found increasing monotonically to 1.75x10^8 m^(-1) and\n1.3x10^8 m^(-1) till 0.5 THz by the pump probe technique at 295 K and 120 K,\nrespectively.", "category": "physics_app-ph" }, { "text": "Ab initio calculation of the detailed balance limit to the photovoltaic\n efficiency of single p-n junction kesterite solar cells: The thermodynamic limit of photovoltaic efficiency for a single-junction\nsolar cell can be readily predicted using the bandgap of the active light\nabsorbing material. Such an approach overlooks the energy loss due to\nnon-radiative electron-hole processes. We propose a practical ab initio\nprocedure to determine the maximum efficiency of a thin-film solar cell that\ntakes into account both radiative and non-radiative recombination. The required\ninput includes the frequency-dependent optical absorption coefficient, as well\nas the capture cross-sections and equilibrium populations of point defects. For\nkesterite-structured Cu$_2$ZnSnS$_4$, the radiative limit is reached for a film\nthickness of around 2.6 micrometer, where the efficiency gain due to light\nabsorption is counterbalanced by losses due to the increase in recombination\ncurrent.", "category": "physics_app-ph" }, { "text": "Observation of bound states in the continuum in a micromechanical\n resonator: Bound states in the continuum (BICs) refer to physical states that possess\nintrinsic zero dissipation loss even though they are located in the continuous\nenergy spectrum. BICs have been widely explored in optical and acoustic\nstructures, leading to applications in sensing and lasing. Realizing BICs in\nmicromechanical structures is of significant importance for both fundamental\nresearch and engineering applications. Here, we fabricated, with\nCMOS-compatible processes on a silicon chip, a wheel-shaped micromechanical\nresonator, in which we experimentally observed the BIC in the micromechanical\ndomain. Such BICs result from destructive interference between two dissipative\nmodes of the mechanical structure under broken azimuthal symmetry. These BICs\nare found to be robust against size variations of the dissipation channels. The\ndemonstrated mechanical BIC can be obtained with a large and robust supporting\nstructure, which substantially reduces device fabrication difficulty and allows\nfor its operation in versatile environments for broader application areas. Our\nresults open a new way of phonon trapping in micromechanical structures with\ndissipation channels, and produce long phonon lifetimes that are desired in\nmany mechanical applications such as mechanical oscillators, sensors, and\nquantum information processors.", "category": "physics_app-ph" }, { "text": "Observation of Optical Gain in Er-Doped GaN Epilayers: Rare-earth based lasing action in GaN semiconductor at the telecommunication\nwavelength of 1.5 micron has been demonstrated at room temperature. We have\nreported the stimulated emission under the above bandgap excitation from Er\ndoped GaN epilayers prepared by metal-organic chemical vapor deposition. Using\nthe variable stripe technique, the observation of the stimulated emission has\nbeen demonstrated through characteristic features of threshold behavior of\nemission intensity as functions of pump intensity, excitation length, and\nspectral linewidth narrowing. Using the variable stripe setup, the optical gain\nup to 75 cm-1 has been obtained in the GaN:Er epilayers. The near infrared\nlasing from GaN semiconductor opens up new possibilities for extended\nfunctionalities and integration capabilities for optoelectronic devices.", "category": "physics_app-ph" }, { "text": "An integrated cryogenic optical modulator: Integrated electrical and photonic circuits (PIC) operating at cryogenic\ntemperatures are fundamental building blocks required to achieve scalable\nquantum computing, and cryogenic computing technologies. Optical interconnects\noffer better performance and thermal insulation than electrical wires and are\nimperative for true quantum communication. Silicon PICs have matured for room\ntemperature applications but their cryogenic performance is limited by the\nabsence of efficient low temperature electro-optic (EO) modulation. While\ndetectors and lasers perform better at low temperature, cryogenic optical\nswitching remains an unsolved challenge. Here we demonstrate EO switching and\nmodulation from room temperature down to 4 K by using the Pockels effect in\nintegrated barium titanate (BaTiO3)-based devices. We report the nonlinear\noptical (NLO) properties of BaTiO3 in a temperature range which has previously\nnot been explored, showing an effective Pockels coefficient of 200 pm/V at 4 K.\nWe demonstrate the largest EO bandwidth (30 GHz) of any cryogenic switch to\ndate, ultra-low-power tuning which is 10^9 times more efficient than thermal\ntuning, and high-speed data modulation at 20 Gbps. Our results demonstrate a\nmissing component for cryogenic PICs. It removes major roadblocks for the\nrealisation of novel cryogenic-compatible systems in the field of quantum\ncomputing and supercomputing, and for interfacing those systems with the real\nworld at room-temperature.", "category": "physics_app-ph" }, { "text": "High-frequency traveling-wave phononic cavity with sub-micron wavelength: Thin-film gallium nitride (GaN) as a proven piezoelectric material is a\npromising platform for the phononic integrated circuits, which hold great\npotential for scalable information processing processors. Here, an unsuspended\ntraveling phononic resonator based on high-acoustic-index-contrast mechanism is\nrealized in GaN-on-Sapphire with a frequency up to 5 GHz, which matches the\ntypical superconducting qubit frequency. A sixfold increment in quality factor\nwas found when temperature decreases from room temperature ($Q=5000$) to\n$7\\,\\mathrm{K}$ ($Q=30000$) and thus a frequency-quality factor product of\n$1.5\\times10^{14}$ is obtained. Higher quality factors are available when the\nfabrication process is further optimized. Our system shows great potential in\nhybrid quantum devices via circuit quantum acoustodynamics.", "category": "physics_app-ph" }, { "text": "Controlling acoustic waves using magnetoelastic Fano resonances: We propose and analyze theoretically a class of energy-efficient\nmagneto-elastic devices for analogue signal processing. The signals are carried\nby transverse acoustic waves while the bias magnetic field controls their\nscattering from a magneto-elastic slab. By tuning the bias field, one can alter\nthe resonant frequency at which the propagating acoustic waves hybridize with\nthe magnetic modes, and thereby control transmission and reflection\ncoefficients of the acoustic waves. The scattering coefficients exhibit\nBreit-Wigner/Fano resonant behaviour akin to inelastic scattering in atomic and\nnuclear physics. Employing oblique incidence geometry, one can effectively\nenhance the strength of magnetoelastic coupling, and thus countermand the\nmagnetic losses due to the Gilbert damping. We apply our theory to discuss\npotential benefits and issues in realistic systems and suggest further routes\nto enhance performance of the proposed devices.", "category": "physics_app-ph" }, { "text": "Gamow factors and current densities in cold field emission theory: a\n comparative study: The factors that contribute to the accuracy of the cold field emission\ncurrent within the contemporary frameworks are investigated. It is found that\nso long as the net current is evaluated using an expression for the local\ncurrent density obtained by linearizing the Gamow factor, the primary source of\nerror is the choice of the energy at which the Taylor expansion is done, but\nnot as much on the choice of the method used to arrive at the approximate Gamow\nfactor. A suitable choice of linearization energy and the implementation of the\nKemble correction, allows the restriction of errors to below 3\\% across a wide\nrange of local fields.", "category": "physics_app-ph" }, { "text": "Active Magnetoelectric Control of Terahertz Spin Current: Electrical control of photogenerated THz spin current pulses from a\nspintronic emitter has been at the forefront for the development of scalable,\ncost-efficient, wideband opto-spintronics devices. Artificially combined\nferroelectric and ferromagnet heterostructure provides the potential avenue to\ncontrol the spin dynamics efficiently utilizing the magnetoelectric coupling.\nThe demonstration of the electric field control of spin dynamics has so far\nbeen limited up to gigahertz frequencies. Here, we demonstrate the electric\nfield mediated piezoelectric strain control of photogenerated THz spin current\npulse from a multiferroic spintronic emitter. The phase reversal of the THz\nspin current pulse is obtained from the combined effect of piezoelectric strain\nand a small constant magnetic field applied opposite to the initial\nmagnetization of the ferromagnet. The piezoelectric strain-controlled phase\nswitching of THz spin current thus opens a door to develop efficient strain\nengineered scalable on-chip THz spintronics devices.", "category": "physics_app-ph" }, { "text": "A finite element analysis of rolling of bilayer films to cylindrical and\n conical tubes: With recent developments in nanotechnology, self-assembled structures are\nproviding convenient, cheaper and more precise ways of manufacturing various\npatterns and shapes with less complexity. Of these self-assembled structures,\nrolled-up nano-tubes play a vital role in various aspects. The notion is, the\nutilization of strain energy developed during epitaxial growth of a bilayer\nthin film over a substrate, mediated by a sacrificial layer. While the\nsacrificial layer is etched, the bilayer film is subjected to release its own\nin-built strain energy in the out-of-plane direction (3D structure) due to a\nbending stress induced by biaxial strain through the thickness, in the bilayer.\nThis paper proposes a new method of fabricating conical self-rolled assembly by\nthickness and strain variations along the width of the bilayer and, cylindrical\nstructure of variable radius due to thickness and strain variations along the\nlength.", "category": "physics_app-ph" }, { "text": "Oxygen-based digital etching of AlGaN/GaN structures with AlN as\n etch-stop layers: O2-plamsa-based digital etching of Al0.25Ga0.75N with a 0.8 nm AlN spacer on\nGaN was investigated. At 40 W RF bias power and 40 sccm oxygen flow, the etch\ndepth of Al0.25Ga0.75N was 5.7 nm per cycle. The 0.8 nm AlN spacer layer acted\nas an etch-stop layer in 3 cycles. The surface roughness improved to 0.33 nm\nafter 7 digital etch cycles. Compared to the dry etch only approach, this\ntechnique causes less damages. It was shown to be effective in precisely\ncontrolling the AlGaN etch depth required for recessed-AlGaN HEMTs.", "category": "physics_app-ph" }, { "text": "Graphene/fluorinated graphene systems for a wide spectrum of electronics\n application: Heterostructures prepared from graphene and fluorographene (FG) using the\ntechnology of 2D printing on solid and flexible substrates were fabricated and\nstudied. Excellent stability of printed graphene layers and, to a lesser\ndegree, composite graphene: PEDOT: PSS layers were shown. Extraordinary\nproperties of FG as an insulating layer for graphene-based heterostructures at\nfluorination degree above 30% were demonstrated. It is shown that the leakage\ncurrent in thin (20-40 nm) films is normally smaller than 10^-8 A/cm2, the\nbreakdown field being greater than 108 V/cm. In hybrid structures with printed\nFG layers in which graphene was transferred onto, or capsulated with, an FG\nlayer, an increase in charge-carrier mobility and material conductivity\namounting to 5-6 times was observed. The spectrum of future applications of FG\nlayers can be further extended due to the possibility of obtaining, from weakly\nfluorinated graphene (< 20%), functional layers exhibiting a negative\ndifferential resistance behavior and, at fluorination degrees of 20-23%,\nfield-effect-transistor channels with current modulation reaching several\norders. Composite or bilayer films based on fluorographene and V2O5 or\npolyvinyl alcohol exhibit a stable resistive switching behavior. On the whole,\ngraphene/FG heterostructures enjoy huge potential for their use in a wide\nspectrum of application, including flexible electronics.", "category": "physics_app-ph" }, { "text": "Quantum gas-enabled direct mapping of active current density in\n percolating networks of nanowires: Electrically percolating nanowire networks are amongst the most promising\ncandidates for next-generation transparent electrodes. Scientific interest in\nthese materials stems from their intrinsic current distribution heterogeneity,\nleading to phenomena like percolating pathway re-routing and localized\nself-heating, which can cause irreversible damage. Without an experimental\ntechnique to resolve the current distribution, and an underpinning nonlinear\npercolation model, one relies on empirical rules and safety factors to engineer\nthese materials. We introduce Bose-Einstein microscopy to address the\nlong-standing problem of imaging active current flow in 2D materials. We report\non improvement of the performance of this technique, whereby observation of\ndynamic redistribution of current pathways becomes feasible. We show how this,\ncombined with existing thermal imaging methods, eliminates the need for\nassumptions between electrical and thermal properties. This will enable testing\nand modelling individual junction behaviour and hotspot formation.\nInvestigating both reversible and irreversible mechanisms will contribute to\nthe advancement of devices with improved performance and reliability.", "category": "physics_app-ph" }, { "text": "$\\textit{In situ}$ hydride breathing during the template-assisted\n electrodeposition of Pd nanowires: We investigated the structural evolution of electrochemically fabricated Pd\nnanowires $\\textit{in situ}$ by means of grazing-incidence transmission small-\nand wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF)\nand 2-dimensional surface optical reflectance (2D-SOR). This shows how\nelectrodeposition and the hydrogen evolution reaction (HER) compete and\ninteract during Pd electrodepositon. During the bottom-up growth of the\nnanowires, we show that $\\beta$-phase Pd hydride is formed. Suspending the\nelectrodeposition then leads to a phase transition from $\\beta$- to\n$\\alpha$-phase Pd hydride. Additionally, we find that grain coalescence later\nhinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR\nprovide complementary information on the volume fraction of the pores occupied\nby Pd, while XRF was used to monitor the amount of Pd electrodeposited.", "category": "physics_app-ph" }, { "text": "Enhancing the Open-Circuit Voltage of Perovskite Solar Cells by up to\n 120 mV using \u03c0-Extended Phosphoniumfluorene Electrolytes as Hole Blocking\n Layers: Four {\\pi}-extended phosphoniumfluorene electrolytes ({\\pi}-PFEs) are\nintroduced as hole-blocking layers (HBL) in inverted architecture planar\nperovskite solar cells (PVSCs) with the structure of\nITO/PEDOT:PSS/MAPbI3/PCBM/HBL/Ag. The deep-lying highest occupied molecular\norbital (HOMO) energy level of the {\\pi}-PFEs effectively blocks holes,\ndecreasing contact recombination. We demonstrate that the incorporation of\n{\\pi}-PFEs introduces a dipole moment at the PCBM/Ag interface, resulting in a\nsignificant enhancement of the built-in potential of the device. This\nenhancement results in an increase in the open-circuit voltage of the device by\nup to 120 mV, when compared to the commonly used bathocuproine HBL. The results\nare confirmed both experimentally and by numerical simulation. Our work\ndemonstrates that interfacial engineering of the transport layer/contact\ninterface by small molecule electrolytes is a promising route to suppress\nnon-radiative recombination in perovskite devices and compensate for a\nnon-ideal energetic alignment at the hole-transport layer/perovskite interface.", "category": "physics_app-ph" }, { "text": "Stress-induced modification of gyration dynamics in stacked\n double-vortex structures studied by micromagnetic simulations: In this paper, using micromagnetic simulations, we investigate the\nstress-induced frequency tunability of double-vortex nano-oscillators\ncomprising magnetostrictive and non-magnetostrictive ferromagnetic layers\nseparated vertically by a non-magnetic spacer. We show that the the relative\norientations of the vortex core polarities $p_{1}$ and $p_{2}$ have a strong\nimpact on the eigen-frequencies of the dynamic modes. When the two vortices\nwith antiparallel polarities have different eigen-frequencies and the\nmagnetostatic coupling between them is sufficiently strong, the stress-induced\nmagnetoelastic anisotropy can lead to the single-frequency gyration mode of the\ntwo vortex cores. Additionally, for the case of parallel polarities, we\ndemonstrate that for sufficiently strong magnetostatic coupling, the\nmagnetoelastic anisotropy leads to the coupled vortex gyration in the\nstochastic regime and to the lateral separation of the vortex core\ntrajectories. These findings offer a fine control over gyration frequencies and\ntrajectories in vortex-based oscillators via adjustable elastic stress, which\ncan be easily generated and tuned electrically, mechanically or optically.", "category": "physics_app-ph" }, { "text": "Taylor cones of ionic liquids from capillary tubes as sources of pure\n ions: The role of surface tension and electrical conductivity: The emissions of Taylor cones from a wide range of ionic liquids (ILs) have\nbeen tested in vacuo in an attempt to identify what physical properties favor\nthe purely ionic regime (PIR). This regime is well known in the case of Taylor\ncones of liquid metals. For nonmetallic liquids, it has been previously\nobserved in conventional (capillary tube) electrospray sources at room\ntemperature only for the room temperature molten salt (ionic liquid) EMI-BF4\n(EMI=1-ethyl-3-methylimidazolium). A large number of other ILs and their\nmixtures have been studied here, most of which (but not all) are unable to\nreach the PIR at room temperature. Based on these results and additional\ntheoretical considerations, strong support is assembled for the notion that the\nPIR is favored by ILs not only of high electrical conductivity but also of high\nsurface tension. This hypothesis is confirmed by tests with three recently\nsynthesized ILs, EMI-GaCl4, EMI-C(CN)3, and EMI-N(CN)2, all of which combine\nexceptional surface tension and electrical conductivity, and all of which reach\nthe PIR at room temperature far more readily than EMI-BF4.", "category": "physics_app-ph" }, { "text": "Beyond 1 ms Charge-Carrier Recombination Dynamics in the CsPbBr3\n Perovskite: Knowledge of the charge-carrier recombination lifetime, tau, is crucial for\nthe various applications of photovoltaic perovskites. We studied the novel\ninorganic perovskite, CsPbBr3 and we observe recombination dynamics beyond 1 ms\nbelow 200 K and tau approaching 100 us at room temperature. Time-resolved\nmicrowave-detected photoconductivity decay (TRMCD), used in combination with\ninjection dependence, evidence that tau is dominated by impurity charge\ntrapping. The observed injection dependence is well corroborated by modeling of\nthe trap mechanism. The ultra-long decay time is also consistent with\nphotoconductivity measurements with a continuous-wave excitation at powers\ncorresponding to around one Sun irradiation. While in principle charge-carrier\ntrapping may limit the photovoltaic efficiency in single-cell photovoltaic\ndevices, it could also lead to enhanced efficiency in tandem cells as well as\nfor alternative applications including photodetection and quantum information\nstorage.", "category": "physics_app-ph" }, { "text": "Numerical analysis of the Maxwell-Cattaneo-Vernotte nonlinear model: In the literature, one can find numerous modifications of Fourier's law from\nwhich the first one is called Maxwell-Cattaneo-Vernotte heat equation. Although\nthis model has been known for decades and successfully used to model\nlow-temperature damped heat wave propagation, its nonlinear properties are\nrarely investigated. In this paper, we aim to present the functional\nrelationship between the transport coefficients and the consequences of their\ntemperature dependence. Furthermore, we introduce a particular implicit\nnumerical scheme in order to solve such nonlinear heat equations reliably. We\ninvestigate the scheme's stability, dissipation, and dispersion attributes as\nwell. We demonstrate the effect of temperature-dependent thermal conductivity\non two different initial-boundary value problems, including time-dependent\nboundaries and heterogeneous initial conditions.", "category": "physics_app-ph" }, { "text": "The spin resonance clock transition of the endohedral fullerene\n $^{15}\\mathrm{N@C}_{60}$: The endohedral fullerene $^{15}\\mathrm{N@C}_{60}$ has narrow electron\nparamagnetic resonance lines which have been proposed as the basis for a\ncondensed-matter portable atomic clock. We measure the low-frequency spectrum\nof this molecule, identifying and characterizing a clock transition at which\nthe frequency becomes insensitive to magnetic field. We infer a linewidth at\nthe clock field of 100 kHz. Using experimental data, we are able to place a\nbound on the clock's projected frequency stability. We discuss ways to improve\nthe frequency stability to be competitive with existing miniature clocks.", "category": "physics_app-ph" }, { "text": "Near-direct bandgap $WSe_2$/$ReS_2$ type-II pn heterojunction for\n enhanced ultrafast photodetection and high-performance photovoltaics: PN heterojunctions comprising layered van der Waals (vdW) semiconductors have\nbeen used to demonstrate current rectifiers, photodetectors, and photovoltaic\ndevices. However, a direct or near-direct bandgap at the heterointerface that\ncan significantly enhance optical generation, for high light absorbing\nfew/multi-layer vdW materials, has not yet been shown. In this work, for the\nfirst time, few-layer group-6 transition metal dichalcogenide (TMD) $WSe_2$ is\nshown to form a sizeable (0.7 eV) near-direct bandgap with type-II band\nalignment at its interface with the group-7 TMD $ReS_2$ through density\nfunctional theory calculations. Further, the type-II alignment and\nphotogeneration across the interlayer bandgap have been experimentally\nconfirmed through micro-photoluminescence and IR photodetection measurements,\nrespectively. High optical absorption in few-layer flakes, large conduction and\nvalence band offsets for efficient electron-hole separation and stacking of\nlight facing, direct bandgap $ReS_2$ on top of gate tunable $WSe_2$ are shown\nto result in excellent and tunable photodetection as well as photovoltaic\nperformance through flake thickness dependent optoelectronic measurements.\nFew-layer flakes demonstrate ultrafast response time (5 $\\mu$s) at high\nresponsivity (3 A/W) and large photocurrent generation and responsivity\nenhancement at the heterostructure overlap region (10-100X) for 532 nm laser\nillumination. Large open-circuit voltage of 0.64 V and short-circuit current of\n2.6 $\\mu$A enables high output electrical power. Finally, long term\nair-stability and a facile single contact metal fabrication process makes the\nmulti-functional few-layer $WSe_2$/$ReS_2$ heterostructure diode\ntechnologically promising for next-generation optoelectronic applications.", "category": "physics_app-ph" }, { "text": "Selection of optimal wavelengths for optical soiling modelling and\n detection in photovoltaic modules: Soiling impacts the photovoltaic (PV) module performance by reducing the\namount of light reaching the photovoltaic cells and by changing their external\nspectral response. Currently, the soiling monitoring market is moving toward\noptical sensors that measure transmittance or reflectance, rather than directly\nmeasuring the impact of soiling on the performance of photovoltaic modules.\nThese sensors, which use a single optical measurement, are not able to correct\nthe soiling losses that depend on the solar irradiance spectra and on the\nspectral response of the monitored PV material. This work investigates methods\nthat can improve the optical detection of soiling by extracting the full\nsoiling spectrum profiles using only two or three monochromatic measurements.\nSpectral transmittance data, measured with a spectrophotometer and collected\nduring a 46-week experimental soiling study carried out in Ja\\'en, Spain, was\nanalysed in this work. The use of a spectral profile for the hemispherical\ntransmittance of soiled PV glass is found to significantly improve the soiling\ndetection, returning the lowest errors independently of the PV materials and\nirradiance conditions. In addition, this work shows that it is also possible to\nselect the measurement wavelengths to minimize the soiling loss detection error\ndepending on the monitored PV semiconductor material (silicon, CdTe, a-Si, CIGS\nand a representative perovskite). The approaches discussed in this work are\nalso found to be more robust to potential measurement errors compared to single\nwavelength measurement techniques.", "category": "physics_app-ph" }, { "text": "Van der Waals heterostructures for high-performance device applications:\n challenges and opportunities: Discovery of two-dimensional materials with unique electronic, superior\noptoelectronic or intrinsic magnetic order have triggered worldwide interests\namong the fields of material science, condensed matter physics and device\nphysics. Vertically stacking of two-dimensional materials with distinct\nelectronic and optical as well as magnetic properties enables to create a large\nvariety of van der Waals heterostructures. The diverse properties of the\nvertical heterostructures open up unprecedented opportunities for various kinds\nof device applications, e.g. vertical field effect transistors, ultrasensitive\ninfrared photodetectors, spin-filtering devices and so on, which are\ninaccessible in the conventional material heterostructures. Here, we review the\ncurrent status of vertical heterostructures device applications in vertical\ntransistors, infrared photodetectors and spintronic memory/transistors. The\nrelevant challenges for achieving high-performance devices are presented. We\nalso provide outlook on future development of vertical heterostructure devices\nwith integrated electronic and optoelectronic as well as spintronic\nfunctinalities.", "category": "physics_app-ph" }, { "text": "Different Synthesis Routes of Graphene-Based Metal Nanocomposites: Nanocomposite material proves to be the best candidate to match todays\ntechnological need as fascinating properties can be achieved by combining two\nor more nanomaterials. Among various nanomaterials, graphene is able to stand\nout far ahead of all others because of its novel structure and exclusive\ncharacteristics. In particular, graphene metal nanocomposites have attracted\nenormous interest for their prospective use in various fields, including\nelectronics and electrical and energy related areas. However, for the utmost\nuse of potential of graphene, it has to be homogenously embedded into metal\nmatrices. Thus, appropriate synthesis route is decisive to obtain graphene\nmetal nanocomposites with desired properties. This chapter will summarize the\ndifferent synthesis routes of high quality graphene metal nanocomposites along\nwith their current developments.", "category": "physics_app-ph" }, { "text": "On the suitability of hBN as an insulator for 2D material-based\n ultrascaled CMOS devices: Complementary metal oxide semiconductor (CMOS) logic circuits at the ultimate\nscaling limit place the utmost demands on the properties of all materials\ninvolved. The requirements for semiconductors are well explored and could\npossibly be satisfied by a number of layered two-dimensional (2D) materials,\nlike for example transition-metal dichalcogenides or black phosphorus. The\nrequirements for the gate insulator are arguably even more challenging and\ndifficult to meet. In particular the combination of insulator to semiconductor\nwhich forms the central element of the metal oxide semiconductor field effect\ntransistor (MOSFET) has to be of superior quality in order to build competitive\ndevices. At the moment, hexagonal boron nitride (hBN) is the most common\ntwo-dimensional insulator and widely considered to be the most promising gate\ninsulator in nanoscaled 2D material-based transistors. Here, we critically\nassess the material parameters of hBN and conclude that while its properties\nrender hBN an ideal candidate for many applications in 2D nanoelectronics, hBN\nis most likely not suitable as a gate insulator for ultrascaled CMOS devices.", "category": "physics_app-ph" }, { "text": "An efficient method to estimate sorption isotherm curve coefficients: This paper deals with an inverse problem applied to the field of building\nphysics to experimentally estimate three sorption isotherm coefficients of a\nwood fiber material. First, the mathematical model, based on convective\ntransport of moisture, the Optimal Experiment Design (OED) and the experimental\nset-up are presented. Then measurements of relative humidity within the\nmaterial are carried out, after searching the OED, which is based on the\ncomputation of the sensitivity functions and a priori values of the unknown\nparameters employed in the mathematical model. The OED enables to plan the\nexperimental conditions in terms of sensor positioning and boundary conditions\nout of 20 possible designs, ensuring the best accuracy for the identification\nmethod and, thus, for the estimated parameter. Two experimental procedures were\nidentified: i) single step of relative humidity from 10% to 75% and ii)\nmultiple steps of relative humidity 10-75-33-75% with an 8-day duration period\nfor each step. For both experiment designs, it has been shown that the sensor\nhas to be placed near the impermeable boundary. After the measurements, the\nparameter estimation problem is solved using an interior point algorithm to\nminimize the cost function. Several tests are performed for the definition of\nthe cost function, by using the L^2 or L^\\infty norm and considering the\nexperiments separately or at the same time. It has been found out that the\nresidual between the experimental data and the numerical model is minimized\nwhen considering the discrete Euclidean norm and both experiments separately.\nIt means that two parameters are estimated using one experiment while the third\nparameter is determined with the other experiment. Two cost functions are\ndefined and minimized for this approach. Moreover, the algorithm requires less\nthan 100 computations of the direct model to obtain the solution. In addition,\nthe OED sensitivity functions enable to capture an approximation of the\nprobability distribution function of the estimated parameters. The determined\nsorption isotherm coefficients calibrate the numerical model to fit better the\nexperimental data. However, some discrepancies still appear since the model\ndoes not take into account the hysteresis effects on the sorption capacity.\nTherefore, the model is improved proposing a second differential equation for\nthe sorption capacity to take into account the hysteresis between the main\nadsorption and desorption curves. The OED approach is also illustrated for the\nestimation of five of the coefficients involved in the hysteresis model. To\nconclude, the prediction of the model with hysteresis are compared with the\nexperimental observations to illustrate the improvement of the prediction.", "category": "physics_app-ph" }, { "text": "Antibacterial Melamine Foams Decorated with in Situ Synthesized Silver\n Nanoparticles: A new and straightforward single-step route to decorate melamine foams with\nsilver nanoparticles (ME/Ag) is proposed.", "category": "physics_app-ph" }, { "text": "Arbitrary Wave Transformations with Huygens' Metasurfaces through\n Surface-Wave Optimization: Huygens' metasurfaces have demonstrated the ability to tailor electromagnetic\nwavefronts with passive low-profile structures. The fundamental constraint\nenabling passive and ideally lossless solutions is the conservation of the\nnormal real power locally along the metasurface. In this work, we examine the\nuse of auxiliary surface waves to overcome this limitation and design Huygens'\nmetasurfaces for wave transformations with different incident and output power\ndensity profiles. The developed method relies on the optimization of a\nsurface-wave distribution that is utilized to redistribute the power at the\ninput side of the metasurface without incurring any reflections. A full design\nexample is presented with a linear patch array along the H-plane illuminating a\nmetasurface that produces uniform output fields along the E-plane. A high\naperture illumination efficiency of 92% is obtained despite the small distance\nbetween the source and the metasurface. Moreover, the effects of the evanescent\nspectrum to the losses and the bandwidth of the structure are discussed.", "category": "physics_app-ph" }, { "text": "Mechanical mode engineering with orthotropic metamaterial membranes: Metamaterials are structures engineered at a small scale with respect to the\nwavelength of the excitations they interact with. These structures behave as\nartificial materials whose properties can be chosen by design, mocking and even\noutperforming natural materials and making them the quintessential tool for\nmanipulation of wave systems. In this Letter we show how the acoustic\nproperties of a silicon nitride membrane can be affected by nanopatterning. The\ndegree of asymmetry in the pattern geometry induces an artificial anisotropic\nelasticity, resulting in the splitting of otherwise degenerate mechanical\nmodes. The artificial material we introduce has a maximum Ledbetter-Migliori\nanisotropy of 1.568, favorably comparing to most bulk natural crystals. With an\nadditional freedom in defining arbitrary asymmetry axes by pattern rotation,\nour approach can be useful for fundamental investigation of material properties\nas well as for devising improved sensors of light, mass or acceleration based\non micromechanical resonators.", "category": "physics_app-ph" }, { "text": "Device physics of van der Waals heterojunction solar cells: Heterostructures based on atomically thin semiconductors are considered a\npromising emerging technology for the realization of ultrathin and ultralight\nphotovoltaic solar cells on flexible substrates. Much progress has been made in\nrecent years on a technological level, but a clear picture of the physical\nprocesses that govern the photovoltaic response remains elusive. Here, we\npresent a device model that is able to fully reproduce the current-voltage\ncharacteristics of type-II van der Waals heterojunctions under optical\nillumination, including some peculiar behaviors such as exceedingly high\nideality factors or bias-dependent photocurrents. While we find the spatial\ncharge transfer across the junction to be very efficient, we also find a\nconsiderable accumulation of photogenerated carriers in the active device\nregion due to poor electrical transport properties, giving rise to significant\ncarrier recombination losses. Our results are important to optimize future\ndevice architectures and increase power conversion efficiencies of atomically\nthin solar cells.", "category": "physics_app-ph" }, { "text": "Magnet-Free Nonreciprocal Phase-Shifter Based on Time Modulation: Recently, nonreciprocal phase shifters have attracted a surge of interest\nthanks to the advent of nonreciprocal electromagnetic systems, such as\nnonreciprocal metasurfaces, nonreciprocal-beam antennas, and invisibility\ncloaks. To overcome the limitations associated with conventional technologies\nfor realizing nonreciprocal phase shifters and gyrators, here we propose a\nlow-noise, lightweight, low-profile, and linear magnetless nonreciprocal phase\nshifter formed by two temporal loops. The proposed temporal apparatus operates\nbased on the generation of time-harmonic signals and destructive and\nconstructive interferences for the undesired and desired time harmonics,\nrespectively, at different locations of the structure. An external\ntime-harmonic modulation signal injects an effective electronic angular\nmomentum to the system to control the phase and frequency of the two loops.\nSuch a temporal nonreciprocal phase shifter offers low insertion loss, and a\nlarge return loss (input matching) of greater than 28.1 dB. Additionally, this\nnonreciprocal phase shifter possesses a reconfigurable architecture and can be\ndirectly embedded in integrated circuit (IC) technology to create high power\nhandling and linear IC-based nonreciprocal phase shifters.", "category": "physics_app-ph" }, { "text": "Self-formed 2D/3D Heterostructure on the Edge of 2D Ruddlesden-Popper\n Hybrid Perovskites Responsible for Intriguing Optoelectronic Properties and\n Higher Cell Efficiency: The observation of low energy edge photoluminescence and its beneficial\neffect on the solar cell efficiency of Ruddlesden-Popper perovskites has\nunleashed an intensive research effort to reveal its origin. This effort,\nhowever, has been met with more challenges as the underlying material structure\nhas still not been identified; new modellings and observations also do not seem\nto converge. Using 2D (BA)2(MA)2Pb3Br10 as an example, we show that 3D MAPbBr3\nis formed due to the loss of BA on the edge. This self-formed MAPbBr3 can\nexplain the reported edge emission under various conditions, while the reported\nintriguing optoelectronic properties such as fast exciton trapping from the\ninterior 2D perovskite, rapid exciton dissociation and long carrier lifetime\ncan be understood via the self-formed 2D/3D lateral perovskite heterostructure.\nThe 3D perovskite is identified by submicron infrared spectroscopy, the\nemergence of XRD signature from freezer-milled nanometer-sized 2D perovskite\nand its photoluminescence response to external hydrostatic pressure. The\nrevelation of this edge emission mystery and the identification of a\nself-formed 2D/3D heterostructure provide a new approach to engineering 2D\nperovskites for high-performance optoelectronic devices.", "category": "physics_app-ph" }, { "text": "Electrical readout microwave-free sensing with diamond: While nitrogen-vacancy (NV-) centers have been extensively investigated in\nthe context of spin-based quantum technologies, the spin-state readout is\nconventionally performed optically, which may limit miniaturization and\nscalability. Here, we report photoelectric readout of ground-state\ncross-relaxation features, which serves as a method for measuring electron spin\nresonance spectra of nanoscale electronic environments and also for\nmicrowave-free sensing. As a proof of concept, by systematically tuning NV\ncenters into resonance with the target electronic system, we extracted the\nspectra for the P1 electronic spin bath in diamond. Such detection may enable\nprobing optically inactive defects and the dynamics of local spin environment.\nWe also demonstrate a magnetometer based on photoelectric detection of the\nground-state level anticrossings (GSLAC), which exhibits a favorable detection\nefficiency as well as magnetic sensitivity. This approach may offer potential\nsolutions for determining spin densities and characterizing local environment.", "category": "physics_app-ph" }, { "text": "Stability tests in time of OAM multiplexing schemes in highly disturbed\n environments: We report the results of tests of data transmission and signal stability in\ntime of two different wide-band multiplexing (MUX) schemes, each in a\npoint-to-point configuration, based on electromagnetic waves carrying Orbital\nAngular Momentum (OAM) in noisy real-world settings. Each radio link\ntransmitted two high definition wide--band analog TV channels in the same\nfrequency band with FM-carrier centered at $2.414$ GHz and $27$ MHz bandwidth,\nencoded with different OAM modes in the same polarization state,\nuninterruptedly for $5$ months during the world exhibition\n``Globale--Digitale'' at ZKM in Karlsruhe and in other $2$ months time slots\ntaken in the following $4$ years, $24$ hours per day. We show the practical\nfeasibility of the use of stable OAM radio/TV links in the real world for a\nlong time, paving the way for for secure and efficient communication schemes\nalso under electromagnetic jamming conditions.", "category": "physics_app-ph" }, { "text": "Magnetic Nanoparticle Relaxation Dynamics-based Magnetic Particle\n Spectroscopy (MPS) for Rapid and Wash-free Molecular Sensing: Magnetic nanoparticles (MNPs) have been extensively used as contrasts and\ntracers for bioimaging, heating sources for tumor therapy, carriers for\ncontrolled drug delivery, and labels for magnetic immunoassays. Here, we\ndescribe a MNP relaxation dynamics-based magnetic particle spectroscopy (MPS)\nmethod for the quantitative detection of molecular biomarkers. In MPS\nmeasurements, the harmonics of oscillating MNPs are recorded and used as a\nmetric for the freedom of rotational motion, which indicates the bound states\nof the MNPs. These harmonics can be collected from microgram quantities of iron\noxide nanoparticles within 10 seconds. Using a streptavidin-biotin binding\nsystem, we demonstrate the feasibility of using MPS to sense these molecular\ninteractions, showing this method is able to achieve rapid, wash-free\nbioassays, and is suitable for future point-of-care (POC), sensitive, and\nversatile diagnosis.", "category": "physics_app-ph" }, { "text": "Maximal nighttime electrical power generation via optimal radiative\n cooling: We present a systematic optimization of nighttime thermoelectric power\ngeneration system utilizing radiative cooling. We show that an electrical power\ndensity over 2 W/m2, two orders of magnitude higher than the previously\nreported experimental result, is achievable using existing technologies. This\nsystem combines radiative cooling and thermoelectric power generation and\noperates at night when solar energy harvesting is unavailable. The\nthermoelectric power generator (TEG) itself covers less than 1 percent of the\nsystem footprint area when achieving this optimal power generation, showing\neconomic feasibility. We study the influence of emissivity spectra, thermal\nconvection, thermoelectric figure of merit and the area ratio between the TEG\nand the radiative cooler on the power generation performance. We optimize the\nthermal radiation emitter attached to the cold side and propose practical\nmaterial implementation. The importance of the optimal emitter is elucidated by\nthe gain of 153% in power density compared to regular blackbody emitters.", "category": "physics_app-ph" }, { "text": "Metasurfaces with Interleaved Electric and Magnetic Resonances for\n Broadband Arbitrary Group Delay in Reflection: Metasurfaces impart phase discontinuities on impinging electromagnetic waves\nthat are typically limited to 0-2$\\pi$. Here, we show that they can break free\nfrom this limitation and supply arbitrarily-large phase modulation over\nultra-wide bandwidths. This is achieved by implementing multiple,\nproperly-arranged resonances in the electric and magnetic sheet admittivities.\nWe demonstrate metasurfaces that can perfectly reflect a broadband pulse\nimparting a prescribed group delay without distorting the pulse shape, opening\nnew possibilities for temporal control and dispersion engineering across deeply\nsubwavelength physical scales.", "category": "physics_app-ph" }, { "text": "A simple strategy to measure the contact resistance between metals and\n doped organic films: Charge injection from electrodes into doped organic films is a widespread\ntechnology used in the majority of state-of-the-art organic semiconductor\ndevices. Although such interfaces are commonly considered to form Ohmic\ncontacts via strong band bending, an experiment that directly measures the\ncontact resistance has not yet been demonstrated. In this study, we use a\nsimple metal/doped organic semiconductor/metal stack and study its\nvoltage-dependent resistance. A transport layer thickness variation proves that\nthe presented experiment gains direct access to the contact resistance of the\ndevice. We can quantify that for an operating current density of 10mA/cm2 the\ninvestigated material system exhibits a voltage drop over the metal/organic\ninterface of about 200mV, which can be reduced by more than one order of\nmagnitude when employing an additional injection layer. The presented\nexperiment proposes a simple strategy to measure the contact resistance between\nany metal and doped organic film without applying numerical tools or elaborate\ntechniques. Furthermore, the simplistic device architecture allows for very\nhigh, homogeneous, and tunable electric fields within the organic layer, which\nenables a clear investigation of the Poole-Frenkel effect.", "category": "physics_app-ph" }, { "text": "500 GHz plasmonic Mach-Zehnder modulator enabling sub-THz microwave\n photonics: Broadband electro-optic intensity modulators are essential to convert\nelectrical signals to the optical domain. The growing interest in THz wireless\napplications demands modulators with frequency responses to the sub-THz range,\nhigh power handling and very low nonlinear distortions, simultaneously.\nHowever, a modulator with all those characteristics has not been demonstrated\nto date. Here we experimentally demonstrate that plasmonic modulators do not\ntrade off any performance parameter, featuring - at the same time - a short\nlength of 10s of micrometers, record-high flat frequency response beyond 500\nGHz, high power handling and high linearity, and we use them to create a\nsub-THz radio-over-fiber analog optical link. These devices have the potential\nto become a new tool in the general field of microwave photonics, making the\nsub-THz range accessible to e.g. 5G wireless communications, antenna remoting,\nIoT, sensing, and more.", "category": "physics_app-ph" }, { "text": "Rapid, Quantitative Therapeutic Screening for Alzheimer's Enzymes\n Enabled by Optimal Signal Transduction with Transistors: We show that simple, commercially sourced n-channel silicon field-effect\ntransistors (nFETs) operating under closed loop control exhibit an ~3-fold\nimprovement in pH readout resolution to (7.2+/-0.3)x10^-3 at a bandwidth of 10\nHz when compared with the open loop operation commonly employed by integrated\nion-sensitive field-effect transistors (ISFETs). We leveraged the improved nFET\nperformance to measure the change in solution pH arising from the activity of a\npathological form of the kinase Cdk5, an enzyme implicated in Alzheimer's\ndisease, and showed quantitative agreement with previous measurements. The\nimproved pH resolution was realized while the devices were operated in a remote\nsensing configuration with the pH sensing element off-chip and connected\nelectrically to the FET gate terminal. We compared these results with those\nmeasured by using a custom-built dual-gate 2D field-effect transistor (dg2DFET)\nfabricated with 2D semi-conducting MoS2 channels and a moderate device gain,\nalpha=8. Under identical solution conditions the pH resolution of the nFETs was\nonly 2-fold worse than the dg2DFETs pH resolution of (3.9+/-0.7)x10^-3.\nFinally, using the nFETs, we demonstrated the effectiveness of a custom\npolypeptide, p5, as a therapeutic agent in restoring the function of Cdk5. We\nexpect that the straight-forward modifications to commercially sourced nFETs\ndemonstrated here will lower the barrier to widespread adoption of these\nremote-gate devices and enable sensitive bioanalytical measurements for high\nthroughput screening in drug discovery and precision medicine applications.", "category": "physics_app-ph" }, { "text": "Breaking Through the Plasma Wavelength Barrier to Extend the\n Transparency Range of Ultrathin Indium Tin Oxide Films into the Far Infrared: Indium tin oxide (ITO) film, which is the most commonly used transparent\nconductive film (TCF), has traditionally been believed to be transparent in the\nvisible spectrum but to reflect infrared (IR) light beyond the plasma\nwavelength (${\\lambda}_p$). However, our theoretical analysis challenges this\nnotion by demonstrating that an ultrathin ITO TCF that is thinner than the\nlight's penetration depth, can overcome the transmission barrier at\n${\\lambda}_p$. To validate the theoretical modeling, we have successfully\nfabricated ITO films that, despite having ${\\lambda}_p \\approx$ 1 ${\\mu}$m,\nremain transparent from 400 nm to 20 ${\\mu}$m. This represents the broadest\ntransparency range ever reported for any In$_2$O$_3$-based TCF. The 10-nm-thick\nITO TCFs have high visible transmittance (91.0% at 550 nm), low resistivity (5\n$\\times$ 10$^{-4}$ ${\\Omega}\\cdot$ cm), and good IR transmittance (averaging\n60% over 1.35 $\\unicode{x2013}$ 18.35 ${\\mu}$m). Their IR transparency\nfacilitates radiative cooling of the underlying circuitry. When an operational\nresistor is enclosed by commercial ITO TCFs that are 140 nm thick, its\ntemperature increases. However, using 10-nm-thick ITO TCFs instead of the\ncommercial ones can completely avoid this temperature rise. Moreover, attaching\na silver grid to a 10-nm-thick ITO TCF can reduce the effective sheet\nresistance to ~10 ${\\Omega}/\\square$ at the expense of only ~3% transmittance.\nThis development paves the way for large-scale applications that require low\nsheet resistance and far-IR transparency.", "category": "physics_app-ph" }, { "text": "BAlN alloy for enhanced two-dimensional electron gas characteristics of\n GaN-based high electron mobility transistor: The emerging wide bandgap BAlN alloys have potentials for improved\nIII-nitride power devices including high electron mobility transistor (HEMT).\nYet few relevant studies have been carried. In this work, we have investigated\nthe use of the B0.14Al0.86N alloy as part or entirety of the interlayer between\nthe GaN buffer and the AlGaN barrier in the conventional GaN-based high\nelectron mobility transistor (HEMT). The numerical results show considerable\nimprovement of the two-dimensional electron gas (2DEG) concentration with small\n2DEG leakage into the ternary layer by replacing the conventional AlN\ninterlayer by either the B0.14Al0.86N interlayer or the B0.14Al0.86N/AlN hybrid\ninterlayer. Consequently, the transfer characteristics can be improved. The\nsaturation current can be enhanced as well. For instance, the saturation\ncurrents for HEMTs with the 0.5 nm B0.14Al0.86N/0.5 nm AlN hybrid interlayer\nand the 1 nm B0.14Al0.86N interlayer are 5.8% and 2.2% higher than that for the\nAlN interlayer when VGS-Vth= +3 V.", "category": "physics_app-ph" }, { "text": "A wireless triboelectric nanogenerator: We demonstrate a new paradigm for the wireless harvesting of mechanical\nenergy via a 3D-printed triboelectric nanogenerator (TENG) which comprises a\ngraphene polylactic acid (gPLA) nanocomposite and Teflon. The synergistic\ncombination of eco-friendly PLA with graphene in our TENG exhibited an output\nvoltage > 2 kV with an instantaneous peak power of 70 mW, which in turn\ngenerated a strong electric field to enable the wireless transmission of\nharvested energy over a distance of 3 m. Specifically, we demonstrate wireless\nand secure actuatation of smart-home applications such as smart tint windows,\ntemperature sensors, liquid crystal displays, and security alarms either with a\nsingle or a specific user-defined passcode of mechanical pulses (e.g.,\nFibonacci sequence). Notably, such high electric output of a gPLA-based TENG\nenabled unprecedented wireless transmission of harvested mechanical energy into\na capacitor, thus obviating the need for additional electronics or energy\nsources. The scalable additive manufacturing approach for gPLA-based TENGs,\nalong with their high electrical output can revolutionize the present method of\nharnessing the mechanical energy available in our environment.", "category": "physics_app-ph" }, { "text": "Polariton-Based Room Temperature Quantum Phototransistors: Strong light-matter coupling is a quantum process in which light and matter\nare coupled together, generating hybridized states. This is similar to the\nnotion of molecular hybridization, but one of the components is light. Here, we\nutilized the idea and prepared quantum phototransistors using donor-acceptor\ncombinations that can transfer energy via Rabi oscillations. As a prototype\nexperiment, we used a cyanine J-aggregate (TDBC; donor) and MoS2 monolayer\n(acceptor) in a field effect transistor cavity and studied the\nphotoresponsivity. The energy migrates through the newly formed polaritonic\nladder, and the relative efficiency of the device is nearly seven-fold at the\nON resonance. Further, the photon mixing fraction is calculated for each\nindependent device and correlated with energy transfer efficiency. In the\nstrongly coupled system, newly formed polaritonic states reshuffle the\nprobability function. A theoretical model based on the time dependent\nSchr\\\"odinger equation is also used to interpret the results. Here, the\nentangled light-matter states act as a strong channel for funnelling the energy\nto the MoS2 monolayer, thereby boosting its ability to show the highest\nphotoresponsivity at ON-resonance. These experimental findings and the proposed\nmodel suggest novel applications of strong light-matter coupling in quantum\nmaterials.", "category": "physics_app-ph" }, { "text": "Stiffness modeling for near field acoustic levitation bearings: The dynamic characteristics of near-field levitation bearings have been\ninvestigated in this study. Through theoretical analysis, two different types\nof system stiffness are defined and derived analytically. The dynamic stiffness\nrelates the excitation amplitude to the dynamic force amplitude, while the\neffective stiffness governs the time-averaged force-displacement relationship.\nThe results indicate two non-linear and asymmetric spring constants that can\neffectively predict levitation force and height. The models are verified with a\ncarefully designed experimental setup to eliminate the structural resonance\neffect. Besides, some unique dynamic behaviors are investigated and predicted\nbased on the proposed stiffness model.", "category": "physics_app-ph" }, { "text": "The Software-Defined Metasurfaces Concept and Electromagnetic Aspects: We present the concept and electromagnetic aspects of HyperSurFaces (HSFs),\nartificial, ultrathin structures with software controlled electromagnetic\nproperties. The HSFs key unit is the metasurface, a plane with designed\nsubwavelength features whose electromagnetic response can be tuned via\nvoltage-controlled continuously-tunable electrical elements that provide local\ncontrol of the surface impedance and advanced functionalities, such as tunable\nperfect absorption or wavefront manipulation. A nanonetwork of controllers\nenables software defined HSFs control related to the emerging Internet of\nThings paradigm.", "category": "physics_app-ph" }, { "text": "Tunable RF and microwave photonic sideband generator based on cascaded\n 49GHz and 200GHz integrated ring resonators: We demonstrate a continuously RF tunable orthogonally polarized optical\nsingle sideband (OP-OSSB) generator based on dual cascaded micro-ring\nresonators. By splitting the input double sideband signal into an orthogonally\npolarized carrier and lower sideband via TE- and TM-polarized MRRs, an OP-OSSB\nsignal is generated. A large tuning range of the optical carrier to sideband\nratio of up to 57.3 dB is achieved by adjusting the polarization angle of the\ninput light. The operation RF frequency of the OP-OSSB generator can be\ncontinuously tuned with a 21.4 GHz range via independent thermal control of the\ntwo MRRs. Our device represents a competitive approach towards OP-OSSB\ngeneration with wideband tunable RF operation, and is promising for photonic RF\nsignal transmission and processing in radar and communication systems.", "category": "physics_app-ph" }, { "text": "Nanoscale sensing based on nitrogen vacancy centersin single crystal\n diamond and nanodiamonds:achievements and challenges: Powered by the mutual developments in instrumentation, materials\nandtheoretical descriptions, sensing and imaging capabilities of quantum\nemitters insolids have significantly increased in the past two decades. Quantum\nemitters insolids, whose properties resemble those of atoms and ions, provide\nalternative waysto probing natural and artificial nanoscopic systems with\nminimum disturbance andultimate spatial resolution. Among those emerging\nquantum emitters, the nitrogen-vacancy (NV) color center in diamond is an\noutstanding example due to its intrinsicproperties at room temperature\n(highly-luminescent, photo-stable, biocompatible,highly-coherent spin states).\nThis review article summarizes recent advances andachievements in using NV\ncenters within nano- and single crystal diamonds in sensingand imaging. We also\nhighlight prevalent challenges and material aspects for differenttypes of\ndiamond and outline the main parameters to consider when using color centersas\nsensors. As a novel sensing resource, we highlight the properties of NV\ncentersas light emitting electrical dipoles and their coupling to other\nnanoscale dipoles e.g.graphene.", "category": "physics_app-ph" }, { "text": "Depth resolution in piezoresponse force microscopy: Piezoresponse Force Microscopy (PFM) is one of the most widespread methods\nfor investigating and visualizing ferroelectric domain structures down to the\nnanometer length scale. PFM makes use of the direct coupling of the\npiezoelectric response to the crystal lattice, and hence is most often applied\nto spatially map the 3-dimensional (3D) near-surface domain distribution of any\npolar or ferroic sample. Nonetheless, since most samples investigated by PFM\nare at least semiconducting or fully insulating, the electric ac field emerging\nfrom the conductive scanning force microscopy (SFM) tip, penetrates the sample,\nand hence may also couple to polar features that are deeply buried into the\nbulk of the sample under investigation. Thus, in the work presented here, we\nexperimentally and theoretically explore the contrast and depth resolution\ncapabilities of PFM, by analyzing the dependence of several key parameters.\nThese key parameters include the depth of the buried feature, i.e. here a\ndomain wall (DW), as well as PFM-relevant technical parameters such as the tip\nradius, the PFM drive voltage and frequency, and the signal-to-noise ratio. The\ntheoretical predictions are experimentally verified using x-cut\nperiodically-poled lithium niobate single crystals that are specially prepared\ninto wedge-shaped samples, in order to allow the buried feature, here the DW,\nto be `positioned' at any depth into the bulk. This inspection essentially\ncontributes to the fundamental understanding in PFM contrast analysis, and to\nthe reconstruction of 3D domain structures down to a 1-$\\mu$m-penetration depth\ninto the sample.", "category": "physics_app-ph" }, { "text": "Radiation Shielding Properties of $Nd_{0.6}Sr_{0.4}Mn_{1-y}Ni_{y}O_{3}$\n Substitute with Different Concentrations of Nickle: In this work, we investigate the effect of Ni concentration on several\nshielding properties of $Nd_{0.6}Sr_{0.4}Mn_{1-y}Ni_{y}O_{3}$ (0.00 $\\leq$ y\n$\\leq$ 0.20) perovskite ceramic for possible use as radiation shielding\nmaterials. X-ray diffraction (XRD) analysis revealed that these ceramics have\nthe orthorhombic structure with group space Pnma over a wide range of\nNi-substitutions. Moreover, the analysis showed a nearly linear decrease in the\nlattice parameters and the unit cell volume (V) causing a gradual increase in\nthe packing density with increasing Ni concentration. The shielding features\nfor photons, neutrons, and protons of all ceramic samples were assessed. The\nmass attenuation coefficient (MAC) was computed at 0.1, 0.6, 1.25, 5 and 15 MeV\nby utilizing (MCNP) (version 5.0); the results were compared with the\ncorresponding values obtained using Phy-X and XCOM program. The results\nobtained showed slight enhancement with increasing Ni contents. The\nsubstitution of Ni leads to progressive enhancement in effective removal\ncross-section of fast neutron (${\\Sigma}$R) values. Whereas the values of Mass\nStopping Power (MSP) and projected range for the protons showed a gradual\nreduction with increasing Ni concentration. These findings suggest that the\ncurrent ceramic samples can be useful as radiation shielding materials.", "category": "physics_app-ph" }, { "text": "Motion and trapping of micro- and millimeter-sized particles on the\n air-paramagnetic-liquid interface: Understanding the motion of particles on an air-liquid interface can impact a\nwide range of scientific fields and applications. Diamagnetic particles\nfloating on an air-paramagnetic-liquid interface are previously known to have a\nrepulsive motion from a magnet. Here, we show a motion mechanism where the\ndiamagnetic particles floating on the air-paramagnetic-liquid interface are\nattracted and eventually trapped at an off-center distance from the magnet. The\nbehavior of magnetic particles has been also studied and the motion mechanisms\nare theorized in a unified framework, revealing that the motion of particles on\nan air-paramagnetic-liquid interface is governed not only by magnetic energy,\nbut as an interplay of the curvature of the interface deformation created by\nthe nonuniform magnetic field, the gravitational potential, and the magnetic\nenergy from the particle and the liquid. The attractive motion mechanism has\nbeen applied in directed self-assembly and robotic particle guiding.", "category": "physics_app-ph" }, { "text": "Twist Coupled Kirigami Cellular Metamaterials and Mechanisms: Manipulation of thin sheets by folding and cutting offers opportunity to\nengineer structures with novel mechanical properties, and to prescribe complex\nforce-displacement relationships via material elasticity in combination with\nthe trajectory imposed by the fold topology. We study the mechanics of cellular\nKirigami that rotates upon compression, which we call Flexigami; the addition\nof diagonal cuts to an equivalent closed cell permits its reversible collapse\nwithout incurring significant tensile strains in its panels. Using\nfinite-element modeling and experiment we show how the mechanics of flexigami\nis governed by the coupled rigidity of the panels and hinges and we design\nflexigami to achieve reversible force response ranging from smooth\nmono-stability to sharp bi-stability. We then demonstrate the use of flexigami\nto construct laminates with multi-stable behavior, a rotary-linear boom\nactuator, and self-deploying cells with activated hinges. Advanced digital\nfabrication methods can enable the practical use of flexigami and other\nmetamaterials that share its underlying principles, for applications such as\nmorphing structures, soft robotics and medical devices.", "category": "physics_app-ph" }, { "text": "Towards highly efficient thin-film solar cells with a graded-bandgap\n CZTSSe layer: A coupled optoelectronic model was implemented along with the differential\nevolution algorithm to assess the efficacy of grading the bandgap of the CZTSSe\nlayer for enhancing the power conversion efficiency of thin-film CZTSSe solar\ncells. Both linearly and sinusoidally graded bandgaps were examined, with the\nmolybdenum backreflector in the solar cell being either planar or periodically\ncorrugated. Whereas an optimally graded bandgap can dramatically enhance the\nefficiency, the effect of periodically corrugating the backreflector is modest\nat best. An efficiency of 21.74% is predicted with sinusoidal grading of a\n870-nm-thick CZTSSe layer, in comparison to 12.6% efficiency achieved\nexperimentally with a 2200-nm-thick homogeneous CZTSSe layer. High\nelectron-hole-pair generation rates in the narrow-bandgap regions and a high\nopen-circuit voltage due to a wider bandgap close to the front and rear faces\nof the CZTSSe layer are responsible for the high enhancement of efficiency.", "category": "physics_app-ph" }, { "text": "Impact of die carrier on reliability of power LEDs: High power light emitting diodes (LEDs) suffer from heating effects that have\na detrimental impact on the devices characteristics. The use LED carriers with\nhigh thermal conductivity promotes the extraction of heat away from the LED\njunction. Different materials can be used for this purpose, such as alumina,\naluminium nitride, and silicon. Diamond has also been gaining momentum for\ndemanding heat management applications. In order to evaluate the impact of the\ndifferent carriers on the reliability of the devices, the junction temperature\nof Cree white Xamp XB-D LEDs was obtained with Ansys for various carrier at\ndifferent LED current levels. The impact of the junction temperature on the\nLEDs lifetime, emission intensity, footprint and wavelength stability was then\nevaluated for each carrier based on the datasheet of the devices. The results\nprovide additional knowledge regarding the impact of the carrier on the\nperformance of the LED.", "category": "physics_app-ph" }, { "text": "Harvesting the electromagnetic energy confined close to a hot body: In the close vicinity of a hot body, at distances smaller than the thermal\nwavelength, a high electromagnetic energy density exists due to the presence of\nevanescent fields radiated by the partial charges in motion around its surface.\nThis energy density can surpass the energy density in vacuum by several orders\nof magnitude. By approaching a PV cell with a band gap in the infrared\nfrequency range this non-radiative energy can be transferred to it by photon\ntunneling and surface mode coupling. Here we review the basic ideas and recent\nprogress in near-field energy harvesting.", "category": "physics_app-ph" }, { "text": "High-throughput screening of quaternary compounds and new insight for\n excellent thermoelectric performance: It is well known that the high electric conductivity, large Seebeck\ncoefficient, and low thermal conductivity are preferred for enhancing\nthermoelectric performance, but unfortunately, these properties are strongly\ninter-correlated with no rational scenario for their efficient decoupling. This\nbig dilemma for thermoelectric research appeals for alternative strategic\nsolutions, while the high-throughput screening is one of them. In this work, we\nstart from total 3136 real electronic structures of the huge X2YZM4 quaternary\ncompound family and perform the high-throughput searching in terms of enhanced\nthermoelectric properties. The comprehensive data-mining allows an evaluation\nof the electronic and phonon characteristics of those promising thermoelectric\nmaterials. More importantly, a new insight that the enhanced thermoelectric\nperformance benefits substantially from the coexisting quasi-Dirac and heavy\nfermions plus strong optical-acoustic phonon hybridization, is proposed. This\nwork provides a clear guidance to theoretical screening and experimental\nrealization and thus towards development of performance-excellent\nthermoelectric materials.", "category": "physics_app-ph" }, { "text": "Domain Wall Motion Driven by Laplace Pressure in CoFeB-MgO Nanodots with\n Perpendicular Anisotropy: We have studied the magnetization reversal of CoFeB-MgO nanodots with\nperpendicular anisotropy for size ranging from w=400 nm to 1 {\\mu}m. Contrary\nto previous experiments, the switching field distribution is shifted toward\nlower magnetic fields as the size of the elements is reduced with a mean\nswitching field varying as 1/w. We show that this mechanism can be explained by\nthe nucleation of a pinned magnetic domain wall (DW) at the edges of the\nnanodots where damages are introduced by the patterning process. As the surface\ntension (Laplace pressure) applied on the DW increases when reducing the size\nof the nanodots, we demonstrate that the depinning field to reverse the entire\nelements varies as 1/w. These results suggest that the presence of DWs has to\nbe considered in the switching process of nanoscale elements and open a path\ntoward scalable spintronic devices.", "category": "physics_app-ph" }, { "text": "Single TeraFET Radiation Spectrometer: The new TeraFET design with identical source and drain antennas enables a\ntunable resonant polarization-sensitive plasmonic spectrometer operating in the\nsub-terahertz and terahertz (THz) range of frequencies at room temperature. It\ncould be implemented in different materials systems including silicon. The\np-diamond TeraFETs support operation in the 200 to 600 GHz windows.", "category": "physics_app-ph" }, { "text": "Wet Scandium Etching for hard mask formation on a silicon substrate: Nowadays, microelectronics and nanoelectronics require the search for new\nmaterials, including masks for creating structures. Today, the intermediate\nhard mask strategy is one of the key issues in achieving a good balance between\nlithography and etching at the microelectronic fabrication. One of the\ninteresting challenges in microelectronics and photovoltaics is the creation of\ninterspacing, vertically oriented silicon arrays on Si substrate for\nsemiconductor devices with multi-function. The fabrication of such structures\nis still a serious technological problem and requires searching for new\napproaches and materials. In this work, we propose using scandium as a new hard\nmask material over silicon due to its high resistance to plasma chemical\netching and low sputtering coefficient. We have shown that a wet etching of the\nscandium layer with a thickness of several nanometers can be used to obtain\npattern structures with a resolution of up to 4 microns, which is a good result\nfor the wet etching approach. Scandium metal was found to be an excellent\nresistant mask over silicon under the selected plasma etching conditions.\nTherefore, a scandium hard mask can open up new possibilities for the formation\nof different microscale topographical patterns.", "category": "physics_app-ph" }, { "text": "Divinylglycol, a Glycerol-Based Monomer: Valorization, Properties, and\n Applications: In the context of the development of bio-refineries, glycerol and its\nderivatives are co-products of the oleochemistry for which new valorization\nroutes must be found. In this study, the polymerizability of divinylglycol\n(DVG), a symmetrical C-6 glycerol derivative which bears a vicinal diol and two\nvinyl functions was studied. The reactivity of the hydroxyl and vinyl functions\nof DVG through polycondensation and polyaddition reactions was investigated. In\na first step, the synthesis of polyesters was carried out by reaction of DVG\nwith various biosourced diesters. In a second route, DVG was polymerized\nthrough its vinyl functions by ADMET and thiol-ene addition. Finally,\nthree-dimensional epoxy-amine networks were prepared from a series of diamines\nand bis-epoxidized DVG, the latter being prepared by oxidation of the DVG\ndouble bonds. These different polymerization reactions showed that DVG double\nbonds were more reactive than the alcohol ones and that a panel of original\npolymers could be obtained from this bio-sourced synthon.", "category": "physics_app-ph" }, { "text": "Synthesis and optical characterization of perovskite layer for solar\n cell application: Solvent engineering offers fine control over the photovoltaic efficiency,\nfilm morphology, and crystallization quality of perovskite films and also\nenables to optimize light transmittance and absorbance in solar cell\napplications. In the present work, the band gap and reflectance were reduced\nthrough solvent engineering. We found that perovskite thin films produced using\nDMF (Dimethyl formamide) solvent had a band gap that was 0.24 eV less than\nthose produced using IPA (Isopropyl Alcohol) solvent. Perovskite thin films\nproduced using DMF solvent also exhibited considerably lower solar spectrum\nreflectance.", "category": "physics_app-ph" }, { "text": "Coherently Enhanced Wireless Power Transfer: Extraction of electromagnetic energy by an antenna from impinging external\nradiation is at the basis of wireless communications and power transfer (WPT).\nThe maximum of transferred energy is ensured when the antenna is conjugately\nmatched, i.e., when it is resonant and it has an equal coupling with free space\nand its load, which is not easily implemented in near-field WPT. Here, we\nintroduce the concept of coherently enhanced wireless power transfer. We show\nthat a principle similar to the one underlying the operation of coherent\nperfect absorbers can be employed to improve the overall performance of WPT and\npotentially achieve its dynamic control. The concept relies on coherent\nexcitation of the waveguide connected to the antenna load with a backward\npropagating signal of specific amplitude and phase. This signal creates a\nsuitable interference pattern at the load resulting in a modification of the\nlocal wave impedance, which in turn enables conjugate matching and a largely\nincreased amount of energy extracted to the waveguide. We develop an\nillustrative theoretical model describing this concept, demonstrate it with\nfull-wave numerical simulations for the canonical example of a dipole antenna,\nand verify it experimentally in both near-field and far-field regimes.", "category": "physics_app-ph" }, { "text": "On the use of deep neural networks in optical communications: Information transfer rates in optical communications may be dramatically\nincreased by making use of spatially non-Gaussian states of light. Here we\ndemonstrate the ability of deep neural networks to classify\nnumerically-generated, noisy Laguerre-Gauss modes of up to 100 quanta of\norbital angular momentum with near-unity fidelity. The scheme relies only on\nthe intensity profile of the detected modes, allowing for considerable\nsimplification of current measurement schemes required to sort the states\ncontaining increasing degrees of orbital angular momentum. We also present\nresults that show the strength of deep neural networks in the classification of\nexperimental superpositions of Laguerre-Gauss modes when the networks are\ntrained solely using simulated images. It is anticipated that these results\nwill allow for an enhancement of current optical communications technologies.", "category": "physics_app-ph" }, { "text": "A high aspect ratio Fin-Ion Sensitive Field Effect Transistor:\n compromises towards better electrochemical bio-sensing: The development of next generation medicines demand more sensitive and\nreliable label free sensing able to cope with increasing needs of multiplexing\nand shorter times to results. Field effect transistor-based biosensors emerge\nas one of the main possible technologies to cover the existing gap. The general\ntrend for the sensors has been miniaturisation with the expectation of\nimproving sensitivity and response time, but presenting issues with\nreproducibility and noise level. Here we propose a Fin-Field Effect Transistor\n(FinFET) with a high heigth to width aspect ratio for electrochemical\nbiosensing solving the issue of nanosensors in terms of reproducibility and\nnoise, while keeping the fast response time. We fabricated different devices\nand characterised their performance with their response to the pH changes that\nfitted to a Nernst-Poisson model. The experimental data were compared with\nsimulations of devices with different aspect ratio, stablishing an advantage in\ntotal signal and linearity for the FinFETs with higher aspect ratio. In\naddition, these FinFETs promise the optimisation of reliability and efficiency\nin terms of limits of detection, for which the interplay of the size and\ngeometry of the sensor with the diffusion of the analytes plays a pivotal role.", "category": "physics_app-ph" }, { "text": "Interaction of Love waves with coupled cavity modes in a 2D holey\n phononic crystal: The interaction of Love waves with square array of pillars deposited on a\ncavity defined in a 2D holey phononic crystal is numerically investigated using\nFinite Element Method. First, the existence of SH surface modes is demonstrated\nseparately for phononic crystals that consist of square arrayed holes, or\nrectangular arrayed Ni pillars, respectively in, or on, a SiO2 film deposited\non a ST-cut quartz substrate. The coupling between SH modes and torsional mode\nin pillars induces a transmission dip that occurs at a frequency located in the\nrange of the band-gap of the holey phononic crystal. Second, a cavity is\nconstructed by removing lines of holes in the holey phononic crystal and\nresults in a transmission peak that matches the dip. The optimal geometrical\nparameters enable us to create a coupling of the cavity mode and the localized\npillar mode by introducing lines of pillars into the cavity, which\nsignificantly improved the efficiency of the cavity without increasing the\ncrystal size. The obtained results will pave the way to implement advanced\ndesigns of high-performance electroacoustic sensors based on coupling modes in\nphononic crystals.", "category": "physics_app-ph" }, { "text": "Octave-Tunable Magnetostatic Wave YIG Resonators on a Chip: We have designed, fabricated, and characterized magnetostatic wave (MSW)\nresonators on a chip. The resonators are fabricated by patterning\nsingle-crystal yttrium iron garnet (YIG) film on a gadolinium gallium garnet\n(GGG) substrate and excited by loop-inductor transducers. We achieved this\ntechnology breakthrough by developing a YIG film etching process and\nfabricating thick aluminum coplanar waveguide (CPW) inductor loop around each\nresonator to individually address and excite MSWs. At 4.77 GHz, the 0.68 square\nmm resonator achieves a quality factor Q > 5000 with a bias field of 987 Oe. We\nalso demonstrate YIG resonator tuning by more than one octave from 3.63 to 7.63\nGHz by applying an in-plane external magnetic field. The measured quality\nfactor of the resonator is consistently over 3000 above 4 GHz. The\nmicromachining technology enables the fabrication of multiple single- and\ntwo-port YIG resonators on the same chip with all resonators demonstrating\noctave tunability and high Q .", "category": "physics_app-ph" }, { "text": "Crystallographic Orientation Dependent Reactive Ion Etch in Single\n Crystal Diamond: Sculpturing desired shapes in single crystal diamond is ever more crucial in\nthe realization of complex devices for nanophotonics, quantum computing, and\nquantum optics. The crystallographic orientation dependent wet etch of single\ncrystalline silicon in potassium hydroxide (KOH) allows a range of shapes\nformed and has significant impacts on MEMS (microelectromechanical systems),\nAFM (atomic force microscopy), and microfluidics. Here, a crystal direction\ndependent dry etching principle in an inductively-coupled plasma reactive ion\netcher is presented, which allows to selectively reveal desired crystal planes\nin monocrystalline diamond by controlling the etching conditions. The principle\nis demonstrated when the kinetic energy of incident ions on diamond surfaces is\nreduced below a certain threshold leading to anisotropic etching and faceting\nalong specific crystal planes. Using the principle, monolithic diamond\nnanopillars for magnetometry using nitrogen vacancy centers are fabricated. In\nthese nanopillars, a half-tapering angle up to 21{\\deg} is achieved, the\nhighest angle reported, which leads to a high photon efficiency and high\nmechanical strength of the nanopillar. These results represent the first\ndemonstration of crystallographic orientation dependent reactive ion etch\nprinciple, which opens a new window for shaping specific nanostructures which\nis at the heart of nanotechnology. It is believed that this principle will\nprove to be valuable for structuring and patterning of other single crystal\nmaterials as well.", "category": "physics_app-ph" }, { "text": "Nature of the growth of plasma electrolyte oxidation coating on Aluminum: The localized dielectric breakdown had been considered as the driving force\nfor growth of plasma electrolytic oxide (PEO) coatings for several decades.\nHowever, the TEM study here reveals the dielectric breakdown behavior has\nlittle contribution for coating thickening. The presented evidences show the\nnature of PEO coating growth in all three consecutive stages I-III is ionic\nmigration behavior inside the amorphous alumina layer (AAL) at the\ncoating/matrix interface. The evolution of morphological characterizations in\nthe PEO process is attributed to the interfacial reactions of AAL/alkaline\n(stage I), AAL/discharge-on-surface (stage II) and AAL/discharge-in-pore (stage\nIII).", "category": "physics_app-ph" }, { "text": "Effect of Annealing Temperature on Minimum Domain Size of Ferroelectric\n Hafnia: Here, we optimized the annealing temperature of HZO/TiN thin film\nheterostructure via multiscale analysis of remnant polarization,\ncrystallographic phase, minimum ferroelectric domain size, and average grain\nsize. We found that the remnant polarization was closely related to the\nrelative amount of the orthorhombic phase whereas the minimum domain size was\nto the relative amount of the monoclinic phase. The minimum domain size was\nobtained at the annealing temperature of 500$^\\cird$C while the optimum remnant\npolarization and capacitance at the annealing temperature of 600$^\\circ$C. We\nconclude that the minimum domain size is more important than the sheer\nmagnitude of remnant polarization considering the retention and fatigue of\nswitchable polarization in nanoscale ferroelectric devices. Our results are\nexpected to contribute to the development of ultra-low-power logic transistors\nand next-generation non-volatile memory devices.", "category": "physics_app-ph" }, { "text": "A Missing Active Device - Trancitor for a New Paradigm of Electronics: In this article, we first point out a missing active-device while providing\nits theoretical definition and impact on electronics. This type of active\ndevices has an inverse functionality of transistors, and is suggested to be\ncalled trancitor rather than transistor because it directly transfers an input\nsignal into a voltage output. It is expected that a trancitor coupled with a\ntransistor can provide a minimal circuit configuration, i.e., low circuit\ncomplexity, helping virtually to meet the Moore's law. And this may also lead\nto a lower power-consumption and higher speed of circuits compared to a\ntransistor-only circuit. These are supported with a circuit simulation and\nsimple Tetris-like block analysis. In this regards, in the future, it should be\nrequired to find a trancitor to be another foundation of electronics along with\ntransistors.", "category": "physics_app-ph" }, { "text": "Stress in a polymer brush: We study the stress distribution in a polymer brush material over a range of\ngraft densities using molecular dynamics (MD) simulations and theory. Flexible\npolymer chains are treated as beads connected by nonlinear springs governed by\na modified finitely extensible nonlinear elastic (FENE) potential in MD\nsimulations. Simulations confirmed the quartic variation of the normal stress\nparallel to the substrate, within the bulk of the brush, as predicted in our\nprevious work, for low graft densities. However, in the high graft density\nregime, the Gaussian chain elasticity assumption is violated by finite\nextensibility effects (force-extension divergence) and the restriction to\nbinary interaction among monomers is insufficient. This motivated us to extend\na semi-analytical strong stretching mean field theory (SST) for polymer\nbrushes, based on Langevin chains and a modified Carnahan-Starling equation of\nstate to model monomer interactions. Our extended theory elucidates the stress\nand monomer density profiles obtained from MD simulations, as well as\nreproduces Gaussian chain results for small graft densities. A good agreement\nis observed between predictions of MD and Langevin chain SST for monomer\ndensity profile, end density profile and stress profile in high graft density\nregime, without fitting parameters (virial coefficients). Quantitative\ncomparisons of MD results with various available theories suggest that excluded\nvolume correlations may be important.", "category": "physics_app-ph" }, { "text": "Experimental realization of on-chip topological nanoelectromechanical\n metamaterials: Topological mechanical metamaterials translate condensed matter phenomena,\nlike non-reciprocity and robustness to defects, into classical platforms. At\nsmall scales, topological nanoelectromechanical metamaterials (NEMM) can enable\nthe realization of on-chip acoustic components, like unidirectional waveguides\nand compact delay-lines for mobile devices. Here, we report the experimental\nrealization of NEMM phononic topological insulators, consisting of\ntwo-dimensional arrays of free-standing silicon nitride (SiN) nanomembranes\nthat operate at high frequencies (10-20 MHz). We experimentally demonstrate the\npresence of edge states, by characterizing their localization and Dirac\ncone-like frequency dispersion. Our topological waveguides also exhibit\nrobustness to waveguide distortions and pseudospin-dependent transport. The\nsuggested devices open wide opportunities to develop functional acoustic\nsystems for high-frequency signal processing applications.", "category": "physics_app-ph" }, { "text": "Strongly exchange-coupled and surface-state-modulated magnetization\n dynamics in Bi2Se3/YIG heterostructures: We report strong interfacial exchange coupling in Bi2Se3/yttrium iron garnet\n(YIG) bilayers manifested as large in-plane interfacial magnetic anisotropy\n(IMA) and enhancement of damping probed by ferromagnetic resonance (FMR). The\nIMA and spin mixing conductance reached a maximum when Bi2Se3 was around 6\nquintuple-layer (QL) thick. The unconventional Bi2Se3 thickness dependence of\nthe IMA and spin mixing conductance are correlated with the evolution of\nsurface band structure of Bi2Se3, indicating that topological surface states\nplay an important role in the magnetization dynamics of YIG.\nTemperature-dependent FMR of Bi2Se3/YIG revealed signatures of magnetic\nproximity effect of $T_c$ as high as 180 K, and an effective field parallel to\nthe YIG magnetization direction at low temperature. Our study sheds light on\nthe effects of topological insulators on magnetization dynamics, essential for\ndevelopment of TI-based spintronic devices.", "category": "physics_app-ph" }, { "text": "Blackhole-Inspired Thermal Trapping with Graded Heat-Conduction\n Metadevices: Black holes are one of the most intriguing predictions of general relativity.\nSo far, metadevices have enabled analogous black holes to trap light or sound\nin laboratory spacetime. However, trapping heat in a conductive ambient is\nstill challenging because diffusive behaviors are directionless. Inspired by\nblack holes, we construct graded heat-conduction metadevices to achieve thermal\ntrapping, resorting to the imitated advection produced by graded thermal\nconductivities rather than the trivial solution of using insulation materials\nto confine thermal diffusion. We experimentally demonstrate thermal trapping\nfor guiding hot spots to diffuse towards the center. Graded heat-conduction\nmetadevices have advantages in energy-efficient thermal regulation because the\nimitated advection has a similar temperature field effect to the realistic\nadvection that is usually driven by external energy sources. These results also\nprovide insights into correlating transformation thermotics with other\ndisciplines such as cosmology for emerging heat control schemes.", "category": "physics_app-ph" }, { "text": "Lattice thermal conductivity in isotope diamond asymmetric superlattices: We study lattice thermal conductivity of isotope diamond superlattices\nconsisting of 12C and 13C diamond layers at various superlattice periods. It is\nfound that the thermal conductivity of a superlattice is significantly deduced\nfrom that of pure diamond because of the reduction of the phonon group velocity\nnear the folded Brillouin zone. The results show that asymmetric superlattices\nwith different number of layers of 12C and 13C diamonds exhibit higher thermal\nconductivity than symmetric superlattices even with the same superlattice\nperiod, and we find that this can be explained by the trade-off between the\neffects of phonon specific heat and phonon group velocity. Furthermore,\nimpurities and imperfect superlattice structures are also found to\nsignificantly reduce the thermal conductivity, suggesting that these effects\ncan be exploited to control the thermal conductivity over a wide range.", "category": "physics_app-ph" }, { "text": "Optical Pre-Emphasis by Cascaded Graphene Electro Absorption Modulators: A simple optical circuit made by a cascade of two graphene-on-silicon electro\nabsorption modulators (EAMs) of different length is used for the optical\npre-emphasis of 10 Gb/s non-return-to-zero (NRZ) signals by\ndelay-inverse-weight compensation. Transmission up to 100 km on single mode\nfiber (SMF) without dispersion compensation is reported, showing also the large\nperformance advantage (6 dB in back-to back and around 5 dB in transmission) in\nrespect of the conventional single EAM transmitter configuration.", "category": "physics_app-ph" }, { "text": "Sub-10-micron thick Ge thin films from bulk-Ge substrates via a wet\n etching method: Low-defect-density Ge thin films are critical in Ge based optical devices\n(optical detectors, LEDs and Lasers) integrated with Si electronic devices for\nlow-cost, highly integrated photonic circuits. In this work, Ge thin films\nprepared by wet etching with four different solutions were studied in terms of\nthe surface morphology, defect density and achievable thickness. Both\nnanostrip-based solution (1:1:10) and HCl-based solution (1:1:5) were able to\nwet-etch 535 micron thick bulk-Ge substrates to Ge films thinner than 10 micron\nwithin 53 hours. The corresponding RMS surface roughness was 32 nm for the\nnanostrip-based solution and 10 nm for the HCl-based solution. The good quality\nof bulk-Ge was preserved before and after the etching process according to the\nHRXRD results. The low threading dislocation density of 6000-7000 cm-2 was\nmaintained in the process of wet etching without introducing extra defects.\nThis approach provides an inexpensive and convenient way to prepare\nsub-10-micron thick Ge thin films, enabling future studies of\nlow-defect-density Ge-based devices such as photodetectors, LEDs, and lasers.", "category": "physics_app-ph" }, { "text": "Effect of Volume Fraction and Fiber Distribution on Stress Transfer in a\n Stochastic Framework of Continuous Fiber Composite: A Micromechanical Study: In fiber Reinforced Composites (FRC) fiber breakage is a common phenomenon\nresulting in stress concentration. This high stress gets transfer in the\nvicinity of the breakage which is quantified by Stress Transfer Coefficient\n(STC). In this paper, an attempt is made to check the effect of fiber volume\nfraction and the distribution of the fibers on STC and ineffective length. The\nfiber volume fraction is changed considering three cases: 1) by changing the\nnumber of fibers, 2) by changing the dimension of the Represntative Volume\nElement (RVE) and 3) by changing the fiber radius. Cases with change in\ndimension of RVE and change in fiber radius, periodic and semi-random\narrangents of fibers are considered. From the analysis of 200 RVE's for each\nvolume fraction in random and semi-random arrangements, it is observed that the\ndistribution of STC does not follow any standard distribution, even if the\nfiber arrangement follows the normal distribution. The fiber cross-sectional\ndimension plays a critical role in regaining the broken fiber strength. The\nperiodic arrangement of fibers can be said to be beneficial over the random\narrangement considering the stress transfer from the broken fiber.", "category": "physics_app-ph" }, { "text": "Vector Magnetic Current Imaging of an 8 nm Process Node Chip and 3D\n Current Distributions Using the Quantum Diamond Microscope: The adoption of 3D packaging technology necessitates the development of new\napproaches to failure electronic device analysis. To that end, our team is\ndeveloping a tool called the quantum diamond microscope (QDM) that leverages an\nensemble of nitrogen vacancy (NV) centers in diamond, achieving vector magnetic\nimaging with a wide field-of-view and high spatial resolution under ambient\nconditions. Here, we present the QDM measurement of 2D current distributions in\nan 8-nm flip chip IC and 3D current distributions in a multi-layer PCB.\nMagnetic field emanations from the C4 bumps in the flip chip dominate the QDM\nmeasurements, but these prove to be useful for image registration and can be\nsubtracted to resolve adjacent current traces in the die at the micron scale.\nVias in 3D ICs display only Bx and By magnetic fields due to their vertical\norientation and are difficult to detect with magnetometers that only measure\nthe Bz component (orthogonal to the IC surface). Using the multi-layer PCB, we\nshow that the QDM's ability to simultaneously measure Bx, By, and Bz is\nadvantageous for resolving magnetic fields from vias as current passes between\nlayers. We also show how spacing between conducting layers is determined by\nmagnetic field images and how it agrees with the design specifications of the\nPCB. In our initial efforts to provide further z-depth information for current\nsources in complex 3D circuits, we show how magnetic field images of individual\nlayers can be subtracted from the magnetic field image of the total structure.\nThis allows for isolation of signal layers and can be used to map embedded\ncurrent paths via solution of the 2D magnetic inverse. In addition, the paper\nalso discusses the use of neural networks to identify 2D current distributions\nand its potential for analyzing 3D structures.", "category": "physics_app-ph" }, { "text": "Room temperature infrared photodetectors with hybrid structure based on\n 2D materials: Two-dimensional (2D) materials, such as graphene, transition metal\ndichalcogenides (TMDs), black phosphorus (BP) and related derivatives, have\nattracted great attention due to their advantages of flexibility, strong\nlight-matter interaction, broadband absorption and high carrier mobility, and\nhave become a powerful contender for next-generation infrared photodetectors.\nHowever, since the thickness of two-dimensional materials is on the order of\nnanometers, the absorption of two-dimensional materials is very weak, which\nlimits the detection performance of 2D materials-based infrared photodetector.\nIn order to solve this problem, scientific researchers have tried to use\noptimized device structures to combine with two-dimensional materials for\nimproving the performance of infrared photodetector. In this review, we review\nthe progress of room temperature infrared photodetectors with hybrid structure\nbased on 2D materials in recent years, focusing mainly on 2D-nD (n = 0, 1, 2)\nheterostructures, the integration between 2D materials and on-chip or plasmonic\nstructure. Finally, we summarize the current challenges and point out the\nfuture development direction.", "category": "physics_app-ph" }, { "text": "Spray-Coated Graphene/Quantum Dots Paper-Based Photodetectors: Paper is an ideal substrate for the development of flexible and\nenvironmentally sustainable ubiquitous electronic systems. When combined with\nnanomaterials, it can be harnessed for various Internet-of-Things applications,\nranging from wearable electronics to smart packaging. In this study, we present\na non-vacuum spray deposition of arrays of hybrid single layer graphene\n(SLG)-CsPbBr3 perovskite quantum dots (QDs) photodetectors on a paper\nsubstrate. This approach combines the advantages of two large-area techniques:\nchemical vapor deposition (CVD) and spray-coating. The first technique allows\nfor the pre-deposition of CVD SLG, while the second enables the spray coating\nof a mask to pattern CVD SLG, electrode contacts, and photoactive QDs layers.\nThe prepared paper-based photodetectors achieved an external responsivity of\n520 A/W under 405 nm illumination at <1V operating voltage. By fabricating\narrays of photodetectors on a paper substrate in the air, this work highlights\nthe potential of this scalable approach for enabling ubiquitous electronics on\npaper.", "category": "physics_app-ph" }, { "text": "Dependence of the kinetic energy absorption capacity of bistable\n mechanical metamaterials on impactor mass and velocity: Using an alternative mechanism to dissipation or scattering, bistable\nstructures and mechanical metamaterials have shown promise for mitigating the\ndetrimental effects of impact by reversibly locking energy into strained\nmaterial. Herein, we extend prior works on impact absorption via bistable\nmetamaterials to computationally explore the dependence of kinetic energy\ntransmission on the velocity and mass of the impactor, with strain rates\nexceeding $10^2$ s$^{-1}$. We observe a large dependence on both impactor\nparameters, ranging from significantly better to worse performance than a\ncomparative linear material. We then correlate the variability in performance\nto solitary wave formation in the system and give analytical estimates of\nidealized energy absorption capacity under dynamic loading. In addition, we\nfind a significant dependence on damping accompanied by a qualitative\ndifference in solitary wave propagation within the system. The complex dynamics\nrevealed in this study offer potential future guidance for the application of\nbistable metamaterials to applications including human and engineered system\nshock and impact protection devices.", "category": "physics_app-ph" }, { "text": "Experimental demonstration of a rapid sweep-tuned spectrum analyzer with\n temporal resolution based on a spin-torque nano-oscillator: It is demonstrated experimentally that a spin-torque nano-oscillator (STNO)\nrapidly sweep-tuned by a bias voltage can be used for time-resolved spectrum\nanalysis of frequency-manipulated microwave signals with complicated multi-tone\nspectra. The critical reduction in the time of spectrum analysis comes from the\nnaturally small time constants of a nano-sized STNO (1-100 ns). The\ndemonstration is performed on a vortex-state STNO generating in a frequency\nrange around 300 MHz, with frequency down-conversion and matched filtering used\nfor signal processing. It is shown that this STNO-based spectrum analyzer can\nperform analysis of multi-tone signals, and signals with rapidly changing\nfrequency components with time resolution on a $\\mu$s time scale and frequency\nresolution limited only by the 'bandwidth' theorem. The proposed concept of\nrapid time-resolved spectrum analysis can be implemented with any type of micro\nand nano-scale frequency-swept oscillators having low time constants and high\noscillation frequency.", "category": "physics_app-ph" }, { "text": "Applications of Earth-to-Air Heat Exchangers: A Holistic Review: The building sector is responsible for 40% of primary energy consumption,\nwith heating/cooling covering the most significant portion. Thus, passive\nheating/cooling applications have gained significant ground during the last\nthree decades, with many research activities on the subject. Among passive\ncooling/heating applications, ground cooling (especially earth-to-air heat\nexchangers) has been highlighted as a remarkably attractive technological\nresearch subjects because of its significant contribution to the reduction of\nheating/cooling energy loads; the improvement of indoor thermal comfort\nconditions; and the amelioration of the urban environment. This paper presents\na holistic review of state-of-the-art research, methodologies, and technologies\nof earth-to-air heat exchangers that help achieve energy conservation and\nthermal comfort in the built environment. The review covers the critical\nsubject of the thermal performance of earth-to-air heat exchanger systems;\nexperimental studies and applications; parametric studies for investigating the\nimpact of their main characteristics on thermal efficiency; and recent advances\nand trends including hybrid technologies and systems. The models describing the\nthermal performance of earth-to-air heat exchangers systems were classified in\nnumerical, analytical, and data-driven; their main theoretical principles were\npresented; and experimental validation was mentioned when carried out. System\nparameters were grouped into three categories: system design, soil types, and\nsoil surface coverage. System design parameters, especially length and burial\ndepth, bore the most important influence on the thermal efficiency of the\nsystem. The paper was rounded up with an economic assessment of system\napplication, and the conclusions highlighted the need for more experimental\nwork including laboratory simulators.", "category": "physics_app-ph" }, { "text": "A Surface Impedance-Based Three-Channel Acoustic Metasurface\n Retroreflector: We propose the design and measurement of an acoustic metasurface\nretroreflector that works at three discrete incident angles. An impedance model\nis developed such that for acoustic waves impinging at -60 degrees, the\nreflected wave is defined by the surface impedance of the metasurface, which is\nrealized by a periodic grating. At 0 and 60 degrees, the retroreflection\ncondition can be fulfilled by the diffraction of the surface. The thickness of\nthe metasurface is about half of the operating wavelength and the\nretroreflector functions without parasitic diffraction associated with\nconventional gradient-index metasurfaces. Such highly efficient and compact\nretroreflectors open up possibilities in metamaterial-based acoustic sensing\nand communications.", "category": "physics_app-ph" }, { "text": "Electrically function switchable magnetic domain-wall memory: More-versatile memory is strongly desired for end-users to protect their\ninformation in the information era. In particular, bit-level switchable memory,\nfrom rewritable to read-only function, allows end-users to prevent any\nimportant data from being tampered with. However, no such switchable memory has\nbeen reported. We demonstrated the rewritable function can be converted into a\nread-only function by a sufficiently large current pulse in a U-shaped\ndomain-wall memory composed of an asymmetric Pt/Co/Ru/AlOx heterostructure with\nstrong Dzyaloshinskii-Moriya interaction. Wafer-scale switchable magnetic\ndomain-wall memory arrays on 4-inch Si/SiO2 substrate were designed and\nfabricated. Furthermore, we confirmed the information can be stored in\nrewritable or read-only state at bit-level according to the security-needs of\nend-users. Our work not only provides a solution for personal confidential\ndata, but also paves the way for developing multi-functional spintronic\ndevices.", "category": "physics_app-ph" }, { "text": "An Open-Cell Environmental Transmission Electron Microscopy Technique\n for In Situ Characterization of Samples in Aqueous Liquid Solutions: The desire to image specimens in liquids has led to the development of\nopen-cell and closed-cell techniques in transmission electron microscopy (TEM).\nThe closed-cell approach is currently more common in TEM and has yielded new\ninsights into a number of biological and materials processes in liquid\nenvironments. The open-cell approach, which requires an environmental TEM\n(ETEM), is technically challenging but may be advantageous in certain\ncircumstances due to fewer restrictions on specimen and detector geometry.\nHere, we demonstrate a novel approach to open-cell liquid TEM, in which we use\nsalt particles to facilitate the in situ formation of droplets of aqueous\nsolution that envelope specimen particles coloaded with the salt. This is\nachieved by controlling sample temperature between 1 and 10{\\deg}C and\nintroducing water vapor to the ETEM chamber above the critical pressure for the\nformation of liquid water on the salt particles. Our use of in situ hydration\nenables specimens to be loaded into a microscope in a dry state using standard\n3 mm TEM grids, allowing specimens to be prepared using trivial sample\npreparation techniques. Our future aim will be to combine this technique with\nan in situ light source to study photocorrosion in aqueous environments.", "category": "physics_app-ph" }, { "text": "Reverberation Time Control by Acoustic Metamaterials in a Small Room: In recent years, metamaterials have gained considerable attention as a\npromising material technology due to their unique properties and customizable\ndesign, distinguishing them from traditional materials. This article delves\ninto the value of acoustic metamaterials in room acoustics, particularly in\nsmall room acoustics that poses specific challenges due to their significant\ncavity resonant nature. Small rooms usually exhibit an inhomogeneous frequency\nresponse spectrum, requiring higher wall absorption with specific spectrum to\nachieve a uniform acoustic environment, i.e., a constant reverberation time\nover a wide audible frequency band. To tackle this issue, we developed a design\nthat simultaneously incorporates numerous subwavelength acoustic resonators at\ndifferent frequencies to achieve customized broadband absorption for the walls\nof a specific example room. The on-site experimental measurements agree well\nwith the numerical predictions, attesting to the robustness of the design and\nmethod. The proposed method of reverse-engineering metamaterials by targeting\nspecific acoustic requirements has broad applicability and unique advantages in\nsmall confined spaces with high acoustic requirements, such as recording\nstudios, listening rooms, and car cabins.", "category": "physics_app-ph" }, { "text": "Edge modes in 1D microwave photonic crystal: The microstrip of modulated width is a realization of a one-dimensional\nphotonic crystal operating in the microwave regime. Like any photonic crystal,\nthe periodic microstrip is characterised by the presence of frequency bands and\nband gaps that enable and prohibit wave propagation, respectively. The\nfrequency bands for microstrip of symmetric unit cell can be distinguished by\n$0$ or $\\pi$ Zak phase. The sum of these topological parameters for all bands\nbelow a given frequency gap determines the value of the surface impedance and\nwhether or not edge modes are present at the end of the microstrip. We\ndemonstrate that edge modes are absent in a finite microstrip terminated at\nboth ends in the centres of unit cells, but they can be induced by adding the\ndefected cells. Edge modes present at both ends of the microstrip enable\nmicrowave tunneling with high transitivity in the frequency gap with or without\na change in phase. This has been demonstrated experimentally and developed in\ndetail using numerical simulations and model calculations. The investigated\nsystem, with a doublet of edge modes in the frequency gap, can be considered as\na narrow passband filter of high selectivity.", "category": "physics_app-ph" }, { "text": "Low-power threshold gas discharge by enhanced local electric field in\n electromagnetically-induced-transparencylike metamolecules: To realize efficient nonlinear metamaterials, we investigate a method for\nenhancing the local electric field in a metamolecule composed of two\nradiatively coupled cut-wire resonators where resonance of the cut-wire\nresonators and low-group-velocity propagation of an incident electromagnetic\nwave simultaneously occur. Numerical analysis shows that the local electric\nfield in the metamolecule can be enhanced by decreasing the electrode size and\nthe gap of the capacitor structure of the cut-wire resonators while keeping the\nequivalent electrical circuit parameters of the metamolecule constant. We\nmeasure and compare the threshold incident power for a gas discharge in the\nmetamolecule fabricated in our previous study and that in the metamolecule with\nshrunken capacitor structures. The experiment reveals that shrinking the\ncapacitor structure while keeping the resonance frequency of the metamolecule\ndecreases the threshold incident power for a gas discharge and may increase the\ngas pressure where the threshold incident power is minimum. Further development\nof this work will enable us to realize efficient nonlinear metamaterials that\nhave atmospheric-pressure gas as a nonlinear element.", "category": "physics_app-ph" }, { "text": "Optical Transistor for an Amplification of Radiation in a Broadband THz\n Domain: We propose a new type of optical transistor for a broadband amplification of\nTHz radiation. It is made of a graphene--superconductor hybrid, where electrons\nand Cooper pairs couple by Coulomb forces. The transistor operates via the\npropagation of surface plasmons in both layers, and the origin of amplification\nis the quantum capacitance of graphene. It leads to THz waves amplification,\nthe negative power absorption, and as a result, the system yields positive\ngain, and the hybrid acts like an optical transistor, operating with the\nterahertz light. It can, in principle, amplify even a whole spectrum of chaotic\nsignals (or noise), that is required for numerous biological applications.", "category": "physics_app-ph" }, { "text": "Ultrahigh-sensitivity optical power monitor for Si photonic circuits: A phototransistor is a promising candidate as an optical power monitor in Si\nphotonic circuits since the internal gain of photocurrent enables high\nsensitivity. However, state-of-the-art waveguide-coupled phototransistors\nsuffer from a responsivity of lower than $10^3$ A/W, which is insufficient for\ndetecting very low power light. Here, we present a waveguide-coupled\nphototransistor consisting of an InGaAs ultrathin channel on a Si waveguide\nworking as a gate electrode to increase the responsivity. The Si waveguide gate\nunderneath the InGaAs ultrathin channel enables the effective control of\ntransistor current without optical absorption by the gate metal. As a result,\nour phototransistor achieved the highest responsivity of approximately $10^6$\nA/W among the waveguide-coupled phototransistors, allowing us to detect light\nof 621 fW propagating in the Si waveguide. The high responsivity and the\nreasonable response time of approximately 100 $\\mu$s make our phototransistor\npromising as an effective optical power monitor in Si photonics circuits.", "category": "physics_app-ph" }, { "text": "Density-controlled growth of vertical InP nanowires on Si(111)\n substrates: A procedure to achieve the density-controlled growth of gold-catalyzed InP\nnanowires (NWs) on (111) silicon substrates using the vapor-liquid-solid method\nby molecular beam epitaxy is reported. We develop an effective and mask-free\nmethod based on controlling the number and the size of the Au-In catalyst\ndroplets in addition to the conditions for the NW nucleation. We show that the\nNW density can be tuned with values in the range of 18 {\\mu}m-2 to < 0.1\n{\\mu}m-2 by the suitable choice of the In/Au catalyst beam equivalent pressure\n(BEP) ratio, by the phosphorous BEP and the growth temperature. The same degree\nof control is transferred to InAs/InP quantum dot-nanowires, taking advantage\nof the ultra-low density to study by micro-photoluminescence the optical\nproperties of a single quantum dot-nanowires emitting in the telecom band\nmonolithically grown on silicon. Optical spectroscopy at cryogenic temperature\nsuccessfully confirmed the relevance of our method to excite single InAs\nquantum dots on the as-grown sample, which opens the path for large-scale\napplications based on single quantum dot-nanowire devices integrated on\nsilicon.", "category": "physics_app-ph" }, { "text": "Performance-driven 3D printing of continuous curved fibre reinforced\n polymer composites a preliminary numerical study: This paper presents a new concept to place continuous curved fibres for CFRP\ncomposites, which can be fulfilled by potential additive or hybrid\nmanufacturing technology. Based on the loading condition, principal stress\ntrajectories are generated through finite element analysis (FEA) and used as\nthe guidance of the placement paths for carbon fibres. Three numerical cases,\nan open-hole single ply lamina under uniaxial tension and an open-hole\ncross-ply laminate under biaxial tension and normal pressure, are studied and\ncompared with traditional reinforced composites with unidirectional fibres. The\nmodelling results show that the stress concentration in both fibre and matrix\nare reduced significantly by the curved fibre placement and the stiffness of\nCFRP composites have been improved. This concept of performance-driven\noptimization method could lead to a useful tool for the design of future 3D\nprinting process for fibre reinforced composites.", "category": "physics_app-ph" }, { "text": "Terahertz to mid-infrared dielectric properties of polymethacrylates for\n stereolithographic single layer assembly: The fabrication of terahertz (THz) optics with arbitrary shapes via\npoly-methacrylate-based stereolithography is very attractive as it may offer a\nrapid, low-cost avenue towards optimized THz imaging applications. In order to\ndesign such THz optical components appropriately, accurate knowledge of the\ncomplex dielectric function of the materials used for stereolithographic\nfabrication is crucial. In this paper we report on the complex dielectric\nfunctions of several polymethacrylates frequently used for stereolithographic\nfabrication. Spectroscopic ellipsometry data sets from the THz to mid-infrared\nspectral range were obtained from isotropically cross-linked polymethacrylate\nsamples. The data sets were analyzed using stratified layer optical model\ncalculations with parameterized model dielectric functions. While the infrared\nspectral range is dominated by a number of strong absorption features with\nGaussian profiles, these materials are found to exhibit only weak absorption in\nthe THz frequency range. In conclusion, we find that thin transmissive THz\noptics can be efficiently fabricated using polymethacrylate-based\nstereolithographic fabrication.", "category": "physics_app-ph" }, { "text": "Strong 4-mode coupling of nanomechanical string resonators: We investigate mechanical mode coupling between the four fundamental flexural\nmodes of two doubly-clamped, high-Q silicon-nitride nanomechanical string\nresonators. Strong mechanical coupling between the strings is induced by the\nstrain mediated via a shared clamping point, engineered to increase the\nexchange of oscillatory energy. One of the resonators is controlled\ndielectrically, which results in strong coupling between its out-of-plane and\nin-plane flexural modes. We show both, inter-string out-of-plane-in-plane and\n3-mode resonance of the four coupled fundamental vibrational modes of a\nresonator pair, giving rise to a simple and a multimode avoided crossing,\nrespectively.", "category": "physics_app-ph" }, { "text": "Direct in- and out-of-plane writing of metals on insulators by\n electron-beam-enabled, confined electrodeposition with submicrometer feature\n size: Additive microfabrication processes based on localized electroplating enable\nthe one-step deposition of micro-scale metal structures with outstanding\nperformance, e.g. high electrical conductivity and mechanical strength. They\nare therefore evaluated as an exciting and enabling addition to the existing\nrepertoire of microfabrication technologies. Yet, electrochemical processes are\ngenerally restricted to conductive or semiconductive substrates, precluding\ntheir application in the manufacturing of functional electric devices where\ndirect deposition onto insulators is often required. Here, we demonstrate the\ndirect, localized electrodeposition of copper on a variety of insulating\nsubstrates, namely Al2O3, glass and flexible polyethylene, enabled by\nelectron-beam-induced reduction in a highly confined liquid electrolyte\nreservoir. The nanometer-size of the electrolyte reservoir, fed by\nelectrohydrodynamic ejection, enables a minimal feature size on the order of\n200 nm. The fact that the transient reservoir is established and stabilized by\nelectrohydrodynamic ejection rather than specialized liquid cells could offer\ngreater flexibility towards deposition on arbitrary substrate geometries and\nmaterials. Installed in a low-vacuum scanning electron microscope, the setup\nfurther allows for operando, nanoscale observation and analysis of the\nmanufacturing process.", "category": "physics_app-ph" }, { "text": "Tunable Casimir equilibria with phase change materials: from quantum\n trapping to its release: A stable suspension of nanoscale particles due to the Casimir force is of\ngreat interest for many applications such as sensing, non-contract\nnano-machines. However, the suspension properties are difficult to change once\nthe devices are fabricated. Vanadium dioxide (VO$_2$) is a phase change\nmaterial, which undergoes a transition from a low-temperature insulating phase\nto a high-temperature metallic phase around a temperature of 340 K. In this\nwork, we study Casimir forces between a nanoplate (gold or Teflon) and a\nlayered structure containing a VO$_2$ film. It is found that stable Casimir\nsuspensions of nanoplates can be realized in a liquid environment, and the\nequilibrium distances are determined, not only by the layer thicknesses but\nalso by the matter phases of VO$_2$. Under proper designs, a switch from\nquantum trapping of the gold nanoplate (\"on\" state) to its release (\"off\"\nstate) as a result of the metal-to-insulator transition of VO$_2$, is revealed.\nOn the other hand, the quantum trapping and release of a Teflon nanoplate is\nfound under the insulator-to-metal transition of VO$_2 $. Our findings offer\nthe possibility of designing switchable devices for applications in micro-and\nnano-electromechanical systems.", "category": "physics_app-ph" }, { "text": "Terahertz emission from $\u03b1$-W/CoFe epitaxial spintronic emitters: We report efficient terahertz (THz) generation in epitaxial\n$\\alpha$-W/Co$_6$0Fe$_4$0 spintronic emitters. Two types of emitters have been\ninvestigated; epitaxial $\\alpha$-W(110)/Co$_6$0Fe$_4$0(110) and\n$\\alpha$-W(001)/Co$_6$0Fe$_4$0(001) deposited on single crystalline\nAl$_2$O$_3$(11-20) and MgO(001) substrates, respectively. The generated THz\nradiation is about 10% larger for $\\alpha$-W(110)/Co$_6$0Fe$_4$0(110) grown on\nsingle crystalline Al$_2$O$_3$(11-20), which is explained by the fact that the\n$\\alpha$-W(110)/Co$_6$0Fe$_4$0(110) interface for this emitter is more\ntransparent to the spin current due to the presence of Angstrom-scale interface\nintermixing at the W/CoFe interface. Our results also reveal that the\ngeneration of THz radiation is larger when pumping with the laser light from\nthe substrate side, which is explained by a larger part of the laser light due\nto interference effects in the film stack being absorbed in the ferromagnetic\nCo$_6$0Fe$_4$0 layer in this measurement configuration.", "category": "physics_app-ph" }, { "text": "Enhanced Second-harmonic Generation Using Nonlinear Metamaterials: We demonstrate a nonlinear metamaterial which enhance higher order harmonics\nin microwave frequency regime. Nonlinearity in the structure is introduced by\nadding a varactor diode in the common slit of the double split ring resonator\n(DSRR) design. By engineering the structure such that inner ring resonance\nfrequency of the DSRR is twice as the outer ring resonance frequency, we have\ndemonstrated that the second harmonic of the outer ring can be enhanced\nsignificantly. By comparing with a single ring (SRR) unit cell structure, DSRR\nhas an enhancement factor of 70. Furthermore, we elucidate that the second\nharmonic signals generated by two identical double split rings interfere and we\ncan use its constructive interference positions to construct an array of DSRRs\nthat gives a maximum second harmonic signal with phase matching condition. When\nthe phase matching condition occurs the enhancement factor of an array is more\nthan the contribution of individual unit cells which proves that the\nenhancement is due to not only constructive interference of the second harmonic\ngenerated by individual unit cells but also due to cavity mechanism occurred in\nthe array structure.", "category": "physics_app-ph" }, { "text": "Anticorrosion and biocompatibility of a functionalized layer formed on\n ZK60 Mg alloy via hydroxyl ion implantation: Magnesium and its alloys have aroused tremendous interests because of their\npromising mechanical properties and biocompatibility. However, their\nexcessively fast corrosion rate hinders the development of Mg alloys in the\nbiomedical fields. Inspired by conventional ion implantation, a less-toxic\nfunctional group (hydroxyl) is used as the ion source to bombard the ZK60 Mg\nalloy surface to form a functionalized oxide layer. This functionalized oxide\nlayer significantly facilitates the corrosion resistance of the ZK60 Mg alloy\nsubstrate and the proliferation of MC3T3-E1 cells, which is confirmed by\nelectrochemical, immersion, and in vitro cytocompatibility tests. In comparison\nwith results of ZK60 alloy implanted with carboxyl ions in our previous work,\nit is concluded that hydroxyl-treated alloys exhibit slightly higher corrosion\nrate while better biocompatibility. In summary, less-toxic functional ion\nimplantation can be an effective strategy for inhibiting corrosion of Mg alloy\nimplants and promoting their biocompatibility.", "category": "physics_app-ph" }, { "text": "Enhancement of superconductivity in NbN nanowires by negative\n electron-beam lithography with positive resist: We performed comparative experimental investigation of superconducting NbN\nnanowires which were prepared by means of positive-and negative electron-beam\nlithography with the same positive tone Poly-methyl-methacrylate (PMMA) resist.\nWe show that nanowires with a thickness 4.9 nm and widths less than 100 nm\ndemonstrate at 4.2 K higher critical temperature and higher density of critical\nand retrapping currents when they are prepared by negative lithography. Also\nthe ratio of the experimental critical-current to the depairing critical\ncurrent is larger for nanowires prepared by negative lithography. We associate\nthe observed enhancement of superconducting properties with the difference in\nthe degree of damage that nanowire edges sustain in the lithographic process. A\nwhole range of advantages which is offered by the negative lithography with\npositive PMMA resist ensures high potential of this technology for improving\nperformance metrics of superconducting nanowire singe-photon detectors.", "category": "physics_app-ph" }, { "text": "Magnetically Tunable Organic Semiconductors with Superparamagnetic\n Nanoparticles: Magnetic nanoparticles (MNPs) exhibiting superparamagnetic properties might\ngenerate large magnetic dipole-dipole interaction with electron spins in\norganic semiconductors (OSECs). This concept could be considered analogous to\nthe effect of hyperfine interaction (HFI). In order to investigate this model,\nFe3O4 MNPs are used as a dopant for generating random hyperfine-like magnetic\nfields in a HFI-dominant {\\pi}-conjugated polymer host,\npoly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MeH-PPV). The\nmagnetoconductance (MC) response in organic light emitting diodes made by\nMeH-PPV/MNP blends is used to estimate the effective hyperfine field in the\nblends. Firstly, we find that the shape of the MC response essentially remains\nthe same regardless of the MNP concentration, which is attributed to the\nsimilar functionality between the nuclear spins and the MNPs. Secondly, the\nwidth of MC increases with increasing MNP concentration. Magneto-optical Kerr\neffect experiments and micromagnetic simulation indicate that the additional\nincrease of the MC width is associated with the strength of the magnetization\nof the blend. Finally, the MC broadening has the same temperature dependent\ntrend as the magnetization of the MNPs where the unique effect of the MNPs in\ntheir superparamagnetic and ferromagnetic regimes on the MC response is\nobserved. Magneto-photoinduced absorption (MPA) spectroscopy confirms that the\nMC broadening is not due to defects introduced by the MNPs, but is a result of\nunique superparamagnetic behavior. Our study yields a new pathway for tuning\nOSECs' magnetic functionality, which is essential to organic optoelectronic\ndevices and magnetic sensor applications.", "category": "physics_app-ph" }, { "text": "Tuning Optical Properties of Self-Assembled Nanoparticle Network with\n External Optical Excitation: DNA-driven self-assembly enables precise positioning of the colloidal\nnanoparticles owing to specific Watson-Crick interactions. Another important\nfeature of this self-assembly method is its reversibility by controlling the\ntemperature of the medium. In this work, we study the potential of another\nmechanism to control binding/unbinding process of the DNA-functionalized gold\nnanoparticles. We employ the laser radiation that can be absorbed by the gold\nnanoparticles to heat their network and disassociate it. Here, we show that we\ncan actively control the optical properties of the nanoparticle network by an\nexternal optical excitation. We find out that by irradiating the structure with\na green hand-held laser the total transmittance can increase by ~30% compared\nto the transmittance of the sample not irradiated by the laser. Similarly, the\noptical microscopy images indicate the transformation of the nanoparticle\nnetwork from opaque to transparent while the nanoparticles formed a network\nagain after the laser irradiation stopped. Our results prove that the optical\nexcitation can be used to tailor the structure and thus the optical properties\nof the DNA-self-assembled nanoparticle networks.", "category": "physics_app-ph" }, { "text": "Quantitative description of complex magnetic nanoparticle arrays: First-order reversal curves (FORC) measurements are broadly used for\ncharacterization of complex magnetic nanostructures, but a robust framework for\nquantitative analysis of the FORC data is still obscure despite numerous\nstudies over decades. In this paper, we first establish a framework for\nextracting quantitative parameters from the FORC measurements conducted on\nsamples including a single type of magnetic nanostructures to interpret their\nmagnetic properties. We then generalize our framework for quantitative\ncharacterization of the samples including multiple types of magnetic\nnanostructures to determine the most reliable and reproducible parameter for\ndetailed analysis of the samples. Our approach provides an insightful path for\na more accurate quantitative description of complex magnetic nanostructures\nincluding various different magnetic subcomponents and/or magnetic phases.", "category": "physics_app-ph" }, { "text": "Insight into Potential Well Based Nanoscale FDSOI MOSFET Using Doped\n Silicon Tubs- A Simulation and Device Physics Based Study: Part I: Theory and\n Methodology: A novel planar device having doped silicon regions (tubs) under the source\nand drain of an FDSOI MOSFET is reported at 20 nm gate length. The doped\nsilicon regions result in formation of potential wells (PW) in the source and\ndrain regions of FDSOI MOSFET and thus, the device being called as Potential\nWell Based FDSOI MOSFET (PWFDSOI MOSFET). Simulation and device physics study\non PWFDSOI MOSFET showed reduction in the OFF current of the device by orders\nof magnitude. A low IOF F of 22 pA/um, high ION /IOF F ratio of 1.5 x 107 and\nsubthreshold swing of 76 mV/decade were achieved in 20 nm gate length PWFDSOI\nMOSFET. The study was performed on devices with unstrained silicon channel.", "category": "physics_app-ph" }, { "text": "Normal incidence sound insulation provided by Sonic Crystal Acoustic\n Screens made from rigid scatterers, assessment of different simulation\n methods: Sonic crystal acoustic screens have been in progressive research and\ndevelopment in the last two decades as a technical solution for mitigating\ntraffic noise. Their behaviour is quite different from that observed in\nclassical barriers, with the latter being based on physically blocking the\ndirect sound propagation path (only allowing diffracted noise to reach sensible\nreceivers), and sonic crystals providing attenuation efficiency based on the\ncreation of band-gaps at specific frequency ranges, due to the Bragg's\ninterference phenomenon. The distinct physical mechanisms of these two types of\nnoise barriers complicates the use of classical simplified or even numerical\nmodels developed for traditional barriers to simulate and predict the\nattenuation performance of a sonic crystal, and alternative methods become thus\nrequired. In the acoustics scientific literature, several authors have proposed\nestimation and simulation methods based on different numerical tools to predict\nthe sound insulation provided by these new noise abatement solutions. This\npaper presents a comparative evaluation of some of these methods, with emphasis\nto the assessment of their accuracy versus memory usage in order to determine\nwhich one is the most suitable for optimization methodologies in the design of\nnew devices with improved acoustic performance.", "category": "physics_app-ph" }, { "text": "Designable spectrometer-free index sensing using plasmonic Doppler\n gratings: Typical nanoparticle-based plasmonic index sensors detect the spectral shift\nof localized surface plasmon resonance (LSPR) upon the change of environmental\nindex. Therefore, they require broadband illumination and spectrometers. The\nsensitivity and flexibility of nanoparticle-based index sensors are usually\nlimited because LSPR peaks are usually broad and the spectral position cannot\nbe freely designed. Here, we present a fully designable index sensing platform\nusing a plasmonic Doppler grating (PDG), which provides broadband and azimuthal\nangle-dependent grating periodicities. Different from LSPR, the PDG index\nsensor is based on the momentum matching between photons and surface plasmons\nvia the lattice momentum of the grating. Therefore, index change is translated\ninto the variation of in-plane azimuthal angle for photon-to-plasmon coupling,\nwhich manifests as directly observable dark bands in the reflection image. The\nPDG can be freely designed to optimally match the range of index variation for\nspecific applications. In this work, we demonstrate PDG index sensors for large\n(n = 1.00 to 1.52) and small index variation (n = 1.3330 to 1.3650). The tiny\nand nonlinear index change of water-ethanol mixture has been clearly observed\nand accurately quantified. Since the PDG is a dispersive device, it enables\non-site and single-color index sensing without a spectrometer and provides a\npromising spectroscopic platform for on-chip analytical applications.", "category": "physics_app-ph" }, { "text": "Proposed high-power beta cells from MgAlB14-type icosahedral-boron\n semiconductors: Beta cells generate electric power as carrier-producing beta irradiation from\nincorporated radioisotopes bombard a series of p-n-junctions. However,\nradiation damage to the semiconductors commonly used in solar cells limits beta\ncells to extremely weak irradiations that generate concomitantly miniscule\nelectric powers, e.g. micro-Watts. By contrast, beta cells that generate many\norders-of-magnitude larger powers are possible with icosahedral boron-rich\nsemiconductors since their bombardment-induced atomic displacements\nspontaneously self-heal. Furthermore, substitutions for Mg and Al atoms of\nicosahedral-boron-rich semiconductors based on the MgAlB14 structure can\nproduce p-n junctions as electron transfers from doping-induced interstitial\nextra-icosahedral atoms convert some normally p-type materials to n-type.\nMoreover, electron-phonon interactions of the resulting readily displaceable\ninterstitial cations with charge carriers foster their forming large polarons.\nOppositely charged polarons repel one another at short range. These repulsions\nsuppress the recombination of n-type with p-type polarons thereby increasing\nthe beta-cell efficiency. All told, use of these icosahedral boron-rich\nsemiconductors could enable beta cells with electric powers that are many\norders of magnitude larger than those of existing beta cells. This development\nopens a new avenue for generating electricity from nuclear decays.", "category": "physics_app-ph" }, { "text": "Methodical engineering of defects in Mn$_x$Zn$_{1-x}$ O($x$ = 0.03, and\n 0.05) nanostructures by electron beam for nonlinear optical applications: A\n new insight: A series of MnxZn1-xO (x=0.03, 0.05) nanostructures have been grown via the\nsolution based chemical spray pyrolysis technique. Electron beam induced\nmodifications on structural, linear and nonlinear optical and surface\nmorphological properties have been studied and elaborated. GXRD (glancing angle\nX-ray diffraction) patterns show sharp diffraction peaks matching with the\nhexagonal wurtzite structure of ZnO thin films. The upsurge in ebeam dosage\nresulted in the shifting of XRD peaks (101) and (002) towards lower angle side,\nand increase in FWHM value. Gaussian deconvolution on PL spectra reveals the\nquenching of defect centers, implying the role of electron beam irradiation\nregulating luminescence and defect centers in the nanostructures. Irradiation\ninduced spatial confinement and phonon localization effects have been observed\nin the films via micro Raman studies. The later are evident from spectral peak\nshifts and broadening. Detailed investigations on the effect of electron beam\nirradiation on third order nonlinear optical properties under continuous and\npulsed mode of laser operation regimes are deliberated. Third order absorptive\nnonlinearity of the nanostructures evaluated using the open aperture Z-scan\ntechnique in both continuous and pulsed laser regimes shows strong nonlinear\nabsorption coefficient \\b{eta} eff of the order 10-4 cm/W confirming their\nsuitability for passive optical limiting applications under intense radiation\nenvironments. Laser induced third harmonic generation (LITHG) experiment\nresults supports the significant variation in nonlinearities upon electron beam\nirradiation, and the effect can be utilized for frequency conversion mechanisms\nin high power laser sources and UV light emitters.", "category": "physics_app-ph" }, { "text": "Hall sensors batch-fabricated on all-CVD h-BN/graphene/h-BN\n heterostructures: The two-dimensional (2D) material graphene is highly promising for Hall\nsensors due to its potential of having high charge carrier mobility and low\ncarrier concentration at room temperature. Here, we report the scalable\nbatch-fabrication of magnetic Hall sensors on graphene encapsulated in\nhexagonal boron nitride (h-BN) using commercially available large area CVD\ngrown materials. The all-CVD grown h-BN/graphene/h-BN van der Waals\nheterostructures were prepared by layer transfer technique and Hall sensors\nwere batch-fabricated with 1D edge metal contacts. The current-related Hall\nsensitivities up to 97 V/AT are measured at room temperature. The Hall sensors\nshowed robust performance over the wafer scale with stable characteristics over\nsix months in ambient environment. This work opens avenues for further\ndevelopment of growth and fabrication technologies of all-CVD 2D material\nheterostructures and allows further improvements in Hall sensor performance for\npractical applications.", "category": "physics_app-ph" }, { "text": "Experimental investigation of amplification, via a mechanical\n delay-line, in a rainbow-based metasurface for energy harvesting: We demonstrate that a rainbow-based metasurface, created by a graded array of\nresonant rods attached to an elastic beam, operates as a mechanical delay-line\nby slowing down surface elastic waves to take advantage of wave interaction\nwith resonance. Experiments demonstrate that the rainbow effect reduces the\namplitude of the propagating wave in the host structure. At the same time it\ndramatically increases both the period of interaction between the waves and the\nresonators, and the wavefield amplitude in the rod endowed with the harvester.\nIncreased energy is thus fed into the resonators over time, we show the\nenhanced energy harvesting capabilities of this system.", "category": "physics_app-ph" }, { "text": "Comparison of Tensor Boundary Conditions (TBCs) with Generalized Sheet\n Transition Conditions (GSTCs): This paper compares Tensor Boundary Conditions (TBCs), which were introduced\nto model multilayered dielectric structures, with Generalized Sheet Transition\nConditions (GSTCs), which have been recently used to model metasurfaces. It\nshows that TBCs, with their 3 scalar parameters, are equivalent to the\ndirect-isotropic -- cross-antiisotropic, reciprocal and nongyrotropic subset of\nGSTCs, whose 16 tangential (particular case of zero normal polarizations) or 36\ngeneral susceptibility parameters can handle the most general bianisotropic\nsheet structures. It further shows that extending that TBCs scalar parameters\nto tensors and allowing a doubly-occurring parameter to take different values\nleads to a TBCs formulation that is equivalent to the tangential GSTCs, but\nwithout reflecting the polarization physics of sheet media, such as\nmetasurfaces and two-dimensional material allotropes.", "category": "physics_app-ph" }, { "text": "Bespoke magnetic field design for a magnetically shielded cold atom\n interferometer: Quantum sensors based on cold atoms are being developed which produce\nmeasurements of unprecedented accuracy. Due to shifts in atomic energy levels,\nquantum sensors often have stringent requirements on their internal magnetic\nfield environment. Typically, background magnetic fields are attenuated using\nhigh permeability magnetic shielding, with the cancelling of residual and\nintroduction of quantisation fields implemented with coils inside the shield.\nThe high permeability shield, however, distorts all magnetic fields, including\nthose generated inside the sensor. Here, we demonstrate a solution by designing\nmultiple coils overlaid on a 3D-printed former to generate three uniform and\nthree constant linear gradient magnetic fields inside the capped cylindrical\nmagnetic shield of a cold atom interferometer. The fields are characterised\nin-situ and match their desired forms to high accuracy. For example, the\nuniform transverse field, $B_x$, deviates by less than $0.2$% over more than\n$40$% of the length of the shield. We also map the field directly using the\ncold atoms and investigate the potential of the coil system to reduce bias from\nthe quadratic Zeeman effect. This coil design technology enables targeted field\ncompensation over large spatial volumes and has the potential to reduce\nsystematic shifts and noise in numerous cold atom systems.", "category": "physics_app-ph" }, { "text": "High-sensitive MIS structures with silicon nanocrystals grown via\n solid-state dewetting of silicon-on-insulator for solar cell and\n photodetector applications: This work reports an original method for the fabrication of\nMetal-Isulator-Semiconductor (MIS) structures with silicon nanocrystals (Si\nNCs) based active layers embedded in the insulating SiO 2 oxide, for high\nperformance solar cell and photodetector applications. The Si NCs are produced\nvia the in situ solid-state dewetting of ultra-pure amorphous\nsilicon-oninsulator (a-SOI) grown by solid source molecular beam epitaxy\n(SSMBE). The size and density of Si NCs are precisely tuned by varying the\ndeposited thickness of silicon. The morphological characterization carried out\nby using atomic force microscopy (AFM) and scanning electron microscopy (SEM)\nshows that the Si NCs have homogeneous size with welldefined spherical shape\nand densities up to ~10 12 /cm 2 (inversely proportional to the square of\nnominal a-Si thickness). The structural investigations by high resolution\ntransmission electron microscopy (HR-TEM) show that the ultra-small Si NCs\n(with mean diameter ~7 nm) are monocrystalline and free of structural defects.\nThe electrical measurements performed by current versus voltage (I-V) and\nphotocurrent spectroscopies on the Si-NCs based MIS structures prove the\nefficiency of Si NCs to enhance the electrical conduction in MIS structures and\nto increase (x10 times) the photocurrent (i.e. at bias voltage V =-1 V) via the\nphotogeneration of additional electron-hole pairs in the MIS structures. These\nresults evidence that the Si NCs obtained by the combination of MBE growth and\nsolid-state dewetting are perfectly suitable for the development of novel high\nperformance optoelectronic devices compatible with the CMOS technology.", "category": "physics_app-ph" }, { "text": "Heterogeneous integration of superconducting thin films and epitaxial\n semiconductor heterostructures with Lithium Niobate: We report on scalable heterointegration of superconducting electrodes and\nepitaxial semiconductor quantum dots on strong piezoelectric and optically\nnonlinear lithium niobate. The implemented processes combine the\nsputter-deposited thin film superconductor niobium nitride and III-V compound\nsemiconductor membranes onto the host substrate. The superconducting thin film\nis employed as a zero-resistivity electrode material for a surface acoustic\nwave resonator with internal quality factors $Q \\approx 17000$ representing a\nthree-fold enhancement compared to identical devices with normal conducting\nelectrodes. Superconducting operation of $\\approx 400\\,\\mathrm{MHz}$ resonators\nis achieved to temperatures $T>7\\,\\mathrm{K}$ and electrical radio frequency\npowers $P_{\\mathrm{rf}}>+9\\,\\mathrm{dBm}$. Heterogeneously integrated single\nquantum dots couple to the resonant phononic field of the surface acoustic wave\nresonator operated in the superconducting regime. Position and frequency\nselective coupling mediated by deformation potential coupling is validated\nusing time-integrated and time-resolved optical spectroscopy. Furthermore,\nacoustoelectric charge state control is achieved in a modified device geometry\nharnessing large piezoelectric fields inside the resonator. The hybrid quantum\ndot - surface acoustic wave resonator can be scaled to higher operation\nfrequencies and smaller mode volumes for quantum phase modulation and\ntransduction between photons and phonons via the quantum dot. Finally, the\nemployed materials allow for the realization of other types of optoelectronic\ndevices, including superconducting single photon detectors and integrated\nphotonic and phononic circuits.", "category": "physics_app-ph" }, { "text": "Chemical Sensing with Nanogap AND Chemi-mechanical Devices: This article presents a new class of batch-fabricated, low-power and highly\nsensitive chemiresistive sensors. We first present the design, fabrication and\ncharacterization of batch-fabricated sidewall etched vertical nanogap\ntunnelling-junctions for bio-sensing. Using these devices we demonstrate the\nelectrical detection of certain organic molecules from measurements of\ntunneling characteristics of target-mediated molecular junctions formed across\nnanogaps.", "category": "physics_app-ph" }, { "text": "Rolled-up self-assembly of compact magnetic inductors, transformers and\n resonators: Three-dimensional self-assembly of lithographically patterned ultrathin films\nopens a path to manufacture microelectronic architectures with functionalities\nand integration schemes not accessible by conventional two-dimensional\ntechnologies. Among other microelectronic components, inductances,\ntransformers, antennas and resonators often rely on three-dimensional\nconfigurations and interactions with electromagnetic fields requiring\nexponential fabrication efforts when downscaled to the micrometer range. Here,\nthe controlled self-assembly of functional structures is demonstrated. By\nrolling-up ultrathin films into cylindrically shaped microelectronic devices we\nrealized electromagnetic resonators, inductive and mutually coupled coils.\nElectrical performance of these devices is improved purely by transformation of\na planar into a cylindrical geometry. This is accompanied by an overall\ndownscaling of the device footprint area by more than 50 times. Application of\ncompact self-assembled microstructures has significant impact on electronics,\nreducing size, fabrication efforts, and offering a wealth of new features in\ndevices by 3D shaping.", "category": "physics_app-ph" }, { "text": "Black phosphorus nanodevices at terahertz frequencies: photodetectors\n and future challenges: The discovery of graphene triggered a rapid rise of unexplored\ntwo-dimensional materials and heterostructures having optoelectronic and\nphotonics properties that can be tailored on the nanoscale. Among these\nmaterials, black phosphorus (BP) has attracted a remarkable interest thanks to\nmany favorable properties, such as high carrier mobility, in-plane anisotropy,\nthe possibility to alter its transport via electrical gating and direct\nband-gap, that can be tuned by thickness from 0.3 eV (bulk crystalline) to 1.7\neV (single atomic layer). When integrated in a microscopic field effect\ntransistor (FET), a few-layer BP flake can detect Terahertz (THz) frequency\nradiation. Remarkably, the in-plane crystalline anisotropy can be exploited to\ntailor the mechanisms that dominate the photoresponse; a BP-based field effect\ntransistor can be engineered to act as a plasma-wave rectifier, a\nthermoelectric sensor or a thermal bolometer. Here we present a review on\nrecent research on BP detectors operating from 0.26 THz to 3.4 THz with\nparticular emphasis on the underlying physical mechanisms and the future\nchallenges that are yet to be addressed for making BP the active core of stable\nand reliable optical and electronic technologies.", "category": "physics_app-ph" }, { "text": "Flash Temperature and Force Measurements in Single Diamond Scratch Tests: Analysis of the highest temperature in the machining processes, namely the\nflash temperature, helps to understand the physics of the process, to improve\ncutting tool geometry, and to achieve high performance machining. In the\npresent work, the interaction between cutting grain and workpiece material in\ngrinding process is analyzed. Single diamonds are considered for machining,\nwhich operates in comparison to other measurements in the range of grinding\nspeed. The highest temperature in the grain-material interaction and cutting\nforces are measured. In order to measure the flash temperature, an innovative\nmethod to measure and analyze the temperature through the diamond grain in the\ncutting zone by a two-color pyrometer is proposed. Furthermore, cutting forces\nare measured simultaneously. In order to measure the temperature in the cutting\nzone, an accurate connection between diamond and pyrometer fiber is required.\nThus, the diamond tool holders are manufactured by electrical discharge\nmachining (EDM) milling in deionized water. A 0.5-mm-diameter hole is drilled\nin each holder to connect the diamond precisely to the pyrometer fiber.\nMachining processes are performed with 30 {\\mu}m depth of cut, cutting length\nof 20 mm, and cutting speed of 65 m/s on Ti6Al4V. The cutting tool is fixed,\nand the shape of the rotating workpiece is optimized. The diamond holder with\nthe specific shape is designed and manufactured. Quasi-static, dynamic, modal,\nand harmonic response analyses are performed in order to reduce vibrations and\nchattering. The measured flash temperature is 1380 {\\deg}C and cutting normal,\ntangential, and axial forces are measured.", "category": "physics_app-ph" }, { "text": "Validation of a fast and accurate magnetic tracker operating in the\n environmental field: We characterize the performance of a system based on a magnetoresistor array.\nThis instrument is developed to map the magnetic field, and to track a dipolar\nmagnetic source in the presence of a static homogeneous field. The position and\norientation of the magnetic source with respect to the sensor frame is\nretrieved together with the orientation of the frame with respect to the\nenvironmental field. A nonlinear best-fit procedure is used, and its precision,\ntime performance, and reliability are analyzed. This analysis is performed in\nview of the practical application for which the system is designed that is an\neye-tracking diagnostics and rehabilitative tool for medical purposes, which\nrequire high speed ($\\ge 100$~Sa/s) and sub-millimetric spatial resolution. A\nthroughout investigation on the results makes it possible to list several\nobservations, suggestions, and hints, which will be useful in the design of\nsimilar setups.", "category": "physics_app-ph" }, { "text": "General Conditions to Realize Exceptional Points of Degeneracy in Two\n Uniform Coupled Transmission Lines: We present the general conditions to realize a fourth order exceptional point\nof degeneracy (EPD) in two uniform (i.e., invariant along z) lossless and\ngainless coupled transmission lines (CTLs), namely, a degenerate band edge\n(DBE). Until now the DBE has been shown only in periodic structures. In\ncontrast, the CTLs considered here are uniform and subdivided into four cases\nwhere the two TLs support combinations of forward propagation, backward\npropagation and evanescent modes (when neglecting the mutual coupling). We\ndemonstrate for the first time that a DBE is supported in uniform CTLs when\nthere is proper coupling between: (i) propagating modes and evanescent modes,\n(ii) forward and backward propagating modes, or (iii) four evanescent modes\n(two in each direction). We also show that the loaded quality factor of uniform\nCTLs exhibiting a fourth order EPD at k=0 is robust to series losses due to the\nfact that the degenerate modes do not advance in phase. We also provide a\nmicrostrip possible implementation of a uniform CTL exhibiting a DBE using\nperiodic series capacitors with very sub-wavelength unit-cell length. Finally,\nwe show an experimental verification of the existence DBE for a microstrip\nimplementation of a CTL supporting coupled propagating and evanescent modes.", "category": "physics_app-ph" }, { "text": "Chalcogen Assisted Enhanced Atomic Orbital Interaction at TMDs - Metal\n Interface & Chalcogen Passivation of TMD Channel For Overall Performance\n Boost of 2D TMD FETs: Metal-semiconductor interface is a bottleneck for efficient transport of\ncharge carriers through Transition Metal Dichalcogenide (TMD) based\nfield-effect transistors (FETs). Injection of charge carriers across such\ninterfaces is mostly limited by Schottky barrier at the contacts which must be\nreduced to achieve highly efficient contacts for carrier injection into the\nchannel. Here we introduce a universal approach involving dry chemistry to\nenhance atomic orbital interaction between various TMDs (MoS2, WS2, MoSe2 and\nWSe2) & metal contacts has been experimentally demonstrated. Quantum chemistry\nbetween TMDs, Chalcogens and metals has been explored using detailed atomistic\n(DFT & NEGF) simulations, which is then verified using Raman, PL and XPS\ninvestigations. Atomistic investigations revealed lower contact resistance due\nto enhanced orbital interaction and unique physics of charge sharing between\nconstituent atoms in TMDs with introduced Chalcogen atoms which is subsequently\nvalidated through experiments. Besides contact engineering, which lowered\ncontact resistance by 72, 86, 1.8, 13 times in MoS2, WS2, MoSe2 and WSe2\nrespectively, a novel approach to cure / passivate dangling bonds present at\nthe 2D TMD channel surface has been demonstrated. While the contact engineering\nimproved the ON-state performance (ION, gm, mobility and RON) of 2D TMD FETs by\norders of magnitude, Chalcogen based channel passivation was found to improve\ngate control (IOFF, SS, & VTH) significantly. This resulted in an overall\nperformance boost. The engineered TMD FETs were shown to have performance on\npar with best reported till date.", "category": "physics_app-ph" }, { "text": "Using Programmable Graphene Channels as Weights in Spin-Diffusive\n Neuromorphic Computing: A graphene-based spin-diffusive (GrSD) neural network is presented in this\nwork that takes advantage of the locally tunable spin transport of graphene and\nthe non-volatility of nanomagnets. By using electrostatically gated graphene as\nspintronic synapses, a weighted summation operation can be performed in the\nspin domain while the weights can be programmed using circuits in the charge\ndomain. Four-component spin/charge circuit simulations coupled to magnetic\ndynamics are used to show the feasibility of the neuron-synapse functionality\nand quantify the analog weighting capability of the graphene under different\nspin relaxation mechanisms. By realizing transistor-free weight implementation,\nthe graphene spin-diffusive neural network reduces the energy consumption to\n0.08-0.32 fJ per cell-synapse and achieves significantly better scalability\ncompared to its digital counterparts, particularly as the number and bit\naccuracy of the synapses increases.", "category": "physics_app-ph" }, { "text": "Coupled Colloidal Quantum Dot Molecules: Coupling of atoms is the basis of chemistry, yielding the beauty and richness\nof molecules. We utilize semiconductor nanocrystals as artificial atoms to form\nnanocrystal molecules that are structurally and electronically coupled.\nCdSe/CdS core/shell nanocrystals are linked to form dimers which are then fused\nvia constrained oriented attachment. The possible nanocrystal facets in which\nsuch fusion takes place are analyzed with atomic resolution revealing the\ndistribution of possible crystal fusion scenarios. Coherent coupling and\nwavefunction hybridization are manifested by a red shift of the band gap, in\nagreement with quantum mechanical simulations. Single nanoparticle spectroscopy\nunravels the attributes of coupled nanocrystal dimers related to the unique\ncombination of quantum mechanical tunneling and energy transfer mechanisms.\nThis sets the stage for nanocrystals chemistry to yield a diverse selection of\ncoupled nanocrystal molecules constructed from controlled core/shell\nnanocrystal building blocks. These are of direct relevance for numerous\napplications in displays, sensing, biological tagging and emerging quantum\ntechnologies.", "category": "physics_app-ph" }, { "text": "Optofluidic Force Induction as a Process Analytical Technology: Manufacturers of nanoparticle-based products rely on detailed information\nabout critical process parameters, such as particle size and size\ndistributions, concentration, and material composition, which directly reflect\nthe quality of the final product. These process parameters are often obtained\nusing offline characterization techniques that cannot provide the temporal\nresolution to detect dynamic changes in particle ensembles during a production\nprocess. To overcome this deficiency, we have recently introduced Optofluidic\nForce Induction (OF2i) for optical real-time counting with single particle\nsensitivity and high throughput. In this paper, we apply OF2i to highly\npolydisperse and multi modal particle systems, where we also monitor\nevolutionary processes over large time scales. For oil-in-water emulsions we\ndetect in real time the transition between high-pressure homogenization states.\nFor silicon carbide nanoparticles, we exploit the dynamic OF2i measurement\ncapabilities to introduce a novel process feedback parameter based on the\ndissociation of particle agglomerates. Our results demonstrate that OF2i\nprovides a versatile workbench for process feedback in a wide range of\napplications.", "category": "physics_app-ph" }, { "text": "Photosensitivity and reflectivity of the active layer in Tamm plasmon\n polariton based organic solar cell: The paper proposes a model of an organic solar cell based on Tamm plasmon\npolariton localized at the boundary of the active layer doped with plasmon\nnanoparticles and a multilayer mirror. It is shown that the integral absorption\nin the active layer can be increased by 10% compared to the optimized planar\nsolar cell.", "category": "physics_app-ph" }, { "text": "Polystyrene-based nanocomposites with different fillers: fabrication and\n mechanical properties: The paper presents a comprehensive analysis of elastic properties of\npolystyrene-based nanocomposites filled with different types of inclusions:\nsmall spherical particles (SiO2 and Al2O3), alumosilicates (montmorillonite,\nhalloysite natural tubules and Mica) and carbon nanofillers (carbon black and\nmulti-walled carbon nanotubes). Composites were fabricated by melt technology.\nThe analysis of composite melts showed that the introduction of\nMontmorillonite, Multi-walled carbon nanotubes, and Al2O3 particles provided an\nincrease in melt viscosity by an average of 2 to 5 orders of magnitude over the\npure polystyrene. Block samples of composites with different filler\nconcentrations were prepared, and their linear and nonlinear elastic properties\nwere studied. The introduction of more rigid particles led to a more profound\nincrease in the elastic modulus of the composite, with the highest rise of\nabout 80% obtained with carbon fillers. Carbon black particles provided also an\nenhanced strength at break of about 20% higher than that of pure polystyrene.\n The nonlinear elastic moduli of composites were shown to be more sensitive to\naddition of filler particles to the polymer matrix than the linear ones. The\nnonlinearity coefficient $\\beta$ comprising the combination of linear and\nnonlinear elastic moduli of a material demonstrated considerable changes\ncorrelating with changes of the Young's modulus. The absolute value of $\\beta$\nshowed rise in 1.5-1.6 times in the CB- and HNT-containing composites as\ncompared to that of pure PS. The changes in nonlinear elasticity of fabricated\ncomposites were compared with measurements of the parameters of bulk nonlinear\nstrain waves in them. Variations of wave velocity and decay decrement\ncorrelated with observed enhancement of materials nonlinearity.", "category": "physics_app-ph" } ]