bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of hot electrons in shock ignition constrained by experiment at the National Ignition Facility
Authors: Barlow D. , Goffrey T. , Bennett K. , Scott R. H. H. , Glize K. , Theobald W. , Anderson K. , Solodov A. A. , Rosenberg M. J. , Hohenberger M. , Woolsey N. C. , Bradford P. , Khan M. , Arber T. D.
Published: August 2022

Shock ignition is a scheme for direct drive inertial confinement fusion that offers the potential for high gain with the current generation of laser facility; however, the benefits are thought to be dependent on the use of low adiabat implosions without laser–plasma instabilities reducing drive and generating hot electrons. A National Ignition Facility direct drive solid target experiment was used to calibrate a 3D Monte Carlo hot-electron model for 2D radiation-hydrodynamic simulations of a shock ignition implosion. The α=2.5 adiabat implosion was calculated to suffer a 35% peak areal density decrease when the hot electron population with temperature Th=55 keV and energy Eh=13 kJ was added to the simulation. Optimizing the pulse shape can recover ∼1/3 of the peak areal density lost due to a change in shock timing. Despite the harmful impact of laser–plasma instabilities, the simulations indicate shock ignition as a viable method to improve performance and broaden the design space of near ignition high adiabat implosions.
Reversible band structure engineering in semimetal SrIrO3 films using atomic hydrogen
Authors: Sun Wenjie , Guo Wei , Yang Jiangfeng , Liu Ruxin , Li Yueying , Gu Chenyi , Gu Zhengbin , Wang Xuefeng , Nie Yuefeng
Published: August 2022

We report on the atomic hydrogen annealing to in situ manipulate the electronic structures in semimetal SrIrO3 films. Carriers are found to be effectively doped into epitaxial SrIrO3 films by atomic hydrogen annealing without degrading the lattice structure, as revealed by transport and structural measurements. Using angle-resolved photoemission spectroscopy, the low-lying hole bands exhibit a nearly rigid band shift toward the higher binding energy upon atomic hydrogen annealing, which can be further restored by the ozone annealing. Unlike the typical in situ alkali-metal surface doping method, our atomic-hydrogen-treated SrIrO3 films are stable in air, which warrants ex situ characterizations. Our work shows a reversible and effective in situ carrier doping method to explore exotic phases in strongly correlated systems, such as the potential superconductivity in iridates.
Flexible joint parameters identification method based on improved tracking differentiator and adaptive differential evolution
Authors: Song Chuanming , Du Qinjun , Yang Shuxin , Feng Han , Pang Hao , Li Cunhe
Published: August 2022

The assembly error of flexible joints and the change in joint stiffness during movement make the actual value of joint parameters inconsistent with the given value, which affects the joint control accuracy. In order to suppress the influence of parameters error, a parameters identification method for flexible joint combined offline identification and online compensation is proposed. First, the offline identification model of inertia, mass, and damping and the online identification model of joint stiffness are established, respectively. Then, a hybrid tracking differentiator based on an improved Sigmoid function is designed to track the differential signals of joint motion parameters, and the Lyapunov function is designed to prove its convergence. The adaptive differential evolution is used as the identification algorithm, and the improved adaptive crossover, mutation factor, and Metropolis acceptance criterion are designed to improve the convergence speed. Finally, a feedforward control structure based on identification is designed to compensate for the model deviation. Simulation and experimental results show that the improved differentiator can effectively improve the tracking speed and derivation accuracy of the signals. Compared with other algorithms, the proposed identification method has a faster convergence speed and higher identification accuracy, and feedforward compensation control can effectively correct model parameters and improve control accuracy.
Unusual temperature dependence of the photoluminescence emission of MgV centers in diamond
Authors: Osmic E. , Pezzagna S. , Lühmann T. , Böhlmann W. , Meijer J.
Published: August 2022

Magnesium-and germanium-vacancy centers were produced in diamond by ion implantation and the post-annealing process. Photoluminescence spectroscopy (PL) measurements were performed between 20 and 50 °C. The PL results of the GeV centers are in agreement with those found in the literature, while the MgV center is newly discovered and a not yet broadly investigated color center, but the room temperature PL results are in agreement with the first report. The temperature dependence of the MgV centers above room temperature is unusual: by increasing the temperature, its PL shifts to higher energies, contrary to what is observed for the GeV centers and other known centers in the literature. The zero phonon line width of both centers broadens by increasing the temperature in both investigated centers. The origin of the blue shift observed in the MgV centers as a confinement effect is discarded, because sample is bulk and its origin should lay on the influence of the temperature on the local static structure and the overlapping of the electronic wave functions. Our results show the ability of MgV to be used in future for thermometry. The center is bright and photostable, with a narrow full width at half maximum compared to other centers in diamond and its shift with the temperature is also larger.
Improved gradual resistive switching range and 1000× on/off ratio in HfOx RRAM achieved with a Ge2Sb2Te5 thermal barrier
Authors: Islam R. , Qin S. , Deshmukh S. , Yu Z. , Köroğlu C. , Khan A. I. , Schauble K. , Saraswat K. C. , Pop E. , Wong H.-S. P.
Published: August 2022

Gradual switching between multiple resistance levels is desirable for analog in-memory computing using resistive random-access memory (RRAM). However, the filamentary switching of HfOx-based conventional RRAM often yields only two stable memory states instead of gradual switching between multiple resistance states. Here, we demonstrate that a thermal barrier of Ge2Sb2Te5 (GST) between HfOx and the bottom electrode (TiN) enables wider and weaker filaments, by promoting heat spreading laterally inside the HfOx. Scanning thermal microscopy suggests that HfOx + GST devices have a wider heating region than control devices with only HfOx, indicating the formation of a wider filament. Such wider filaments can have multiple stable conduction paths, resulting in a memory device with more gradual and linear switching. The thermally enhanced HfOx + GST devices also have higher on/off ratio (>103) than control devices (<102) and a median set voltage lower by approximately 1 V (∼35%), with a corresponding reduction of the switching power. Our HfOx + GST RRAM shows 2× gradual switching range using fast (∼ns) identical pulse trains with amplitude less than 2 V.
Bismuth nanowires with in situ shadow deposited Josephson junctions
Authors: Wang Hui , Deacon Russell S. , Ishibashi Koji
Published: August 2022

Single crystal bismuth nanowires have been recently identified as a high-order topological system, in which the crystal “hinges” host a one dimensional helical transport channel. To date, studies on the superconducting transport in these channels have relied on an aggressive surface treatment required to strip the oxidized nanowire surface prior to deposition of a superconductor in a process that will inevitably cause some damage to the surface. In this report, we describe the growth and characterization of bismuth nanowires with in situ deposited superconducting contacts, which avoid the requirement to treat the nanowire surface for oxide removal. The described shadow deposition method may avoid damage to the bismuth nanowire surface, supplying a higher-quality platform for exploring the topological quantum transport in bismuth nanowire based Josephson junctions.
Scattering anisotropy in HgTe (013) quantum well
Authors: Khudaiberdiev D. A. , Savchenko M. L. , Kozlov D. A. , Mikhailov N. N. , Kvon Z. D.
Published: August 2022

We report on a detailed experimental study of the electron transport anisotropy in HgTe (013) quantum well of 22 nm width in the directions [100] and [031¯] as the electron density function n. The anisotropy is absent at the minimal electron density near a charge neutrality point. The anisotropy increases with the increase in n and reaches about 10% when the Fermi level is within the first subband H1. There is a sharp increase in the anisotropy (up to 60%) when the Fermi level reaches the second subband E2. We conclude that the first effect is due to the small intra-subband anisotropic interface roughness scattering, and the second one is due to the strongly anisotropic inter-subband roughness scattering, but the microscopical reason for such a strong change in the anisotropy remains unknown.
On the emergence of heat waves in the transient thermal grating geometry
Authors: Zhang Chuang , Huberman Samuel , Wu Lei
Published: August 2022

The propagation of heat in the transient thermal grating geometry is studied based on the phonon Boltzmann transport equation (BTE) in different phonon transport regimes. Our analytical and numerical results show that the phonon dispersion relation and temperature govern the emergence of heat waves. For the frequency-independent BTE, a heat wave manifests in both the ballistic and hydrodynamic regimes. For the frequency-dependent BTE, heat waves are present in the hydrodynamic regime but may be absent in the ballistic regime. In the context of real materials, we predict the emergence of heat waves in the suspended graphene (ballistic and hydrodynamic regimes) and silicon (ballistic regime) at extremely low temperatures.
Sheath formation around a dielectric droplet in a He atmospheric pressure plasma
Authors: Meyer Mackenzie , Nayak Gaurav , Bruggeman Peter J. , Kushner Mark J.
Published: August 2022

Interactions at the interface between atmospheric pressure plasmas and liquids are being investigated to address applications ranging from nanoparticle synthesis to decontamination and fertilizer production. Many of these applications involve activation of droplets wherein the droplet is fully immersed in the plasma and synergistically interacts with the plasma. To better understand these interactions, two-dimensional modeling of radio frequency (RF) glow discharges at atmospheric pressure operated in He with an embedded lossy dielectric droplet (tens of microns in size) was performed. The properties of the sheath that forms around the droplet were investigated over the RF cycle. The electric field in the bulk plasma polarizes the dielectric droplet while the electron drift in the external electric field is shadowed by the droplet. The interaction between the bulk and sheath electric fields produces a maximum in E/N (electric field/gas number density) at the equator on one side of the droplet where the bulk and sheath fields are aligned in the same direction and a minimum along the opposite equator. Due to resistive heating, the electron temperature Te is maximum 45° above and below the equator of the droplet where power deposition per electron is the highest. Although the droplet is, on the average, negatively charged, the charge density on the droplet is positive on the poles and negative on the equator, as the electron motion is primarily due to diffusion at the poles but due to drift at the equator.
High-speed, low-voltage programmable/erasable flexible 2-bit organic transistor nonvolatile memory with a monolayer buffered ferroelectric terpolymer insulator
Authors: Xu Meili , Qi Weihao , Xie Wenfa , Wang Wei
Published: August 2022

Achieving multi-bit data storage in one transistor is a promising strategy to further multiply the storage density of the nonvolatile memories (NVMs). Low-voltage programming/erasing (P/E) operation is a prerequisite for the commercialization of the multi-bit NVMs. And, the fast P/E switching is also a desirable figure of merit for the practical NVMs. Here, we develop a route to achieve a high-speed, low-voltage P/E flexible organic transistor-based NVM, by processing a monolayer buffered ferroelectric terpolymer insulator. The physical mechanisms for achieving the high-speed, low-voltage P/E properties in the organic transistor-based NVMs are investigated. As a result, high-performance flexible 2-bit NVMs are achieved, with the low P/E voltage of ±15 V, fast P/E switching capability of 50 ns, high mobility up to 7.4 cm2 V−1 s−1, high stable retention time up to 10 years, reliable endurance over 200 cycles, good mechanical bending durability, and atmosphere stability.
A systematic study of hidden errors in the bounce-back scheme and their various effects in the lattice Boltzmann simulation of viscous flows
Authors: Dong Zhi-Qiang , Wang Lian-Ping , Peng Cheng , Chen Tao
Published: August 2022

Bounce-back schemes represent the most popular boundary treatments in the lattice Boltzmann method (LBM) when reproducing the no-slip condition at a solid boundary. While the lattice Boltzmann equation used in LBM for interior nodes is known to reproduce the Navier–Stokes (N–S) equations under the Chapman–Enskog (CE) approximation, the unknown distribution functions reconstructed from a bounce-back scheme at boundary nodes may not be consistent with the CE approximation. This problem could lead to undesirable effects such as nonphysical slip velocity, grid-scale velocity, pressure noises, the local inconsistency with the N–S equations, and sometimes even a reduction of the overall numerical-accuracy order of LBM. Here, we provide a systematic study of these undesirable effects. We first derive the explicit structure of the mesoscopic distribution function for interior nodes. Then, the bounce-back distribution function is examined to identify the hidden errors. It is shown that the relaxation parameters in the collision models play a key role in determining the magnitude of the hidden error terms, and there exists an optimal setting, which can suppress or eliminate most of these undesirable effects. While the existence of this optimal setting is derived previously for unidirectional flows, here, we show that this optimal setting can be extended to non-uniform flows under certain conditions. Finally, a systematic numerical benchmark study is carried out, including non-uniform and unsteady flows. It is shown that, in all these flows, our theoretical analyses of the hidden errors can guide us to significantly improve the quality of the simulation results.
Evaporation and liquid-phase separation of ethanol–cyclohexane binary drops under acoustic levitation
Authors: Chen Hongyue , Li Anna , Zhang Yongjian , Zhang Xiaoqiang , Zang Duyang
Published: August 2022

Evaporation of cyclohexane and ethanol binary drops under acoustic levitation was investigated. The aim was to understand the effect of acoustic levitation on the evaporation dynamics and involved physical processes of the binary drops. We report the occurrence of liquid-phase separation of the binary drop during evaporation under acoustic levitation. Through systematic experiments, it was found that the enhanced evaporation rate of the drop under acoustic levitation led to a significant temperature decrease. In addition, driven by external acoustic streaming, water vapor tended to be enriched and condensed on the drop surface. Because ethanol is extremely soluble in water, tiny cyclohexane droplets were extracted from ethanol owing to water condensation. In addition, driven by the internal flow of the acoustically levitated drop, the extracted cyclohexane droplets coalesced, eventually resulting in macro-segregation in the drop. These findings provide new insights into the evaporation dynamics of acoustically levitated drops, thus, shedding light on industrial purification and separation of volatile liquids with opposite water solubilities, such as cyclohexane and ethanol.
Using a Au/pitted a-plane GaN substrate to aggregate polar molecules for highly efficient surface-enhanced Raman scattering
Authors: Ko Tsung-Shine , Kuo Kai-Yuan
Published: August 2022

Searching for efficient surface-enhanced Raman scattering (SERS) substrates remains a challenge. In this study, we used metal–organic chemical vapor deposition to directly grow a pitted a-plane GaN thin film, subsequently covered by a thin Au layer (∼25 nm), for use as a SERS substrate, without the need for any additional etching or lithography process. The SERS substrate containing these micrometer-sized pits provided a low limit of detection (∼10−9 M) for Rhodamine 6G (R6G), with a high enhancement factor (4.27 × 108) relative to normal Raman spectroscopy. Furthermore, Raman spectral mapping indicated that most of the R6G molecules were concentrated in the pits, enhancing the localization of the probe molecules for further analysis. The same molecular localization phenomenon was also effective for polar methylene blue but not for nonpolar paraffin. The molecular aggregation became more ambiguous upon increasing the thickness of the Au layer, suggesting that the polarity of the Ga and N atoms in the pits was responsible for the efficient aggregation of the polar R6G molecules, which could be potentially beneficial for biomedical detection.
Grating-based microcavity with independent control of resonance energy and linewidth for non-Hermitian polariton system
Authors: Hu Jiaqi , Lydick Nathanial , Wang Zhaorong , Jabeen F. , Schneider C. , Höfling S. , Deng Hui
Published: August 2022

Exciton–polaritons have become an emerging platform for implementing non-Hermitian physics. The implementation commonly requires control of both the real and imaginary parts of the eigenmodes of the system. We present an experimental method to achieve this purpose using microcavities with sub-wavelength gratings as reflectors. The reflectivity and reflection phase of the grating can be changed by its geometric parameters, and they determine the energy and linewidth of the polariton modes. We demonstrate that this method allows a wide range of possible polariton energy and linewidth, suitable for implementing non-Hermitian polariton systems with coupled modes.
An analysis of emotions and the prominence of positivity in #BlackLivesMatter tweets
Authors: Field Anjalie , Park Chan Young , Theophilo Antonio , Watson-Daniels Jamelle , Tsvetkov Yulia
Published: August 2022

Emotions are a central driving force of activism; they motivate participation in movements and encourage sustained involvement. We use natural language processing techniques to analyze emotions expressed or solicited in tweets about 2020 Black Lives Matter protests. Traditional off-the-shelf emotion analysis tools often fail to generalize to new datasets and are unable to adapt to how social movements can raise new ideas and perspectives in short time spans. Instead, we use a few-shot domain adaptation approach for measuring emotions perceived in this specific domain: tweets about protests in May 2020 following the death of George Floyd. While our analysis identifies high levels of expressed anger and disgust across overall posts, it additionally reveals the prominence of positive emotions (encompassing, e.g., pride, hope, and optimism), which are more prevalent in tweets with explicit pro-BlackLivesMatter hashtags and correlated with on the ground protests. The prevalence of positivity contradicts stereotypical portrayals of protesters as primarily perpetuating anger and outrage. Our work offers data, analyses, and methods to support investigations of online activism and the role of emotions in social movements.
A history of the Basque prosodic systems
Authors: Egurtzegi Ander , Elordieta Gorka
Published: August 2022

This paper presents new proposals for the reconstruction of Proto-Basque accentuation, as well as the development and chronology of the main accentual systems of the modern dialects, grounded in phonetic, historical and typological evidence. It is the first attempt to reconstruct Basque accentuation from a pre-Roman stage to the dialectalization that followed Common Basque. We suggest that Old Proto-Basque had prosodic prominence in the root, i.e., [(C)V.'CVC]. This system evolved into phrase-level prominence in Modern Proto-Basque, giving rise to unaccentedness in non-phrase final positions, with marked stress only introduced later, through Latin loanwords (2nd–3rd century CE). This would become the common system, which still persists in the west. Not long after the dialectification, word-level systems developed in non-western areas, first as peninitial and then as penultimate stress (in eastern dialects). Finally, we propose that the Goizueta prosodic system can be derived from the Central system, which is an alternative view toHualde (in press).
Contrasting signed and spoken languages
Authors: Gabarró-López Sílvia , Meurant Laurence
Published: August 2022

For years, the study of spoken languages, on the basis of written and then also oral productions, was the only way to investigate the human language capacity. As an introduction to this first volume ofLanguages in Contrastdevoted to the comparison of spoken and signed languages, we propose to look at the reasons for the late emergence of the consideration of signed languages and multimodality in language studies. Next, the main stages of the history of sign language research are summarized. We highlight the benefits of studying cross-modal and multimodal data, as opposed to the isolated investigation of signed or spoken languages, and point out the remaining methodological obstacles to this approach. This contextualization prefaces the presentation of the outline of the volume.
Influence of Spatial Correlation Function on Characteristics of Wideband Electromagnetic Wave Absorbers with Chaotic Surface
Authors: Zhang Rui , Ding Fan , Yuan Xujin , Chen Mingji
Published: August 2022

Electromagnetic metasurface with chaos patterned surface could bring rich interaction modes contributing to fully disordered random motions in deterministic systems, which preform uncertainty, irreducibility and unpredictability. We investigate the influence of the correlation function (CF) properties of surface random patterns on the wave absorption performance. The complicated correlation function provides a fully developed random state, broadening the absorption bandwidth significantly and is helpful for reaching higher absorption rate. With the increasing number of peaks in the correlation function, the absorption band at –15 dB reflectivity widens significantly, band at –20 dB reflectivity begins to emerge. As the first peak’s distance from the original point in the CF is enlarged, the absorption trough is gradually formed and deepened to –35 dB level. The results give in-depth understanding of the relation between absorption behavior and controlling parameters including correlation, image information and foam spacer layer thickness. This high absorption absorber has great application potential in customizable radio communication compatibility device and anechoic testing chamber.
Loss mechanisms of multi-frequency whispering gallery mode RF-MEMS resonators
Authors: Liu Wenli , Chen Zeji , Lu Yujie , Zhao Junyuan , Zhu Yinfang , Yang Jinling , Yang Fuhua
Published: August 2022

This work investigates the dominant loss mechanisms of the multi-frequency whispering gallery mode (WGM) resonators theoretically and experimentally, which provides a deep understanding about the working principles of the devices and guidance on their high-end applications. For the first time, the distinct Akhiezer damping (AKE) effects on various order WGMs were comprehensively clarified. At atmosphere, the air damping, which is conventionally expected to be negligible in high-order bulk acoustic wave (BAW) modes, is nonnegligible for all the WGMs. In vacuum, substantial Q enhancements more than two times were obtained. The high-order WGMs benefit more f × Q improvement from the high vacuum than the low-order ones, achieving a promising f × Q product of 1.16 × 1013. What’s more, the Q dynamics over a wide temperature range were characterized, which matched well with the theoretical analysis. The AKE is comparable with anchor loss in low-order modes, while it becomes dominated in the high-order ones. Therefore, the high-order WGMs exhibit higher Q enhancements at cryogenic temperatures. An excellent f × Q product up to 5.91 × 1013 was implemented at 7 K.
Switchable triple plasmon-induced transparency in graphene sandwich metamaterial structures
Authors: Li Junyi , Weng Jun , Li Jiaqi , Chen Shuxian , Guo Zicong , Xu Pengbai , Liu Wenjie , Wen Kunhua , Qin Yuwen
Published: August 2022

In this research, a metamaterial structure composed of graphene sandwich structure is put forward to achieve triple plasmon-induced transparency. This phenomenon is generated by bright–bright modes interaction in the proposed structure, and the results calculated though couple mode theory are consistent with the simulation ones using finite difference time domain method. In addition, the effects of graphene Fermi level and scattering rate on the transmission spectrum are also discussed. It is found that the five-fold switching effects are achieved with the modulation depths (MDs) of 92%, 91%, 95%, 90% and 94%, respectively. What is more, the different graphene strip can also be adjusted by changing Fermi levels to achieve the switching effects with the MDs of 98% and 97%. This model has the prospect to be applied in multi-functional modulators and optical switches in terahertz band.
Evidence for topological features in the electronic and phononic bands of ZGeSb (Z = Hf, Zr, Ti) class of compounds
Authors: G Rishi , V Anusree C , Kanchana V
Published: August 2022

Nontrivial topological properties in materials have been found in either the electronic or the phononic bands, but they have seldom been shown in both for a compound. With the aid of first-principle calculations, our paper attempts to find topological features in the electron and phonon band structures of ZGeSb (Z = Hf, Zr, Ti) class of compounds. The electron band structure exhibits two nodal rings in each of these compounds. Furthermore, drumhead surface states (DSS) have also been shown. The phonon band structure depicts one nodal ring in each of these compounds. DSS is also seen in the phonon surface states. Layering possibility has also been explored in HfGeSb, which admits a nodal ring each in its electronic and phononic band structure. Finally, these compounds (bulk and mono-layer) possess Dirac points robust to spin–orbit coupling effects, with at least one such Dirac point with its linear dispersion extending to the Fermi energy. Therefore, these compounds fall under the topological nodal line metals class, which is rarely seen in materials. These compounds’ theoretical nontrivial topological nature in their electronic and phononic band structure provides a profound grasp of electronic and phononic nodal-line physics and is a good candidate for experimental verification. The existence of Dirac points close to the Fermi level could also motivate one to look for extreme magnetoresistance in these compounds. Moreover, given their largely metallic nature, these compounds become an excellent arena for novel device applications.
Parallel adversarial feature learning and enhancement of feature discriminability for fault diagnosis of a planetary gearbox under time-varying speed conditions
Authors: Zhao Chuan , Zhang Yinglin
Published: August 2022

The intelligent fault diagnosis of a planetary gearbox under variable speed is still a challenging topic. Due to the similar spectrum structure, overlapping features occur and result in decreasing diagnosis accuracy. Autoencoder-based methods can extract features adaptively but few studies have proposed approaches to enhance the discriminability of features from different classes under variable speeds. Besides, the adverse variability of encoder weights may result in an adverse effect on the decoder. Adversarially learned inference (ALI) trains the encoder and decoder independently, but it is time-consuming to reach Nash equilibrium. To address the issues, a parallel adversarial learning inference (PALI) model is proposed, which aims at validating the parallel training of encoder and decoder and enhancing the discriminability of features. Specifically, time-frequency analysis is utilized to reveal the time-varying characteristics of raw signals and obtain time-frequency images as input for the encoder. Then, an explicit multi-dimensional uniform distribution is used for the merit of a simple probability density function to construct visualized and well-classified samples as input for the decoder. After that, a parallel adversarial game is explored to train the encoder and decoder simultaneously and independently, which will reduce computing interference and make the extracted features similar to the well-classified samples and reconstruct the raw signals. Finally, a Softmax classifier is trained and tested by the features. This method and its generability are validated via a planetary gearbox data set and a public bearing data under variable speed. The results indicate that the proposed parallel adversarial game is valid for training encoder and decoder independently, and that PALI works as well as the adversarial autoencoder (AAE) and outperforms ALI, the variational autoencoder (VAE) in obtaining well-clustered features over different training data. Compared to Wigner–Ville distribution (WVD) and continuous wavelet transform (CWT), PALI based on short-time Fourier transformation (STFT) works better over different training data.
Nanoscale mapping of surface strain in tapered nanorods using confocal photoluminescence spectroscopy
Authors: Hwang Hyeong-Yong , Baek Hyeonjun , Yi Gyu-Chul , Jho Young-Dahl
Published: August 2022

The strain occurs spontaneously at the heterogeneous interfaces of virtually all crystalline materials. Consequently, the analysis across multiple interfaces requires a complementary characterization scheme with a resolution that fits the deformation scale. By implementing two-photon confocal laser scanning nanoscopy with an axial resolution of 10 nm, we extract the surface strain from the photoluminescence (PL) spectra, epitomized by a 2-fold enhancement at the tapered tips in comparison to the substrate of ZnO nanorods. We firstly traced the well-established contribution from quantum confinement (QC) to PL shift in three geometrically classified regions: (I) a strongly tapered region where the diameter increases from 3 to 20 nm; (II) a weakly tapered region with a gradually increasing diameter from 20 to 58 nm; (III) round cylindrical region interfacing the sapphire substrate. The measured PL shift influenced by the deformation is significantly stronger than the attained QC effect. Particularly, surface strain at the strongly tapered region turned out to drastically increase the PL shift which matches well with the analysis based on the surface to volume ratio incorporating mechanical parameters such as the compliance tensor component, strain dislocation constant, and surface stress. The surface strain increased at a lower temperature, further disclosing its inherent dependence on the thermal expansion coefficients in clear contrast to the temperature-invariant characteristics of QC.
Optical determination of layered-materials InSe thickness via RGB contrast method and regression analysis
Authors: Lu Yi-Ying , Yu Hsiao-Ching , Wang You-Xin , Hung Chih-Keng , Chen You-Ren , Jhou Jie , Yen Peter Tsung-Wen , Hsu Jui-Hung , Sankar Raman
Published: August 2022

Indium selenide (InSe) features intriguing thickness-dependent optoelectronic properties, and a simple, and precise way to identify the thickness is essential for the rapid development of InSe research. Here, a red, green, and blue (RGB) color contrast method with regression analysis for quantitative correlation of three optical contrasts from RGB channels with the InSe thickness (1–35 nm), is demonstrated. The lower accuracy of the thickness identification obtained from the individual channels was discussed. Moreover, the effective refractive indices in the three RGB regions can be extracted from the Fresnel equation and numerical analysis by finding the best fit to the experimental optical contrast. After further consideration of the wavelength-dependent refractive indices, the slope of the regression line between the estimated thickness and that obtained from the atomic force microscope was improved from 1.59 ± 0.05 to 0.97 ± 0.02. The complex refractive index spectra of InSe (1–10 layers) generated from ab initio numerical calculation results were also adopted to identify the InSe thickness. Compared to dispersion, the evolution of the band structure had less effect on thickness identification. This work could be extended to other layered materials, facilitate the thickness-dependent study of layered materials, and expedite the realization of their practical applications.
Self-catalyzed InAs nanowires grown on Si: the key role of kinetics on their morphology
Authors: Dhungana Daya S , Mallet Nicolas , Fazzini Pier-Francesco , Larrieu Guilhem , Cristiano Fuccio , Plissard Sébastien R
Published: August 2022

Integrating self-catalyzed InAs nanowires on Si(111) is an important step toward building vertical gate-all-around transistors. The complementary metal oxide semiconductor (CMOS) compatibility and the nanowire aspect ratio are two crucial parameters to consider. In this work, we optimize the InAs nanowire morphology by changing the growth mode from Vapor–Solid to Vapor–Liquid–Solid in a CMOS compatible process. We study the key role of the Hydrogen surface preparation on nanowire growths and bound it to a change of the chemical potential and adatoms diffusion length on the substrate. We transfer the optimized process to patterned wafers and adapt both the surface preparation and the growth conditions. Once group III and V fluxes are balances, aspect ratio can be improved by increasing the system kinetics. Overall, we propose a method for large scale integration of CMOS compatible InAs nanowire on silicon and highlight the major role of kinetics on the growth mechanism.
Hot electron and x-ray generation by sub-ns kJ-class laser-produced tantalum plasma
Authors: Singh Sushil , Krupka Michal , Istokskaia Valeria , Krasa Josef , Giuffrida Lorenzo , Dudzak Roman , Dostal Jan , Burian Tomas , Versaci Roberto , Margarone Daniele , Pisarczyk Tadeusz , Krus Miroslav , Juha Libor
Published: August 2022

This paper presents experimental investigation of temperature scaling and threshold of instability in hot electron and bremsstrahlung radiation from the interaction of sub-nanosecond and kilo-joule class laser pulses with a tantalum foil target at Prague Asterix Laser System. The laser intensity was varied between

4
×

10

15

and

3
×

10

16

 W · cm−2 at the target focus. The energy distribution functions of electrons were measured by an angular array of magnetic spectrometers indicating the electron temperature in the range between 30 keV and 70 keV. The bremsstrahlung spectrum was characterized using a scintillator-based calorimeter. In particular, we show the laser-energy scaling of the total flux of hot electrons in the forward and backward directions with respect to the laser vector, the conversion efficiency of the laser energy to the energy carried by hot electrons, and the temperature of hot electrons as well as the unfolded bremsstrahlung temperature using a Monte Carlo code consistent with signals of the scintillator detector. The scaling shows that the electron flux increases discontinuously with increasing laser intensity from

∼

1
−
2
×

10

16

 W · cm−2 with consequent instability in the production of hot electrons and bremsstrahlung radiation.
The effect of obstacles near a silo outlet on the discharge of soft spheres
Authors: Wang Jing , Harth Kirsten , Puzyrev Dmitry , Stannarius Ralf
Published: August 2022

Soft smooth particles in silo discharge show peculiar characteristics, including, for example, non-permanent clogging and intermittent flow. This paper describes a study of soft, low-frictional hydrogel spheres in a quasi-2D silo. We enforce a more competitive behavior of these spheres during their discharge by placing an obstacle in front of the outlet of the silo. High-speed optical imaging is used to capture the process of discharge. All particles in the field of view are identified and tracked by means of machine learning software using a mask region-based convolutional neural network algorithm. With particle tracking velocimetry, the fields of velocity, egress time, packing fraction, and kinetic stress are analyzed in this study. In pedestrian dynamics, it is known that the placement of an obstacle in front of a narrow gate may reduce the stress near the exit and enable a more efficient egress. The effect is opposite for our soft grains. Placing an obstacle above the orifice always led to a reduction of the flow rates, in some cases even to increased clogging probabilities.
Fate of the false vacuum in string-inspired nonlocal field theory
Authors: Ghoshal Anish , Nortier Florian
Published: August 2022

In this article, we study Coleman bounce in weakly nonlocal theories which are motivated from string field theory. The kinetic term is extended via an infinite series of high-order derivatives, which comes into play at an energy scale M, without introducing any new states or ghosts in the mass spectrum. We calculate the bubble nucleation in thin-wall approximation, treating the system in semi-classical manner. We find that the effect of nonlocal scale M in the theory is to suppress the vacuum tunneling rate from false to true vacuum compared to the standard local bouncing scenario. Likewise, we show that as we move further away from the bubble wall, the effects of nonlocality gets reduced and this suppression is significant only around the wall of the nucleated bubble. From our investigations, we conclude that the main effect is due to the fact that the nonlocality smears the solution of the local bubble profile. However, the energy of the bubble wall remains unaffected by the microscopic nonlocal behavior of the theory in the thin-wall approximation. We also discuss the cases for Lee-Wick theories and applications of our result to cosmology.
Non-Gaussianity in the squeezed three-point correlation from the relativistic effects
Authors: Yoo Jaiyul , Grimm Nastassia , Mitsou Ermis
Published: August 2022

Assuming a ΛCDM universe in a single-field inflationary scenario, we compute the three-point correlation function of the observed matter density fluctuation in the squeezed triangular configuration, accounting for all the relativistic effects at the second order in perturbations. This squeezed three-point correlation function characterizes the local-type primordial non-Gaussianity, and it has been extensively debated in literature whether there exists a prominent feature in galaxy clustering on large scales in a single-field inflationary scenario either from the primordial origin or the intrinsic nonlinearity in general relativity. First, we show that theoretical descriptions of galaxy bias are incomplete in general relativity due to ambiguities in spatial gauge choice, while those of cosmological observables are independent of spatial gauge choice. Hence a proper relativistic description of galaxy bias is needed to reach a definitive conclusion in galaxy clustering. Second, we demonstrate that the gauge-invariant calculations of the cosmological observables remain unaffected by extra coordinate transformations like CFC or large diffeomorphism like dilatation. Finally, we show that the relativistic effects associated with light propagation in observations cancel each other, and hence there existsnonon-Gaussian contribution from the so-called projection effects in the squeezed three-point correlation function.
Examining the in vivo functionality of the magnetically aligned regenerative tissue-engineered electronic nerve interface (MARTEENI)
Authors: Atkinson Eric W , Kuliasha Cary A , Kasper Mary , Furniturewalla Abbas , Lim Alexander S , Jiracek-Sapieha Ladan , Brake Alexis , Gormaley Anne , Rivera-Llabres Victor , Singh Ishita , Spearman Benjamin , Rinaldi-Ramos Carlos M , Schmidt Christine E , Judy Jack W , Otto Kevin J
Published: August 2022

Objective. Although neural-enabled prostheses have been used to restore some lost functionality in clinical trials, they have faced difficulty in achieving high degree of freedom, natural use compared to healthy limbs. This study investigated the in vivo functionality of a flexible and scalable regenerative peripheral-nerve interface suspended within a microchannel-embedded, tissue-engineered hydrogel (the magnetically aligned regenerative tissue-engineered electronic nerve interface (MARTEENI)) as a potential approach to improving current issues in peripheral nerve interfaces. Approach. Assembled MARTEENI devices were implanted in the gaps of severed sciatic nerves in Lewis rats. Both acute and chronic electrophysiology were recorded, and channel-isolated activity was examined. In terminal experiments, evoked activity during paw compression and stimulus response curves generated from proximal nerve stimulation were examined. Electrochemical impedance spectroscopy was performed to assess the complex impedance of recording sites during chronic data collection. Features of the foreign-body response (FBR) in non-functional implants were examined using immunohistological methods. Main results. Channel-isolated activity was observed in acute, chronic, and terminal experiments and showed a typically biphasic morphology with peak-to-peak amplitudes varying between 50 and 500 µV. For chronic experiments, electrophysiology was observed for 77 days post-implant. Within the templated hydrogel, regenerating axons formed minifascicles that varied in both size and axon count and were also found to surround device threads. No axons were found to penetrate the FBR. Together these results suggest the MARTEENI is a promising approach for interfacing with peripheral nerves. Significance. Findings demonstrate a high likelihood that observed electrophysiological activity recorded from implanted MARTEENIs originated from neural tissue. The variation in minifascicle size seen histologically suggests that amplitude distributions observed in functional MARTEENIs may be due to a combination of individual axon and mini-compound action potentials. This study provided an assessment of a functional MARTEENI in an in vivo animal model for the first time.
Graphene bandgap opening by constructing superlattices with BN or MoO2 under pressure
Authors: Wang Bohan , Song Chaoyang
Published: August 2022

After the isolation of the single layer graphene in 2004, which has overthrown the prediction of the two-dimensional material field, various aspects of its unique properties have been observed, including extremely high strength, carrier mobility and heat conductivity. Being the minority of nonmetallic materials with a conductive property as metals, its possible applications is much widened. Noteworthily, graphene has a zero bandgap. Although making it an excellent conductor, zero bandgap has also constrained its performance as a semiconductor. Fortunately, there are several possible ways to open its bandgap and make it behave like a semiconductor. In this study, we propose that constructing superlattices and controlling hydrostatic pressure to open the bandgap of graphene. Based on first-principles calculations, BN and MoO2 are used to form the superlattice with graphene and 1-30 GPa pressures in the vertical direction of two-dimensional plane are applied. The results show that the pressure can affect the structures and interlayer distances of the superlattice, which further lead to a bandgap of the superlattices containing graphene. Our research shows a method that adjusting the bandgap of graphene through pressure, which is of great significance for the application of graphene in the electronic field.
Surface roughness by selective-dissolving on PVA/PVP nanofibers with mobility driven concentration polarization
Authors: Zhang Zheng , Wang Feipeng
Published: August 2022

Surface roughened polyvinyl alcohol (PVA) nanofibers are produced by electrospinning and selective dissolution in ethanol. By electrospinning of PVA (Mw 74885) and polyvinylpyrrolidone(PVP) (Mw 44000-54000) blend solution, PVA/PVP blend nanofibers with smooth, homogenous surface are prepared. Then the surface roughened nanofibers are achieved via selective dissolution in ethanol. Fourier Transform Infrared Spectra (FTIR) and Energy Dispersive Spectrometer (EDS) result shows a complete removal of PVP from blend nanofibers. In this work, PVA/PVP is the first water-soluble polymer combination adopted to create surface roughened nanofibers by selective dissolution. Moreover, opposite to other selective dissolution schemes which removes polymers of higher Mw, this is the first time creating surface roughened nanofibers by selectively removing polymer of lower Mw successively. Through selective dissolution, rough structures appear on the ultra-fine PVA-PVP nanofibers surface. The successive preparation of surface roughened PVA nanofiber can be attributed to the mobility of PVP molecule. The method claimed in this paper is helpful for developing more types of surface roughened nanofibers in the future.
Preparation and investigation indium tin oxide for transparent electrode of MS Schottky photodiode
Authors: Sangwaranatee N , Srithanachai I
Published: August 2022

In this paper investigation photocurrent of MS Schottky photodiode by using transparent electrode. The transparent material use in this investigation is indium tin oxide (ITO). Transparent electrode can help to get more photocurrent under contact due to light can penetrate though into depletion region then generate photocurrent. ITO will prepare by RF sputtering technique and investigate material characteristics such as electrical and optical properties. Optimize ITO properties after various thickness by growth sputter time show high transparent around 91.2% with low resistance 3.4x10-3 ohm-cm. Build in voltage of device show 0.3V by same with metal contact and current under light exposure show around 1.5mA at 25,000 lux with bias -5V.
Performance of phosphor embedded plastic scintillators through thin film coating
Authors: Rajakrishna K. , Dhanasekaran A. , Yuvaraj N. , Ajoy K.C. , Venkatraman B. , Jose M.T.
Published: August 2022

A novel method of loading phosphor materials in a plastic scintillator (here on PS) is developed to improve light output. In the present work, phosphor materials ZnS(Ag) and ZnO are loaded into the PS medium through the thin-film coating, and the effect of these phosphors on radiation detection is investigated. PS are prepared using polystyrene as the base, xylene as the solvent, PPO and POPOP as primary and secondary flours. ZnS(Ag) and ZnO phosphors are added to the PS in powder form to investigate their effect on luminescence and scintillation output. The thickness of the prepared scintillators is ∼250 ± 30 µm. Photoluminescence, radioluminescence, luminescence lifetime and their detection efficiencies for the typical alpha, beta, gamma and neutron sources are selected as the tools for investigation, and the synthesized scintillators’ performance is studied. The results obtained showed a notable increase in the performance and the outcomes are compared with commercially available PS.
Instrumentation challenges of the strong-field QED experiment LUXE at the European XFEL*
Authors: Fleck K.
Published: August 2022

The LUXE experiment aims at studying strong-field QED in electron-laser and photon-laser interactions, with the 16.5 GeV electron beam of the European XFEL and a laser beam with power of up to 350 TW. The strong-field QED processes are expected to have production rates ranging from 10−3 to 109 per 10 Hz bunch crossing. Additionally, these measurements must be performed in a low-energy, high-radiation background. The LUXE experiment will utilise various detector technologies to overcome these challenges.