bluuebunny/crossref_metadata_2025 huggingface dataset:
Shear-induced self-assembly of linear ABC triblock copolymers in solution: creation of 1D cylindrical micellar structures
Authors: Zhou Yang , Zhou Chun , He Xi , Xue Xianggui , Qian Wen , Luo Shikai , Xia Honggang
Published: December 2015

In this work, shear flow is introduced to create 1D cylindrical micellar structures based on solution self-assembly of linear ABC terpolymers.
Correction: Fabrication and evaluation of a homogeneous electrospun PCL–gelatin hybrid membrane as an anti-adhesion barrier for craniectomy
Authors: Shi Rui , Xue Jiajia , Wang Hanbin , Wang Renxian , Gong Min , Chen Dafu , Zhang Liqun , Tian Wei
Published: December 2015

Correction for ‘Fabrication and evaluation of a homogeneous electrospun PCL–gelatin hybrid membrane as an anti-adhesion barrier for craniectomy’ by Rui Shi et al., J. Mater. Chem. B, 2015, 3, 4063–4073.
Photosensitive polystyrene/silver bromide hybrid colloidal crystals as recoverable colorimetric naked eye probes for bromine gas sensing
Authors: Yu Bing , Zhai Feng , Cong Hailin , Yang Di
Published: December 2015

The color of a hybrid colloidal crystal sensor is changed from deep green to light yellow with increased bromine gas concentrations with a linear relationship between the band gap shift and bromine gas concentration. The sensor has a very reliable performance after repeated sensing and regeneration.
Water stability and orthogonal patterning of flexible micro-electrochemical transistors on plastic
Authors: Zhang Shiming , Hubis Elizabeth , Girard Camille , Kumar Prajwal , DeFranco John , Cicoira Fabio
Published: December 2015

Water-stable, flexible and micro-scale organic electrochemical transistors (OECTs) based on poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) were fabricated on a plastic substrate using a new process based on a fluorinated photoresist.
Effects of probucol on cell proliferation in human ovarian cancer cells
Authors: Chuang Lea-Yea , Guh Jinn-Yuh , Ye Yi-Ling , Lee Ying-Ho , Huang Jau-Shyang
Published: December 2015

Probucol is considered to be an important agent in promoting anti-oxidative action and protecting against tissue injury. However, little is known about the effects of probucol on the progression of ovarian carcinoma. The aim of this study was to investigate the effects of probucol on cellular proliferation in human ovarian cancer cells (PA-1 and SKOV-3) and explore the anti-proliferative mechanism of probucol in these cells. We found that probucol decreased cell growth in PA-1 and SKOV-3 cells in a dose-dependent manner. Treatment with probucol had no effect on cytotoxicity, the percentages of Annexin V-FITC positive cells and caspase-3 activity when compared with the vehicle group. No significant differences in the protein expression of Bcl-2 and cytochrome c were observed, both of which were markers of cells undergoing apoptosis. The inhibition of cellular proliferation by probucol was caused by G1-phase arrest through regulating proteins associated with cell cycle progression, such as cyclin D1, p21Waf1/Cip1, and p27Kip1. A further study revealed that probucol strongly impaired the phosphorylation of IκBα and the nuclear translocation of NF-κB (p65). It also suppressed the activation of ERK/JNK/p38 MAPK signaling. Moreover, the NF-κB inhibitor (PDTC), the ERK inhibitor (PD98059), the JNK inhibitor (SP600125), and the p38 MAPK inhibitor (SB203580) markedly attenuated the growth of these cells. Our results indicate that probucol induces anti-proliferative effects via blocking of cell cycle progression and inactivation of NF-κB and MAPK pathways in human ovarian cancer cells.
Distinctive curves features
Authors: Li B. , Li H. , Söderström U.
Published: December 2015

Curves and lines are geometrical, abstract features of an image. Whereas interest points are more limited, curves and lines provide much more information of the image structure. However, the research done in curve and line detection is very fragmented. The concept of scale space is not yet fused very well into curve and line detection. Keypoint (e.g. SIFT, SURF, ORB) is a successful concept which represent features (e.g. blob, corner etc.) in scale space. Stimulated by the keypoint concept, a method which extracts distinctive curves (DICU) in scale space, including lines as a special form of curve features is proposed. A curve feature can be represented by three keypoints (two end points, and one middle point). A good way to test the quality of detected curves is to analyse the repeatability under various image transformations. DICU using the standard Oxford benchmark is evaluated. The overlap error is calculated by averaging the overlap error of three keypoints on the curve. Experiment results show that DICU achieves good repeatability comparing with other state‐of‐the‐art methods. To match curve features, a relatively uncomplicated way is to combine local descriptors of three keypoints on each curve.
Multi-beamlet investigation of the deflection compensation methods of SPIDER beamlets
Authors: Baltador C. , Veltri P. , Agostinetti P. , Chitarin G. , Serianni G.
Published: December 2015

SPIDER (Source for Production of Ions of Deuterium Extracted from a Rf plasma) is an ion source test bed designed to extract and accelerate a negative ion current up to 40 A and 100 kV whose first beam is expected by the end of 2016. Two main effects perturb beamlet optics during the acceleration stage: space charge repulsion and the deflection induced by the permanent magnets (called co-extracted electron suppression magnets) embedded in the EG. The purpose of this work is to evaluate and compare benefits, collateral effects, and limitations of electrical and magnetic compensation methods for beamlet deflection. The study of these methods has been carried out by means of numerical modeling tools: multi-beamlet simulations have been performed for the first time.
Alternative modeling methods for plasma-based Rf ion sources
Authors: Veitzer Seth A. , Kundrapu Madhusudhan , Stoltz Peter H. , Beckwith Kristian R. C.
Published: December 2015

Rf-driven ion sources for accelerators and many industrial applications benefit from detailed numerical modeling and simulation of plasma characteristics. For instance, modeling of the Spallation Neutron Source (SNS) internal antenna H− source has indicated that a large plasma velocity is induced near bends in the antenna where structural failures are often observed. This could lead to improved designs and ion source performance based on simulation and modeling. However, there are significant separations of time and spatial scales inherent to Rf-driven plasma ion sources, which makes it difficult to model ion sources with explicit, kinetic Particle-In-Cell (PIC) simulation codes. In particular, if both electron and ion motions are to be explicitly modeled, then the simulation time step must be very small, and total simulation times must be large enough to capture the evolution of the plasma ions, as well as extending over many Rf periods. Additional physics processes such as plasma chemistry and surface effects such as secondary electron emission increase the computational requirements in such a way that even fully parallel explicit PIC models cannot be used. One alternative method is to develop fluid-based codes coupled with electromagnetics in order to model ion sources. Time-domain fluid models can simulate plasma evolution, plasma chemistry, and surface physics models with reasonable computational resources by not explicitly resolving electron motions, which thereby leads to an increase in the time step. This is achieved by solving fluid motions coupled with electromagnetics using reduced-physics models, such as single-temperature magnetohydrodynamics (MHD), extended, gas dynamic, and Hall MHD, and two-fluid MHD models. We show recent results on modeling the internal antenna H− ion source for the SNS at Oak Ridge National Laboratory using the fluid plasma modeling code USim. We compare demonstrate plasma temperature equilibration in two-temperature MHD models for the SNS source and present simulation results demonstrating plasma evolution over many Rf periods for different plasma temperatures. We perform the calculations in parallel, on unstructured meshes, using finite-volume solvers in order to obtain results in reasonable time.
The expected perimeter in Eden and related growth processes
Authors: Bouch Gabriel
Published: December 2015

Following Richardson and using results of Kesten on first-passage percolation, we obtain an upper bound on the expected perimeter in an Eden growth process. Using results of the author from a problem in statistical mechanics, we show that the average perimeter of the lattice animals resulting from a very natural family of “growth histories” does not obey a similar bound.
Exciton size and quantum transport in nanoplatelets
Authors: Pelzer Kenley M. , Darling Seth B. , Gray Stephen K. , Schaller Richard D.
Published: December 2015

Two-dimensional nanoplatelets (NPLs) are an exciting class of materials with promising optical and energy transport properties. The possibility of efficient energy transport between nanoplatelets raises questions regarding the nature of energy transfer in these thin, laterally extended systems. A challenge in understanding exciton transport is the uncertainty regarding the size of the exciton. Depending on the material and defects in the nanoplatelet, an exciton could plausibly extend over an entire plate or localize to a small region. The variation in possible exciton sizes raises the question how exciton size impacts the efficiency of transport between nanoplatelet structures. Here, we explore this issue using a quantum master equation approach. This method goes beyond the assumptions of Förster theory to allow for quantum mechanical effects that could increase energy transfer efficiency. The model is extremely flexible in describing different systems, allowing us to test the effect of varying the spatial extent of the exciton. We first discuss qualitative aspects of the relationship between exciton size and transport and then conduct simulations of exciton transport between NPLs for a range of exciton sizes and environmental conditions. Our results reveal that exciton size has a strong effect on energy transfer efficiency and suggest that manipulation of exciton size may be useful in designing NPLs for energy transport.
The mean shape of transition and first-passage paths
Authors: Kim Won Kyu , Netz Roland R.
Published: December 2015

Based on the one-dimensional Fokker-Planck equation in an arbitrary free energy landscape including a general inhomogeneous diffusivity profile, we analytically calculate the mean shape of transition paths and first-passage paths, where the shape of a path is defined as the kinetic profile in the plane spanned by the mean time and the position. The transition path ensemble is the collection of all paths that do not revisit the start position xA and that terminate when first reaching the final position xB. In contrast, a first-passage path can revisit its start position xA before it terminates at xB. Our theoretical framework employs the forward and backward Fokker-Planck equations as well as first-passage, passage, last-passage, and transition-path time distributions, for which we derive the defining integral equations. We show that the mean shape of transition paths, in other words the mean time at which the transition path ensemble visits an intermediate position x, is equivalent to the mean first-passage time of reaching the position xA when starting from x without ever visiting xB. The mean shape of first-passage paths is related to the mean shape of transition paths by a constant time shift. Since for a large barrier height U, the mean first-passage time scales exponentially in U, while the mean transition path time scales linearly inversely in U, the time shift between first-passage and transition path shapes is substantial. We present explicit examples of transition path shapes for linear and harmonic potentials and illustrate our findings by trajectories obtained from Brownian dynamics simulations.
An atomistically informed mesoscale model for growth and coarsening during discharge in lithium-oxygen batteries
Authors: Welland Michael J. , Lau Kah Chun , Redfern Paul C. , Liang Linyun , Zhai Denyun , Wolf Dieter , Curtiss Larry A.
Published: December 2015

An atomistically informed mesoscale model is developed for the deposition of a discharge product in a Li-O2 battery. This mescocale model includes particle growth and coarsening as well as a simplified nucleation model. The model involves LiO2 formation through reaction of O2− and Li+ in the electrolyte, which deposits on the cathode surface when the LiO2 concentration reaches supersaturation in the electrolyte. A reaction-diffusion (rate-equation) model is used to describe the processes occurring in the electrolyte and a phase-field model is used to capture microstructural evolution. This model predicts that coarsening, in which large particles grow and small ones disappear, has a substantial effect on the size distribution of the LiO2 particles during the discharge process. The size evolution during discharge is the result of the interplay between this coarsening process and particle growth. The growth through continued deposition of LiO2 has the effect of causing large particles to grow ever faster while delaying the dissolution of small particles. The predicted size evolution is consistent with experimental results for a previously reported cathode material based on activated carbon during discharge and when it is at rest, although kinetic factors need to be included. The approach described in this paper synergistically combines models on different length scales with experimental observations and should have applications in studying other related discharge processes, such as Li2O2 deposition, in Li-O2 batteries and nucleation and growth in Li-S batteries.
Gentlest ascent dynamics for calculating first excited state and exploring energy landscape of Kohn-Sham density functionals
Authors: Li Chen , Lu Jianfeng , Yang Weitao
Published: December 2015

We develop the gentlest ascent dynamics for Kohn-Sham density functional theory to search for the index-1 saddle points on the energy landscape of the Kohn-Sham density functionals. These stationary solutions correspond to excited states in the ground state functionals. As shown by various examples, the first excited states of many chemical systems are given by these index-1 saddle points. Our novel approach provides an alternative, more robust way to obtain these excited states, compared with the widely used ΔSCF approach. The method can be easily generalized to target higher index saddle points. Our results also reveal the physical interest and relevance of studying the Kohn-Sham energy landscape.
Orientation dependent annealing kinetics of ion tracks in c-SiO2
Authors: Schauries D. , Leino A. A. , Afra B. , Rodriguez M. D. , Djurabekova F. , Nordlund K. , Kirby N. , Trautmann C. , Kluth P.
Published: December 2015

The structure and thermal response of amorphous ion tracks formed along the [112¯0], [101¯0], and [0001]-directions in crystalline quartz have been investigated using small angle x-ray scattering. The radii of the ion tracks vary by about 5% (0.3 nm) for tracks along different crystallographic directions. Molecular dynamics simulations reproduce this anisotropy along the [101¯0] and [0001] directions and suggest that differences in thermal conductivity along these directions are partly responsible for this observation. Using in situ annealing, tracks along the [101¯0] and [0001] directions were shown to recrystallize during thermal annealing around 960–1020 °C with activations energies around 6 eV, while those along the [112¯0]-direction already disappeared at 640 °C with a significantly lower activation energy around 3–4 eV.
The influence of charged-induced variations in the local permittivity on the static and dynamic properties of polyelectrolyte solutions
Authors: Fahrenberger Florian , Hickey Owen A. , Smiatek Jens , Holm Christian
Published: December 2015

There is a large body of literature investigating the static and dynamic properties of polyelectrolytes due both to their widespread application in industrial processes and their ubiquitous presence in biology. Because of their highly charged nature, polyelectrolytes tend to alter the local dielectric permittivity of the solution within a few nanometers of their backbone. This effect has, however, been almost entirely ignored in both simulations and theoretical work. In this article, we apply our recently developed electrostatic solver based on Maxwell’s equations to examine the effects of the permittivity reduction in the vicinity of the polyelectrolyte. We first verify our new approach by calculating and comparing ion distributions around a linear fixed polyelectrolyte and find both quantitative and qualitative changes in the ion distribution. Further simulations with an applied electric field show that the reduction in the local dielectric constant increases the mobility of the chains by approximately ten percent. More importantly, variations in the local dielectric constant lead to qualitatively different behavior of the conductivity.
Some studies on generalized coordinate sets for polyatomic molecules
Authors: Li Wenjin , Ma Ao
Published: December 2015

Generalized coordinates are widely used in various analyses of the trajectories of polyatomic molecules from molecular dynamics simulations, such as normal mode analysis and force distribution analysis. Here, we presented detailed discussions on the properties of some specific sets of generalized coordinates, which separate translational, rotational, and vibrational motions of a molecule from one another once the trajectories of dynamical systems are known. Efficient methods were suggested for estimating the transformation matrix between generalized and Cartesian coordinates. Some properties of the well-known BAT coordinates (bond length, angle, and torsional coordinates) were discussed as well.
Two-fluid numerical simulations of turbulence inside Kelvin-Helmholtz vortices: Intermittency and reconnecting current sheets
Authors: Rossi C. , Califano F. , Retinò A. , Sorriso-Valvo L. , Henri P. , Servidio S. , Valentini F. , Chasapis A. , Rezeau L.
Published: December 2015

The turbulence developing inside Kelvin-Helmholtz vortices has been studied using a two-fluid numerical simulation. From an initial large-scale velocity shear, the nonlinear evolution of the instability leads to the formation of a region inside the initial vortex characterized by small-scale fluctuations and structures. The magnetic energy spectrum is compatible with a Kolmogorov-like power-law decay, followed by a steeper power-law below proton scales, in agreement with other studies. The magnetic field increments show non-Gaussian distributions with increasing tails going towards smaller scales, consistent with presence of intermittency. The strong magnetic field fluctuations populating the tails of the distributions have been identified as current sheets by using the Partial Variance of the Increments (PVI) method. The strongest current sheets (largest PVI) appear around proton scales and below. By selecting several of such current sheets, it has been found that most of them are consistent with ongoing magnetic reconnection. The detailed study of one reconnecting current sheet as crossed by a virtual spacecraft is also presented. Inflow and outflow regions have been identified and the reconnection rate has been estimated. The observation of reconnection rates higher than typical fast rate ∼0.1 suggests that reconnection in turbulent plasma can be faster than laminar reconnection. This study indicates that intermittency and reconnecting current sheets are important ingredients of turbulence within Kelvin-Helmholtz vortices and that reconnection can play an important role for energy dissipation therein.
On certain generalizations of the Schrödinger-Virasoro algebra
Authors: Li Haisheng , Sun Jiancai
Published: December 2015

We study certain generalizations of the Schrödinger-Virasoro algebra, introduced by Roger and Unterberger, in the context of vertex algebras. As the main result, we associate these Lie algebras with vertex algebras and their twisted modules with respect to semi-simple (not necessarily finite order) automorphisms, and we give a connection among these Lie algebras in terms of twisted current algebras of conformal Lie algebras.
Plasma nitriding monitoring reactor: A model reactor for studying plasma nitriding processes using an active screen
Authors: Hamann S. , Börner K. , Burlacov I. , Spies H.-J. , Strämke M. , Strämke S. , Röpcke J.
Published: December 2015

A laboratory scale plasma nitriding monitoring reactor (PLANIMOR) has been designed to study the basics of active screen plasma nitriding (ASPN) processes. PLANIMOR consists of a tube reactor vessel, made of borosilicate glass, enabling optical emission spectroscopy (OES) and infrared absorption spectroscopy. The linear setup of the electrode system of the reactor has the advantages to apply the diagnostic approaches on each part of the plasma process, separately. Furthermore, possible changes of the electrical field and of the heat generation, as they could appear in down-scaled cylindrical ASPN reactors, are avoided. PLANIMOR has been used for the nitriding of steel samples, achieving similar results as in an industrial scale ASPN reactor. A compact spectrometer using an external cavity quantum cascade laser combined with an optical multi-pass cell has been applied for the detection of molecular reaction products. This allowed the determination of the concentrations of four stable molecular species (CH4, C2H2, HCN, and NH3). With the help of OES, the rotational temperature of the screen plasma could be determined.
Nonadiabatic dynamics with intersystem crossings: A time-dependent density functional theory implementation
Authors: Franco de Carvalho F. , Tavernelli I.
Published: December 2015

In this work, we derive a method to perform trajectory-based nonadiabatic dynamics that is able to describe both nonadiabatic transitions and intersystem crossing events (transitions between states of different spin-multiplicity) at the same level of theory, namely, time-dependent density functional theory (TDDFT). To this end, we combined our previously developed TDDFT-based trajectory surface hopping scheme with an accurate and efficient algorithm for the calculation of the spin-orbit coupling (SOC) matrix elements. More specifically, we designed two algorithms for the calculation of intersystem crossing transitions, one based on an extended Tully’s surface hopping scheme including SOC and the second based on a Landau-Zener approximation applied to the spin sector of the electronic Hilbert space. This development allows for the design of an efficient on-the-fly nonadiabatic approach that can handle, on an equal footing, nonadiabatic and intersystem crossing transitions. The method is applied to the study of the photophysics of sulfur dioxide (SO2) in gas and liquid phases.
Coarse-grained model of adsorption of blood plasma proteins onto nanoparticles
Authors: Lopez Hender , Lobaskin Vladimir
Published: December 2015

We present a coarse-grained model for evaluation of interactions of globular proteins with nanoparticles (NPs). The protein molecules are represented by one bead per aminoacid and the nanoparticle by a homogeneous sphere that interacts with the aminoacids via a central force that depends on the nanoparticle size. The proposed methodology is used to predict the adsorption energies for six common human blood plasma proteins on hydrophobic charged or neutral nanoparticles of different sizes as well as the preferred orientation of the molecules upon adsorption. Our approach allows one to rank the proteins by their binding affinity to the nanoparticle, which can be used for predicting the composition of the NP-protein corona. The predicted ranking is in good agreement with known experimental data for protein adsorption on surfaces.
On the asymptotic distribution of block-modified random matrices
Authors: Arizmendi Octavio , Nechita Ion , Vargas Carlos
Published: December 2015

We study random matrices acting on tensor product spaces which have been transformed by a linear block operation. Using operator-valued free probability theory, under some mild assumptions on the linear map acting on the blocks, we compute the asymptotic eigenvalue distribution of the modified matrices in terms of the initial asymptotic distribution. Moreover, using recent results on operator-valued subordination, we present an algorithm that computes, numerically but in full generality, the limiting eigenvalue distribution of the modified matrices. Our analytical results cover many cases of interest in quantum information theory: we unify some known results and we obtain new distributions and various generalizations.
Canonical transformations and minimal length
Authors: Valtancoli P.
Published: December 2015

We show how to modify the canonical transformations to make them compatible with non-commutative Poisson brackets.
Influence of toroidal rotation on resistive tearing modes in tokamaks
Authors: Wang S. , Ma Z. W.
Published: December 2015

Influence of toroidal equilibrium plasma rotation on m/n = 2/1 resistive tearing modes is studied numerically using a 3D toroidal MHD code (CLT). It is found that the toroidal rotation with or without shear can suppress the tearing instability and the Coriolis effect in the toroidal geometry plays a dominant role on the rotation induced stabilization. For a high viscosity plasma (τR/τV ≫ 1, where τR and τV represent resistive and viscous diffusion time, respectively), the effect of the rotation shear combined with the viscosity appears to be stabilizing. For a low viscosity plasmas (τR/τV ≪ 1), the rotation shear shows a destabilizing effect when the rotation is large.
A crude model to study radio frequency induced density modification close to launchers
Authors: Van Eester Dirk , Crombé Kristel
Published: December 2015

The interplay between radio frequency (RF) waves and the density is discussed by adopting the general framework of a 2-time-scale multi-fluid treatment, allowing to separate the dynamics on the RF time scale from that on the time scale on which macroscopic density and flows vary as a result of the presence of electromagnetic and/or electrostatic fields. The focus is on regions close to launchers where charge neutrality is incomplete and waves are commonly evanescent. The fast time scale dynamics influences the slow time scale behavior via quasilinear terms (the Ponderomotive force for the case of the equation of motion). Electrons and ions are treated on the same footing. Also, both fast and slow waves are retained in the wave description. Although this work is meant as a subtopic of a large study—the wave induced “convective cell” physics at hand is of a 2- or 3-dimensional nature while this paper limits itself to a single dimension—a few tentative examples are presented.
New terahertz dielectric spectroscopy for the study of aqueous solutions
Authors: George Deepu K. , Charkhesht Ali , Vinh N. Q.
Published: December 2015

We present the development of a high precision, tunable far-infrared (terahertz) frequency-domain dielectric spectrometer for studying the dynamics of biomolecules in aqueous solutions in the gigahertz-to-terahertz frequency. As an important benchmark system, we report on the measurements of the absorption and refractive index for liquid water in the frequency range from 5 GHz to 1.12 THz (0.17–37.36 cm−1 or 0.268–60 mm). The system provides a coherent radiation source with power up to 20 mW in the gigahertz-to-terahertz region. The dynamic range of our instrument reaches 1012 and the system achieves a spectral resolution of less than 100 Hz. The temperature of samples can be controlled precisely with error bars of ±0.02 °C from 0 °C to 90 °C. Given these attributes, our spectrometer provides unique capabilities for the accurate measurement of even very strongly absorbing materials such as aqueous solutions.
Optical, electrical, and photovoltaic properties of silicon nanoparticles with different crystallinities
Authors: Ding Yi , Zhou Shu , Juangsa Firman B. , Sugaya Michihiro , Asano Yasunori , Zhang Xiaodan , Zhao Ying , Nozaki Tomohiro
Published: December 2015

Current researches on silicon nanoparticles (Si NPs) are mainly focusing on the crystallized one, while some basic optical and electrical properties of particles with different crystallinities are still unclear. Hence, in this work, Si NPs with different crystallinities were easily fabricated with non-thermal plasma by changing the input power, and the crystallinity effects on the optical, electrical, and photovoltaic properties of particles were extensively studied. It is found that amorphous particles have strong light absorption, especially in short wavelength region; however, the carrier mobility is relatively poor. This is mainly because of numerous dangling bonds and defects that exist in Si NPs with poor crystallinity, which work as carrier trapping centers. As a result, the efficiency of Si NPs-based hybrid solar cells increases monotonously with particle crystallinity. This indicates that highly crystallized Si nanocrystals with less defects are desirable for high efficiency solar cells.
Domain imaging on multiferroic BiFeO3(001) by linear and circular dichroism in threshold photoemission
Authors: Sander Anke , Christl Maik , Chiang Cheng-Tien , Alexe Marin , Widdra Wolf
Published: December 2015

We demonstrate ferroelectric domain imaging at BiFeO3(001) single crystal surfaces with laser-based threshold photoemission electron microscopy (PEEM). Work function differences and linear dichroism allow for the identification of the eight independent ferroelectric domain configurations in the PEEM images. There, the determined domain structure is consistent with piezoresponse force microscopy of the sample surface and can also be related to the circular dichroic PEEM images. Our results provide a method for efficient mapping of complex ferroelectric domains with laser-excited PEEM and may allow lab-based time-resolved studies of the domain dynamics in the future.
Growth and characterization of insulating ferromagnetic semiconductor (Al,Fe)Sb
Authors: Anh Le Duc , Kaneko Daiki , Hai Pham Nam , Tanaka Masaaki
Published: December 2015

We investigate the crystal structure, transport, and magnetic properties of Fe-doped ferromagnetic semiconductor (Al1−x,Fex)Sb thin films up to x = 14% grown by molecular beam epitaxy. All the samples show p-type conduction at room temperature and insulating behavior at low temperature. The (Al1−x,Fex)Sb thin films with x ≤ 10% maintain the zinc blende crystal structure of the host material AlSb. The (Al1−x,Fex)Sb thin film with x = 10% shows intrinsic ferromagnetism with a Curie temperature (TC) of 40 K. In the (Al1−x,Fex)Sb thin film with x = 14%, a sudden drop of the hole mobility and TC was observed, which may be due to the microscopic phase separation. The observation of ferromagnetism in (Al,Fe)Sb paves the way to realize a spin-filtering tunnel barrier that is compatible with well-established III-V semiconductor devices.
Multiscale recurrence analysis of spatio-temporal data
Authors: Riedl M. , Marwan N. , Kurths J.
Published: December 2015

The description and analysis of spatio-temporal dynamics is a crucial task in many scientific disciplines. In this work, we propose a method which uses the mapogram as a similarity measure between spatially distributed data instances at different time points. The resulting similarity values of the pairwise comparison are used to construct a recurrence plot in order to benefit from established tools of recurrence quantification analysis and recurrence network analysis. In contrast to other recurrence tools for this purpose, the mapogram approach allows the specific focus on different spatial scales that can be used in a multi-scale analysis of spatio-temporal dynamics. We illustrate this approach by application on mixed dynamics, such as traveling parallel wave fronts with additive noise, as well as more complicate examples, pseudo-random numbers and coupled map lattices with a semi-logistic mapping rule. Especially the complicate examples show the usefulness of the multi-scale consideration in order to take spatial pattern of different scales and with different rhythms into account. So, this mapogram approach promises new insights in problems of climatology, ecology, or medicine.
Impact of carrier recombination on fill factor for large area heterojunction crystalline silicon solar cell with 25.1% efficiency
Authors: Adachi Daisuke , Hernández José Luis , Yamamoto Kenji
Published: December 2015

We have achieved a certified 25.1% conversion efficiency in a large area (151.9 cm2) heterojunction (HJ) crystalline Si (c-Si) solar cell with amorphous Si (a-Si) passivation layer. This efficiency is a world record in a both-side-contacted c-Si solar cell. Our high efficiency HJ c-Si solar cells are investigated from the standpoint of the effective minority carrier lifetime (τe), and the impact of τe on fill factor (FF) is discussed. The τe measurements of our high efficiency HJ c-Si solar cells reveal that τe at an injection level corresponding to an operation point of maximum power is dominated by the carrier recombination at the a-Si/c-Si interface. By optimization of the process conditions, the carrier recombination at the a-Si/c-Si interface is reduced, which leads to an improvement of the FF by an absolute value of 2.7%, and a conversion efficiency of 25.1% has been achieved. These results indicate that the reduction of carrier recombination centers at the a-Si/c-Si interface should be one of the most crucial issues for further improvement of FF even in the HJ c-Si solar cells with efficiency over 25%.
Dynamics of metal-induced crystallization of ultrathin Ge films by rapid thermal annealing
Authors: Liao Yuanxun , Huang Shujuan , Shrestha Santosh , Conibeer Gavin
Published: December 2015

Though Ge crystallization has been widely studied, few works investigate metal-induced crystallization of ultrathin Ge films. For 2 nm Ge films in oxide matrix, crystallization becomes challenging due to easy oxidation and low mobility of Ge atoms. Introducing metal atoms may alleviate these problems, but the functions and the behaviours of metal atoms need to be clarified. This paper investigates the crystallization dynamics of a multilayer structure 1.9 nm Ge/0.5 nm Al/1.5 nm Al2O3 under rapid thermal annealing (RTA). The functions of metal atoms, like effective anti-oxidation, downshifting Raman peaks, and incapability to decrease crystallization temperature, are found and explained. The metal behaviours, such as inter-diffusion and defect generation, are supported with direct evidences, Al-Ge nanobicrystals, and Al cluster in Ge atoms. With these understandings, a two-step RTA process achieves high-quality 2 nm nanocrystal Ge films with Raman peak at 298 cm−1 of FWHM 10.3 cm−1 and atomic smooth interfaces.
Epitaxial growth of three dimensionally structured III-V photonic crystal via hydride vapor phase epitaxy
Authors: Zheng Qiye , Kim Honggyu , Zhang Runyu , Sardela Mauro , Zuo Jianmin , Balaji Manavaimaran , Lourdudoss Sebastian , Sun Yan-Ting , Braun Paul V.
Published: December 2015

Three-dimensional (3D) photonic crystals are one class of materials where epitaxy, and the resultant attractive electronic properties, would enable new functionalities for optoelectronic devices. Here we utilize self-assembled colloidal templates to fabricate epitaxially grown single crystal 3D mesostructured GaxIn1−xP (GaInP) semiconductor photonic crystals using hydride vapor phase epitaxy (HVPE). The epitaxial relationship between the 3D GaInP and the substrate is preserved during the growth through the complex geometry of the template as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy. XRD reciprocal space mapping of the 3D epitaxial layer further demonstrates the film to be nearly fully relaxed with a negligible strain gradient. Fourier transform infrared spectroscopy reflection measurement indicates the optical properties of the photonic crystal which agree with finite difference time domain simulations. This work extends the scope of the very few known methods for the fabrication of epitaxial III-V 3D mesostructured materials to the well-developed HVPE technique.
Broadband ultra-high transmission of terahertz radiation through monolayer MoS2
Authors: Deng Xue-Yong , Deng Xin-Hua , Su Fu-Hai , Liu Nian-Hua , Liu Jiang-Tao
Published: December 2015

In this study, the terahertz (THz) absorption and transmission of monolayer MoS2 with different carrier concentrations were investigated theoretically. The calculation shows that the THz absorption of monolayer MoS2 is very low even under high carrier concentrations and large incident angles. The sum of reflection and absorption losses of monolayer MoS2 is lower than that of graphene by one to three orders of magnitude. The transmission of monolayer MoS2 is higher than that of two-dimensional electron gases in traditional GaAs and InAs. The field-effect tube structure formed by monolayer MoS2-insulation-layer-graphene is also studied. The THz absorption of graphene can reach saturation under low voltage by tuning the voltage between MoS2 and graphene layers in the structure. The maximum THz absorption of monolayer MoS2 is approximately 5%. Thus, monolayer MoS2 is a promising candidate for THz transparent electrodes.
Two-electrode gas switch with electrodynamical acceleration of a discharge channel
Authors: Kovalchuk B. M. , Kharlov A. V. , Kumpyak E. V. , Tsoy N. V.
Published: December 2015

High-energy switches and trigger generators are required for MJ-level capacitor banks. We have developed a compact gas switch and a matched series injection trigger generator. A series inductance is required for isolation of the trigger pulse from the surrounded circuit. A saturable inductor is employed here because low inductance is needed after the switch breakdown. The switch is of coaxial two-electrode design with electrodynamic acceleration of a spark channel. The switch operates at atmospheric pressure. The spark gap can be triggered reliably down to zero voltage (at 50 kV self-breakdown voltage) with less than 35 ns timing jitter. Energy losses in this spark gap have been accurately investigated. The main results are as follows: energy losses in the switch do not exceed 4% at voltages higher than 15 kV, i.e., when operation voltage exceeds ∼36% of the self-breakdown voltage. The spark gap is designed for 24 kV charging voltage, at a current up to 250 kA, and ∼70 C charge transfer. In this paper, we present a design for the spark gap, inductor and trigger generator. Test bed schematics and results of the tests are also described.
Universal low-frequency asymptotes of dynamic conic nanopore rectification: An ionic nanofluidic inductor
Authors: Yan Yu , Schiffbauer Jarrod , Yossifon Gilad , Chang Hsueh-Chia
Published: December 2015

We report the first nanofluidic inductor (L) to complement the known nanofluidic capacitors (C), resistors (R), and diodes for ion currents. Under negative bias, the nanopore behaves like a parallel RC circuit at low frequencies; however, under positive bias, the asymptotic dynamics is that of a serial RL circuit. This new ionic circuit element can lead to nanofluidic RLC or diode-inductor oscillator circuits and new intrapore biosensing/rapid sequencing strategies. A universal theory, with explicit estimates for the capacitance and inductance at opposite biases, is derived to collapse the rectified dynamics of all conic nanopores to facilitate design of this new nanofluidic circuit.
Gate-modulated transport properties and mechanism for nanowire cross junction based on SnO2 semiconductor
Authors: Chen Xi , Tong Yanhong , Wang Guorui , Tang Qingxin , Liu Yichun
Published: December 2015

The transport properties and mechanism of the three-terminal field-effect nanowire cross junction have been systematically investigated. An interesting phenomenon, such as applied voltage bias on nanowire cross junction makes the ON/OFF current ratio of the transistor improved by over 2 orders of magnitude, has been observed. Different from the two-terminal nanowire cross junctions, the cross junction induced potential barrier in three-terminal counterparts is found to be capable to prevent the current of the top semiconductor nanowire from injecting into the bottom nanowire at off state, while to make the current of the top semiconductor nanowire contribute to the current of the bottom nanowire at on state, resulting in the current switch between on state and off state by the gate voltage modulation.
Quantum sized Ag nanocluster assisted fluorescence enhancement in Tm3+-Yb3+ doped optical fiber beyond plasmonics
Authors: Chattopadhyay Rik , Haldar Arindam , Paul Mukul C. , Das Shyamal , Bhadra Shyamal K.
Published: December 2015

We report a process for enhancing fluorescence emission from conventional rare earth ions in optical fiber by metal nanocluster (MNC) in nonresonant indirect pumping. The process is completely different from formal metal enhanced fluorescence phenomenon as the MNCs are too small in size to support localized surface plasmon and the excitation wavelength is far from plasmon resonance frequency. We used an established theory of two coupled oscillators to explain the simultaneous enhancement of Ytterbium (Yb3+) and Thulium (Tm3+) emission by silver (Ag) NCs under nonresonant pumping in optical fiber. The fiber is pumped with a 980 nm fiber pigtailed laser diode with input power of 20–100 mW to excite the Yb3+. Four times enhancement of Yb3+ emission of 900–1100 nm and Tm3+ upconversion emission around 474 nm, 650 nm, and 790 nm is observed in the fiber with Ag NCs.
Improved memory functions in multiferroic tunnel junctions with a dielectric/ferroelectric composite barrier
Authors: Ruan Jieji , Qiu Xiangbiao , Yuan Zhoushen , Ji Dianxiang , Wang Peng , Li Aidong , Wu Di
Published: December 2015

Four-state non-volatile memory functions are demonstrated in all-oxide multiferroic tunnel junctions (MFTJs), composed of La0.7Sr0.3MnO3 and La0.7Sr0.3Mn0.8Ru0.2O3 ferromagnetic electrodes and a SrTiO3/BaTiO3 dielectric/ferroelectric composite barrier. Compared with MFTJs with a single BaTiO3 barrier, the insertion of a SrTiO3 dielectric barrier is shown effective to enhance both the electroresistance and the magnetoresistance of the MFTJs. In particular, the tunneling electroresistance ratio is greatly improved by two orders. This is discussed in terms of the enhanced asymmetry in the electrostatic modulation on the barrier profile with respect to the ferroelectric polarization direction.
Manipulation of a grid-generated mixing with an active honeycomb dielectric barrier plasma discharge
Authors: Benard N. , Mizuno A. , Moreau E.
Published: December 2015

This study defines and characterizes an active system for turbulent and scalar mixing enhancement. This system is made of an active grid composed of 121 holes where the gas flows. A high voltage is applied between printed electrodes and embedded ground electrodes in order to produce a non-thermal surface discharge at the hole exits. The goal is to modify the flow downstream of the active grid. First, electrical and optical characterizations of the actuator are proposed. Second, it is shown that the discharge strongly modifies the flow distribution of the multi-jet exhaust, and the flow change depends on the high voltage applied to the active plasma grid. A minimization of the potential core by 40% is reported when discharge frequency corresponds to jet column mode instability.
Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy
Authors: Kolkovsky Vl. , Zytkiewicz Z. R. , Korona K. P. , Sobanska M. , Klosek K.
Published: December 2015

The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 102 and the leakage current of about 10−4 A/cm2 at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ∼2 nm thick SiNx layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 1015 cm−3. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiNx interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.
Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods
Authors: Rana Amit Kumar , J Aneesh , Kumar Yogendra , M. S Arjunan , Adarsh K. V. , Sen Somaditya , Shirage Parasharam M.
Published: December 2015

In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.
Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride
Authors: Wan Yimao , Yan Di , Bullock James , Zhang Xinyu , Cuevas Andres
Published: December 2015

A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiNx) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiNx stack, recombination current density J0 values of 9, 11, 47, and 87 fA/cm2 are obtained on 10 Ω·cm n-type, 0.8 Ω·cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J0 on n-type 10 Ω·cm wafers is further reduced to 2.5 ± 0.5 fA/cm2 when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiNx stack is thermally stable at 400 °C in N2 for 60 min on all four c-Si surfaces. Capacitance–voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiNx stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.
Plasma antennas driven by 5–20 kHz AC power supply
Authors: Zhao Jiansen , Chen Yuli , Sun Yang , Wu Huafeng , Liu Yue , Yuan Qiumeng
Published: December 2015

The experiments described in this work were performed with the aim of introducing a new plasma antenna that was excited by a 5–20 kHz alternating current (AC) power supply, where the antenna was transformed into a U-shape. The results show that the impedance, voltage standing-wave ratio (VSWR), radiation pattern and gain characteristics of the antenna can be controlled rapidly by varying not only the discharge power, but also by varying the discharge frequency in the range from 5 to 20 kHz. When the discharge frequency is adjusted from 10 to 12 kHz, the gain is higher within a relatively broad frequency band and the switch-on time is less than 1 ms when the discharge power is less than 5 W, meaning that the plasma antenna can be turned on and off rapidly.