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This paper reports on the observation of substantial rotation and reflection enhancements with thin magnetic films evaporated on the base of high index prisms with films of suitable index on only the air side of the magnetic thin film. Angles of incidence at the prism‐magnetic thin‐film interface were near the critical angle for total internal reflection. The magnetic film thickness and the thicknesses and indices of the dielectrics were obtained with the help of a computer program which calculated the reflection coefficients as well as the Kerr rotations and energy mode transfer. Enhancements of rsp up to a factor of 20 were obtained.

The solvent‐casting process preferentially aligns polymeric chains in the plane of the film. This paper proposes that the mechanism responsible for this behavior is the competition between the relaxation times of the concentrating solution and the time scales associated with the physical collapse of the film. The orientation of molecules has been determined as a function of the coating conditions (film thickness, polymer molecular weight, plasticizer content, casting solvent, and substrate temperature) by measuring the optical anisotropy of the coating with a single‐prism film coupler. This orientation is shown to reflect both the stresses supported by the entanglement network and the alignment of localized segments and to be a function of the difference between the casting temperature and the Tg of the film.

Hydrogenated amorphous carbon films were deposited on Si (100) substrates using dc-pulse plasma chemical vapor deposition. Structurally, the as-deposited carbon films could be considered as nanocomposite thin films with fullerenelike microstructure in diamondlike carbon matrix based on our previous result [Q. Wang et al., Appl. Phys. Lett. 91, 141902 (2007)]. In this paper, the evolution of the structure and the mechanical properties of hydrogenated carbon films with fullerenelike microstructure on the annealing in vacuum was investigated. The fullerenelike hydrogenated carbon films annealed at 500 °C showed higher hardness (16.9% harder) and higher elastic recovery (11.2% higher) than the as-deposited films. The friction coefficient of fullerenelike hydrogenated carbon films in air with 40% relative humidity remained constant at about 0.037 when annealed at 600 °C. The wear rate of the films decreased sharply when annealed at 200 or 300 °C. Structural analysis shows that annealing at 300 °C improved trib...

In an experimental investigation of electronic transport across individual grain boundaries in cast silicon, we have recently arrived at the conclusion that the diffusion potential at the grain boundary may in many cases exhibit appreciable variation over the boundary plane. The present paper describes an interpretation of the experimental observations in terms of a Gaussian distribution of interface potential over the grain‐boundary surface, and a majority carrier transport to the boundary which is diffusion limited. In the grain boundaries studied the mean value of the diffusion potential was found to vary from 〈Vd〉 ≂0.70 to 〈Vd〉 ≂0.32 eV and the standard deviation from σ≂0 to σ≂0.11 eV. These values were derived from the change in activation energy with temperature. For the particular grain boundaries with spatial uniformity (σ≂0) excellent agreement of the characteristics with an emission/diffusion model of majority‐carrier transport is obtained. It is concluded (i) that it is not generally proper to ...

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility ( μe), electron transport time ( TR), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μe and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μe decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties.

[EN] This tutorial explores the problem of Joule heating on metallic micro or nanostrips, still one of the most popular geometries in modern spintronics. Many of the effects that result from the interaction of a spin polarized current and the local magnetization, require of a sizeable current density. This implies, quite often, an unneglectable Joule heating. Despite the few articles devoted to some aspects of Joule heating, there is still disinformation and many misconceptions in this topic, which is key for the correct interpretation of the scientific results. In this tutorial, we highlight the material parameters that are important to keep the temperature of the strip under control and those that give only a marginal advantage. In the vast majority of papers, at least one of these parameters is missing. We also focus on some misconceptions, such as the belief that performing the measurement on a cryostat, rules Joule heating out. In fact, for a fixed current density, measuring in a cryostat decreases the temperature but not enough to justify the use of such a costly measuring set-up. At the practical level, we put forward a 1D model to calculate, in few seconds, if Joule heating is present and if it should be taken into account when interpreting the results. Finally, and importantly, we describe a simple fabrication route to enhance the dissipation of heat in the strip considerably. This fabrication strategy is more effective at keeping the temperature under control than performing the experiment at cryogenic temperatures., Project MAT2017-87072-C4-3-P and MAT2017-87072-C4-1-P from the Spanish government Project No. SA299P18 from Consejería de Educación Junta de Castilla y León

This paper proposes an explicit solution for the design of a target-frequency-customized, one-dimensional phononic crystal (PNC) with a defect for piezoelectric energy harvesting under longitudinal waves. Due to the innate narrow bandwidth nature of the defect modes of a PNC at the target frequency, there is a great need to generate an electromechanically coupled defect band of a piezoelectric-defect-introduced PNC. This work considers the transfer matrix method which has been widely used in analytical approaches. The need for defect bands to be included in a bandgap inspires the use of a quarter-wave stack as a unit cell to match the bandgap's central frequency with the target frequency. In band structure analysis, considering that the electromechanically coupled defect band corresponds to a set of real wavenumbers despite being within the bandgap, several possible solutions for the piezoelectric defect's length are derived in an explicit fashion. Since switching from a short- to an open-circuit condition causes defect bands to slightly increase due to piezoelectric effects, an explicit solution that reflects the piezoelectric defect's electrical characteristics is finally proposed. Finite-element-based numerical validation studies are conducted to study two aspects, specifically parametric studies (i.e., the natural numbers in the solution to the piezoelectric defect's length, the supercell sizes, and the defect locations) and supporting studies (i.e., the electrical boundary conditions and unit cell designs). At the target frequency, it is demonstrated that the proposed PNC design actualizes the formation of one defect band and the representation of the peak output voltage.

Semi-transparent photovoltaic devices for building integrated applications have the potential to provide simultaneous power generation and natural light penetration. CuIn$_{1-x}$Ga$_x$Se$_2$ (CIGS) has been established as a mature technology for thin-film photovoltaics, however, its potential for Semi-Transparent Photovoltaics (STPV) is yet to be explored. In this paper, we present its carrier transport physics explaining the trend seen in recently published experiments. STPV requires deposition of films of only a few hundred nanometers to make them transparent and manifests several unique properties compared to a conventional thin-film solar cell. Our analysis shows that the short-circuit current, Jsc is dominated by carriers generated in the depletion region, making it nearly independent of bulk and back-surface recombination. The bulk recombination, which limits the open-circuit voltage Voc, appears to be higher than usual attributable to numerous grain boundaries. When the absorber layer is reduced below 500 nm, grain size reduces resulting in more grain boundaries and higher resistance. This produces an inverse relationship between series resistance and absorber thickness. We also present a thickness-dependent model of shunt resistance showing its impact in these ultra-thin devices. For various scenarios of bulk and interface recombinations, shunt and series resistances, AVT and composition of CuIn$_{1-x}$Ga$_x$Se$_2$, we project the efficiency limit which - for most practical cases - is found to be $\leq$10% for AVT $\geq$25%.

This paper presents systematic modeling and performance analyses of a 340-GHz dual-polarized antenna-coupled single-sideband (SSB) high-Tc superconducting (HTS) mixer for terahertz (THz) communication systems. The mixer features a fully monolithic-integrated circuit layout, which enables both sensitive heterodyne detection and high image rejection by appropriate polarization-manipulating operation. To predict the comprehensive performance of such a HTS mixer with relatively complicated network architecture and polarization relationships, an innovative modified three-port modeling approach is presented and developed by theoretical derivations. Using the measured Josephson junction parameters of our previous experimentally demonstrated HTS mixer module at the same band, the best conversion gain and SSB noise temperature of the presented mixer are predicted to be around −5 dB and 1200 K at the operating temperature of 40 K, respectively. In addition, the mixer exhibits a flat frequency response over a wide intermediate-frequency range from 15 to 25 GHz and high image rejection of more than 17 dB over the radio frequency operation range. The SSB HTS Josephson mixer will be useful for THz wireless communication applications.

Microwave-induced thermoacoustic imaging (TAI) is a hybrid imaging technique that combines electromagnetic radiation and ultrasonic waves to achieve high imaging contrast and submillimeter spatial resolution. These characteristics make TAI a good candidate to detect material anomalies that change the material electric properties without a noticeable variation in material density. Conventional pulsed TAI systems work by sending a single short pulse to the imaged target and then detecting the generated pressure signal; therefore, a very high peak power microwave pulse or data averaging is needed to produce images with a high signal-to-noise ratio (SNR). In this paper, we propose to enhance the SNR of pulsed TAI systems by using non-coherent pulse compression. In this approach, a predefined pulse coded signal is used to illuminate the imaged sample and the received pressure signal is cross correlated with a template that is related to the power profile of the excitation signal. The proposed approach can be easily deployed to pulsed TAI systems without the need for major system modifications to the RF source because it only requires a timing circuit to control the triggering time of the RF pulses. In this paper, we demonstrate experimentally that the proposed approach highly improves the SNR of TAI signals and images and can be used to reduce the acquisition time by lowering the number of data averaging or reduce the required peak power from RF sources.

Structure-engineered silicon exhibits a wealth of unique optical properties below its bandgap, which holds promise for mid-infrared and terahertz applications such as photodetection, thermophotovoltaics, radiative cooling, and spectroscopy. In this paper, we investigate enhancement mechanisms of sub-bandgap absorption of black silicon fabricated into periodic pyramids. Our measurements indicate that the pyramid structure leads to an enhanced broadband absorption in the wavelength region from 1.5 to 13.07 μm with an efficiency of over 80%. The broadband absorption enhancement is shown to originate from the Rayleigh–Wood anomaly, localized magnetic plasmonic resonance, and graded-index effect, which together facilitate the interaction between light and free-carriers in silicon. These results are helpful for understanding the interaction between light and black silicon.

A graphite anode ablates in an arc system producing nanoparticles. Experiments show that the ablation rate increases sharply when the current density at the anode exceeds some critical value, which separates the low ablation and high ablation modes. According to the existing hypotheses, the high ablation mode takes place when the anode voltage drop, which is negative in the low ablation mode, turns positive. Based on the work of Nemchinsky [J. Appl. Phys. 130, 103304 (2021)], where the anode voltage drop was evaluated, in this paper, the thermal regime of the anode is considered. It is shown that the main heating mechanism is electron condensation on the anode. The main cooling mechanism is radiation in the low ablation mode and cooling by sublimation in the high ablation mode. In the last case, the energy necessary to compensate for the strong cooling effect of sublimation is delivered by electrons accelerated at the positive anode drop inside the anode sheath. The proposed model allows one to find the ablation rate for a wide range of arc currents and anode diameters. Comparison to the available experimental data shows reasonable agreement. Based on analysis of the experiments and calculations, it was hypothesized that the ablation rate is not sensitive to the presence of a catalyst.

Low temperature plasmas are an emerging method to synthesize high quality nanoparticles (NPs). An established and successful technique to produce NPs is using a capacitively coupled plasma (CCP) in cylindrical geometry. Although a robust synthesis technique, optimizing or specifying NP properties using CCPs, is challenging. In this paper, results from a computational investigation for the growth of silicon NPs in flowing inductively coupled plasmas (ICPs) using Ar/SiH4 gas mixtures of up to a few Torr are discussed. ICPs produce more locally constrained and quiescent plasma potentials. These positive plasma potentials produce an electrostatic trap for negatively charged NPs, which can significantly extend the residence time of NPs in the plasma, which in turn provides a controllable period for particle growth. The computational platforms used in this study consist of a two-dimensional plasma hydrodynamics model, a three-dimensional nanoparticle growth and trajectory tracking model, and a molecular dynamics simulation for deriving reactive sticking coefficients of silane radicals on Si NPs. Trends for the nanoparticle growth as a function of SiH4 inlet fraction, gas residence time, energy deposition per particle, pressure, and reactor diameter are discussed. The general path for particle synthesis is the trapping of small NPs in the positive electrostatic potential, followed by entrainment in the gas flow upon reaching a critical particle size. Optimizing or controlling NP synthesis then depends on the spatial distribution of plasma potential, the density of growth species, and the relative time that particles spend in the electrostatic trap and flowing through higher densities of growth species upon leaving the trap.

Austenitic stainless steels are subject to the precipitation of chromium carbides (M23C6) during exposure to high temperatures, causing these alloys to be susceptible to intergranular corrosion due to chromium depletion along grain boundaries. The acoustic nonlinearity parameter, β, shows sensitivity to the formation of carbides in these alloys. The Thermo-Calc TC-PRISMA module was used to model the nucleation and growth of grain boundary M23C6 carbides. The model was verified with scanning transmission electron microscopy analysis that allowed measurements of the grain boundary precipitates. The paper introduces a reduced-order model of the acoustic nonlinearity based on the formation of misfit dislocations at the interface of the grain boundary precipitate and matrix to explain the change in β during isothermal aging. A direct relationship between the radius of the M23C6 grain boundary carbides and β was observed and verified with nonlinear ultrasound measurements on 304L and 316L stainless steels.

International audience; This paper reports on a mode of analysis of semi-adiabatic relaxation data allowing to account for exotic phenomena sometimes observed in first-order transitions. The principal interest is to get a detailed characterization of the latent heat while using the same experimental configuration as that employed for accurate heat capacity measurements outside the transition. Special attention is paid to the recalescence/antirecalescence effects as well as to the existence of spikes in the time-dependent exchange of latent heat. The present approach —based on the notion of “power of latent heat”— is shown to be consistent with differential scanning calorimetry, magnetization measurements and the usual analysis in terms of heat capacity. The study is carried out on a LaFe10.77Si1.23Co0.28 compound which belongs to one of the most promising families of giant magnetocaloric materials.

Thanks to their excellent properties such as superelasticity, high hardness, and shape memory effect, polycrystalline shape memory alloys (SMAs) have extensive applications in various engineering fields including automobile, functional materials, and aerospace. Using molecular dynamics simulations, the present paper aims to a systematic study of the fundamental tensile behavior in the nanoscale of polycrystalline B2-CuZr SMAs with mean grain sizes in the range of 6–25 nm. Effects of mean grain size, temperature, and tensile rate on mechanical properties are considered. Our results show that along with the increase in mean grain size came increases in Young's modulus, yield strength, flow stress, and ultimate tensile strength. The development of amorphous regions in the grain cores is the major deformation mode in polycrystalline CuZr SMAs with larger grain sizes, while the grain boundary sliding and grain rotation for smaller grain sizes. Besides, an increased temperature results in mechanical performance degradation and the temperature sensitivity of mechanical properties does not depend on the mean grain size. Our work would lay the groundwork for the optimization of the mechanical properties of polycrystalline SMAs as well as serving as a useful theoretical guideline for their practical engineering applications.

Naturally occurring materials with hyperbolic optical properties are attracting considerable interest due to their ability to confine light in small volumes and their resulting potential for applications in photonics. This paper uses a first-principles theoretical approach without adjustable parameters to investigate the hyperbolic optical properties of bulk calcite (CaCO3). This material exhibits natural hyperbolic behavior within its Reststrahlen bands at 1403–1552 and 864–887 cm−1. The calculated results are shown to be in good agreement with our reflectance data obtained from frequency- and polarization-dependent measurements. These results show that calcite is an attractive natural hyperbolic material; in addition, it has the advantage of low losses and is available commercially in a variety of crystal orientations.

In this paper, a two dimensional (2D) axisymmetric fluid model is built to study the effect of the ratio of CF4 admixture on the plasma dynamics and F-containing species concentration in He atmospheric pressure plasma jet. The steady mole fraction distribution of He and CF4 is first studied, which presents that the mole fractions of CF4 show peaks at 5 mm from the symmetry axis on the dielectric surface due to the dual influences of the boundary layer effect and air mixing. The CF4 admixture enhances the propagation speed of ionization wave, and the axial velocity reaches the peak value in the case of He + 1.5% CF4. The conversion from the ring-shaped plasma–surface interaction to a solid-disk one results from the addition of CF4. The Penning ionization of CF4 accelerates the plasma jet propagation within 1.5% CF4. However, the excitation energy loss and electron attachment caused by the addition of CF4 also quench the propagation of plasma jet, which become obvious in the case of 2% CF4. F-containing groups (CF4+, CF3+, CF3−, F−, CF3, and F), mainly produced by the Penning ionization reaction, electron attachment reaction, and He+ + CF4 → He + CF3+ + F, also show peaks for He + 1.5% CF4. On the dielectric surface, as the radial distance increases, the ratio of F-containing neutral species (CF3 and F) to O atom at 200 ns decreases due to the increase of O atom concentration and then increases at the streamer head because the surface flux of CF3 reaches the maximum value. The maximum surface flux radial distribution distance for ratio of F-containing species to O atom, CF3 and F appear in the case of 1.5% CF4.

In the initiation process of microsecond pulsed discharge in water, Joule heating is believed to be responsible for the formation of a low-density region. Then, electron avalanche can be easily induced in this low-density region. The aim of this paper is to study the feasibility of the quantitative schlieren method in the temperature measurement of water in the initiation process of microsecond pulsed discharge. A lens-type schlieren system was applied in the measurement of the radial temperature around the tip of the electrode. Finite element analysis was used to simulate the electric field and temperature during the discharge. Measurement results of the schlieren quantitative schlieren method are compared with the simulation results of finite element analysis in terms of temperature and energy conversion. The comparison shows that most electrical energy is consumed in Joule heating of water in the initiation process of microsecond pulsed discharge. In the region with no thermal fluid, the temperature distributions obtained by the quantitative schlieren method and finite element analysis are in good agreement. This work is helpful in the quantitative study of the role of Joule heating in the initiation of the streamer in water.

In recent years, MnFePGe magnetocaloric materials have been widely studied as promising candidates for magnetic refrigeration materials. The Curie temperature of MnFePGe can be adjusted to around room temperature by changing the element ratio or doping with other elements. Due to its first-order magnetic and structural transition, it engenders a large entropy change but unfortunately also exhibits a large thermal hysteresis during the phase transition, which leads to energy loss and lower refrigeration capability. In this paper, we establish a correlation between the in-plane covalent bonding and Curie temperature (TC), thermal hysteresis (ΔThys), two-phase coexistence zone (ΔTcoex), and entropy change (ΔSDSC) using 54 Mn2−xFexPyGe1−yMz (where M is a metallic or nonmetallic doped element) samples with different components. Neutron diffraction and XRD diffraction data and refinements have been employed to allow a detailed electron density reconstruction of six typical samples with the maximum entropy method. We find that the length of the in-plane bonding is closely correlated with the TC and ΔThys, while the TC, ΔThys, ΔTcoex, and ΔSDSC have no significant correlation with the length of the interlayer covalent bond. Moreover, we find that the ΔThys correlates most strongly with the change in the bond length when undergoing the paramagnetic-to-ferromagnetic phase transition rather than the absolute value of the bond length. These results provide an understanding of how to control the properties, enabling effective ways to tune the composition of magnetic refrigeration materials to tailor magnetocaloric properties for optimal performance.

Granular molecular crystals show a large variation in the orientation, length, shape, and cohesive interactions of interfaces when embedded in a polymer matrix. But the determination of the associated excess of free energy is not straightforward, especially due to the entropic contribution which is not negligible for molecular compounds. The surface free energy (SFE) is also important to predict crystal shapes and growth or to prove crucial insights into the mesoscale interfaces in the granular composites often with interfacial defects, voids, and pores. In this paper, we use Molecular Dynamics (MD) and assess and adapt two non-equilibrium methods, namely, non-equilibrium thermodynamic integration (NETI) and modified steered MD (SMD), to determine the SFE of various facets of a high-energy molecular crystal of interest: β-HMX. Starting with defect-free surfaces, both methods agree well with experiment concerning the most stable facets, whose energy is further lowered by a large entropic contribution. For some facets, surface creation (debonding process) and annihilation (bonding process) show fundamentally different paths, henceforth irreversible. Then, we discuss some sources of discrepancy between theoretical and experimental SFE, considering non-reversible dissipative events, surface roughness, and differences between various experimental techniques. These non-equilibrium methods can be applied to a wide range of molecular crystals and to study interface stability in polycrystals or with binding polymers, including the effects of various defects.

Graphene is a highly promising material in the field of spin electronics. Recent experiments on electron spin resonance have observed a reduction in the g-factor of graphene. In our previous paper [J. Phys. Soc. Jpn. 88, 094707 (2019)], we demonstrated that one of sources for this reduction is the diamagnetic property of graphene. However, the diamagnetic property by itself does not fully account for the magnitude of the reduction observed in the experiments. In this paper, we focus on the Rashba effect, which is caused by the work function existing near the surface of graphene. The Rashba effect tilts the spin magnetic moment to the in-plane direction of the graphene sheet, potentially reducing the g-factor. We evaluate this reduction using a simple model system incorporating the Rashba and spin Zeeman effects. We then demonstrate that the resultant g-factor is in close agreement with that observed in the prior experiments, indicating that the Rashba effect is able to account for the remaining reduction in the g-factor of graphene., 24 pages, 2 figure, 2 tables

Two-dimensional black phosphorene (BP) has attracted much interest for application in electronic devices. Contacts between BP and metal electrodes are critical components of BP-based devices and can dramatically affect device performances. In this paper, we adopted first-principles calculations to explore binding energies, electronic structures, and potential distribution for interface systems of Al-, Au-, Cu-, Ni-, and Ti-monolayer BP in surface contact and edge contact (EC) types. Moreover, we also used density functional theoretical coupled with the nonequilibrium Green’s function method to investigate contact resistances and Schottky barrier heights (SBHs) for transport systems of monolayer BP with Al, Au, Cu, Ni, and Ti electrodes. Our calculated results indicate that the contact type between BP and metals may greatly affect electrical properties of BP–metal contacts. Changing contact type between metal electrodes and BP channel can change the type of Schottky barrier of metal–BP contacts. The contact barrier of metal–BP depends on the metal material. Selecting an appropriate contact type and metal can effectively regulate the contact barrier of metal–BP. Specifically exciting, our estimated lateral SBHs for the Ni–BP system in EC-type agree well with the experimental results. We have provided a new strategy on choosing an appropriate contact type to achieve low contact resistance for the metal–BP interface.

Reflection high energy electron diffraction (RHEED) information is critical for the growth of thin films; however, only a small percentage of the data from RHEED videos is typically used. The use of full videos in machine learning can require dimension reduction techniques. In this paper, three dimension reduction techniques, principal component analysis (PCA), non-negative matrix factorization (NMF), and kmeans clustering, are compared to investigate their benefits to the analysis of RHEED data. Three different heterostructures with different growth modes, all deposited on Ti-terminated strontium titanate by pulsed laser deposition, were used for the analysis: lanthanum aluminate with layer-by-layer growth, lithium cobalt oxide with island growth, and strontium ruthenate with a transition from layer-by-layer to step-flow growth. A phase shift in intensity fluctuations of different RHEED spots was discovered and discussed in terms of their sensitivity to the film growth characterization. The diffraction spots that were more sensitive to the growth were differentiated from the spots that are affected by the substrate as a function of film thickness. It was concluded that NMF provides the analysis that is easiest to interpret without the loss of detailed physical information due to its non-negativity constraint and lack of forced orthogonality such as in PCA. Analysis of the full RHEED videos enables a more detailed understanding of growth characteristics and control of growth processes as aided by dimension reduction.

Sputtered thin films with strong near-infrared absorption and high visible transmission and electrical resistivity (≥102 Ω cm) have been obtained using highly conductive cesium tungsten bronze targets. The origin of the low electrical conductivity and high near-infrared absorption of the films has been investigated by focusing on internal defects and reported in two parts. In Paper I, the optical and electrical properties of the films and their microstructural characterization using x-ray diffraction and high-resolution transmission electron microscopy are presented. Abundant planar W and Cs defects were found on hexagonal prismatic planes that locally expanded the defect plane and triggered the hexagonal-to-orthorhombic crystallographic transition. These cationic defects diminished conduction electrons and suppressed electrical conduction, whereas oxygen vacancies generated W5+-trapped electrons to activate polaronic excitations for strong near-infrared absorption.

Orhorhombic $\alpha$-MoO$_3$ is a layered oxide with various applications and with excellent potential to be exfoliated as a 2D ultrathin film or monolayer. In this paper, we present a first-principles computational study of its vibrational properties. Our focus is on the zone center modes which can be measured by a combination of infared and Raman spectroscopy. The polarization dependent spectra are simulated. Calculations are also performed for a monolayer form in which "double layers" of Mo$_2$O$_6$ which are weakly van der Waals bonded in the $\alpha$-structure are isolated. Shift in phonon frequencies are analyzed., Comment: 13 pages, 13 figures, 14 tables

In SiN/AlGaN/GaN heterostructures, the evaluation of interface charges at the SiN/AlGaN and AlGaN/GaN interfaces is crucial since they both rule the formation of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. In this paper, we conducted a thorough analysis of the gate-to-channel capacitance CGC(VG) and of the drain current ID(VG) over a gate voltage VG range enabling the depletion of the 2DEG and the formation of the electron channel at the SiN/AlGaN interface. This work includes the establishment of analytical equations for VTH1 (formation of the 2DEG) and VTH2 (formation of the electron channel at the SiN/AlGaN interface) as a function of interface charges and of the p-doping below the 2DEG. The inclusion of the p-doped layer below the 2DEG and the use we made of VTH2 have not been reported in previous studies. Our analysis allows a reliable estimate of the interface charges at the AlxGa1−xN/GaN and SiN/AlxGa1−xN interfaces for various Al concentrations x as well as to demonstrate that the polarization charge at the SiN/AlxGa1−xN interface is compensated, which confirms previous findings. Moreover, this compensation is found to be induced by the AlGaN layer rather than the SiN layer.

Imprint, the preferential orientation of the polarization of a ferroelectric device subjected to elevated temperatures, is a primary reliability concern afflicting data retention in ferroelectric RAM. In this paper, we demonstrate Preisach-based hysteresis modeling, which can be used to predict imprint behavior in ferroelectric thin films. A method was developed for capturing imprint in the context of a Preisach model and a numerical approach for evaluating the Preisach distribution was expanded upon. Interpolation and curve fitting were used to make predictions of the Preisach distributions of imprinted ferroelectric hafnium zirconium oxide devices after short-duration bakes at 23–260 °C and long-term bakes at 85 and 125 °C. In the case of long-term bakes, imprint-induced coercive shifts were modeled as shifts in the derivative of the top and bottom hysteretic polarization curves. The shift in the curves is modeled by fitting experimental data to a commonly used empirically logarithmic relationship reported in the literature. Simulations give remanent polarizations and coercive fields within

In this paper, we investigate the formation of a photonic terajet and tune its optical properties using the high-resolution finite-difference time-domain method. A Dirac semimetal is coated onto the surface of a dielectric rod and illuminated with an incident plane wave. The refractive index of the Dirac semimetal can be modulated by changing its Fermi energy. It was demonstrated that the presence of the Dirac semimetal layer can significantly affect the characteristics of the photonic terajet, such as focal distance, intensity, full-width at half maximum, and length.

Since their initial demonstration in 1995, light-emitting electrochemical cells (LECs) have received attention due to potential advantages over traditional polymer optoelectronic devices. A standard LEC consists of two electrodes surrounding an active layer that contains polymer and mobile ions. When a bias is applied, the ions separate and move toward the electrodes, creating a reversible p–n junction analog. Immobilizing the ions after ion dissociation using one of several demonstrated methods to create a “fixed-junction LEC” allows the device to produce a significant photovoltaic response. Recently, our group demonstrated chemically fixed junction LECs using a polymerizable ionic liquid (ATOA-AS) that conferred important advantages over first-generation chemically fixed junction devices, including improved phase compatibility and turn-on time. Early tests showed improvements in the performance of these devices over the first chemically fixed junctions in terms of light-emitting properties. However, their photovoltaic behavior has not been previously investigated. In this paper, we demonstrate photovoltaic behavior in chemically fixed junction LECs based on the polymerizable ionic liquid ATOA-AS as the ion source. While further improvements in the photovoltaic performance of fixed-junction devices still need to be made before they are considered a commercially viable technology, we find that the devices reported here compare well to other single-layer polymer homojunction solar cells and demonstrate an exceptionally high VOC (>1.8 V for some configurations). We also explore the effects that changes to various aspects of device composition and testing procedures have on device performance.

A monoclinic phase is the bridge between the rhombohedral and tetragonal phases in the Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystal near the morphotropic phase boundary (MPB), which is related to the superior piezoelectric performance. In this paper, the different phase transition process in the unpoled PIN–PMN–PT single crystals near MPB induced by composition variation was presented first. Based on this, direct current poling (DCP) and alternating current treatment (ACT) were applied on these samples. Also, the crystals by DCP–ACT have shown a more complex ferroelectric phase transition process than that by DCP, which is related to the induced monoclinic phase by applying an AC electric field. The transverse piezoelectric properties of the PIN–PMN–PT single crystal with various compositions by DCP and DCP–ACT were compared. ACT enhanced the electromechanical coupling coefficient k31, elastic compliance constant S11E, and dielectric permittivity e33T/e0 of the pre-DCP PIN–PMN–PT single crystals in the macrorhombohedral phase. As a result, the transverse piezoelectric constant d31 of the crystals with various compositions was enhanced to be −1240, −1663, and −1252 pC/N by DCP–ACT, which were 61.7%, 73.0%, and 60.8% higher than that by DCP. However, ACT has little effect on the pre-DCP PIN–PMN–PT crystal with macrocoexistence of rhombohedral and monoclinic phases. The AC electric field could be a useful way for tuning the coexistence of rhombohedral and monoclinic phases in the PIN–PMN–PT crystal near MPB to achieve high transverse piezoelectric performance.

This paper studies photoelectron emission from metal surfaces with laser wavelengths from 200 to 1200 nm (i.e., ultraviolet to near-infrared), using a recent quantum model based on the exact solution of time-dependent Schrodinger equation. The dominant electron emission mechanism varies from different multiphoton emission processes to dc or optical field emission, depending on the laser intensity, wavelength, and dc bias field. The parametric dependence of the quantum efficiency (QE) is analyzed in detail. It is found that QE can be increased nonlinearly by the non-equilibrium electron heating produced by intense sub-picosecond laser pulses. This increase of QE due to laser heating is the strongest near laser wavelengths where the cathode work function is an integer multiple of the corresponding laser photon energy. The quantum model, with laser heating effects included, reproduces previous experimental results, which further validates our quantum model and the importance of laser heating.