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The article discusses the highlights of the 11th International Surface X-ray and Neutron Scattering (SXNS-11) Conference that took place at the Northwestern University (NU) campus in Evanston, Illinois from July 13-17, 2010. The conference, which was hosted by the NU Materials Research Science and Engineering Center, has gathered 164 delegates from 16 countries. Information on papers presented at the conference are presented.

An introduction to the topics discussed within the publication is presented, which are selected papers from the International Conference on Flexible and Printed Electronics held in Jeju Island, Korea on November 11 to 13, 2009, including articles on the difficulties posed by printing methods over ink materials to flexible and printed devices.

The article discusses conference papers on topics related to physics which were featured at the the Fourth International Conference on Multiscale Materials Modeling, which was held October 27-31 in 2008 in Tallahassee, Florida.

A preface to the Special Topic section of selected papers for the 20th International Symposium on Integrated Ferroelectrics is presented.

A preface to "Plenary and Invited Papers" from the 28th International Conference on the Physics of Semiconductors, Vienna, Austria, 2006 is presented.

This paper analyses the behavioral features of ohmic contacts under the conditions of traditional isothermal annealing. The purpose of this paper is to study the value change of the semiconductor contact resistance when applying electric current pulses of different powers. For the experiments, structures were formed of metal-sublayer-semiconductor wafer Al–(Ti, Ni, Mo)–Si. The quality control of the deposited films was carried out microscopically by the four-probe method. The presented results indicate the solid-phase interaction of components during diffusion annealing Si–Me–Al thin-film systems. This rearrangement of atoms, which occurs with grain-boundary diffusion, significantly affects the electrical and thermal characteristics of the formed contacts. The novelty of the paper is that the optimal parameters of a rectangular current pulse were selected, which made it possible to reduce the value of the transition resistance by 1.6 times. [ABSTRACT FROM AUTHOR]

A pure bending semiconductor beam that exhibits a non-homogeneous cross section variation enhanced flexoelectric coupling effect is investigated in this paper from the point of view of theoretical analysis and numerical calculations. According to the macroscopic theory of flexoelectric semiconductors, a one-dimensional bending model for a simple-supported beam with variable cross section is developed. The semi-analytical method, which is composed of cosine series and supplementary functions, is introduced to solve the partial differential equations with variable coefficients. Before the analysis, the convergence and correctness of the semi-analytical method are demonstrated systematically. The calculated results show that both the electric potential and the charge carrier distribute non-homogeneously in the entire beam under a pair of symmetric bending moments. It is revealed that more carriers, a larger electric potential, and more charges tend to concentrate in the zone near the ends. After introducing a dimensionless carrier density, this paper systematically investigates the non-homogeneous cross section variation effect on the flexoelectric coupling for charge carrier redistribution. It is indicated that more perturbation carriers in a non-uniform beam are produced by the enhanced flexoelectric coupling. The demonstration of this concept could be potential guidance for designing new semiconductor devices. [ABSTRACT FROM AUTHOR]

Piezotronic devices have attracted a great deal of attention due to their potential applications in self-powered tactile sensing, nano-device memory, human-electronic interface, etc. As the size of piezotronic devices shrinks, some interesting quantum effects begin to appear. In this paper, we establish a theory oriented to the engineering application of piezoelectric semiconductors, called quantum-corrected phenomenological (QCP) theory, by coupling the density-gradient theory and the linear piezoelectricity theory through Gauss's law. For numerical verification, we specifically studied the electromechanical behaviors in GaN/AlGaN heterostructure quantum wells (QWs) with both infinite and finite barrier height. The results of electron density, electric potential, and quantum potential are provided, and their dependence on the doping density, the applied stress, and the Al mole fraction is investigated. Some interesting quantum effects are revealed, and their influencing mechanisms are well investigated from a macroscopic perspective. Not only do the conclusions drawn in this paper enrich the fundamental understanding of the piezotronic effect in a QW structure, but also the proposed QCP theory can serve as a valuable tool for future device engineering. [ABSTRACT FROM AUTHOR]

Understanding the properties of N-implanted β-Ga2O3 is fundamental for the optimization of doping and isolation structures based on gallium oxide. This paper reports an extensive analysis of the impact of thermal annealing on the concentration and properties of deep levels in N-implanted β-Ga2O3 Schottky barrier diodes by means of capacitance isothermal transient spectroscopy. Samples with annealing temperatures from 800 to 1200 °C were considered. The original results presented in this paper demonstrate the following: (a) The instability of current–voltage characteristics detected for all the samples under test can be attributed to the presence of three electron traps with activation energies of 0.6, 0.7, and 1 eV, consistent with previous reports in β-Ga2O3. (b) The detected traps are not the nitrogen level but intrinsic defects whose concentration is increased by the implantation process. (c) The concentration of deep levels decreases as the annealing temperature increases, demonstrating that the annealing process can effectively restore the quality of the material while keeping the conductivity decrease related to the presence of the nitrogen. Finally, (d) we demonstrate that the residual leakage and the turn-on voltage shift are correlated with the Arrhenius signature of the detected deep levels. An interpretation is proposed to explain the measurement results. [ABSTRACT FROM AUTHOR]

A preface to the special issue of the "Journal of Applied Physics," which focused on piezoresponse force microscopy and nanoscale phenomena in polar materials, is presented.

Phase-change alloy Ge 2 Sb 2 Te 5 (GST) forms a favorable material platform for modern optics, photonics, and electronics thanks to a pronounced increase in conductivity with thermally induced phase transitions from amorphous (a-GST) into cubic (c-GST) and then hexagonal (h-GST) crystalline states at the temperatures of ≃ 150 and ≃ 300 ° C, respectively. Nevertheless, the data on broadband electrodynamic response of distinct GST phases are still missing, which hamper the design and implementation of related devices and technologies. In this paper, a-, c-, and h-GST films on a sapphire substrate are studied using broadband dielectric spectroscopy. For all GST phases, complex dielectric permittivity is retrieved using Drude and Lorentz models in the frequency range of 0.06 – 50 THz or the wavelength range of ≃ 5000 – 6 μ m. A contribution from the free charge-carriers conductivity and vibrational modes to the broadband response of an analyte is quantified. In this way, the Drude model allows for estimation of the static (direct current—DC) and dynamic (at 1.0 THz) conductivity values, caused by motions of free charges only, which are as high as σ DC ≃ 15 and 40 S/cm and σ 1.0 THz ≃ 8.8 and 28.6 S/cm for the c- and h-GSTs, respectively. This overall agrees with the results of electrical measurements of GST conductivity using the four-point probe technique. The broadband electrodynamic response models obtained for the three GST phases are important for further research and developments of GST-based devices and technologies. [ABSTRACT FROM AUTHOR]

One-to-many wireless power transfer (WPT) is one of the leading directions in WPT systems development due to the rapid growth of consumer devices. The most challenging task is to ensure high efficiency for free-positioned receivers and provide low-cost compact WPT systems. In this paper, a transmitting metasurface-based resonator for one-to-many WPT systems is proposed and experimentally studied. The resonator design and matching method provides the self-tuning ability and allows to simplify the control and communication units of WPT systems. The resonator is composed of periodically arranged unit-cells, implemented as two crossed conductors separated by a thick substrate with a 330 pF capacitor mounted at the cross-hair of the conductors. The prototype of the proposed metasurface-based resonator is fabricated and experimentally studied for free-positioned single- and multi-receivers. The WPT efficiency to a free-positioned receiver varies from 19.7% to 84.8%. The overall efficiency for a three-receiver case reaches 83.2% which is suitable for one-to-many WPT systems. [ABSTRACT FROM AUTHOR]

The holy grail of achieving efficient operation of infrared (IR) rectennas continues to be the realization of a high performance rectifier. In this paper, we have fabricated metal–insulator–metal (MIM) diodes based on TiO2, ZnO, and NiO thin films using shadow mask evaporation, photolithography, and sputtering. The electron affinities of oxides have been measured by a combination of variable angle spectroscopic ellipsometry and x-ray photoelectron spectroscopy, as well as deduction from the extraction of metal/oxide barrier heights of Fowler–Nordheim tunneling plots. Our results confirm a low value for the electron affinity of NiOx of ∼2.1–2.5 eV, which correlates with the high zero-bias dynamic resistance (RD0) of ∼500 kΩ of an associated MIM diode. These values render NiOx to be unsuitable for use in a rectenna device. Better performance has been observed from diodes based on TiO2 and ZnOx films. The best rectification performance was achieved for a Au/2.6 nm ZnOx/Cr diode, scaled down to 1 μm2 device area, showing a zero-bias dynamic resistance of RD0 = 71 kΩ, zero-bias responsivity β0 = 0.28 A/W, and a coupling efficiency of ηc = 2.4 × 10−5% for rectification at 28.3 THz. The main significance of this study is that it employs a methodology whereby key parameters of the MIM stack are derived from physical measurements, which are then used to assist in the fitting of electrical current–voltage data to produce a reliable appraisal of diode performance in an IR rectenna. [ABSTRACT FROM AUTHOR]

This paper presents an advanced measurement method for controlling the surface charge carrier density of passivated silicon wafers during photoconductance and photoluminescence measurements, by employing semitransparent poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) electrodes with an applied bias voltage. This is employed to study and analyze charge carrier dynamics in dielectric layers by measuring their direct influence on effective lifetime. With this method, the carrier population at the surface and the effective carrier lifetimes of n- and p-type samples can be investigated, from which the fixed charge carrier density Qf of the passivation can be extracted. Additionally, the defect density Dit can also be derived from the minimum lifetime values at flatband voltage. In SiO2/Al2O3 stacks with varying SiO2 interlayer thickness, it was shown that by changing the SiO2 thickness, the carrier density Qf can be tuned to a wide range of values, which corresponds to the results obtained in other studies. An increase in interlayer thickness resulted in a decrease in Qf. Varying the SiO2 thickness, the behavior of the respective effective lifetime under bias voltage also changes, exhibiting hysteresis-like effects, which are attributed to additional charges getting trapped at the surface during bias-voltage application. This effect is much more pronounced for samples with a thinner SiO2 layer as well as for the n-type samples. Additionally, the doping type also influences the magnitude of Qf, with p-type samples generally reaching lower absolute values. It was also shown that aging of the samples had a significant effect on the measured Qf, which was increased compared to the initial Qf of the passivation. This effect was more pronounced for the n-type samples. The measurements were realized by a cost-effective and easy-to-use microcontroller-based potentiostat, which can be used as a simple add-on to existing photoconductance or photoluminescence measurement setups. [ABSTRACT FROM AUTHOR]

This paper explores direct density modulation of high-current electron beam emission from an RF cold cathode using optical excitation. We theoretically study the photo-assisted field emission of periodically bunched electron beams of various pulse shapes under the combined excitation of an RF field and an optical field, using an exact quantum model. Both continuous-wave (CW) and pulsed optical fields are considered. The emission current pulse amplitude, pulse width, electron number density per pulse, as well as pulse shape and its harmonic contents are investigated in detail. For CW photon sources in the UV to NIR range (i.e., 200–1200 nm), increasing the optical intensity under an RF bias tends to change the current pulse from a Gaussian to sinusoidal-like shape, thus offering strong flexibility to control the frequency components in beam current emission. Pulsed photon sources combined with an RF field can produce sharp, high-current electron bunches with pulse duration comparable with or even less than that of the optical pulse. A contour map of the density modulation depth is constructed for different combinations of RF and laser fields. The results provide insight into unlocking new opportunities to achieve direct density modulation during electron current emission by optical means. [ABSTRACT FROM AUTHOR]

This paper reports that the in situ growth magnetic field (Hg) during magnetic-phase CoFeB deposition impacts the electric-field control of magnetic anisotropy in Co40Fe40B20/(011)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 [CoFeB/(011)-PMN-PT] composite multiferroic heterostructures at room temperature. In the Hg1 mode (in situ Hg along the [ 01 1 ¯ ] direction of the ferroelectric PMN-PT substrate), the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS are approximately −47% and +156%, respectively. However, in the Hg2 mode (in situ Hg along the [100] direction of the ferroelectric PMN-PT substrate) of the CoFeB/(011)-PMN-PT multiferroic heterostructure, the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS can reach as high as +162% and +393%, respectively. Moreover, the electric-field-controlled magnetic coercive field HC exhibits a butterfly shape when plotted versus the applied electric fields in both modes, which matches the in-plane butterfly strain loop of the ferroelectric PMN-PT substrate. However, the electric-field-controlled saturation magnetic field HS presents a square loop, which is very consistent with the ferroelectric loop of the PMN-PT substrate. This result may be ascribed to the distinct pathway of the ferroelastic domain switching in the (011)-oriented PMN-PT substrate. This study provides a new idea for the design of spintronic devices based on multiferroic heterostructures. [ABSTRACT FROM AUTHOR]

This paper proposes a physics-based model based on possible chemical processes responsible for the resistive switching of sputter-deposited silicon oxide films. Diffusion–reaction differential equations are utilized to pursue physical and chemical origins of the switching phenomenon. Based on the theoretical model, the chemical reaction process is analytically and numerically solved, and an analytical model is proposed to elucidate the phenomenon. Theoretical simulation results are examined from the point of view of suitability of parameter values, and the analytical model is used to interpret the simulation results. Simulation results greatly assist in understanding the switching processes of silicon oxide films; that is, the diffusion processes of hydrogen and water molecules primarily rule the switching processes, and the displacement of oxygen atoms is assisted by those processes. The analytical model predicts that high-speed switching requires a large number of traps in the oxide, a relatively large binding energy, and a low leakage current; all of them can easily be satisfied for sputter-deposited oxide films. A combination of the theoretical simulation model and the analytical model gives a guideline of how the sputter-deposited silicon oxide films can be made suitable for high-speed resistive switching applications. [ABSTRACT FROM AUTHOR]

High-power lasers are routinely used to generate energetic positively charged ions, and this paper reports on the observation of negative ions in these experiments. A large number of negative ions and neutral atoms at MeV energies was obtained from the interaction of a high intensity laser pulse with a water spray along with positive ions [Abicht et al., Appl. Phys. Lett. 103, 253501 (2013)]. Beams of negative ions and neutral atoms have the same properties as beams of positive ions. However, the mechanism of negative ion formation and acceleration is still under discussion. In order to gain more information about physics of generation negative ions and neutrals, we present a new experiment where all species, positive, negative ions, and neutrals, are spatially separated, and the electron capture and loss of each in water spray is evaluated. The formation of negative ions and neutral atoms of hydrogen and carbon with energies up to 140 keV and 1.2 MeV, respectively, is confirmed. It is suggested that the electrification of spray droplets plays a decisive role in these charge-exchange processes. [ABSTRACT FROM AUTHOR]

The impact of a time-varying external magnetic field on carbon nanotubes has been studied using Maxwell's equations in the mentioned articles. However, the Maxwell's equations are erroneously presented in the papers. The incorrect Maxwell's equations, their derivatives, and the Lorentz force equations have all been examined in this work. In this article, we have endeavored to ensure that the equations are formatted correctly and have made an effort to do so. We have made an effort to intuitively correct the equations' errors. We did not comment on the other portions of the mentioned articles; instead, we restricted ourselves to the examination of the impact of Maxwell's equations and Lorentz force equations. [ABSTRACT FROM AUTHOR]

In a recent paper, Mandelis et al. [J. Appl. Phys. 133, 055102 (2023)] describe a photothermal methodology and a new inversion technique which, when applied to a heterogeneous material, is claimed to allow a simultaneous reconstruction of the depth profiles of thermal conductivity and density (assuming that the specific heat is a known constant). In this Comment we recall that, for the thermophysical configuration considered, the thermal conductivity and volumetric heat capacity profiles cannot be identified simultaneously because they are fully correlated. The exposed problem exhibits unconditional non-identifiability leading to the non-uniqueness of the solution. The apparent success of the inversion tests does not preclude the fact that, for any (apparently) optimal solution, an infinite multiplicity of equally satisfactory pairs of conjugate profiles can be built. The simultaneous identification of the density and thermal conductivity profiles is here an unsolvable inverse problem. [ABSTRACT FROM AUTHOR]

GaN caps are commonly used to reduce sheet charge modulation induced by AlGaN/GaN surface potential. However, the details on how GaN caps affect C – V and G – V characteristics are still unclear. In this paper, we report a difference between these characteristics with and without GaN caps, and we discovered a mechanism in which GaN caps act as quantum wells to affect the charging and discharging of interface states. Finally, we developed a numerical model to simulate admittance characteristics of AlGaN/GaN MIS structures with a GaN cap in high accuracy. [ABSTRACT FROM AUTHOR]

In this paper, we numerically study the influence of saturable absorber parameters, namely, modulation depth, recovery time, and saturation energy, on the performance of an ultrafast fiber laser that is mode-locked by a hybrid scheme of a saturation absorber (SA) and a nonlinear polarization rotation (NPR). Maps of mode-locked states related to intracavity wave-plates are created to evaluate the operation of hybrid mode-locking under different modulation depths of the SA. Along with the improvement of modulation depth of the SA, the mode-locked pulse results from a combination effect of the SA and NPR. The numerical analysis reveals that the SA parameters can significantly impact the pulse profile, peak power, and operation state. Moreover, they can also impact the selection of NPR mode-locked points, resulting in variation in stable single pulse output. A higher modulation depth can suppress the unstable multiple pulses' operation and convert them into harmonic mode-locked pulses. The obtained results indicate that the selection of appropriate SA parameters can effectively improve the output characteristics of hybrid mode-locked fiber lasers. [ABSTRACT FROM AUTHOR]

At optical frequencies, the collective excitation of the periodic array of metallic meta-molecules can support surface lattice resonances (SLRs) due to the coupling of localized surface-plasmon (LSP) resonances to Rayleigh anomaly diffraction. However, the LSP effect in metal blocks becomes negligible in the microwave region. Thus, how the SLRs behave in the microwave regime is very interesting. In this paper, a microwave metasurface consisting of periodic metallic cubes on an ultrathin dielectric substrate is investigated. Two high-Q transmission dips are found, which can be attributed, respectively, to electric-dipole SLRs (ED-SLRs) and magnetic-dipole SLRs (MD-SLRs), because of the non-resonant Rayleigh-like scattering of single cubes and diffraction coupling of the periodic array. The frequencies of both ED- and MD-SLRs are sensitive to the refractive index of the substrate, suggesting that the proposed metasurface may be used to measure the refractive index in the microwave range. [ABSTRACT FROM AUTHOR]

Electric field distortion caused by space charge accumulation is one of the challenges in the development of insulating liquid immersed converter transformers and battery energy storage. This paper studies the impact of temperature and moisture content on field distortion in synthetic ester through an improved computational model incorporating the time-development permittivity of insulating liquid, and the test results indicated highly accurate simulation results of electric field distribution can be produced compared with the previous model. Charge mobility and charge density in synthetic ester were extracted from frequency dielectric spectroscopy test results, which were then used to calculate field distortion by the developed computational model. Simulation results indicated that the field distortion in synthetic ester decreases with temperature due to the enhanced permittivity caused by space charge accumulation, while it increases with moisture content due to the increased charge density from the dissociation of water. [ABSTRACT FROM AUTHOR]

Polycrystalline thin films are widely used for devices and energy-related applications, such as power electronics, solar cells, and thermal management of devices. In many cases, large-scale crystallization during thin-film growth is challenging, so columnar grains are often found in metal and semiconductor thin films. These rough columnar grain boundaries may also have different phonon specularities from that for typically smoother top/bottom film surfaces. A simple analytical model to separately treat these boundaries and interfaces for phonon scattering is currently unavailable, although the in-plane thermal transport is critical to heat spreading within thin-film devices. In this paper, we extend the effective medium formulation from three-dimensional polycrystalline bulk materials to columnar-grained thin films. The model predictions agree well with those given by frequency-dependent phonon Monte Carlo simulations, considering varied phonon specularity at top/bottom film surfaces and grain-boundary phonon transmissivity. The analytical model is further used to analyze the existing data on polycrystalline ZnO thin films with columnar grains. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the optical response of the PbBiI single-layer by developing a strain-induced Kane–Mele model from Peierls substitution and by employing the Kubo formula at low temperatures. We address three different regimes of uniform and non-uniform classes created by tuning the strength of the strain. From a detailed analysis of the electronic band structure, we find that the Rashba spin splitting gap is destroyed with strain, while the bulk gap slightly changes. We also find that interband optical transitions exhibit a blueshift spectrum with strain. Interestingly, all these findings are independent of the regime and class of strain. However, our simulations show that only the non-uniform class of strain leads to anisotropic optical conductivity. These results enhance optoelectronic applications of low-dimensional materials. [ABSTRACT FROM AUTHOR]

Aiming at the large-scale application of metasurface in the field of radar stealth, we present a hybrid resonance-based and dispersion substrate integrated checkerboard metasurface (CMS) for reducing the radar cross section (RCS) of flat metallic targets. Considering the frequency-dependent characteristics of such a dispersion material, a pair of single and dual resonant artificial magnetic conductor meta-atoms with the modified "crusades-like" cell topologies is employed to maximize the operating bandwidth; besides, a comprehensive and thorough investigation on the resonance mechanism is conducted in this paper to provide an intuitive physical insight of meta-atoms' reflection responses. By comparing the predicted results with simulations, the quasi-periodic effect is introduced to explain the frequency shift of 10 dB RCS reduction bandwidth. In the implementation procedure, a prototype of the designed RCS reducer with a total dimension of 180 × 180 mm2 is fabricated and measured, the 10 dB RCS reduction bandwidth of theoretical simulation and experimental measurement are basically consistent, and the performance improvement of 8 dB RCS reduction in the experimental results can be attributed to the dispersion effects of the dielectric substrate. With a better figure of merit, our efforts may serve as a useful exemplar for the economical CMS architecture in radar evasive applications. [ABSTRACT FROM AUTHOR]

In a thick-dielectric electroluminescent (TDEL) device, which is a variation of thin-film electroluminescent devices, one of the insulation layers is replaced by a thick-film dielectric layer. High brightness and reliability are the features of TDEL owing to a higher withstanding voltage of the thick-film dielectric layer. This paper presents a new type of TDEL with a bottom emission structure. The thick-film dielectric layer was manufactured by spin coating using an ink material, which is a mixture of BaTiO3 powder and a binder resin. The thicknesses of the phosphor and dielectric layers were minimized to reduce the operating voltage. A threshold voltage as low as 50 V and a maximum luminance of 1000 cd/m2 were obtained at 60 V. [ABSTRACT FROM AUTHOR]

This paper is concerned with a theoretical analysis of the behavior of optically excited spin currents in bilayer and multilayer systems of ferromagnetic and normal metals. As the propagation, control, and manipulation of the spin currents created in ferromagnets by femtosecond optical pulses is of particular interest, we examine the influence of different thicknesses of the constituent layers for the case of electrons excited several electronvolts above the Fermi level. Using a Monte-Carlo simulation framework for such highly excited electrons, we first examine the spatiotemporal characteristics of the spin current density driven in a Fe layer, where the absorption profile of the light pulse plays an important role. Further, we examine how the combination of light absorption profile, spin-dependent transmission probabilities, and iron layer thickness affects spin current density in a Fe/Au bilayer system. For high-energy electrons studied here, the interface and secondary electron generation have a small influence on spin transport in the bilayer system. However, we find that spin injection from one layer to another is most effective within a certain range of iron layer thicknesses. [ABSTRACT FROM AUTHOR]

The use of high-power lasers to reach the high temperatures typical for off-normal conditions in nuclear reactor fuel or to determine its properties at high temperature is a relevant and proven technique in the nuclear research community. Conducting studies at high temperature with full control in space and time of the thermal gradients is, however, a challenge. In this paper, we present a combination of methodologies, experiments, and models to drive nuclear fuel samples in thermal conditions relevant to the study of nuclear fuel materials. Based on the use of high-power (kW) lasers with beam shaping and temporal laser control, our experimental approach allows one to heat depleted UO2 samples and obtain precise control of the temporal gradients, in the ms range, and spatial gradients, in the 100 μm range. The coupling with numerical simulations allows one to determine the temperature distribution in the depth of the sample and to develop a thermo-mechanical interpretation of the results. We will present the methodology allowing one to properly compare experimental and simulation results by taking into account the optical response of the instrumentation, the laser–UO2 interaction, and the resulting heat source term. We will show that we can express the heat source term resulting from the laser loading either by an analytical description or statistically based on Monte-Carlo simulation. A fairly good agreement between the recorded temperature and the simulation results is shown. The presented methodology can be extended to other materials with a proper choice of laser wavelength and instrumentation based on the optical properties of the investigated material. [ABSTRACT FROM AUTHOR]

Within the framework of the macroscopic dielectric continuum model, the dispersive spectra of polar optical phonon modes of III-nitride based nanostructures with different inner and outer dielectric media are investigated in this paper. The dielectric and quantum size effects on the dispersive frequencies of phonon modes are focused and emphasized. In the case of GaN quantum rings (QRs), we found that the dielectric constant of the inner/outer medium could significantly influence the dispersive spectra of the surface optical (SO) phonon mode as the high/low-frequency SO phonon modes are mainly localized at the inner/outer surface of QRs, respectively. Moreover, such effects associated with different crystallographic structures of GaN, i.e., the wurtzite (WZ) and zinc blende (ZB) crystal structures, are also studied in detail, showing the different degenerating behavior and electron–phonon coupling strength. The results obtained in this study provide a beneficial opportunity to independently adjust dispersive spectra of the two branches of SO modes in GaN nanostructures; thus, it could be used to design and develop phonon-based detectors and sensors. [ABSTRACT FROM AUTHOR]

This paper presents the investigation of a metastructure, built with periodic arrays of inertial amplification (IA) cantilever-type resonators on a host beam, to improve its low-frequency flexural wave attenuation performance. The IA mechanism is composed of an additional mass and three rigid bars, which are connected by hinges and embedded on the host beam and cantilever-type resonators, respectively. The dynamical model of an IA cantilever-type resonant beam (IACRB) is established by the spectral element method, and its bandgap characteristics and vibration transmissibility are verified numerically and experimentally. The bandgaps of the lumped mass cantilever-type resonant beam are compared to those of the IACRB, showing that the latter has better low-frequency wave attenuation ability. To reveal the underlying physics, the effects of the amplification ratio, IA span, and length ratio of cantilever-type resonators on the band diagram of the IACRB are investigated. It is found that the variation of the amplification ratio results in the bandgap near-coupling phenomenon and the bandgap transposition phenomenon. The increase of IA span by changing position 1 weakens the coupling effect of local resonance and IA. However, the increase of IA span by changing position 2 creates the super-wide pseudo-bandgap as well, which is potential in engineering practices. The variation of the length ratio of cantilever-type resonators decreases its first bending modal frequency and shifts the IA bandgap to a lower frequency range slightly. The modal analysis results of the IACRB show that the proposed mechanism affects the modal distributions of the host structure. The modal frequencies existing in bandgaps are caused by the local vibration mode of the ends of the IACRB. [ABSTRACT FROM AUTHOR]

Semiconductor industry is experiencing unprecedented growth, still driven by Moore's law, which is continually delivering devices with improved performance at lower costs. The continuation of this development places the industry in a divergent trade-off between economic attractiveness, technological feasibility, and the need for further performance improvement. Since the mainstream semiconductor technologies are silicon-based, new disruptive innovations are needed to gain additional performance margins. The use of nanowires is the preferred approach for preserving electrostatic control in the MOS transistor channel, and the application of mechanical stress is a booster of carrier mobility. It is in this context that this paper presents the design, fabrication, theoretical modeling, and characterization of a measurement platform to characterize the mechanical tensile stress of extremely narrow Si nanowires as small as 14.2 ± 1.12 nm in width. The proposed measurement platform enables a precise control of uniaxial strain, in terms of both amplitude and location, through the implementation of a stoichiometric Si3N4 pulling strand exerting a high tensile force on silicon nanowires. Reported devices are fabricated using a silicon-on-insulator wafer with fully complementary metal–oxide–semiconductor-compatible processing and top-down approach. It is observed that the mechanical strength of nanostructured Si is size-dependent and increases with miniaturization. Characterization revealed a record tensile strength value of 7.53 ± 0.8% (12.73 ± 1.35 GPa) for the narrowest nanowires fabricated using a top-down approach. [ABSTRACT FROM AUTHOR]

The secondary electron spectrum (SES) contains complex surface information and is widely used in surface analysis technology. A theoretical model of the SES for metals was proposed to reveal the effect of the surface potential barrier on the SES. In our model, an improved inner secondary electron energy distribution was established according to the free electron gas model. The transmission coefficient of inner secondary electrons was determined by solving the density of electronic states. Finally, the model was verified by our experiments, and the effects of the coverage fraction and potential barrier height, width, and form on the SES were comprehensively analyzed. The results show that H2O adsorption lowers the barrier height and enhances the tunneling effect, resulting in the most probable energy shifting toward the low-energy end and full width at half maximum narrowing. In addition, increasing or broadening the barrier can weaken the secondary electron tunneling effect, reduce the secondary electron number, and increase the most probable energy and the full width at half maximum. The model in this paper provides a reliable analysis method for studying the SES under different surface barriers for metals. Relevant results have significant value for the analysis of scanning electron microscopy images and optimization of secondary electron detection systems. [ABSTRACT FROM AUTHOR]

The underwater streamer discharges have a variety of potential applications in environmental science and technology. The electrical characteristics of the plasma filament generated by underwater streamer discharges play an important role in its propagation through water and influence the production of the chemical reactive species and the energy injected into the plasma filament. In this paper, we studied the electric field inside the plasma filament, the electric field at the head of the plasma filament, and the electrical conductivity of the plasma filament. By measuring the maximum length and the radius of the plasma filament, we found that the linear relation between the maximum length of the plasma filament and the applied voltage is not affected by the water conductivity within the range of 60–540 μS/cm. Based on such kind of linear relation, the electric field inside the plasma filament and the electric field at the head of the plasma filament were estimated as 26.0 ± 1.2 and 372 ± 52 kV/cm on average, respectively, being independent of the water conductivity within the range of 60–540 μS/cm. The electrical conductivity of the plasma filament was 0.4–3.7 S/cm within the range studied, being 3–4 orders of magnitude greater than that of the ambient water and depending significantly on the water conductivity. The experimental data obtained in the present work will be beneficial for the design of the reactor of pulsed underwater discharges. [ABSTRACT FROM AUTHOR]

In highly doped semiconductor quantum wells (QWs), electrons populate various energy states from different subbands and, therefore, several optical intersubband transitions (ISBTs) can occur simultaneously. Coulomb coupling between these ISBTs gathers the strength of all the individual transitions and concentrates all the oscillator strength in a single collective excitation: the multisubband plasmon (MSP). MSPs are an excellent platform for the study of collective and exotic effects in semiconductors and for the demonstration of novel device concepts. Indeed, the high electronic densities involved in the collective excitation greatly enhance the coupling strength and enable the ultra-strong coupling regime between MSPs and either optical modes in a cavity or phonons in the semiconductor. In this Perspectives paper, after addressing the basic physics of MSPs and the state of the art, we outline the most promising paths for the research community in this topic from the point of view of basic physics, material platforms, and applications of MSPs. [ABSTRACT FROM AUTHOR]

In this paper, we report the use of three pendeo-epitaxy growth approaches as a way of reducing the threading dislocation density (TDD) of 20 × 20 μm2 GaN platelets to be used for the development of micro light-emitting diodes (μLEDs). The method relies on the coalescence of GaN crystallites grown on top of a network of deformable pillars etched into a silicon-on-insulator substrate. Our approach takes advantage of the creeping properties of SiO2 at the usual GaN epitaxial growth temperature, allowing the GaN crystallites to align and reduce the grain boundary dislocations. Furthermore, this bottom-up approach allows to get rid of the dry plasma etching step for μLEDs fabrication, which highly deteriorates sidewalls, reducing the efficiency of future displays. By optimizing the growth conditions and inducing asymmetric nucleation, a TDD of 2.5 × 108 cm−2 has been achieved on the GaN platelets, while keeping a smooth surface. [ABSTRACT FROM AUTHOR]

This paper demonstrates an acoustic metasurface for energy harvesting at tunable frequencies. The support structure of the metasurface was fabricated by additive manufacturing. The acoustic absorption coefficient and sound transmission loss of the metasurface can be tuned by optimization of various structural parameters, such as mass, mass size, prestress, membrane thickness, and array arrangement. The impedance tube was used to test the sound absorption ability of the fabricated metasurface, and the numerical simulation agreed well with the experiment, with a minimum acoustic absorption coefficient at ∼400 Hz. A PZT structure was designed and integrated into the acoustic metasurface, transforming the absorbed acoustic energy into electrical energy. Real-time acoustic energy harvesting was realized, and the peak voltage of 1.469 V was successfully monitored under the excitation of 410 Hz. For future applications, the energy harvesting efficiency can be further increased by improving the isolation components of the whole system. [ABSTRACT FROM AUTHOR]

In this paper, we aim to numerically resolve linear and nonlinear transient heat conduction problems in multilayer composite materials using a deep learning method called multi-domain physics-informed neural networks (MDPINNs). For this purpose, the multilayer media are first divided into independent sub-domains based on domain decomposition technique. The single-layer deep neural networks are first established, and each sub-domain has its corresponding sub-network. Then, each two sub-networks are connected by continuity conditions on the interface to form a MDPINNs' framework that can directly solve the transient heat conduction problem in multilayer media. The temperature distribution in the computational domain can be obtained by training the MDPINNs, including the temperature values on the interface. A series of numerical experiments are carried out to verify that the proposed framework can achieve satisfactory accuracy, including in micrometer or even nanometer structures. Compared with conventional methods, the MDPINNs have the advantage of directly solving both linear and nonlinear heat conduction problems in multilayer materials in a unified and concise form. [ABSTRACT FROM AUTHOR]

To solve the problem of testing the sensitivity under electromagnetic pulse radiation for a hot bridge wire electro-explosive device (EED), this paper simulated and analyzed the correlation between the critical ignition current under steady and pulse excitation. The simulation results showed that, under single pulse excitation, the critical ignition current of the EED decreases with the increase in the pulse width, and the variation law can be divided into three pieces: adiabatic, transition, and constant; while under pulse train excitation, due to the thermal cumulative effect, the critical ignition current is related to both material properties and excitation parameters. By analyzing the simulation results and considering the thermal ignition theory, the mathematical model of the critical ignition current under pulse excitation was established, and the mathematical model showed that under pulse train excitation, the critical ignition current is relevant not only to the single pulse excitation critical ignition current, pulse period, and duty cycle, but also to the ratio of single pulse and steady excitation critical ignition current and the thermal time constant. It was verified that the errors between the theoretical values obtained from the mathematical model and the results obtained from the simulation were within 2.5%. [ABSTRACT FROM AUTHOR]

Nanostructured topological insulators (TIs) have the potential to impact a wide array of condensed matter physics topics, ranging from Majorana physics to spintronics. However, the most common TI materials, the B i 2 S e 3 family, are easily damaged during nanofabrication of devices. In this paper, we show that electron beam lithography performed with a 30 or 50 kV accelerating voltage—common for nanopatterning in academic facilities—damages both nonmagnetic TIs and their magnetically doped counterparts at unacceptable levels. We additionally demonstrate that electron beam lithography with a 10 kV accelerating voltage produces minimal damage detectable through low-temperature electronic transport. Although reduced accelerating voltages present challenges in creating fine features, we show that with careful choice of processing parameters, particularly the resist, 100 nm features are reliably achievable. [ABSTRACT FROM AUTHOR]

Tunable piezoelectric metasurfaces have been proposed as a means of adaptively steering incident elastic waves for various applications in vibration mitigation and control. Bonding piezoelectric material to thin structures introduces electromechanical coupling, enabling structural dynamics to be altered via tunable electric shunts connected across each unit cell. For example, by carefully calibrating the inductive shunts, it is possible to implement the discrete phase shifts necessary for gradient-based waveguiding behaviors. However, experimental validations of localized phase shifting are challenging due to the narrow bandgap of local resonators, resulting in poor transmission of incident waves and high sensitivity to transient noise. These factors, in combination with the difficulties in experimental circuitry synthesis, can lead to significant variability of data acquired within the bandgap operating region. This paper presents a systematic approach for extracting localized phase shifts by taking advantage of the inherent correlation between the incident and transmitted wavefronts. During this procedure, matched filtering greatly reduces noise in the transmitted signal when operating in or near bandgap frequencies. Experimental results demonstrate phase shifts as large as −170° within the locally resonant bandgap, with an average 28% reduction in error relative to a direct time domain measurement of phase, enabling effective comparison of the dispersive behavior with corresponding analytical and finite element models. In addition to demonstrating the tunable waveguide characteristics of a piezoelectric metasurface, this technique can easily be extended to validate localized phase shifting of other elastic waveguiding metasurfaces. [ABSTRACT FROM AUTHOR]

In this paper, we devise a pentamode metamaterial plate exhibiting topological characteristics. By organizing pentamode metamaterial structural elements, topological boundary states are attained, effectively safeguarding propagation of elastic waves. Moreover, based on the numerical simulation model, we employ a polymer to fabricate a macro-scale specimen via additive manufacturing. Through assessing the vibrational response of the sample, we corroborate its topological attributes in governing elastic wave transmission. This discovery paves the way for a novel approach to manipulating acoustic/elastic waves employing pentamode metamaterials. [ABSTRACT FROM AUTHOR]

Germanium–tin (GeSn) alloys at sufficiently high Sn concentration, above several atomic percent, are the only group IV semiconductor exhibiting a direct bandgap and have generated much recent interest for optoelectronic applications into the mid-infrared region. Because the large lattice mismatch between GeSn and Si results in considerable strain for thin layers and a high defect density for thicker strain-relaxed layers, most reported GeSn growths incorporate a Ge buffer layer rather than depositing directly on Si substrates. Published reports of GeSn growth directly on Si utilize specialized precursors such as higher order germanes (Ge2H6, Ge3H8, or Ge4H10) or SnD4. In this paper, we report GeSn films with up to 10.6% Sn grown directly on Si substrates by remote plasma-enhanced chemical vapor deposition using GeH4 and SnCl4 precursors. These alloys have been characterized in detail using x-ray diffraction (XRD), transmission electron microscopy (TEM), and Rutherford backscattering spectrometry with channeling (RBS-C), as well as Raman spectroscopy (RS) and optical microscopy. The films studied are almost fully relaxed, with small residual strain observed, particularly in thinner films, and contain a high interface density of misfit dislocations that increases with Sn concentration. The defect density decreases toward the surface. Good agreement is found between the various characterization methods for the Sn content (XRD and RBS-C), lattice parameter measurement (XRD and TEM), and defect characterization (RBS-C, TEM, and RS). Such characterization of GeSn grown directly on Si substrates is essential to allow growth parameters to be optimized for the realization of the attractive optoelectronic properties of these alloys. [ABSTRACT FROM AUTHOR]

In this paper, we show that by extending the concept of "microsphere-assisted imaging" into thermal lens (TL) detection, enhancement of photothermal detection is achieved. Furthermore, by integration of TL detection and digital holographic microscopy (DHM), we provide simultaneous measurement of photothermal properties as well as complementary imaging of the sample. Simultaneous acquisition of photothermal properties and imaging is essential for characterization of a variety of samples in biochemistry, material science, and process technologies. TL is a sensitive methodology to detect low concentrations of analytes in low-loss samples, and DHM in the transmission mode is an effective technique for label-free, non-contact, and real-time imaging and measurement of phase objects, such as biomaterials. We demonstrate the usefulness of the TL-DHM integrated system by applying it for acquisition of photothermal maps of samples as well as obtaining their morphometrical information. Additionally, we measure the thermal diffusivity of polydimethylsiloxane because of the focusing effect of polystyrene microspheres. The system has the potential to be applied for a variety of objects including bio-samples and may be proposed as a bench-top characterization device. [ABSTRACT FROM AUTHOR]

This paper presents the experimental evidence of reversible insulator–metal transition (IMT) in thin-film amorphous molybdenum trioxide (MoO3) induced by electric fields of just a few volts. The presence of oxygen vacancies in MoO3 is considered to play a significant role in the reported reversible IMT. The oxygen vacancies not only impact MoO3 stoichiometry but also the optical bandgap. The subthreshold slope for IMT in 10 nm-thick MoO3-based devices is 48.3 mV/decade, which represents a transition from an insulator to a metallic state, and the electric field threshold for such a transition was found to be equal to 0.034 V/Å. Following the IMT in MoO3, there are six orders of magnitude differences between the resistivity of the insulator state (27.5 M Ω at −9 V) and the metallic state (80 Ω between +5 and +9 V). In addition, we reported stabilization of a nanocrystalline hexagonal MoO3 (h-MoO3) phase in thicker MoO3 (150 nm-thick) in the presence of oxygen vacancies that behave as a wide bandgap (3.1 eV) ferroelectric semiconductor with a coercive field of about 50 kV/cm, a saturation polarization of about 30 μC/cm2, and a remanent polarization of about 10 μC/cm2. This ferroelectricity in nanocrystalline h-MoO3 (150 nm-thick) remains stable even after 8 months of storage of the sample in ambient conditions, with remanent polarization increasing up to 20 μC/cm2. These are unexpected results from MoO3. [ABSTRACT FROM AUTHOR]

3D printing, also known as additive manufacturing technique, has recently found applications in various engineering fields due to its ability to produce freeform 3D structures beyond the ability of traditional subtractive manufacturing methods. In this respect, the field of THz photonics is no exception. The adoption of 3D printing technique resulted in a revolution in THz optics and device manufacturing and will continue advancing this field for years to come. In this Perspective paper, we consider, in particular, the fabrication of guided optics devices for the THz operation range using additive manufacturing. We first introduce the technical characteristics of various 3D printing techniques as well as the advantages, disadvantages, and main performance parameters. Then, various 3D printed THz waveguides and fibers and functional devices, such as metalized/metallic/dielectric rectangular waveguides, photonic crystal waveguides, hollow-core anti-resonant/Bragg waveguides, hybrid metal/dielectric waveguides, plasmonic waveguide, porous fibers, magic tee, and serpentine waveguide traveling-wave circuits, are discussed. We also highlight practical applications of 3D printed waveguides/fibers in manipulating THz waves, especially in the fields of sensing and communication, including the analyte thickness and refractive index sensors, subwavelength/suspended core fiber communication links, dispersion compensators, and add-drop multiplexers. Finally, the prospects of 3D printing techniques in the THz field are summarized. [ABSTRACT FROM AUTHOR]