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In this work, three atomic layer deposition (ALD) approaches are used to deposit an Al2O3 gate insulator on n-GaN for application in vertical GaN power switches: thermal ALD (ThALD), plasma-enhanced ALD (PEALD), and their stacked combination. The latter is a novel method to yield the most ideal insulating layer. Also, the influence of an in situ NH3 or H2 plasma pre-treatment is studied. Planar MIS capacitors are used to investigate the electrical properties and robustness of the gate insulators. In vacuo x-ray photoelectron spectroscopy (XPS) is used to study the changes in chemical composition after every surface treatment. XPS shows that all plasma pre-treatments efficiently remove all carbon contamination from the surface, but only NH3 plasma is observed to additionally remove the native oxide from the n-GaN surface. The water precursor step in the ThALD process does not completely remove the CH3 ligands of the trimethylaluminum precursor step, which might electrically be associated with a reduced forward bias robustness. The O2 plasma step in the PEALD process is associated with the removal of carbon and a tremendous increase of the O content in the GaN surface region. Electrically, this strongly correlates to an enhanced forward bias robustness and an increased forward bias hysteresis, respectively. The ThALD/PEALD stack method mitigates the shortcomings of both ALD processes while maintaining its advantages. Electrical measurements indicate that the stack method alongside NH3 plasma pretreatment provides the best characteristics in terms of hysteresis, threshold voltage, forward bias robustness, and interface trap density of states. [ABSTRACT FROM AUTHOR]

Current–voltage characteristics and low-frequency (LF) noise of industrial-quality AlGaAs/InGaAs/GaAs pseudomorphic high-electron-mobility transistors are evaluated as a function of bias stress and temperature. A small positive shift of threshold voltage Vth and negligible degradation in peak transconductance GM are observed under ON-state bias conditions at elevated temperatures. The Vth measurements suggest activation of an acceptor-like defect or impurity center. The GM measurements demonstrate that newly activated defects are not located close enough to the two-dimensional electron gas to scatter carriers strongly. First-principles calculations and comparisons with previous work suggest that OAs impurity centers, other oxygen-related defects, isolated AsGa antisites, and dopant-based DX centers may contribute significantly to low-frequency (LF) noise in as-processed devices. LF noise is relatively unaffected by voltage stress at elevated temperatures, consistent with the small changes in Vth and peak GM. [ABSTRACT FROM AUTHOR]

Due to the ultrawide bandgap (4.9 eV), high carrier mobility (300 cm 2 V − 1 s − 1 ), and high thermal stability, β − Ga 2 O 3 can be a potential candidate for high-temperature thermoelectric materials. However, the intrinsically high thermal conductivity may hinder its application for thermoelectric conversion. In this work, porous β − Ga 2 O 3 was prepared by the solvothermal method together with spark plasma sintering technology. Positron lifetime measurement and N 2 adsorption confirm the introduction of pores by adding sucrose in the sample preparation. The sucrose-derived β − Ga 2 O 3 sintered at a relatively low temperature of 600 ° C remains highly porous, which results in an extremely low thermal conductivity of 0.45 W m − 1 K − 1 at room temperature, and it further decreases to 0.29 W m − 1 K − 1 at 600 ° C. This is the lowest thermal conductivity for β − Ga 2 O 3 reported so far. Our work provides an avenue to reduce the thermal conductivity for β − Ga 2 O 3 and is believed to be widely applicable to many other thermoelectric materials. [ABSTRACT FROM AUTHOR]

Ramp-compression experiments have been performed on the "Z" pulsed-power facility to investigate the strengths of Be and lead–antimony alloy. Yield strength and shear stress near peak pressure were obtained from measurements of the sound speed on release and using the Asay self-consistent method. Two S-65 grade Be samples, from batches that showed a significant difference in yield strength at ambient conditions, were found to have near identical yield strengths, which were also in agreement with similar earlier measurements on S-200 grade Be. Yield strength of the Pb4Sb alloy at ∼120 GPa was 1.35 GPa, while a National Ignition Facility experiment by Krygier et al. [Phys. Rev. Lett. 123, 205701 (2020)] found 3.8 GPa at ∼400 GPa pressure. Our result is intermediate between the ambient value and the one by Krygier et al., but the significantly increased strength is probably not associated with the transition to the high-pressure bcc phase of lead. [ABSTRACT FROM AUTHOR]

Scattering-type scanning near-field optical microscopy (s-SNOM) has been widely used to characterize strongly correlated electronic, two dimensional, and plasmonic materials, and it has enormous potential for biological applications. Many of these materials exhibit anisotropic responses that complicate the extraction of dielectric constants from s-SNOM measurements. Here, we generalize our recently developed approach for retrieving the near-field scattering signal from isotropic systems and apply it to anisotropic dielectrics. Specifically, we compare our theoretical results with experimental measurements on modestly anisotropic sapphire that exhibit strong resonances at the infrared frequency range. Good agreement with the experimental result is found. Our result is important for understanding the near-field response of low damping, anisotropic polaritonic states in dielectric media. [ABSTRACT FROM AUTHOR]

Although the effect of the deformation field size on the mechanical strength of metallic glasses (MGs) has been investigated thoroughly, a few studies have investigated the effect of the deformation field size on the kinetic creep deformation behavior for these materials. This issue is addressed in the current work by investigating the nanoindentation creep kinetics of La-based MGs under the application of spherical indenters with two different tip radii and three different loading rates. The experimental data are fit to a viscoelastic model to extract the activation volume and relaxation time characteristics of the kinetic nanoindentation creep deformation of the samples. The results demonstrate that the nanoindentation creep kinetics are not only strongly dependent on the loading rate, but also vary significantly with the indenter tip radius. The deformation dynamics is interpreted by the stretched exponent β, indicating its relatively small value at a large loading rate along with a large indenter tip radius. Furthermore, the observed effect of the deformation field size can be attributed to an interplay between the deformation field under the spherical indenter and flow defects associated with the excess free volume, shear transition zone, or shear band embryo with an evolution that is essentially dependent on the loading rate. The current findings contribute to a fundamental understanding of the mechanism of shear softening during creep deformation in MGs. [ABSTRACT FROM AUTHOR]

The physical characteristics of the fundamental absorption edge of semi-insulating GaAs and unintentionally doped GaSb, InAs, and InSb are examined using spectroscopic ellipsometry. A five parameter model is developed to describe the key characteristics of the absorption edge. Among these parameters are the bandgap energy, the characteristic energy of the Urbach tail, and the absorption coefficient at the bandgap energy. The results indicate that the Coulomb interaction strongly influences the shape of the band edge with progressively less influence as the bandgap energy decreases. The energy dependence of the optical transition strength is observed to be nearly constant in narrow bandgap InSb. [ABSTRACT FROM AUTHOR]

By means of the embedded-atom method, a Fe–Cu potential has been constructed through a newly mathematic form of cross potential. The newly constructed Fe–Cu potential has demonstrated to be more reliable than the five reported Fe–Cu potentials. Based on the Fe–Cu potential, the mechanical and thermodynamic properties and the structural stability of Fe–Cu solid solutions in the whole composition range are derived by molecular dynamics simulation. It is found that the heat of formation curves of the FexCu100 − x solid solutions with body-centered-cubic (BCC) and face-centered-cubic (FCC) structures intersect at the point of x = 65, implying that FexCu100 − x solid solutions with FCC and BCC structures are thermodynamically stable when 0 ≤ x ≤ 65 and 65 < x ≤ 100, respectively. In addition, the derived lattice constants, structural stability, elastic constants, elastic moduli, heat capacity, and coefficients of thermal expansion of Fe–Cu solid solutions from the new Fe–Cu potential agree well with the data of the experiments, first-principles calculation, and the Miedema model. [ABSTRACT FROM AUTHOR]

Thermal treatment was observed to gradually transform the morphology of Ce0.12Zr0.88O2 (CZ) powder: transitioning from having round edges, to exhibiting clear facets, to particle growth, as a function of increasing treatment temperature. The effect of the morphological changes in the powder on the extent of stress-induced phase transformation upon mechanical compression is reported. The physical changes in the average particle size and the residual levels of monoclinic content (MC) post thermal treatment between 300 °C and 1550 °C are in line with the expectations. However, the extent of transformation upon compression is found to greatly depend on the thermal history of the powder, and generally, post compression, MC can be split into two regimes. Powders heat-treated below ∼1200 °C comprise regime 1, where post compression, MC increases as the preceding thermal processing temperature is increased. The increase in MC is despite the decreasing residual levels of the monoclinic phase in the CZ powder, which is caused by the thermal treatment. For the case of annealing above ∼1200 °C (comprising regime 2), stress-induced transformation becomes exceedingly difficult and the extent of the transformation is significantly reduced. The vital role played by the particle shape alone can be leveraged in the development of new applications of shape memory ceramics. [ABSTRACT FROM AUTHOR]

An Fe-W potential has been constructed by means of the embedded-atom method and has proven to be more realistic than the three published Fe-W potentials in the literature. Based on the constructed Fe-W potential, molecular dynamic simulation has been used to reveal structural stability, thermodynamic properties, and mechanical properties of BCC Fe-W solid solutions within the entire composition range. It is found that the Fe-W interaction in BCC Fe-W solid solutions should be weak and attractive with small and negative heats of formation, which agree well with those from the thermodynamic Miedema model and could clarify the controversy regarding heats of formation of Fe-W solid solutions in the literature. In addition, the derived coefficient of thermal expansion, heat capacity, elastic constants, and elastic moduli of Fe-W solid solutions from the present Fe-W potential are in good agreement with the corresponding data from ab initio calculation or experiments in the literature. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of 210 nm thick InAsSbBi layers grown by molecular beam epitaxy at temperatures between 400 and 430 °C on (100) GaSb substrates are investigated using Rutherford backscattering, X-ray diffraction, transmission electron microscopy, Nomarski optical microscopy, and atomic force microscopy. The results indicate that the layers are nearly lattice matched, coherently strained, and contain dilute Bi mole fractions. Large surface droplets with diameters on the order of 1 μm and densities on the order of 106 cm−2 are observed when the InAsSbBi growth is performed with lean As overpressures around 1%. Surface droplets are not observed when the As overpressure is increased to 4%. Small crystalline droplets with diameters on the order of 70 nm and densities on the order of 1010 cm−2 are observed between the large droplets for InAsSbBi grown at 430 °C. Analysis of one of the small droplets indicates a misoriented zinc blende crystal structure composed primarily of In, Sb, and Bi, with a lattice constant of 6.543 ± 0.038 Å. Lateral modulation in the Bi mole fraction is observed in InAsSbBi layers grown at 400 °C. [ABSTRACT FROM AUTHOR]

The molecular beam epitaxy growth and optical properties of the III-V semiconductor alloy InAsSbBi are investigated over a range of growth temperatures and V/III flux ratios. Bulk and quantum well structures grown on the (100) on-axis and offcut GaSb substrates are examined. Bismuth readily incorporates at growth temperatures around 300 °C but results in materials with limited optical quality. Conversely, higher growth temperatures around 400 °C yield improved optical performance but with limited Bi incorporation. Photoluminescence spectroscopy is used to examine the optical properties and bandgap energies of InAsSbBi layers grown at temperatures from 400 to 430 °C using 0.91 and 0.94 As/In flux ratios, 0.10 and 0.12 Sb/In flux ratios, and 0.05 and 0.10 Bi/In flux ratios. Emission is observed from low to room temperature with peaks ranging from 3.7 to 4.6 μm. The relationships between Bi incorporation, surface morphology, growth temperature, and group-V flux are examined. Large concentrations of Bi-rich surface features are observed on samples where the incident Bi flux neither fully incorporates nor desorbs but instead accumulates on the surface and coalesces into droplets. [ABSTRACT FROM AUTHOR]

In this study, polycrystalline SnSe was synthesized via a rapid, cost-effective, and large-scale synthesis route. The obtained SnSe powders were pressed into pellets via spark plasma sintering (SPS) at different temperatures. Powder X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) were used to characterize the crystal structures and morphology of the SnSe samples. The XRD results indicate that the orientation factors increase monotonously with the increase of sintering temperature. The FESEM images show that sintering temperatures have no obvious influence on the particle size. Positron annihilation measurements indicate that vacancy defects exist in all the sintered SnSe samples, and they recover gradually with increasing sintering temperatures. These vacancy defects are responsible for the lower lattice thermal conductivity in samples sintered at lower temperatures. The electrical conductivity, power factor, thermal conductivity, and figure of merit ZT show nearly the same variation trend, which increases initially with the increasing sintering temperature up to 550 ° C then decreases with further increase of the sintering temperature, which is possibly due to slight oxidation of SnSe. A maximum ZT value of ∼ 0.47 at 430 ° C was achieved for the 550 ° C sintered sample, which is higher than those reported for undoped polycrystalline SnSe around this temperature. Thus, we provide a simple, energy-saving, and effective method to synthesize polycrystalline SnSe in large quantities, and SPS is an effective method to optimize thermoelectric performance. [ABSTRACT FROM AUTHOR]

We study the electrical transport through nanopores affected by the presence of DNA translocations. The current through the pore depends not only on the base pair inside the pore but also on what the neighbouring base pair outside of the pore is, because the neighbouring base pair possesses an electric dipole moment that exerts an electric field at the nanopore with a magnitude which is comparable to the externally applied electric field. This physical effect has not been included in previous studies, which focused on the blockage of the current by the bases inside the pore. There is much interest in extracting the base information from the current through the pore and to sequence the DNA. This extraction including our effect requires an analytical study of the phenomena so that the inverse problem is tractable. To study the electrical transport quantitatively and analytically, we formulate a rigorous analytical circuit theory for the interaction of a conducting medium with the electromagnetic field in the presence of a nanopore. We found that the base pair dipolar field only affects the total current when another base pair is in the pore and blockage occurs. It does not change the current otherwise. The effect of these dipoles is through a change of the diffusion induced by a change at the nanopore of the local charge carrier density and not by a change of the local conductivity. In addition to the effect of the dipoles, we clarify how the large capacitive response affects the current and when it will not do so. [ABSTRACT FROM AUTHOR]

In this work, we study the nonlinear coupling between the transverse modes of nanoresonators such as nanotubes or nanowires in a singly clamped configuration. We previously showed that at high driving, this coupling could result in a transition from independent planar modes to a locked elliptical motion, with important modifications of the resonance curves. Here, we clarify the physical origins, associated with a 1:1 internal resonance, and study in depth this transition as a function of the relevant parameters. We present simple formulae that permit to predict the emergence of this transition as a function of the frequency difference between the polarizations and the nonlinear coefficients and give the "backbone curves" corresponding to the elliptical regime. We also show that the elliptical regime is associated with the emergence of a new set of solutions of which one branch is stable. Finally, we compare single and double clamped configurations and explain why the elliptical transition appears on different polarizations. [ABSTRACT FROM AUTHOR]

A model for the cooling properties of a nanocantilever by a free electron beam is presented for a capacitive interaction. The optimal parameters for position sensing and cooling applications are estimated from previous experimental conditions. In particular, we demonstrate that a purely capacitive force and an electron beam stimulated internal feedback can lower the temperature of a nanocantilever by several orders of magnitude, in striking contrast with the conventional electrostatic damping regime. We propose a step by step protocol to extract the interdependent parameters of the experiments. This work will aid future developments of ultra-sensitive force sensors in electron microscopes. [ABSTRACT FROM AUTHOR]

The effect of grain size and moisture content on the dynamic macroscopic response of granular geological materials was explored by performing uniaxial planar impact experiments on high purity, Oklahoma #1, sand samples composed of either fine (75-150 µm) or coarse (425-500 µm) grain sizes in either dry or fully water-saturated conditions. Oklahoma #1 sand was chosen for its smooth, quasi-spherical grain shapes, narrow grain size distributions, and nearly pure SiO2 composition (99.8wt. %). The water-saturated samples were completely saturated ensuring a two-phase mixture with roughly 65% sand and 35% water. Sand samples were dynamically loaded to pressures between 1 and 11GPa. Three-dimensional meso-scale simulations using an Eulerian hydrocode, CTH, were created to model the response of each sand sample. Multi-phase equations of state were used for both silicon dioxide, which comprised individual sand grains, and water, which surrounded individual grains. Particle velocity profiles measured from the rear surface of the sand, both experimentally and computationally, reveal that fine grain samples have steeper rise characteristics than coarse grain samples and water-saturated samples have an overall much stiffer response than dry samples. The experimentally determined particle velocity vs. shock velocity response of dry sand was linear over this pressure range, with little difference between the two grain sizes investigated. The experimental response for the water saturated sand exhibited a piecewise continuous response with a transition region between particle velocities of 0.6 km s-1 and 0.8 km s-1 and a pressure of 4.5-6GPa. Hypotheses for the cause of this transition region are drawn based on results of the meso-scale simulations. [ABSTRACT FROM AUTHOR]

The observation of a 0.5 x (2e²/h) conductance plateau in asymmetrically biased quantum point contacts (QPCs) with in-plane side gates (SGs) has been attributed to the onset of spin-polarized current through these structures. For InAs QPCs with the same width but a longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the SGs over which the 0.5 x (2e²/h) plateau is observed when the QPC aspect ratio (ratio of length over the width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green's function simulations indicate that the increase in the size of the 0.5 x (2e²/h) plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electronelectron interactions in QPC devices with a larger aspect ratio. The use of asymmetrically biased QPCs with in-plane SGs and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors. [ABSTRACT FROM AUTHOR]

X-ray absorption fine structures (XAFS) and electron energy loss spectroscopy (EELS) at the Si L(sub 3,2) edge is used to investigate a series if Si nanowires. Optical properties of these Si nanowires are studied by using X-ray excited optical luminescence (XEOL).

A study was conducted to show that the emission wavelength of (InP)2/(GaP)2 short-period superlattice quantum wells can be changed by altering the tilt angle of the substrate or by adjusting the interruption time during switching. Variable temperature photoluminescence spectroscopy was carried out to characterize the samples. Results indicated that the growth mechanism can be determined through the bonding preference between the group III adatoms on the surface.

Nanowires (NWs) consisting of P-doped Si/B-doped Ge axial heterojunctions were grown via vapor-liquid-solid synthesis using a combination of Au and AuGa catalyst particles. Off-axis electron holography (EH) was used to measure the electrostatic potential profile across the junction resulting from electrically active dopants, and atom-probe tomography (APT) was used to map total dopant concentration profiles. A comparison of the electrostatic potential profile measured from EH with simulations that were based on the APT results indicates that Ga atoms unintentionally introduced during AuGa catalyst growth were mostly electronically inactive. This finding was also corroborated by in situ electron-holography biasing experiments. Electronic band structure simulations guided by the experimental results helped to provide a much better explanation of the NW electrical behavior. Overall, this work demonstrates that the combination of EH, APT, in situ biasing, and simulations allows a more complete understanding of NW electrical properties to be developed. [ABSTRACT FROM AUTHOR]

We report the strong correlations between the magnetoresistivity and the magnetic entropy change in the cubic antiferromagnetic TbSb compound. The theoretical investigation was performed through a microscopic model which takes into account the crystalline electrical field anisotropy, exchange coupling interactions between the up and down magnetic sublattices, and the Zeeman interaction. The easy magnetization directions changes from 〈001〉 to 〈110〉 and then to 〈111〉 observed experimentally was successfully theoretically described. Also, the calculation of the temperature dependence of electric resistivity showed good agreement with the experimental data. Theoretical predictions were calculated for the temperature dependence of the magnetic entropy and resistivity changes upon magnetic field variation. Besides, the difference in the spin up and down sublattices resistivity was investigated. [ABSTRACT FROM AUTHOR]

Manipulating dielectric properties of polydimethylsiloxane (PDMS) is an important consideration for flexible, low-loss device design. This paper presents a method for reducing dielectric loss (tan δ) by forming PDMS composites loaded with various concentrations of either alumina (Al2O3) or polytetrafluoroethylene (PTFE) particles. The structural, mechanical, and electrical properties of the composites are investigated. Theoretical mixing models were used to predict the relative permittivity (ϵr) of PDMS composites, and good similarity with the measured ϵr was observed. The incorporation of either low dielectric loss filler in the PDMS matrix (up to 50 wt.% filler loading) is shown to reduce the dielectric loss while maintaining the flexibility of the host matrix. The fillers can also control the permittivity of the composite, either increasing or decreasing relative permittivity from that of PDMS. Interestingly, a strain of ~500% can be applied to 15 wt.% PDMS/PTFE composites, compared with ~350% for pure PDMS. [ABSTRACT FROM AUTHOR]

We present a versatile nanomechanical sensing platform for the investigation of magnetostriction in thin films. It is based on a doubly clamped silicon nitride nanobeam resonator covered with a thin magnetostrictive film. Changing the magnetization direction within the film plane by an applied magnetic field generates a magnetoelastic stress and thus changes the resonance frequency of the nanobeam. A measurement of the resulting resonance frequency shift, e.g., by optical interferometry, allows to quantitatively determine the magnetostriction constants of the thin film. In a proof-of-principle experiment, we determine the magnetostriction constants of a 10 nm thick polycrystalline cobalt film, showing very good agreement with literature values. The presented technique aims, in particular, for the precise measurement of magnetostriction in a variety of (conducting and insulating) thin films, which can be deposited by, e.g., electron beam deposition, thermal evaporation, or sputtering. [ABSTRACT FROM AUTHOR]

Excited by 5 ns, 8 kV voltage pulses, a 260 μm-diameter, 8mm long helium plasma jet was generated with a single-electrode configuration in ambient air. Application of fast high voltage pulses (⩾1012 V s-1) resulted in rapid acceleration of the microplasma plumes; within 5 ns the plume velocity reached 8×105 m/s, almost three times higher than that of the plasma jet generated with the pulsed voltage of the same amplitude but with a lower increase rate (1011 V s-1). Importantly, the ultrashort electric pulses were able to efficiently deposit energy in the plasma during the initiation process, which may be responsible for the rapid acceleration of the ionization wavefronts during the streamer onset, as well as efficient production of reactive plasma species including O(5P) and N+2 (B2Σ+u) via electron-induced processes. Emission spectral comparison between the plasma jets excited with 5 ns voltage pulses and with 140 ns voltage pulses showed enhanced O(5P) and N+2 (B2Σ+u emission by the shorter pulses than the longer ones, while the vibrational and rotational temperature for both plasma jets are at 3000K and 300 K, respectively. [ABSTRACT FROM AUTHOR]

We report remarkable results due to the coupling between the magnetization and the electric field induced polarization in EuTiO3. Using a microscopic model Hamiltonian to describe the three coupled sublattices, Eu-(spin-up), Eu-(spin-down), and Ti-(moment), the spin flop and spin reorientation phase transitions were described with and without the electric-magnetic coupling interaction. The external electric field can be used to tune the temperature of the spin reorientation phase transition TSR=TSR(E). When the TSR is tuned around the EuTiO3—Néel temperature (TN=5.5K), an outstanding effect emerges in which EuTiO3 releases heat under magnetic field change. The electric field controlling the spin reorientation transition and the endo-exothermic processes are discussed through the microscopic interactions model parameters. [ABSTRACT FROM AUTHOR]

The intensity of visible photoluminescence from thin films of silicon nanoparticles was found to be dependent upon the degree of surface passivation on the nanoparticles, while the emission energy was independent of the specific chemical properties of the passivating species. All findings were consistent with a simple quantum confinement model of emission where particle size determines emission energy and surface passivation determines emission intensity.

X-ray absorption near-edge structure spectroscopy and low energy electron diffraction studies reveal the properties of the surface defect structures on diamond (100) surfaces. Low energy bombardment with neon ions causes surface defect structures. If bombardment occurs at very low ion fluence, diamond discrete exciton absorption is suppressed. The process of thermal annealing up to 1,100 degrees Celsius has no effect on the bombardment stimulated defect structure.

Vacancies and self interstitials in the near surface region of diamond were formed during argon and carbon ion bombardment of diamond even at bombardment energies less than 1 kilo electron volts. Vacancies and vacancy clusters formed internal surfaces that resembled atomically reconstructed clean diamond surface, while the aggregation of former defects formed edge dislocations.

Disordering in undoped GaAs isotope superlattice structures grown by molecular beam epitaxy on n-type GaAs substrates was investigated using secondary ion mass spectrometry. The results showed that the activation enthalpy of Ga self-diffusivity values was 4 eV. The as-grown superlattice layers were intrinsic and transformed into p-type after anealing. The larger self-diffusivity values were attributed to Si out-diffusion from the substrate.

We describe how the electromagnetic resonance and scattering properties of complex structures of which metallic wire structures are constituents can be studied with multiple scattering theory. The t matrix of individual structures is calculated with our recently developed rigorous equivalent circuit theory in which retardation effects are taken into account. We illustrate our method with the example of a planar periodic array of split ring resonators. The transmission is calculated as a function of frequency. The result is found to agree well with that obtained by a commercial code (COMSOL) but our result is two orders of magnitude faster and requires much less memory. [ABSTRACT FROM AUTHOR]

The processing and performance of Schottky diodes formed from arrays of vertical Ge nanowires (NWs) grown on Ge and Si substrates are reported. The goal of this work is to investigate CMOS compatible processes for integrating NWs as components of vertically scaled integrated circuits, and elucidate transport in vertical Schottky NWs. Vertical phosphorus (P) doped Ge NWs were grown using vapor-liquid-solid epitaxy, and nickel (Ni)-Ge Schottky contacts were made to the tops of the NWs. Current-voltage (I-V) characteristics were measured for variable ranges of NW diameters and numbers of nanowires in the arrays, and the I-V characteristics were fit using modified thermionic emission theory to extract the barrier height and ideality factor. As grown NWs did not show rectifying behavior due to the presence of heavy P side-wall doping during growth, resulting in a tunnel contact. After sidewall etching using a dilute peroxide solution, rectifying behavior was obtained. Schottky barrier heights of 0.3-0.4V and ideality factors close to 2 were extracted using thermionic emission theory, although the model does not give an accurate fit across the whole bias range. Attempts to account for enhanced side-wall conduction due to non-uniform P doping profile during growth through a simple shunt resistance improve the fit, but are still insufficient to provide a good fit. Full three-dimensional numerical modeling using Silvaco Atlas indicates that at least part of this effect is due to the presence of fixed charge and acceptor like traps on the NW surface, which leads to effectively high ideality factors. [ABSTRACT FROM AUTHOR]

Growth of high-density group IV alloy nanowire forests is critical for exploiting their unique functionalities in many applications. Here, the compositional dependence on precursor reactivity and optimized conditions for vertical growth are studied for Si1-xGex alloy nanowires grown by the vapor-liquid-solid method. The nanowire composition versus gas partial-pressure ratio for germane-silane and germane-disilane precursor combinations is obtained at 350 °C over a wide composition range (0.05 ≤ x ≤ 0.98) and a generalized model to predict composition for alloy nanowires is developed based on the relative precursor partial pressures and reactivity ratio. In combination with germane, silane provides more precise compositional control at high Ge concentrations (x > 0.7), whereas disilane greatly increases the Si concentration for a given gas ratio and enables more precise alloy compositional control at small Ge concentrations (x < 0.3). Vertically oriented, non-kinking nanowire forest growth on Si (111) substrates is then discussed for silane/germane over a wide range of compositions, with temperature and precursor partial pressure optimized by monitoring the nanowire growth front using in-situ optical reflectance. For high Ge compositions (x ≈ 0.9), a "two-step" growth approach with nucleation at higher temperatures results in nanowires with high-density and uniform vertical orientation. With increasing Si content (x ≈ 0.8), the optimal growth window is shifted to higher temperatures, which minimizes nanowire kinking morphologies. For Si-rich Si1-xGex alloys (x ≈ 0.25), vertical nanowire growth is enhanced by single-step, higher-temperature growth at reduced pressures. [ABSTRACT FROM AUTHOR]

We consider enhancing the ferromagnetic resonance (FMR) absorption of very thin insulating magnetic films by placing it on top of a dielectric. We find that the signal is enhanced by at least an order of magnitude due to a new nonreciprocal interface resonance that is a mixture of the magnetic surface plasmon mode and a wave guide mode. This resonance occurs over a wide range of thicknesses of the dielectric that is still much less than the wavelength and is made possible by the negative magnetic susceptibility of the magnetic layer. The line width of absorption is reduced by an order of magnitude less than the Gilbert damping parameter. At some frequency, the group velocity of this resonance is negative. Experimentally, very thin yttrium iron garnet (YIG) films are grown on a Gadolinium Gallium Garnet (GGG) substrate which can be considered the dielectric. Our model applies to experiments performed in the YIG/GGG system. Indeed, our picture resolves the disagreement on the magnitude of the spin diffusion lengths obtained with the FMR and the Brillouin scattering techniques. It also provides for a way to make new adaptive thin film miniaturized photonic nonreciprocal devices with low loss. [ABSTRACT FROM AUTHOR]

A study of highly symmetric site-controlled pyramidal In0.25Ga0.75As quantum dots (QDs) is presented. It is discussed that polarization-entangled photons can be also obtained from pyramidal QDs of different designs from the one already reported in Juska et al. [Nat. Photonics 7, 527 (2013)]. Moreover, some of the limitations for a higher density of entangled photon emitters are addressed. Among these issues are (1) a remaining small fine-structure splitting and (2) an effective QD charging under non-resonant excitation conditions, which strongly reduce the number of useful biexciton-exciton recombination events. A possible solution of the charging problem is investigated exploiting a dual-wavelength excitation technique, which allows a gradual QD charge tuning from strongly negative to positive and, eventually, efficient detection of entangled photons from QDs, which would be otherwise ineffective under a single-wavelength (non-resonant) excitation. [ABSTRACT FROM AUTHOR]

Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered material as a uniaxial medium and compare the derived optical parameters to those expected from the effective medium approximation. We also experimentally compare the effect of varying the material outer layer on the homogenization of the composite. Additionally, we introduce a simple empirical method of extracting the epsilon-near-zero point of the nanolaminates from normal incidence reflectance. The results of this study are useful in accurate determination of the hyperbolic material permittivity and in the ability to tune its optical properties. [ABSTRACT FROM AUTHOR]

Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The Snx Zr defect was shown to be dominant across most oxygen partial pressures, with Snn Zr charge compensated by V.. O occurring at partial pressures below 10-31 atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which Snn Zr is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys. [ABSTRACT FROM AUTHOR]

Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The Snx Zr defect was shown to be dominant across most oxygen partial pressures, with Snn Zr charge compensated by V.. O occurring at partial pressures below 10-31 atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which Snn Zr is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys. [ABSTRACT FROM AUTHOR]

We report a theoretical microscopic model to discuss the barocaloric and magnetocaloric effects in the Gd5Si2Ge2 compound based on the recent experimental data by Yuce et al. [Appl. Phys. Lett. 101, 071906 (2012)]. For this purpose, our model Hamiltonian includes three interactions: Zeeman, magnetoelastic, and exchange interactions, considering the magnetic field dependence of phonons entropy. Using this model, the combined magnetocaloric and barocaloric effects were calculated in Gd5Si2Ge2 compound showing satisfactory agreement with the experimental data. Besides, a high entropy change was predicted for simultaneous changes in the applied magnetic field and pressure (the combined magnetocaloric and barocaloric effects). [ABSTRACT FROM AUTHOR]

Polymer-stabilized blue-phase liquid crystal (BPLC) comprising fluorinated compounds with high resistivity and photochemical stability is demonstrated. The Kerr constant, driving voltage, and response time of this BPLC are measured using an in-plane switching liquid crystal cell. At 20 °C, the measured total response time is faster than 0.7 ms and Kerr constant is 2 nm/V2. This fluorinated BPLC material is a promising candidate for next-generation photonic and display devices, because it can be used in active matrix addressed devices. [ABSTRACT FROM AUTHOR]

We report theoretical investigations on the magnetocaloric effect, described by the magnetic entropy change in rare earth--transition metal amorphous systems. The model includes the local anisotropy on the rare earth ions in Harris-Plischke-Zuckermann assumptions. The transition metals ions are treated in terms of itinerant electron ferromagnetism and the magnetic moment of rare earth ions is coupled to the polarized d-band by a local eXchange interaction. The magnetocaloric effect was calculated in DyCo34 system, which presents amorphous sperimagnetic configuration. The calculations predict higher refrigerant capacity in the amorphous DyCo3.4 than in DyCo2 crystal, highlighting the importance of amorphous magnetocaloric materials. Our calculation of the magnetocaloric effect in Dy70Zr30, which presents amorphous asperomagnetic configuration, is in good agreement with the eXperimental result. Furthermore, magnetic entropy changes associated with crystal-amorphous configurations change are estimated. [ABSTRACT FROM AUTHOR]

To study the electromagnetic resonance and scattering properties of complex structures of which metallic wire structures are constituents within multiple scattering theory, the t matrix of individual structures is needed. We have recently developed a rigorous and numerically efficient equivalent circuit theory in which retardation effects are taken into account for metallic wire structures. Here, we show how the t matrix can be calculated analytically within this theory. We illustrate our method with the example of split ring resonators. The density of states and cross sections for scattering and absorption are calculated, which are shown to be remarkably enhanced at resonant frequencies. The t matrix serves as the basic building block to evaluate the interaction of wire structures within the framework of multiple scattering theory. This will open the door to efficient design and optimization of assembly of wire structures. [ABSTRACT FROM AUTHOR]

The development of high-performance visible-light-responsive photocatalytic materials has attracted widespread interest due to their potential applications in the environmental and energy industries. In this work, hierarchical ZnO nanorods films were successfully prepared on the stainless steel mesh substrates via a simple two-step seed-assisted electrodeposition route. Cu2O nanoparticles were then electrodeposited on the surface of ZnO nanorods to form the core-shell heterostructure. The synthesized ZnO/Cu2O nanocomposites were characterized by X-ray diffraction, field-emission scanning electron microscopy, and UV-visible spectrophotometer. Due to the branched hierarchical morphologies and core-shell structure, ZnO/Cu2O nanomaterials show a prominent visible-light-driven photocatalytic performance under the low-intensity light irradiation (40 mW/cm²). The influence of some experimental parameters, such as Cu2O loading amount, ZnO morphologies, the substrate type, and the PH of the Cu2O precursor solution on ZnO/Cu2O photocatalytic performance was evaluated. [ABSTRACT FROM AUTHOR]

We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO2 interface using photoemission, ion scattering, and computational modeling. For standard NO processing of a SiC MOSFET, a sub-monolayer of nitrogen is found in a thin inter-layer between the substrate and the gate oxide (SiO2). Photoemission shows one main nitrogen related core-level peak with two broad, higher energy satellites. Comparison to theory indicates that the main peak is assigned to nitrogen bound with three silicon neighbors, with second nearest neighbors including carbon, nitrogen, and oxygen atoms. Surprisingly, N remains at the surface after the oxide was completely etched by a buffered HF solution. This is in striking contrast to the behavior of Si(100) undergoing the same etching process. We conclude that N is bound directly to the substrate SiC, or incorporated within the first layers of SiC, as opposed to bonding within the oxide network. These observations provide insights into the chemistry and function of N as an interface passivating additive in SiC MOSFETs. [ABSTRACT FROM AUTHOR]

The infrared dielectric property of monoclinic BaTeMo2O9 single crystals is studied by polarized IR reflectance spectra from 20 to 1800 cm-1. Based on the modified Lorentz model, the frequencies, strengths, and dampings of TO modes as well as the orientations of the dipole momenta are determined, agreeing well with Raman spectra and results from First-principles calculation. The observed modes are visually assigned to the specific atoms' motions in the primitive cell based on the theory calculations. A large shift of the internal modes of the anion groups relative to free anion co-ordination polyhedra is observed, which can be used to indicate the distortions of co-ordination polyhedra related to the nonlinear optical properties. Further, the experimental results of the strengths of the oscillators support the elimination and splitting of degenerate modes in free regular polyhedrons. These results offer a way to evaluate the nonlinear optical properties by use of traditional IR reflectivity spectra. [ABSTRACT FROM AUTHOR]