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Imaging and spectroscopy at terahertz (THz) frequencies have become key methods for fundamental studies across the physical sciences. With the emergence of nanoscale materials and devices, holding great promise for photonics, electronics, and communication technologies, the search for THz analysis at the nanoscale arises. Detectorless THz near-field nanoscopy emerged as a versatile method for hyperspectral mapping of light–matter interaction phenomena in bi-dimensional materials and systems. However, it is strongly limited by the weak scattering efficiencies of atomic force microscope (AFM) tips. Here, we experimentally evaluate the performance of unconventional AFM tip shapes to enhance the scattering efficiency, at three frequencies, namely, 2.0, 3.0, and 4.6 THz. The impact of tip geometry is corroborated by numerical simulations. The shorter shank length of the evaluated tips provides a very compelling alternative to commercial tips at frequencies >2 THz. [ABSTRACT FROM AUTHOR]

Yang I et al. i discovered that VO SB I x i sb doping in a NeFe layer coated on a porous nickel cobalt phosphide (NiCoP) electrocatalyst supported by a titanium mesh would reduce the overpotential for both OER and HER.[12] This modified electrocatalyst could be employed as a low-cost bifunctional catalyst to construct both the positive and negative electrodes in an electroyzer.[12] The doping with VO SB I x i sb made the NeFe surface superhydrophilic. While alkaline and PEM electrolyzers are used for commercial-scale hydrogen production, solid-oxide electrolyzers are in the demonstration/pilot-plant stage. In a two-step cycle, a redox material, typically a binary oxide, is reduced to a metallic or oxygen deficient (non-stoichiometric) state at high temperatures and then exposed to water vapor or carbon dioxide or both where the catalyst gets oxidized with the formation of hydrogen and CO. "Global warming of 1.5 °C to 2 °C will be exceeded during the 21st century unless deep reductions in CO SB 2 sb and other greenhouse gas emissions occur in the coming decades" states the United Nations Intergovernmental Panel on Climate Change (IPCC) in its Sixth Assessment Report.[1] In the recent years, IPCC published several reports and presented undisputable evidence associating greenhouse gas accumulation in the atmosphere with global average surface temperature increase and unprecedented changes in the weather patterns and the Earth's ecosystems. [Extracted from the article]

We investigated the dynamics of current-pulse-induced magnetization switching in magnetic tunnel junctions (MTJs) with antiferromagnetically and ferromagnetically coupled synthetic free layers through micromagnetic simulations. We found that a magnetic vortex is formed in thick upper ferromagnetic layers and plays an important role in magnetization switching in both types of synthetic free layers. Furthermore, higher thermal stability is observed in an MTJ with the ferromagnetically coupled free layer at an annealing temperature of 250 °C. [ABSTRACT FROM AUTHOR]

We develop holographic recording techniques for the versatile fabrication of three-dimensional (3D) photonic crystals in photopolymers. We introduce multiplex exposure schemes to overcome the restrictions of four-beam holographic lithography. A three-step exposure process makes it possible to fabricate hexagonal structures with three independent lattice constants. 3D photonic crystals with arbitrary geometry can be created by holographic multiplexing. Next, we extend the holographic lithography to six-beam interference to enable further design flexibility. Thick samples of different photopolymer systems are used for fabricating large-area 3D crystals. Structural properties of the fabricated crystals are investigated in a confocal laser scan setup. [ABSTRACT FROM AUTHOR]

We report the measurement of dwell times of spin polarized Rb atoms on octadecyltrichlorosilane (OTS)- and paraffin-coated surfaces. We find that at a cell temperature of 72 °C the dwell times for OTS- and paraffin-coated surfaces are 0.9±0.1 μs and 1.8±0.2 μs, respectively. Since the relaxation probability on paraffin is almost one order of magnitude smaller than that on OTS, the longer dwell time for paraffin indicates that the average strength of the interactions experienced by Rb atoms while they are inside paraffin is much weaker than while they are inside OTS. [ABSTRACT FROM AUTHOR]

An atomic level micromagnetic model of granular recording media is developed and applied to examine external field-induced grain switching at elevated temperatures which captures nonuniform reversal modes. The results are compared with traditional methods which employ the Landau-Lifshitz-Gilbert equations based on uniformly magnetized grains with assigned intrinsic temperature profiles for M(T) and K(T). Using nominal parameters corresponding to high-anisotropy FePt-type media envisioned for energy assisted magnetic recording, our results demonstrate that atomic-level reversal slightly reduces the field required to switch grains at elevated temperatures, but results in larger fluctuations, when compared to a uniformly magnetized grain model. [ABSTRACT FROM AUTHOR]

We propose an optomechanical structure consisting of a photonic-crystal (holey) membrane suspended above a layered silicon-on-insulator substrate in which resonant bonding/antibonding optical forces created by externally incident light from above enable all-optical control and actuation of stiction effects induced by the Casimir force. In this way, one can control how the Casimir force is expressed in the mechanical dynamics of the membrane, not by changing the Casimir force directly but by optically modifying the geometry and counteracting the mechanical spring constant to bring the system in or out of regimes where Casimir physics dominate. The same optical response (reflection spectrum) of the membrane to the incident light can be exploited to accurately measure the effects of the Casimir force on the equilibrium separation of the membrane. [ABSTRACT FROM AUTHOR]

Crystalline silicon surface passivation by amorphous silicon deposited by three different chemical vapor deposition (CVD) techniques at low (T∼130 °C) temperatures is compared. For all three techniques, surface recombination velocities (SRVs) are reduced by two orders of magnitude after prolonged thermal annealing at 200 °C. This reduction correlates with a decreased dangling bond density at the amorphous-crystalline interface, indicating that dangling bond saturation is the predominant mechanism. All three deposition methods yield excellent surface passivation. For a-Si:H layers deposited by radio frequency plasma enhanced CVD, we obtain outstanding carrier lifetimes of 10.3 ms, corresponding to SRVs below 1.32 cm/s. [ABSTRACT FROM AUTHOR]

There is a class of waveguides problems in which energy is provided by a source distribution of finite extent on the surface of the guide and for which usually the behavior of the acoustic field created is not analytically correlated with the source strength. The present paper aims at providing an analytical model describing the field which can be obtained from such nonuniformly distributed, time-periodic source creating either pressure waves in fluid-filled waveguides or Shear Horizontal waves in isotropic solid plates. This model involves convolution products between appropriate Green's functions and the source stress. A relevant example is finally displayed. [ABSTRACT FROM AUTHOR]

The piezoelectric properties of [001]c poled 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 single crystals were greatly enhanced by controlling their domain configurations. Contrary to the interpretation of charged domain walls being the main contributor to the piezoelectric enhancement, we found that smaller domain size and more neutral domain walls were the main contributors for the piezoelectric enhancement of these multidomain crystals. The properties of 109° neutral domain walls in 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 single crystals were extracted by using a piezoelectric domain wall model. [ABSTRACT FROM AUTHOR]

We report on the interlayer screening effect of graphene using Kelvin probe force microscopy (KPFM). By using a gate device configuration that enables the supply of electronic carriers in graphene sheets, the vertical screening properties were studied from measuring the surface potential gradient. The results show layer-dependence of graphene sheets, as the number of graphene layers increases, the surface potential decreases exponentially. In addition, we calculate the work function-related information of the graphene layers using KPFM. [ABSTRACT FROM AUTHOR]

Optical coupling of nitrogen-vacancy centers in single-crystal diamond to an on-chip microcavity is demonstrated. The microcavity is fabricated from a hybrid gallium phosphide and diamond material system and supports whispering gallery mode resonances with spectrometer resolution limited Q>25 000. [ABSTRACT FROM AUTHOR]

Bi2Sr2CaCu2O8+δ is the only cuprate superconductor that can be made into a round-wire conductor form with a high enough critical current density Jc for applications. Here we show that the Jc(5 T,4.2 K) of such Ag-sheathed filamentary wires can be doubled to more than 1.4×105 A/cm2 by low temperature oxygenation. Careful analysis shows that the improved performance is associated with a 12 K reduction in transition temperature Tc to 80 K, an increase in flux pinning, and particularly a significant enhancement in intergranular connectivity. In spite of the macroscopically untextured nature of the wire, overdoping is highly effective in producing high Jc values. [ABSTRACT FROM AUTHOR]

We show that the generally accepted demagnetizing field corrections are not applicable to the broad class of modern granular magnetic materials, where magnetization reversal occurs via discrete switching of the moments of individual grains, and thus the self-demagnetizing field of a given grain is proportional to the spontaneous magnetization Ms, not to the sample magnetization M. This leads to the fact that the self-demagnetizing field must be considered as a contribution to the coercive field and that the slope of the magnetization variation is higher than the classical demagnetizing field slope. This description of demagnetization processes is confirmed by numerical modeling. [ABSTRACT FROM AUTHOR]

The lattice location of ion implanted antimony in zinc oxide has been determined by means of β- emission channeling from the radioactive 124Sb isotope. Following 30 keV implantation of 124Sb into a single-crystalline ZnO sample to a fluence of 1×1014 cm-2, the angular-dependent emission rate of β- particles around several crystallographic directions was measured with a position-sensitive Si detector. The majority of Sb was found to occupy Zn sites, with the possible fraction on O sites being at maximum 5%–6%. [ABSTRACT FROM AUTHOR]

Based on ab initio atomistic thermodynamics model, the surface adsorption diagram of O/Ni(110) system over a wide range of temperature and pressure conditions has been determined. Different surface phases including oxygen adsorption on reconstructed and unreconstructed substrates are considered. Clean nickel surface, p(2×1)-O and p(3×1)f-O, and bulk oxide phase are found to be the most stable phases under different oxygen chemical potential regions. Our calculations suggest that the unreconstructed (n×1)(n=2,3)-O overlayer and p(3×1)i-O phases are just metastable at the equilibrium condition. These results could effectively solve the debate in different experiments and give a consistent description for the reproducibility of overlayer and p(3×1)i-O reconstructed phases. [ABSTRACT FROM AUTHOR]

Complexes consisting of a vacancy and four oxygen atoms, VO4, were found in oxygen-rich Czochralski silicon wafers subjected to rapid thermal annealing (RTA) at 1250 °C for 30 s in Ar/O2 atmosphere by means of Fourier transform infrared spectroscopy with enhanced sensitivity. An absorption band at 985 cm-1, previously observed only in irradiated Si and assigned to a local vibration mode of VO4, was measured reproducibly in all RTA treated wafers examined. A concentration of about 1.4×1013 cm-3 of thermally induced VO4 was estimated from the integrated intensity of the band at 985 cm-1 using the known calibration factor for interstitial oxygen. [ABSTRACT FROM AUTHOR]

We synthesized a series of polycrystalline YbCd2-xZnxSb2 (x=0, 0.4, 0.8, 1, 1.2, 1.6, and 2) samples and measured their thermoelectric properties. Thermoelectric figure of merit ZT at 700 K is higher than 1.0 for Cd-rich samples (x=0, 0.4, 0.8, and 1.0) and Zn substitute of Cd in YbCd2Sb2 can easily tune carrier concentration and reduce thermal conductivity. When x=0.4, sample exhibits the highest power factor (12–20 μW cm-1 K-2), the lowest lattice thermal conductivity (1.0 W m-1 K-1 at 300 K), highest ZT (1.2 at 700 K), and best “self-compatibility.” The first principles calculations were performed to study the influences of bonding and electronic structures on physical properties. [ABSTRACT FROM AUTHOR]

A density-matrix based theory of transport and lasing in quantum-cascade lasers reveals that large disparity between luminescent linewidth and broadening of the tunneling transition changes the design guidelines to favor strong coupling between injector and upper laser level. This conclusion is supported by the experimental evidence. [ABSTRACT FROM AUTHOR]

From a Raman scattering investigation of folded longitudinal acoustic phonons in zinc-blende CdTe/MgTe superlattices, we demonstrate that this pair of materials displays a large acoustic impedance mismatch Z1/Z2=1.39, which opens promising perspectives for acoustic phonon engineering in semiconductor nanodevices. The determined MgTe sound velocity s=(3.35±0.15)×103 m/s agrees well with ab initio predictions for the same crystalline form. [ABSTRACT FROM AUTHOR]

We report the observation of two distinct modes of rate-dependent behavior during contact cycling tests. One is a higher pull-off force at low cycling rates and the other is a higher pull-off force at high cycling rates. Subsequent investigation of these contacts using scanning electron microscopy (SEM) demonstrates that these two rate-dependent modes can be related to brittle and ductile separation modes. The former behavior is indicative of brittle separation, whereas the latter accompanies ductile separation. Thus by monitoring the rate dependence of the pull-off force, the type of separation mode can be identified during cycling without interrupting the test to perform SEM. [ABSTRACT FROM AUTHOR]

We performed atomistic scale simulations to simulate the heteroepitaxial growth of a film with a 0.62% tensile misfit strain and monitored the stress evolution. The calculated σftf is initially compressive but increases after the first monolayer is completed. We provide theoretical and simulation evidence that this effect is associated with surface stresses. These results demonstrate that wafer curvature measurements lead to unreliable predictions of film stresses when the film is very thin. [ABSTRACT FROM AUTHOR]

The effects of reoxidation on the band structure of N-incorporated SiON films were investigated as a function of thermal treatment in NO and NH3. Reoxidation-associated changes in band gap and valence band offset of the N-incorporated SiON films prepared by sequential thermal annealing in both NO and NH3 were less than those observed for the nitrided film prepared by thermal annealing in only NH3. The differences in band-alignment characteristics of the nitrided films that resulted from use of different nitridation methods were strongly related to the depth distribution of N and the chemical states of N bonded to Si. [ABSTRACT FROM AUTHOR]

The m-plane GaN films grown on LiAlO2(100) by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson–Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN[0001] in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress [variant_greek_epsilon]xx=-0.79% and [variant_greek_epsilon]zz=-0.14% with an out-of-plane dilatation [variant_greek_epsilon]yy=0.38%. This anisotropic strain further separates the energy levels of top valence band at Γ point. The energy splitting as 37 meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature. [ABSTRACT FROM AUTHOR]

Phosphor-free cool white emitting light emitting diodes (LEDs) have been fabricated using a dual stacked InGaN/GaN multiple quantum wells (MQWs) comprising of a lower set of MQWs emitting yellow and an upper set of MQWs emitting blue. The lower set of MQWs incorporates indium-rich InGaN connected-dot nanostructures with a height of ∼1.0 nm in the well. The well is first grown with an InGaN layer serving as the wetting layer, then treated with trimethylindium (TMIn) to initiate nanostructure growth of another InGaN layer to complete the well layer. This gives a broadened yellow emission peak. With the combination of emission from the upper blue emitting InGaN/GaN MQWs subsequently grown, cool white light emission is achieved. The In-rich nanostructures formed during TMIn treatment enhance indium incorporation in InGaN well and also act as effective radiative recombination sites for carriers at the lower set of MQWs. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of pure and Nb-doped TiO2 with anatase structure were calculated using local-density approximation based on the density-functional theory. For the undoped TiO2, the Fermi level locates in the band gap between the conduction band and valence band, while it moves into the conduction band and shows metal-like characteristic after Nb atom was introduced into the TiO2 supercell. The optical absorption coefficients for both compounds are very small in the visible light range. Our calculations provide electronic structure evidence that the Nb-doped anatase TiO2 is a new type transparent conducing metal. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) of titanium dioxide (TiO2) high-κ dielectric films on brominated Ge substrates using titanium tetrachloride and water has been studied. A strong temperature dependence was observed for the TiO2 deposition rate. An accelerated growth rate was measured for the first 15 ALD cycles at 300 °C; this effect is attributed to bromine desorption and resultant deposition on halide-free Ge. Results suggest that TiO2 films were deposited with no interfacial oxide layer at 300 °C. The films were in a crystalline anatase phase at 300 °C, and were amorphous when deposited at 100 °C. [ABSTRACT FROM AUTHOR]

Based on a first-principles approach, we exploit a class of shaped graded materials in which thermal energy is apparently controlled to transfer from a region of lower temperature to a region of higher temperature. This phenomenon, which is in contrast to our common intuition, is indicative of an apparent negative thermal conductivity (ANTC). Further analysis shows that the ANTC is related to a symmetric oscillation of paired thermal conductivities with specific gradation profiles, which are shown to satisfy a sum rule. Such shaped graded materials can serve as good candidates for thermal rectification. [ABSTRACT FROM AUTHOR]

Thin films of ilmenite-hematite solid solution 0.6FeTiO3·0.4Fe2O3 were prepared on α-Al2O3 (001) and (110) single-crystalline substrates. The oxide phases formed in the thin films strongly depended on the oxygen partial pressure (PO2) during deposition. At PO2=1.3×10-3 Pa, regardless of thesubstrate orientation, well-ordered 0.6FeTiO3·0.4Fe2O3 films with R3 symmetry were epitaxially formed. Large saturation magnetization at room temperature was observed in both (001)- and (110)-oriented films. The differences in the magnetization and electrical resistivity curves between the (001)- and (110)-oriented films indicated the anisotropic nature of 0.6FeTiO3·0.4Fe2O3. [ABSTRACT FROM AUTHOR]

We employ a combination of optical and electron-beam lithography to create an atom chip combining submicron wire structures with larger conventional wires on a single substrate. The multilayer fabrication enables crossed wire configurations, greatly enhancing the flexibility in designing potentials for ultracold quantum gases and Bose–Einstein condensates. Large current densities of >6×107 A/cm2 and high voltages of up to 65 V across 0.3 μm gaps are supported by even the smallest wire structures. We experimentally demonstrate the flexibility of the next generation atom chip by producing Bose–Einstein condensates in magnetic traps created by a combination of wires involving all different fabrication methods and structure sizes. [ABSTRACT FROM AUTHOR]

It has been shown earlier that thermodynamic and kinetic driving forces exist for an isolated oxygen defect to segregate to Si:HfO2 interfaces. In the present work, using the first principles calculations, we show that the accumulation of multiple point defects (O vacancies and interstitials) at Si:HfO2 interfaces is also thermodynamically favored and this preference is relatively insensitive to the areal density of interfacial defects. These results indicate that the O point defect chemistry can provide a rationale for the formation of interfacial phases. [ABSTRACT FROM AUTHOR]

Direct domain writing is carried out in single-crystalline stoichiometric LiNbO3 crystals using a scanning probe microscope. The abnormally switched domains with polarization antiparallel to the poling field are observed, and their growth and decay processes are systematically studied. The radius of these domains is proportional to the pulse magnitude while it remains constant as the pulse width varies. These abnormal domains quickly decay, the lifetime of which is linear with the poling pulse magnitude while it stretched exponentially increases with the increasing pulse width. The experimental results are carefully discussed in relation to the reported charge injection model. [ABSTRACT FROM AUTHOR]

ZnO epitaxial films grown by pulsed laser deposition in an ambient of H2 or D2 exhibit qualitatively different electronic properties compared to films grown in vacuum or O2 or bulk single crystals annealed in H2. These include temperature-independent resistivities of ∼0.1 Ω cm, carrier (electron) concentrations in the 1018 cm-3 range, mobilities of 20–40 cm2/V s, and negligible (a few meV) activation energies for conduction. These transport properties are consistent with H (D) forming an ultrashallow donor or conduction band states not achievable by postgrowth annealing in H2. [ABSTRACT FROM AUTHOR]

We determined the critical layer thicknesses for the glide of strain-relaxing dislocations in retrograded semiconductor layers using force balance. For a retro-graded layer, the lattice mismatch varies with distance from the interface y as f=f0+Cfy with sgn(Cf)=-sgn(f0). For a particular combination of f0 and Cf, there may be three different critical thicknesses for which the line tension and glide force of the dislocation are equal. Lattice relaxation by positive glide of grown-in dislocations is favorable for thicknesses in the range hc1hc3. If the grading is sufficiently steep, lattice relaxation will only proceed if h>hc3 [ABSTRACT FROM AUTHOR]

Using Co-decoration technique coupled with in situ scanning tunneling microscope (STM), the evolution of epitaxial graphene was found to preferentially begin at step edges of the silicon carbide surface and occurs with loss of Si and breakdown of C-rich [formula] template, which provides the C source for graphene growth. Interestingly, a new C-rich phase is also formed at the interface and it acts as a buffer layer for graphene from underlying bulk. STM reveals that graphene lies 2.3±0.3 Å above the buffer layer, larger than sp3 C–C bond length (1.54 Å) but shorter than graphite interlayer separation (3.37 Å), suggesting a pseudo-van der Waals interfacial interaction. [ABSTRACT FROM AUTHOR]

We report the synthesis of hierarchically branched semiconducting SnO2 nanowire on metallic Sb-doped SnO2 nanowires by the sequential seeding of multiple nanowire generations with Au nanoparticles as catalysts. Such semiconducting nanowire/metallic backbone complex structures increase the potential functionality of SnO2 nanowires. Branched SnO2 nanowire films are used as sensing materials for high-performance ethanol sensor fabrication. The nanowire sensors show sub-ppm sensitivity and fast response and recovery times at 300 °C. A linear equation relationship between sensitivity and the ethanol vapor concentration was observed. [ABSTRACT FROM AUTHOR]

We present findings on the effect of microstructure on magnetic properties of the epitaxial FePt system. Epitaxial c-axis oriented FePt was synthesized on Si (100) using TiN as a template buffer. The microstructure was progressively varied from a 9 nm nanoparticle system to a 30 nm thick continuous thin film. We found that individual nanoparticles showed higher coercivity than the continuous thin film. Within the nanoparticle regime, coercivity increased with increasing particle size. The highest coercivity of 13 500 Oe was realized for a beadlike microstructure, when the individual nanoparticles just begin to merge to form a continuous thin film. [ABSTRACT FROM AUTHOR]

A technique for evanescent broadside coupling to surface plasmons is described and demonstrated. The technique makes use of a polarization maintaining optical fiber cleaved at a steep angle and positioned near the structure to be excited such that the slow mode of the fiber couples evanescently to the surface plasmon propagating thereon. The technique is applied to excite long-range surface plasmons on a metal stripe supported by a freestanding dielectric membrane. The technique should be useful for coupling to other plasmonic or dielectric waveguides, and for optical wafer probing. [ABSTRACT FROM AUTHOR]

The spatial dynamics of the optical emission from an array of 50×50 individual microplasma devices is reported. The array is operated in noble gas at atmospheric pressure with an ac voltage. The optical emission is analyzed with phase and space resolution. It has been found that the emission is not continuous over the entire ac period, it occurs only twice in each cycle. Each of the observed emission phases shows a self-pulsing of the discharge, with several bursts of emission of a fixed width and repetition rate. Cross-talk between the individual devices can be observed through spatially resolved measurements. [ABSTRACT FROM AUTHOR]

We report a significant enhancement in terahertz emission from the indium nitride (InN) films grown along the a axis (a-plane InN), relative to the InN films grown along the c axis. The primary radiation mechanism of the a-plane InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a axis, which effectively enhances the geometrical coupling of the radiation out of semiconductor. In addition, azimuthal angle dependence measurement shows that the p-polarized terahertz output consists of a large angularly independent component and a weak component with a distinctive fourfold rotation symmetry. [ABSTRACT FROM AUTHOR]

(001) oriented Pt thin films with excellent single crystal quality were epitaxially grown on (001) SrTiO3. The interface relationship was determined and shown to be (001)Pt∥(001)STO and [100]Pt∥[100]STO. Two unexpected “transitions” were found at 138 and 34 K in the evolution of resistivity with temperature as the samples were heated up, which can probably be attributed to phase transitions of the single crystalline SrTiO3. The fact that epitaxial (001) Pt film growth is observed under oxygen plasma is believed to be a result of oxygen ashing of S-containing impurities in the Pt target. [ABSTRACT FROM AUTHOR]

We report rapid crystallization of GeTe–Bi2Te3 mixed layers. The as-deposited (GeTe)1-x(Bi2Te3)x (GBT) layers with x>0.5 are fcc crystalline, while the layers with x<0.5 are amorphous, for cosputter deposition at room temperature. We found that Bi2Te3 significantly enhances the crystallization of the GBT layers. Furthermore, both temperature and minimum time required for crystallization (Tc and tc,min) of GBT layers are smaller than those of (GeTe)1-x(Sb2Te3)x (GST) layers. For example, crystallization of GBT layer with x=0.12 occurs at 155.0 °C within 30.9 ns, which is around 1/3 of 95.7 ns for Ge2Sb2Te5 with Tc=168.5 °C. [ABSTRACT FROM AUTHOR]

This letter presents direct evidence for the existence of the same inherently polar one-dimensional (1D), displacive disorder in BaTaO2N as occurs in paraelectric BaTiO3 as well as in doped BaTiO3 relaxor ferroelectric systems. The inherently polar, off-center and oppositely directed displacements of Ta and neighboring O/N ions along <001> give rise to 1D polar nanoregions (PNRs) and are responsible for the dielectric properties of BaTaO2N. A bond valence sum analysis of the underlying crystal chemistry of BaTaO2N shows clearly that O/N ordering is not directly responsible for inducing the observed 1D PNRs. [ABSTRACT FROM AUTHOR]

Electrodynamical properties of two-dimensional Bragg resonators of planar geometry are studied in the frame of the geometrical-optical approach and in three-dimensional simulations. Results of the theoretical analysis are corroborated by data obtained in “cold” microwave measurements. Formation of the high-Q eigenmodes in the vicinity of the Bragg resonance frequency has been demonstrated. [ABSTRACT FROM AUTHOR]

We investigated charged defects on an n-GaAs(110) surface using light-modulated scanning tunneling spectroscopy. Tunneling via a single defect-induced gap state under photoillumination was observed for the isolated atomic defects. Screened Coulomb potentials induced around a charged Ga vacancy and a step edge were visualized, for the first time, with a nanometer spatial resolution. Furthermore, the charge states of the individual defects were determined on the atomic level. [ABSTRACT FROM AUTHOR]

Self-assembling (SA) conditions of 1O4Sr tetrahedral clusters in ZnTe:(Sr, O) with the Sr concentration of up to 0.02 and in the ultradilute oxygen limit are represented. The cause of SA is a decrease of the strain energy after the formation of the clusters. SA occurs at temperatures of 573, 773, and 973 K if the Sr contents reach 1.23×10-4, 1.26×10-3, and 4.97×10-3, respectively. At the melting temperature of ZnTe, SA is absent at the considered Sr and oxygen concentrations. A temperature when all oxygen atoms are in clusters depends on the Sr and oxygen contents. [ABSTRACT FROM AUTHOR]

We report the postfabrication alignment of multiple microcavity resonances in silicon photonic-crystal (PhC) slabs using laser-pumped thermal tuning. The thermal gradient resulting from a focused laser spot was used to differentially tune the resonant wavelengths of two microcavities spaced about 50 μm apart. The resonant wavelengths could be brought closer together, over a tunable range of more than 5 nm. A cross over in the resonant wavelengths was demonstrated, showing that two microcavities can be tuned to the identical wavelength. The results show that differential thermal tuning can be used to remove slight fabrication differences in nominally identical microcavities, relaxing the fabrication tolerances that will be required to realize coupled-resonator structures in PhCs. [ABSTRACT FROM AUTHOR]

The toughness of Fe-based bulk metallic glasses (BMGs) has been significantly improved via systematic changes in chemistry. Chemistry changes were selected based on their likely effects on critical elastic constants shown to affect plasticity/toughness in various BMGs, in addition to their recently discovered effects on chemical bonding in these Fe-based systems. The fracture energy obtained on notched toughness samples tested in mode I was correlated with chemistry-induced changes to Poisson’s ratio ν and the ratio of the elastic shear modulus μ to the bulk modulus B, as was the strain energy at fracture for smooth cylindrical compression samples that failed under mode II conditions. Fractographic observations correlate well with the observed increases in toughness. [ABSTRACT FROM AUTHOR]

The dynamics of spontaneous emission from GaAs slabs with photonic crystals etched into them are investigated both theoretically and experimentally. It is found that the intensity of spontaneous emission decreases significantly and that photonic crystals significantly shorten the lifetime of emission. The mechanics of enhancement and the reduction of emission from photonic crystals are analyzed by considering the surface recombination of GaAs. The measured and calculated lifetimes agree at a surface recombination velocity of 1.88×105 cm/s. [ABSTRACT FROM AUTHOR]

A spin-polarized vertical cavity surface emitting laser, with InAs/GaAs self-organized quantum dots as the active gain media, has been fabricated and characterized. Electron spin injection is achieved via a MnAs/GaAs Schottky tunnel contact. The laser is operated at 200 K and, at this temperature, the degree of circular polarization in the output is 8% and the maximum threshold current reduction is 14%. These effects are not observed in identical control devices with nonmagnetic contacts. [ABSTRACT FROM AUTHOR]