Photo-induced Magnetic bubbles in the spin glass Alloy Fe2SnTe4

The ternary material Fe₂SnTe₄ is an amorphous metallic alloy that exhibits spin glass behavior with a freezing temperature of T_f = 12 K. When this material is cooled well below the spin glass freezing temperature (T = 5 K) and placed in a magnetization field, the zero-field-cooled spin glass state has been observed to absorb ultraviolet radiation with the concomitant generation of a magnetic bubble on the surface of the material. The photo-induced magnetic bubbles are detected via magnetization measurements with a superconducting SQUID susceptometer. Photomagnetic experiments are reported on the zero-fieldcooled and field-cooled specimens. Each of these experiments results in the generation of a magnetic bubble in the material.     

Solubility and point defect-dopant interactions in gallium arsenide—III: Germanium-doping

The form of the solubility curves for VPE and LPE grown material are rationalised using a thermodynamic model which predicts that compensation of donors in VPE material is due to the donor-gallium vacancy complex Ge_Ga V^?_ga whereas, in LPE material, the dominant acceptor making the material p type is the arsenic substituted state Ge^?_As. Mass action constants for the incorporation reactions for these entities and for the donor Ge⁺_Ga are obtained. The compensation ratio in crystals grown from a congruent melt is predicted to be N_D/N_A ~ 5.9, and the transition to p type conductivity as one grows from Ga-rich solutions at progressively lower temperature is shown to occur at less than 100°C below the congruent melting point so that all LPE material should be p type. The superlinear behaviour of the total-germanium solubility curve at very high doping levels is postulated to be due to the formation of neutral Ge_GaGe_As pairs.     

Antiferromagnetism of quasi two-dimensional manganese stearate

The magnetic properties of manganese stearate, a highly two-dimensional magnetic material, are found to be changed considerably when it is synthesized by a new procedure. Whereas earlier samples behaved like weak-ferromagnets with ordering temperatures about 5 K, the new material is an antiferromagnet with T_n = 10 K. The reason may be a change in the crystal structure.     

Synthesis,photophysical and electro-optical properties of bis-carbazolyl methane based host material for pure-blue phosphorescent OLED

A new high triplet-energy host material, 9-(4-(bis(9-ethyl-9H-carbazol-3-yl)methyl)phenyl)-9H-carbazole (bis-CMPC), was synthesized and its device performance of phosphorescent organic light-emitting diode was investigated. This host material showed a high triplet energy (～2.95 eV) and good thermal stability. Highly efficient pure-blue PHOLED was obtained when employing bis-CMPC as the host material and bis((3,5-difluoro-4-cyanophenyl)pyridine) iridium picolinate as the guest material. The maximum external quantum efficiency of the device reached as high as 13.3% with a pure-blue color coordinate of (0.14, 0.21).     

Regularities of ion-electron emission of one-dimensional carbon-based composite material

The temperature dependences of the ion-electron emission yield γ(T), the crystal structure, and morphology of a surface layer of a carbon-based KUP-VM composite material under high-dose irradiation with N ₂ ⁺ 30 keV ions have been investigated. The complex two-stage nature of the dependence γ(T) is caused by the processes of dynamic annealing of radiation damage in structural components of a composite material.     

Structural and electrical properties of LiCo3/5Cu2/5VO4 ceramics

The LiCo_3/5Cu_2/5VO₄ compound is prepared by a solution-based chemical method and characterized by the techniques of X-ray diffraction, scanning electron microscopy and complex impedance spectroscopy. The X-ray diffraction study shows an orthorhombic unit cell structure of the material with lattice parameters a=13.8263 (30) Å, b=8.7051 (30) Å and c=3.1127 (30) Å. The nature of scanning electron micrographs of a sintered pellet of the material reveals that grains of unequal sizes (～0.2–3 μm) present an average grain size with a polydisperse distribution on the surface of the sample. Complex plane diagrams indicate grain interior and grain boundary contributions to the electrical response in the material. The electrical conductivity study reveals that electrical conduction in the material is a thermally activated process. The frequency dependence of the a.c. conductivity obeys Jonscher’s universal law.     

Love wave propagation in functionally graded piezoelectric material layer

An exact approach is used to investigate Love waves in functionally graded piezoelectric material (FGPM) layer bonded to a semi-infinite homogeneous solid. The piezoelectric material is polarized in z-axis direction and the material properties change gradually with the thickness of the layer. We here assume that all material properties of the piezoelectric layer have the same exponential function distribution along the x-axis direction. The analytical solutions of dispersion relations are obtained for electrically open or short circuit conditions. The effects of the gradient variation of material constants on the phase velocity, the group velocity, and the coupled electromechanical factor are discussed in detail. The displacement, electric potential, and stress distributions along thickness of the graded layer are calculated and plotted. Numerical examples indicate that appropriate gradient distributing of the material properties make Love waves to propagate along the surface of the piezoelectric layer, or a bigger electromechanical coupling factor can be obtained, which is in favor of acquiring a better performance in surface acoustic wave (SAW) devices.     

Characterisation of GaN–In x Ga1−x N quantum-well lasers

An efficient analytical model to calculate the optical gain of the quantum-well laser of the GaN–In _x Ga_1?x N material system is used in this paper. Based on the anisotropic effective mass theories, empirical formulas delineating the relations between optical gain, emission wavelength, well width and material compositions are obtained for such a quantum-well lasers.     

Molecular dynamics investigations on polishing of a silicon wafer with a diamond abrasive

During the final stages of polishing silicon wafers, much of the interactions between silicon and diamond abrasive takes place at the silicon asperities. These interactions, leading to material removal, were investigated in a MD simulation of polishing of a silicon wafer with a diamond abrasive under dry conditions. Simulations were conducted with silicon asperities of different geometries, different abrasive configurations, and polishing speeds. Under the conditions of polishing, the silicon atoms from the asperities were found to bond chemically to the surface of the diamond abrasive. Continued transverse motion of the diamond abrasive (relative to the silicon asperity) leads to tensile pulling, necking, and ultimate separation of the silicon asperity material instead of conventional material removal in polishing (chip formation) involving cutting/ploughing, which takes place in the absence of chemical bonding between the abrasive and the asperity material. This phenomenon has not been reported previously in the literature. The thrust and cutting forces initially increase due to the increase in the number of asperity atoms affected finally reaching a maximum. This is followed by a decrease of these forces due to tensile pulling and formation of individual strings followed by ultimate separation or breakage of the final string. The ratio of thrust force (F _z ) to the cutting force (F _x ), i.e. |(F _z /F _x )| was found to increase continuously to a maximum of ～0.8 followed by continuous decrease to ～0.25. This is in contrast to a more or less constant value of ～2 in the case of tools with rounded radii or tools with large negative rake angles, where material is removed in the form of chips ahead of the tool. Three regions of the asperity have been identified that are useful in the development of a phenomenological model for polishing that enables computation of material removal rates: (1) the region directly in front of the abrasive for which the probability of the removal of an asperity atom is close to unity, (2) the distant region where this probability is nearly zero, and (3) an intermediate region from which the probability of removal is close to half.     

Structuring of material parameters in lithium niobate crystals with low-mass, high-energy ion radiation

Ferroelectric lithium niobate crystals offer a great potential for applications in modern optics. To provide powerful optical components, tailoring of key material parameters, especially of the refractive index n and the ferroelectric domain landscape, is required. Irradiation of lithium niobate crystals with accelerated ions causes strong structured modifications in the material. The effects induced by low-mass, high-energy ions (such as ³He with 41?MeV, which are not implanted, but transmit through the entire crystal volume) are reviewed. Irradiation yields large changes of the refractive index ??n, improved domain engineering capability within the material along the ion track, and waveguiding structures. The periodic modification of ??n as well as the formation of periodically poled lithium niobate (PPLN) (supported by radiation damage) is described. Two-step knock-on displacement processes, ³He??Nb and ³He??O causing thermal spikes, are identified as origin for the material modifications.     

Volume-of-fluid algorithm with different modified dynamic material ordering methods and their comparisons

Volume-of-fluid (VOF) interface reconstruction methods are used to define material interfaces to separate different materials in a mixed cell. These material interfaces are then used to evaluate transport flux at each cell edges in multi-material hydrodynamic calculations. Most of the VOF interface reconstruction methods and volume transport schemes rely on an accurate material order unique to each computational cell. Similarly, to achieve overshoot-free volume fractions, a non-intersecting interface reconstruction procedure has to be performed with the help of a ‘material-order list’ determined prior to interface reconstruction. It is, however, the least explored area of VOF technique especially for ‘onion-skin’ or ‘layered’ model. Also, important technical details how to prevent intersection among different material interfaces are missing in many literature. Here, we present an efficient VOF interface tracking algorithm along with modified ‘material order’ methods and different interface reconstruction methods. The relative accuracy of different methods are evaluated for sample problems. Finally, a convergence study with respect to mesh-size is performed.     

Effect of lattice constant on band-gap energy and optimization and stabilization of high-temperature In x Ga1?x N quantum-dot lasers

We analyze the effect of the lattice constant on the band-gap energy of In _x Ga_1?x N and optimize the structure of the device with a separate-confinement heterostructure. To vary the lattice constants, we change the In molar fraction, which permits us to investigate a wide range of the band gap of the active material employed in diode lasers. In _x Ga_1?x N is a promising active material for high-performance 1.55???m quantum-dot lasers due to its excellent band-gap-energy stability with respect to temperature variations. The band gap of In _x Ga_1?x N decreases from 3.4 to 0.7?eV, and the necessary band gap can be achieved by changing the lattice parameters depending on the device application. It has been found that In_0.86Ga_0.14N can be a promising material for emitting light at a wavelength of 1.55???m.     

Graded finite element simulation of thermal stress in inhomogeneous high-Tc superconductor

YBa₂Cu₃O_y is an orthotropic material with different material properties in a, b and c directions, such as Young’s modulus, coefficient of thermal expansion (CTE), and thermal conductivity. It is assumed that the material properties of inhomogeneous high temperature superconductor (HTS) vary with different height coordinate and temperature. A model is presented in this paper to calculate the thermal stress of inhomogeneous HTS when temperature decreases from ambient to operating conditions (cryogenic temperatures). By fitting a second order polynomial to the experimental data, value of the material properties of inhomogeneous HTS can be obtained. Then, through the proposed graded finite element method, the coupled thermo-mechanical equations were solved numerically. The numerical results show that the temperature profiles distribute the function of time after soaking. It is notable that the temperature profile reaches steady in a very short period of time, so the thermal stress suddenly increases to a very high level for a bulk superconductor. It is also shown that the closer to the sample internal region it is, the larger the heat fluxes are. Besides, the maximum tensile stresses, i.e. the peeling stresses, occur near bottom corner of inhomogeneous HTS. It is intended that the model presented in this paper could be useful to researchers who are interested in mechanical properties of inhomogeneous HTS.     

Epitaxially stabilized AgGaSe2 for high-efficiency spin-polarized electron source

High-quality spin-polarized electron source (SPES) is of fundamental importance in the investigation of spin-dependent phenomena. Generally speaking, an ideal material for SPES application should have both large spin–orbit and positive crystal-field splitting. Currently, almost all sources in use with accelerators are based on photoemission from GaAs and related materials such as strained GaAs grown on GaAsP or InGaAs grown on GaAs. Nevertheless, the reduced critical layer thickness of these strained films leads to poor material quality and, consequently, low quantum efficiency. Besides other ordered ternary semiconductor compounds, tetragonal chalcopyrite ternary compounds have also been considered. However, since all these compounds have zero or negative crystal-field splitting, the achieved polarization and quantum efficiency are rather low. Here we propose a new material, AgGaSe₂ in the CuAu phase, as a high-quality SPES. We show that it is possible to grow epitaxially strain-free AgGaSe₂ in the CuAu phase on ZnSe substrate. Since this material has a direct-band gap, a large spin–orbit splitting, as well as a large positive crystal-field splitting, it is predicted to be a promising material for SPES with 100% spin polarization.     

Application of a model of nonlinear history-dependent magnetic behavior for inductance estimation of a microinductor

This paper presents a method for the numerical inductance calculation of a passive electromagnetic inductive device using cores made of a nonlinear magnetic material. The material model used for this purpose describes the nonlinear magnetic behavior by a set of differential equations. The coupled implicit system of Maxwell equations and material model equations is solved by a simplified algorithm which shall be explained while applied to a new design of a microinductor, the so called I-inductor.     

Trends in surface roughening: analysis of ion-sputtered GaAs(110)

The effects of diffusion kinetics on surface roughness were investigated by measuring the dependence of surface width and step density on the amount of material removed for GaAs(110) sputtered at different temperatures (T). Surfaces after the removal of ten monolayers of material at 625 K were rougher on a small scale than those at 725 K, but they were smoother on a large scale. The increased large-scale roughness at high T was caused by increased diffusion on terraces and along step-edges, but insufficient cross-step transport. The high step-density created at low T enhanced cross-step transport. This mechanism, first proposed for the re-entrant layer-by-layer growth, is expected to cause the long-range roughness to increase with T for many solid surfaces after substantial sputtering or deposition over a certain range of T.     

An overlooked electrostatic force that acts on a non-charged asymmetric conductor in a symmetric (parallel) electric field

Usually, when a material that has charge Q is placed in an electric field E, an electrostatic force F = QE acts on the material. This force does not act on a non-charged material. Nevertheless, when a non-charged material is placed in a convergent field, another electrostatic force acts. This force is called the gradient force. If the material is small and the shape is a sphere, the gradient force can be calculated by an approximate formula, but it cannot be calculated for other shapes. In this paper the gradient force that acts on a symmetric rod conductor in a convergent (asymmetric) field was simulated by an axis symmetry finite difference method.Under same simulation conditions without the next two points, the shape of the conductor and the form of the field were reversed. The shape of the conductor was changed into an asymmetric shape (e.g. bat shape), and the form of the field was changed into a symmetric (parallel) one. The electrostatic force that acts on the asymmetric conductor in the symmetric (parallel) field was simulated. It was found that approximately the same intensity force as in the first simulation also acts on this conductor. This force is thought to be an overlooked electrostatic force. I provisionally call it the asymmetric force in this paper.The asymmetric force with differently shaped conductors was simulated and it was found that the asymmetric force was maximized for a cup shaped conductor.Finally, the asymmetric force with the cup shaped conductor in normal and reversed parallel (symmetric) fields was simulated, and it was confirmed that the asymmetric force remains the same in both fields.     

Gray photorefractive polymeric optical spatial solitons

We show that gray spatial optical solitons are possible in biased photorefractive polymers under steady-state conditions. We find that for a given material parameter the absolute value of a gray photorefractive polymeric soliton's phase decreases with an increase in the beam's grayness, whereas it increases with the material parameter for a given beam's grayness and that the full width half maximum (FWHM) of the gray soliton beam's intensity increases with the beam's grayness when the normalized background intensity and the material parameter are fixed and decreases with an increase in the normalized background intensity when the material parameter is fixed. On the other hand, we also show that N coupled beam evolution equations in biased photorefractive polymers can exhibit multicomponent gray solitons. These multicomponent gray solitons can be obtained provided that the N coupled beams share the same polarization, wavelength, and are incoherent with one another. The characteristics and stability properties of these multicomponent gray solitons are also discussed in detail.     

Far infrared absorption studies of high Tc superconducting material YBa2Cu3O7−x

The high Tc superconducting material YBa₂Cu₃O_7−x has been studied for its absorption in the FIR region. Measurements have been carried out using a Fourier Transform Infrared (FTIR) spectrophotometer at different temperatures above and below Tc. Observed bands are examined in the light of theoretical calculations based on different models. Certain IR absorption bands show screening effects in the measurements below Tc. Experimental values for observed IR bands are compared with the work of other authors and the bands are assigned to different IR active modes of vibration of the material.     

Mechanical properties of superhard diamondlike BC5

Using first-principles calculations, we systematically studied the mechanical properties and electronic structure of the recently synthesized diamondlike BC₅. Our calculated bulk modulus B, shear modulus G, elastic constant c₄₄, and theoretical hardness H confirm that BC₅ is an ultraincompressible and superhard material. Also, it exhibits mechanical stability and metallic features. Electronic structures show that a strong covalent bond network through sp³ hybridization is the origin of the excellent mechanical properties of BC₅. Our results show that BC₅ has good prospects in electronic application as a superhard material.