Chromium and cobalt diffusion in a ZnSe1 ? x S x solid solution

ZnSe_{1 ? x} S _x (1 ?? x ?? 0) crystals are grown from the vapor of binary components in a closed horizontal system. The ZnSe_{1 ? x} S _x crystals doped with chromium and cobalt are prepared by post-growth diffusion. Their absorption spectra are studied depending on the composition of the solid solution and the doping level. The diffusion coefficients of chromium and cobalt at the temperature 1040°C and their dependence on composition are determined.     

Specific features of plastic relaxation of a metastable Ge x Si1 − x layer buried between a silicon substrate and a relaxed germanium layer

Heterostructures Ge/Ge _x Si_{1 ? x} /Si(001) grown by molecular beam epitaxy have been investigated using atomic scale high-resolution electron microscopy. A germanium film (with a thickness of 0.5–1.0 μm) grown at a temperature of 500°C is completely relaxed. An intermediate Ge_0.5Si_0.5 layer remains in a strained metastable state, even though its thickness is 2–4 times larger than the critical value for the introduction of 60° misfit dislocations. It is assumed that the Ge/GeSi interface is a barrier for the penetration of dislocations from a relaxed Ge layer into the GeSi layer. This barrier is overcome during annealing of the heterostructures for 30 min at a temperature of 700°C, after which dislocation networks having different degrees of ordering and consisting predominantly of edge misfit dislocations are observed in the Ge/GeSi and GeSi/Si(001) heteroboundaries.     

Miscibility of In x Ga1−x As alloys: a study using atomistic simulations

Atomistic simulations are used in combination with the two potential energy functions, namely, the Valence Force Field (VFF) model and the Tersoff model, to study the solution thermodynamics of In _x Ga_1?x As alloy. The simulation data, in the form of a T ? x diagram, is contrasted with the results obtained by using the Ho and Stringfellow approach. It is observed that for the VFF model, the upper critical solution temperature obtained from simulation data is approximately 850 K, which is higher than the 729 K predicted by the Ho and Stringfellow treatment. The composition range for which the two-phase heterogeneous region exists is wider than that predicted by the Ho and Stringfellow approach. The Tersoff model predicts a complex miscibility diagram, where the 850 K temperature corresponds to the approximate ‘eutectic’ temperature. Further improvement of model predictions may be made possible by investigation of temperature and composition dependent interaction parameter in a modified regular solution theory, and investigation of non-random, non-ideal solution models in the Ho and Stringfellow treatment, development of temperature dependent VFF model parameters and adjustment of Tersoff model parameters to account for longer range interactions which exist at temperatures above 850 K. The miscibility diagram constructed using the Tersoff model simulation data can be used to provide information on the phase stability and equilibrium Indium content at any given temperature for the crystalline solid solution.     

Electronic and magnetic properties of a new 2D diluted magnetic semiconductor La1 − x Ba x Zn1 − x Mn x AsO from Ab initio calculations

Very recently, on the example of hole- and spin-doped semiconductor LaZnAsO, quite an unexpected area of potential applications of quasi-two-dimensional 1111-like phases was proposed (C. Ding et al., Phys. Rev. B 88, 041102R (2013)) as a promising platform for searching for new diluted magnetic semiconductors (DMSs). In this work, by means of the ab initio calculations, we have examined in detail the electronic and magnetic properties of LaZnAsO alloyed with Ba and Mn. Our results demonstrate that Ba or Mn doping transforms the parent non-magnetic semiconductor LaZnAsO into a non-magnetic metal or a magnetic semiconductor, respectively. On the other hand, the joint effect of these dopants (i.e., co-doping Ba + Mn) leads to transition of La_0.89Ba_0.11Zn_0.89Mn_0.11AsO into the state of magnetic metal, which is formed by alternately stacked semiconducting non-magnetic blocks [La_0.89Ba_0.11O] and metallic-like magnetic blocks [Zn_0.89Mn_0.11As].     

Elastic stress fields caused by a dislocation in Ge x Si1−x /Si film-substrate system

The elastic stress fields caused by a dislocation in Ge_xSi_(1-x) epitaxial layer on Si substrate are investigated in this work. Based on the previous results in an anisotropic bimaterial system,the image method is further developed to determine the stress field of a dislocation in the film-substrate system under coupled condition. The film-substrate system is firstly transformed into a bimaterial system by distributing image dislocation densities on the position of the free surface. Then,the unknown image dislocation densities are solved by using boundary conditions,i.e.,traction free conditions on the free surface. Numerical simulation focuses on the Ge0.1Si0.9/Si film-substrate system. The effects of layer thickness,position of the dislocation and crystallographic orientation on the stress fields are discussed. Results reveal that both the stresses σxx,σxz at the free surface and the stress σxy,σyy,σyz on the interface are influenced by the layer thickness,but the former is stronger. In contrast to the weak dependence of stress field on the crystallographic orientation the stress field was strongly affected by dislocation position. The stress fields both in the film-substrate system and bimaterial system are plotted.     

Microwave properties of film Ba x Sr1 ? x TiO3 ferroelectric variconds with a magnesium-containing additive

The electrophysical properties of bulk ceramics based on Ba _x Sr_{1 ? x} TiO₃ solid solutions with a Mg-containing additive and planar variconds based on ferroelectric films obtained by the ion-plasma sputtering of targets with different elemental compositions are studied. Controllability n(U) = C(0)/C(U) and the dielectric loss tangent (tan??) of ferroelectric variconds are measured as functions of the elemental composition of the ferroelectric. The figure of merit of the variconds is estimated, and the film composition providing the best electrophysical parameters is determined.     

On the nature of a lattice vibrational mode at a frequency of 135 cm−1 in Hg1 − x Cd x Te alloys

The vibrational spectrum of a cadmium impurity atom in the HgTe crystal has been calculated using the microscopic theory of lattice dynamics in the approximation of a low impurity concentration. Within this theory, the behavior of the local and quasi-local modes induced upon substitution of the lighter Cd atom for the Hg atom in the region of the zero or very low one-phonon density of states in the HgTe crystal has been considered. It has been found that, apart from the local mode at a frequency of 155 cm^?1, the calculated vibrational spectra exhibit a weak (but clearly pronounced) feature at a frequency of 134 cm^?1, which coincides with the experimentally observed vibrational mode (the “minicluster” mode) at a frequency of 135 cm^?1 in the Hg_{1 ? x} Cd _x Te (x = 0.2–0.3) alloys at 80 K.     

LaAg x In1−x

The structures of LaAg _x In_1–x alloys withx=0.75, 0.89 are determined by neutron diffraction on powder samples. The space group isI4/mmm (D _4h ^/17 ). The lattice constants splitting, the order parameter and the mean square vibrational amplitudes of the atoms are given in the temperature range from 20 KT300 K.     

Pressure-induced non-linear optical properties in a wurtzite GaN/Al x Ga1− x N strained quantum dot

The effects of hydrostatic pressure on the exciton ground-state binding energy and the interband emission energy in a GaN/Al _x Ga_{1??? x} N quantum dot are investigated. The effects of strain and the internal field due to spontaneous and piezo-electric polarizations are included in the Hamiltonian. Numerical calculations are performed using variational procedure within the framework of single-band effective-mass approximation. The dependence of non-linear optical processes on the dot sizes is brought out in the influence of pressure. Pressure-induced optical properties are obtained using the compact density matrix approach. The effects of hydrostatic pressure on the linear, third-order non-linear optical absorption coefficients and the refractive index changes of the exciton as a function of photon energy are calculated. Our results show that the effects of pressure and the geometrical confinement have great influence on the optical properties of GaN/Al _x Ga_{1??? x} N dot.     

Dynamics of a quantum particle in a static modulated magnetic field B=(0,0,B/cosh ((x−x 0)/δ))

Quantum motion of a particle with its massm and its chargee>0 in thex–y plane under the influence of the static unidirectionally modulated magnetic fieldB=(0,0,B/cosh²((x–x ₀)/)) is studied in this paper. We solved the single-particle problem exactly. Expressions for eigenenergies and eigenfunctions are found. Several physical phenomena are described: the energy spectrum separates into two parts which we call a discrete part and a continuous part—the discrete part of the spectrum corresponds with those states states which describe localized behavior in the direction of the field modulation; these states are extended in the perpendicular direction; the effective mass of this quasi-one-dimensional motion is found to be negative and dependent on the discrete quantum numbern—the states corresponding to the continuous part of the energy spectrum are found to be of two types: the reflection states, which are extended only in that part of thex–y plane where the effective potential barrier is small, and the states describing overbarrier motion in the whole plane; there exists a minimum of the energy for the states from this part of the spectrum which corresponds with a nonzero momentum of the particle motion in they-direction and almost zero momentum for thex-direction motion; there exists twofold degeneracy for those states from the continuous part of the spectrum for which their energy is lower than a certain value.     

Adsorption of carbon monoxide on Si x Ge4– x (x = 0–4) nano-clusters: a hybrid meta density functional study

Theoretical study of carbon monoxide adsorption on Si _x Ge_{4 ? x} (x = 0–4) nano-clusters has been carried out using advanced hybrid meta density functional method of Truhlar (MPW1B95). MG3 semi-diffuse (MG3S) and correlation consistent valence basis sets with relativistic core potential were employed to improve the results. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational frequency changes occur in the bridge structures while the most stable structures occur when CO adsorbs on one silicon atom in a flat surface. The changes of spin densities arising through bridged structures with higher spin multiplicities were rationalized. Adsorption energies of CO on one Si atom are by far more negative than the corresponding value for on Ge atom, at the highest being nearly ?77 and ?35 kJ mol^?1. Comparison was made of adsorbed CO bridging neighbouring and diagonal Si atoms and the former was more stable, having adsorption energy of nearly ?77 kJ mol^?1. Flat surfaces adsorb CO more favourably. Exhaustive vibrational frequency analyses were performed to confirm the local minima energy of all optimized structures.     

Optical properties and structure of ultradispersed particles of CuInSe2x Te2(1−x) in a silicate glass matrixin a silicate glass matrix

We investigate silicate glasses that contain nanodimensional particles of the ternary semiconductor compounds CuInSe₂ and CuInTe₂ and the solid solution CuInSeTe. Based on the data of x-ray examination, it is assumed that the particles of the indicated compounds have a cubic lattice rather than the tetragonal one typical of these compounds in a macroscopic state. In the spectra of optical absorption of the glasses (irrespective of the dimensions of the particles) there is a band at λ_max ≈ 550 nm which can be associated with partial oxidation of copper on the surface of the glasses. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 350–354. May–June, 2000.     

Negatron effects in CdSe1 − x Te x and ZnS1−x Se x films

Various negatron effects in films of alloys of II–VI compounds deposited from solutions as a function of the deposition mode and heat treatment are studied. It is found that the negative photocapacitance effect, which was first discovered in ZnS_1?x Se _x films, and the slowly relaxing negative photoelectric effects, which are caused by the transition of electrons located in a nanoscale surface layer from the shallow energy levels of trapping centers to deeper levels with a lower polarizability and by the presence of nanoscale clusters in these materials, which play the role of a “reservoir” for minority charge carriers, occur according to a single mechanism. A model to explain the basic laws of negative photoconductivity in CdSe_{1 ? x} Te _x films deposited from a solution is proposed. Negative residual conductivity is explained in terms of double-barrier relief model, while negative differential photoconductivity is attributed to the presence of nanoscale electric domains.     

Variations of the band gap of Hg1 ? x Cd x Te solid solutions in response to a magnetic field

The optical transmission spectra of Hg_{1 ? x} Cd _x Te epitaxial layers with a magnetization gradient have been investigated experimentally. The magnetization gradient has been artificially created by the opposite arrangement of the poles of the magnets. The possibility of transforming the shape of the spectral dependences of the optical transmission of the HgCdTe films after their exposure to a magnetic field has been demonstrated. Assumptions about the mechanism underlying this phenomenon have been made.     

a－Si：H／a－SiC＿x：H超晶格的界面特性

报道等离子体化学汽相沉积法制备的ａ－Ｓｉ：Ｈ／ａ－ＳｉＣ：Ｈ超晶格的蓝移现象，用小角度Ｘ射线衍射确定超晶格的界面陡度。通过红外测量和常数光电流测量发现，超晶格界面附近存在较高浓度的Ｈ和较多的Ｓｉ－Ｃ键，界面Ｈ的热稳定性较差，界面缺陷态密度为１．２×１０￣（１１）ｃｍ￣（－２）。     

Modeling of a structural phase transition in La2−x SrxCuO4

The structural, vibrational, and elastic properties of La₂CuO₄ are calculated using a model for calculating the energy of the crystal based on interionic potentials with the multiparticle Jahn-Teller contribution included explicitly. The microscopic reasons for the structural instability of the La₂CuO₄ lattice relative to rotations of the oxygen octahedra are investigated. A structural phase transition from the orthorhombic phase (space group D _2h ¹⁸ ) into the tetragonal phase (space group D _4h ¹⁷ ) under hydrostatic compression of an La_2−x Sr_xCuO₄ crystal is modeled. The (P,x) structural phase diagram for La_2−x Sr_xCuO₄ is constructed. Fiz. Tverd. Tela (St. Petersburg) 41, 1096–1102 (June 1999)     

An In4(Se3)1−x Te3x solid solution as a material for absorption optical filters

We suggest using crystals of the In₄(Se₃)_1−xTe_3x solid solution for manufacturing absorption optical filters with the boundary wavelength regulated from 1.7 to 2.5 μm by changing the composition of the solution. The refractive index is determined for different compositions, and the possibility of making the filters antireflecting is shown. The advantages of the proposed filters are connected with the specific features of the absorption edge of crystals and their structure. To whom correspondence should be addressed. Chernovtsy State University, 2, Kotsyubinskii Str., Chernovtsy, 274012, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 577–579, July–August, 1999.     

利用x|x|控制混沌系统

提出了一种新的混沌控制方法，即对混沌动力系统增加一个具有分段二次函数x|x|形式的非线性反馈控制器，利用它控制了一大类系统从混沌运动转化为各种规则的运动.该控制器是一种活动控制器，它不影响原系统的参数，其结构相当简单而且在物理、电路上都容易实现.数值仿真表明了该控制方法的有效性与可行性. 关键词： 混沌 非线性反馈控制器 分段二次函数     

Dual-wavelength stimulated emission from a double-layer Cd x Hg1 − x Te structure at wavelengths of 2 and 3 μm

Dual-wavelength stimulated emission from a double-layer Cd _x Hg_{1 ? x} Te heterostructure optically pumped by a pulsed Nd:YAG laser at temperatures T = 77–150 K is reported. The emission spectral lines have been observed at wavelengths λ₁ ～ 2 μm and λ₂ ～ 3 μm. Emission spectra recorded at different temperatures are presented.