Theoretical investigation of epitaxial deformation and the hcp-bcc transition of alkali metals

The deformation of alkali metals K, Rb, and Cs under epitaxial deformation is studied via the ab initio pseudopotential plane wave method using the local-density approximation. Under loading from the stable fee phase, metastable stares along directions [001], [111], and [201] are identified. One metastable state, presented at direction [201], has a very low symmetry in contrast to the planes [001] and [201]. Our results show that the softening direction and sequences of growth is significantly affected by the existence of the metastable states and magnitude of the energy barrier. The resulting softening sequences from soft to hard are [201], [110], [001], and [111] under biaxial compression and [001], [111], [201], and [110] under biaxial tension. An orthorhombic deformation path is used to investigate the fact, that the structure of the alkali films K and Cs evolve from the quasihexagonal structure into the (110)-oriented bcc structure, observed by experiments.

可压剪切层线性稳定性特征直接数值模拟=Direct Simulation of the Linear Instabilities in Compressible Shear Layers

基于伪随机数生成技术促生白噪声扰动,以高精度迎风/对称紧致混合差分算法求解二维/三维非定常可压Navier-Stokes方程,揭示了可压自由剪切层初始剪切过程中扰动的线性演化特征,以及该过程对扰动波数和方向的内在选择性.验证了所用算法的有效性,表明线性理论同数值模拟相结合是可压剪切层研究的合理途径之一.

Behaviour analysis of numerical solutions and simulation of coherent structures in compressible mixing layers

For understanding the correctness of simulations the behaviour of numerical solutions is analysed, Tn order to improve the accuracy of solutions three methods are presented. The method with GVC (group velocity control) is used to simulate coherent structures in compressible mixing layers. The effect of initial conditions for the mixing layer with convective Mach number 0.8 on coherent structures is discussed. For the given initial conditions two types of coherent structures in the mixing layer are obtained.

Surface Stability of Epitaxial Elastic Films by Casimir Force

We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical wavelength of the surface perturbation.

Dislocation evolution in epitaxial multilayers and graded composition buffers

This paper presents models to describe the dislocation dynamics of strain relaxation in an epitaxial uniform layer, epitaxial multilayers and graded composition buffers. A set of new evolution equations for nucleation rate and annihilation rate of threading dislocations is developed. The dislocation interactions are incorporated into the kinetics process by introducing a resistance term, which depends only on plastic strain. Both threading dislocation nucleation and threading dislocation annihilation are characterized. The new evolution equations combined with other evolution equations for the plastic strain rate, the mean velocity and the dislocation density rate of the threading dislocations are tested on GexSi1-x/Si(100) heterostructures, including epitaxial multilayers and graded composition buffers. It is shown that the evolution equations successfully predict a wide range of experimental results of strain relaxation and threading dislocation evolution in the materials system. Meanwhile, the simulation results clearly signify that the threading dislocation annihilation plays a vital role in the reduction of threading dislocation density.

Structural, Electrical, And Optical Properties Of Inasxsb1-X Epitaxial Films Grown By Liquid-Phase Epitaxy

The InAsxSb1-x films were grown on (100) GaSb substrates by liquid-phase epitaxy, and their structural, electrical, and optical properties were investigated. The high-resolution x-ray diffraction results reveal that the single crystalline InAsxSb1-x films with a midrange composition are epitaxially grown on the GaSb substrates. Temperature dependence of the Hall mobility was theoretically modeled by considering several predominant scattering mechanisms. The results indicate that ionized impurity and dislocation scatterings dominate at low temperatures, while polar optical phonon scattering is important at room temperature (RT). Furthermore, the InAsxSb1-x films with the higher As composition exhibit the better crystalline quality and the higher mobility. The InAs0.35Sb0.65 film exhibits a Hall mobility of 4.62x10(4) cm(2) V-1 s(-1). The cutoff wavelength of photoresponse is extended to about 12 mu m with a maximum responsivity of 0.21 V/W at RT, showing great potential for RT long-wavelength infrared detection. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989116]

Space experiments of thermocapillary convection in two-liquid layers

In 1999, the space experiments on the Marangoni convection and thermocapillary convection in a system of two immiscible liquid layers in microgravity environment were conducted on board the Chinese scientific satellite SJ-5. A new system of two-layer liquids such as FC-70 liquid and paraffin was used successfully, with the paraffin melted in the space. Two different test-cells are subjected to a temperature gradient perpendicular or parallel to the interface to study the Marangoni convection and thermocapillary convection, respectively. The experimental data obtained in the first Chinese space experiment of fluid are presented. Two-dimensional numerical simulations of thermocapillary convections are carried out using SIMPLEC method A reasonable agreement between the experimental investigation and the numerical results is obtained.

InAs0.3Sb0.7 films grown on (100) GaSb substrates with a buffer layer by liquid-phase epitaxy

The growth of InAsxSb1-x films on (100) GaSb substrates by liquid-phase epitaxy (LPE) has been investigated and epitaxial InAs0.3Sb0.7 films with InAs0.9Sb0.09 buffer layers have been successfully obtained. The low X-ray rocking curve FHWM values of InAs0.3Sb0.7 layer shows the high quality of crystal-orientation structure. Hall measurements show that the highest electron mobility in the samples obtained is 2.9 x 10(4) cm(2) V-1 s(-1) and the carrier density is 2.78 x 10(16)cm(-3) at room temperature (RT). The In As0.3Sb0.7 films grown on (10 0) GaSb substrates exhibit excellent optical performance with a cut-off wavelength of 12 mu m. (c) 2007 Elsevier B.V. All rights reserved.

Numerical simulation of coherent structure in two-dimensional compressible mixing layers

The coherent structure in two-dimensional mixing layers is simulated numerically with the compressible Navier-Stokes equations. The Navier-Stokes equations are discretized with high-order accurate upwind compact schemes. The process of development of flow structure is presented: loss of stability, development of Kelvin-Helmholtz instability, rolling up and pairing. The time and space development of the plane mixing layer and influence of the compressibility are investigated.

Statistics of Turbulence in Benthal Boundary Layers

This paper deals with turbulence behavior inbenthalboundarylayers by means of large eddy simulation (LES). The flow is modeled by moving an infinite plate in an otherwise quiescent water with an oscillatory and a steady velocity components. The oscillatory one aims to simulate wave effect on the flow. A number of large-scale turbulence databases have been established, based on which we have obtained turbulencestatisticsof the boundarylayers, such as Reynolds stress, turbulence intensity, skewness and flatness ofturbulence, and temporal and spatial scales of turbulent bursts, etc. Particular attention is paid to the dependences of those statistics on two nondimensional parameters, namely the Reynolds number and the current-wave velocity ratio defined as the steady current velocity over the oscillatory velocity amplitude. It is found that the Reynolds stress and turbulence intensity profile differently from phase to phase, and exhibit two types of distributions in an oscillatory cycle. One is monotonic occurring during the time when current and wave-induced components are in the same direction, and the other inflectional occurring during the time when current and wave-induced components are in opposite directions. Current component makes an asymmetrical time series of Reynolds stress, as well as turbulence intensity, although the mean velocity series is symmetrical as a sine/cosine function. The skewness and flatness variations suggest that the turbulence distribution is not a normal function but approaches to a normal one with the increasing of Reynolds number and the current-wave velocity ratio as well. As for turbulent bursting, the dimensionless period and the mean area of all bursts per unit bed area tend to increase with Reynolds number and current-wave velocity ratio, rather than being constant as in steady channel flows.

用VTE方法在蓝宝石衬底上生长γ-LiAlO2薄膜

利用气相传输平衡技术(VTE)和后退火处理工艺在(0001)蓝宝石衬底上获得了高度[100]取向的γ-LiAlO2薄膜．X射线衍射表明是由单相的γ-LiAlO2所组成,此薄膜经850～900℃／120h空气中退火处理后显示出高度的[100]取向,这一实验结果意味着有望通过VTE方法制备用于GaN基器件外延生长的γ-LiAlO2(100)-Al2O3(0001)复合衬底.

Effects of sapphire substrate annealing on ZnO epitaxial films grown by MOCVD

The annealing effects of sapphire substrate on the quality of epitaxial ZnO films grown by metalorganic chemical vapor deposition (MOCVD) were studied. The atomic steps formed on (0 0 0 1) sapphire (alpha-Al2O3) substrate surface by annealing at high temperature was analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the ZnO films were examined by X-ray diffraction (XRD), AFM and photoluminescence (PL) measurements. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate surface., The optimum annealing temperature of sapphire substrates is given. (c) 2006 Elsevier B.V. All rights reserved.

Epitaxial growth of ZnO films on (100) and (001) gamma-LiAlO2 substrates by pulsed laser deposition

Structural and optical properties were investigated for ZnO films grown on (100) and (001) gamma-LiAlO2 (LAO) substrates by pulsed laser deposition method. According XRD results, it is intuitionistic that (100) LAO is suitable for fabricating high quality ZnO film, while (001) LAO is unsuitable. The FWHM of XRD, stress in film and FWHM of UV PL spectra for ZnO films on (100) LAO show a decreasing with increasing substrate temperature from 300 to 600 degrees C. ZnO film fabricated at 600 degrees C has the greatest grain size, the smallest stress (0.47 Gpa) and PL FWHM value (similar to 85 meV). This means that the substrate temperature of 600 degrees C is optimum for ZnO film deposited on (100) LAO. Moreover, it was found that the UV PL spectra intensity of ZnO film is not only related to the grain size and stoichiometric, but also depends on the stress in the film.

Epitaxial growth of ZnO thin films on LiGaO2 substrates by pulsed-laser deposition

Lattice-matched (Delta(a/a) = 1.8-3.4%) (001) LiGaO2 substrates have been employed for the first time to grow ZnO thin films by pulsed-laser deposition at 350-650 degrees C with oxygen partial pressure of 20Pa. XRD shows that a highly c-axis-oriented ZnO film can be deposited on (001) LiGaO2 substrate at 500 degrees C. AFM images reveal the surfaces of as-deposited ZnO films are smooth and root-mean-square values are 6.662, 5.765 and 6.834 nm at 350, 500 and 650 degrees C, respectively. PL spectra indicate only near-band-edge UV emission appears in the curve of ZnO film deposited at 500 degrees C. The deep-level emission of ZnO film deposited at 650 degrees C probably results from Li diffusion into the film. All the results illustrate substrate temperature plays a pretty important role in obtaining ZnO film with a high quality on LiGaO2 substrate by pulsed-laser deposition. (c) 2006 Elsevier B.V. All rights reserved.