共查询到20条相似文献,搜索用时 140 毫秒
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用X射线衍射动力学理论,模拟计算InP衬底上InGaAs/AllnAs超晶格和InGaAs单层膜的X射线双晶摇摆曲线,计算结果表明:薄膜界面粗糙对单层膜的衍射峰和超晶格的零级衍射峰影响较小,但却明显影响单层膜衍射干涉条纹和超晶格的±1级卫星峰,随着平均界面粗糙度的增大,单层膜衍射干涉条纹强度减弱并趋于消失;超晶格的±1级卫星峰变弱并逐渐展宽,理论计算的模拟双晶摇摆曲线与超晶格实验曲线比较表明:高质量匹配In0.53Ga0.47As(85?)/Al0.4
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用电化学方法制备了不发光多孔硅和发光多孔硅,用X射线双晶衍射对两类多孔硅表面进行了微结构分析和晶体质量表征,实验表明两类多孔硅的微结构间存在着很大差别。不发光多孔硅表面对X射线的双晶衍射摇摆曲线可解叠成两个峰,它们分别来自样品多孔层和单晶硅衬底,而发光多孔硅对X射线的双晶衍射摇摆曲线呈高斯对称分布,不可解叠。发光多孔硅比不发光多孔硅表面晶体质量差,且电化学腐蚀越严重,表面晶体质量下降也越严重。 相似文献
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用金属有机物化学气相沉积方法在r面蓝宝石上生长了非极性a面GaN薄膜,通过采用AlGaN多量子阱插入层,得到了高质量的非极性GaN材料. 用原子力显微镜和高分辨X射线衍射仪研究了a面GaN的表面形貌和结晶质量,发现非极性材料上典型的三角坑缺陷被消除,(1120)面X射线双晶摇摆曲线的半峰宽为680″.
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GaN
原子力显微镜
高分辨X射线衍射仪
非极性 相似文献
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用X射线双晶衍射摇摆曲线以及双晶X射线形貌对两个SrTiO3基片的单晶质量进行了对比研究,并用X射线掠入射镜面反射及漫散射研究了它们的表面粗糙结构.结果表明,两个SrTiO3基片中都存在镶嵌缺陷,其中一个样品的晶体质量相对较高.两个样品的表面粗糙结构相差很大,包括均方根粗糙度σ和横向相关长度ξ.σ分别为(0.5±0.1)和(1.3±0.1)nm,ξ分别为(1200±200)和(300±20)nm.样品的表面粗糙将增加X射线的漫散射强度而降低镜面反射的强度.晶体质
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The electron spin polarization (ESP) of triplet of the primary donor (3P) ofRhodopseudomonas viridis reaction centers (RCs) is anomalous at temperatures above 25 K, i.e. the steady-state ESP changes from AEEAAE to AEAEAE. Fast, time-resolved EPR measurements in solid solution and single crystals of RCs show that this phenomenon results most probably from fast anisotropic spin-lattice relaxation in the radical pair triplet state (k r≈ 5·109s?1 at 25 K). 相似文献
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The dynamics of relativistic electrons subjected to planar channeling in distorted crystals is investigated using step-by-step numerical integration of the Schrödinger equation. It is shown that periodic distortion of a planar channel (the formation of a “superlattice”) can cause complete reorganization of the mode structure of the wave function. In the limit of weak perturbations of the crystal lattice, the simulation results are consistent with the analytical results from perturbation theory. The position of each line in the spontaneous emission spectrum in the case of resonant distortions depends on the length of the superlattice period. 相似文献
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A complete classification of cylindrically symmetric static Lorentzian manifolds according to their Ricci collineations (RCs) is provided. The Lie algebras of RCs for the non-degenerate Ricci tensor have dimensions 3 to 10, excluding 8 and 9. For the degenerate tensor the algebra is mostly but not always infinite dimensional; there are cases of 10-, 5-, 4- and 3-dimensional algebras. The RCs are compared with the Killing vectors (KVs) and homothetic motions (HMs). The (non-linear) constraints corresponding to the Lie algebras are solved to construct examples which include some exact solutions admitting proper RCs. Their physical interpretation is given. The classification of plane symmetric static spacetimes emerges as a special case of this classification when the cylinder is unfolded. 相似文献
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We theoretically and experimentally investigate the wave front distortion in critically phase-matched continuous-wave (CW) second harmonic generation (SHG). Due to the walk-off effect in the nonlinear crystal, the generated second harmonic is extremely elliptical and quite non-Gaussian, which causes a very low matching and coupling efficiency in experiment. Cylindrical lenses and walk-off compensating crystals are adopted to correct distorted wave fronts, and obtain a good TEM00 mode efficiently. Theoretically, we simulate the correction effect of 266-nm laser generated with SHG. The experiment results accord well with the theoretical simulation and an above 80% TEM00 component is obtained for 266-nm continuous-wave laser with a 4.8°-walk-off angle in beta barium borate (BBO) crystal. 相似文献
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CARMEN DOMENE PATRICK W. FOWLER MARK WILSON PAUL A. MADDEN 《Molecular physics》2013,111(24):3847-3865
Electronic structure calculations of the induced dipole and quadrupole moments on a fluoride ion at low symmetry sites in a model crystalline environments are described. The results are used to characterize the short range contributions to the induced multipoles on the F? ion that arise from overlap between the wavefunctions of the ions. These are represented by general functions of the positions of the surrounding ions, suitable for use in a computationally tractable simulation model. The present calculations are designed to test the transferability to other classes of materials of this representation which, to date, largely has been deduced from calculations on distorted alkali halide crystals. First, the induced multipoles in mixed crystals of the alkali halides are considered, in order to check that they are predicted reliably by combining the representations deduced for the corresponding pure materials. Second, polarization effects in the alkaline earth fluorides MgF2, and CaF2, in a locally distorted fluorite crystal structure are examined. It is found that the material-specific parameters in the representation are related through simple functions of the ionic radii. This relationship holds between MgF2, and CaF2, in the fluorite structure, but also extends to the alkali fluorides previously studied. In order to illustrate the significance of polarization effects, the polarization model for CaF2 is combined with an ab initio pair potential for the repulsion and dispersion interactions and used in a molecular dynamics simulation. Inclusion of the polarization term improves greatly the calculated phonon frequencies in the crystal. 相似文献
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C. Haas 《Solid State Communications》1978,26(11):709-712
The lattice distortions of a hexagonal layer are discussed in terms of a simple model with isotropic interactions. If only nearest-neighbour interactions are considered, the only stable distorted structures are the MnP structure (with zig-zag chains) and the low-temperature NbS structure (with triangles of metal atoms). If also interactions with more distant atoms are considered, more complicated distortions, as observed in crystals with charge density waves, are possible. 相似文献
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Kalb SS Tolkacheva EG Schaeffer DG Gauthier DJ Krassowska W 《Chaos (Woodbury, N.Y.)》2005,15(2):23701
Restitution, the characteristic shortening of action potential duration (APD) with increased heart rate, has been studied extensively because of its purported link to the onset of fibrillation. Restitution is often represented in the form of mapping models where APD is a function of previous diastolic intervals (DIs) and/or APDs, A(n+1)=F(D(n),A(n),D(n-1),A(n-1),...), where A(n+1) is the APD following a DI given by D(n). The number of variables previous to D(n) determines the degree of memory in the mapping model. Recent experiments have shown that mapping models should contain at least three variables (D(n),A(n),D(n-1)) to reproduce a restitution portrait (RP) that is qualitatively similar to that seen experimentally, where the RP shows three different types of restitution curves (RCs) [dynamic, S1-S2, and constant-basic cycle length (BCL)] simultaneously. However, an interpretation of the different RCs has only been presented in detail for mapping models of one and two variables. Here we present an analysis of the different RCs in the RP for mapping models with an arbitrary amount of memory. We determine the number of variables necessary to represent the different RCs in the RP. We also present a graphical visualization of these RCs. Our analysis reveals that the dynamic and S1-S2 RCs reside on two-dimensional surfaces, and therefore provide limited information for mapping models with more than two variables. However, constant-BCL restitution is a feature of the RP that depends on higher dimensions and can possibly be used to determine a lower bound on the dimensionality of cardiac dynamics. 相似文献
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Analysis of the long-wave edge of the self-absorption spectrum of gallium phosphide crystals not distorted by line structure at low temperatures enabled us to determine the characteristic parameters of indirect transitions. In GaP crystals of a different type the appearance of a discrete structure in the long-wave absorption edge is related to the localization of excitons near impurities of an unknown nature. This is confirmed by the appearance in these crystals of an intense green electroluminescence band at low temperatures.The authors are grateful to I. Ryzhikov, A. Kruchinin, and Yu. Il'in for providing the crystals used in the experiments. 相似文献