Photoluminescence of Ge nanostructures grown by gas source molecular beam epitaxy on silicon (1 1 8) surface

In this paper, we present a photoluminescence (PL) study of Si/Ge/SiGe/Si structures grown by gas source molecular beam epitaxy on an (1 1 8) undulated surface with various Ge coverage. Nucleation and growth of Ge films is obtained by the Stranski–Krastanov mechanism. The influence of the substrate orientation on the changeover 2D–3D growth mode is investigated. Furthermore, we show the use of growing an SiGe wetting layer to control the uniformity of the Ge island size. The PL signal related to the Ge islands is found to be highly dependent of the power excitation and is observed up to room temperature.     

Transmission resonances in magnetic-barrier structures

Quantum transport properties of electrons in simple magnetic-barrier (MB) structures and in finite MB superlattices are investigated in detail. It is shown that there exists a transition of transmission resonances, i.e., from incomplete transmission resonances in simple MB structures consisting of unidentical blocks, to complete transmission resonances in comparatively complex MB structures (, n is the number of barriers). In simple unidentical block arrangements in double- and triple-MB structures we can also obtain complete transmission by properly adjusting parameters of the building blocks according to k_y-value (k_y is the wave vector in y direction). Strong suppression of the transmission and of the conductance is found in MB superlattices which are periodic arrangements of two different blocks. The resonance splitting effect in finite MB superlattices is examined. It is confirmed that the rule (i.e., for n-barrier tunneling the splitting would be (n-1)-fold) obtained in periodic electric superlattices can be extended to periodically arranged MB superlattices of identical blocks through which electrons with tunnel, and it is no longer proper for electrons with k _y <0 to tunnel. Received: 18 August 1997 / Revised: 20 September 1997 / Accepted: 13 October 1997     

Generalized Supersymmetric Perturbation Theory

Using the basic ingredient of supersymmetry, a simple alternative approach is developed to perturbation theory in one-dimensional non-relativistic quantum mechanics. The formulae for the energy shifts and wavefunctions do not involve tedious calculations which appear in the available perturbation theories. The model applicable in the same form to both the ground state and excited bound states, unlike the recently introduced supersymmetric perturbation technique which, together with other approaches based on logarithmic perturbation theory, are involved within the more general framework of the present formalism.     

Numerical simulation for the flow inside V-shapes using grid generation

In this paper, we determined a numerical solution of the Navier-Stokes equations for the flow of incompressible fluid inside the contraction geometry. The governing equations are written in the vorticity-stream function formulations. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system by transforming the governing equation into the computational plane. The transformed equations are approximated using central differences and solved simultaneously by the alternating direction implicit method and successive over relaxation iteration method.     

GaInP2/GaAs/Ge叠层太阳电池材料的低压MOCVD外延生长

本文采用自制的LP-MOCVD设备,外延生长出GaInP₂/GaAs/Ge叠层太阳电池结构片,对电池材料进行了X射线衍射测试分析.另外,采用二次离子质谱仪测试了电池结构的剖面曲线.用此材料做出的叠层太阳电池,AMO条件下光电转换效率η=13.6%,开路电压V_oc=2230mV,短路电流密度J_sc=12.6mA/cm².     

Stochastic resonance in a model of opinion formation on small-world networks

We analyze the phenomenon of stochastic resonance in an Ising-like system on a small-world network. The system, which is subject to the combined action of noise and an external modulation, can be interpreted as a stylized model of opinion formation by imitation under the effects of a “fashion wave”. Both the amplitude threshold for the detection of the external modulation and the width of the stochastic-resonance peak show considerable variation as the randomness of the underlying small-world network is changed. Received 19 December 2001     

Minority opinion spreading in random geometry

The dynamics of spreading of the minority opinion in public debates (a reform proposal, a behavior change, a military retaliation) is studied using a diffusion reaction model. People move by discrete step on a landscape of random geometry shaped by social life (offices, houses, bars, and restaurants). A perfect world is considered with no advantage to the minority. A one person-one argument principle is applied to determine locally individual mind changes. In case of equality, a collective doubt is evoked which in turn favors the Status Quo. Starting from a large in favor of the proposal initial majority, repeated random size local discussions are found to drive the majority reversal along the minority hostile view. Total opinion refusal is completed within few days. Recent national collective issues are revisited. The model may apply to rumor and fear propagation. Received 23 January 2002     

Vortex glass phase and flux creep in YBa2Cu3O y epitaxial film

Nonlinear I–V characteristics of YBa₂Cu₃O _y epitaxial film at different temperatures in a magnetic field of up to 5T and angles between the direction of the field and the a–b plane of 0°, 30°, 45°, 60°, and 90° were measured. We find that there are the vortex glass phase and vortex liquid phase in the mixed state. The flux creep exists in the vortex glass phase, and it obviously appears in the area around the boundary between the vortex glass phase and the vortex liquid phase.     

Thermally induced oscillatory relaxation of dc resistivity and ac susceptibility in Y−Ba−Cu−O during N−S transition

Dc resistivity and ac susceptibility have been measured simultaneously on Y–Ba–Cu–O specimens under the effect of a temperature gradient. During cooling process, an intermediate (normal-superconducting) state of samples forms in the vicinity ofT _c and an artificial, local, step-like change of temperature induces an oscillatory relaxation of the measured parameter. This phenomenon has been interpreted in the framework of a vortexglass model as a collective relaxation of vortices inside a domain volume defined by vortex-glass correlation length. Close to theT _c the domain relaxation time and the correlation length have been determined as 51 s and 2 mm, respectively.     

H^＋注入锗酸铋晶体表面层的性质

Ｈ＾＋注入锗酸铋（Ｂｉ４Ｇｅ３Ｏ１２或ＢＧＯ）晶体引起某些效应，如辐射损伤，光学吸收和近表层区域的晶体分解。经Ｈ＾＋注入后，ＢＧＯ晶体的颜色变成棕色，但实验中证实不了该变化是由色心的产生所引起。此外，实验中也示观察到Ｈ＾＋注入ＢＧＯ晶体中有离子束诱发的光学活性变化。可见在注入过程中，未发生从Ｂｉ４Ｇｅ３Ｏ１２转变到Ｂｉ１２ＧｅＯ２０的结构相变，由此预见，注入过程中可能发生离子束引起的晶体分解。Ｈ＾