三势垒隧穿结构中由外加垂直磁场引入的高子带非热占据

在一个特殊设计的三垒双阱异质结构中 ,注入到入射端量子阱中的电子 ,首先经过子带间弛豫填充到较低能级 ,紧接着通过共振隧穿逃逸出后面的双势垒结构 ,流入收集电极 ,完成了整个输运过程。通过比较带间光荧光谱中E2 HH1 与E1 HH1 两峰的强度 ,我们发现外加垂直磁场可以抑制子带间的LO声子和LA声子散射 ,使能量较高的子带上出现了明显的非热平衡占据。这一发现提供了一种新的控制子带间散射速率 (量子级联激光器的主要机制 )的有效方法 ,使得在量子阱子带间实现粒子数反转变得更加容易。     

Stress communication and filtering of viscoelastic layers in oscillatory shear

We revisit a classical topic: response functions of viscoelastic layers in large amplitude oscillatory shear. Motivated by questions concerning protective biological layers, we focus on boundary stresses in a parallel plate geometry with imposed oscillatory strain or stress. These features are gleaned from resolution and analysis of coupled standing waves of deformation and stress. We identify a robust non-monotone variation in boundary stress signals with respect to all experimental controls: viscoelastic moduli of the layer, layer thickness, and driving frequency. This structure of peaks and valleys in boundary values of shear and normal stress indicates redundant mechanisms for stress communication (by tuning to the peaks) and stress filtering (by tuning to the valleys). In this paper, we first restrict to a single-mode non-linear Maxwell model for the viscoelastic layer, where analysis renders a transparent explanation of the phenomena. We then consider a Giesekus constitutive model of the layer, where analysis is supplanted by numerical simulations of coupled non-linear partial differential equations. Parametric studies of wall stress values from standing waves confirm persistence of the Maxwell model phenomena. The analysis and simulations rely on and extend our recent studies of shear waves in a micro parallel plate rheometer [S.M. Mitran, M.G. Forest, L. Yao, B. Lindley, D. Hill, Extenstions of the Ferry shear wave model for active linear and nonlinear microrheology, J. Non-Newtonian Fluid Mech. 154 (2008) 120–135; D.B. Hill, B. Lindley, M.G. Forest, S.M. Mitran, R. Superfine, Experimental and modeling protocols from a micro-parallel plate rheometer, UNC Preprint, 2008].     

硅基多孔氧化铝膜的AES多层结构分析和生长过程研究

将电子束蒸发在硅衬底（Ｐ型，〈１００〉晶向，０－５ Ω·ｃｍ） 上厚度４００ ｎｍ 、纯度９９－９９ ％的铝膜，浸入具有中等溶解能力的１５ ｗｔ％ Ｈ２ＳＯ４ 中，ＤＣ恒压６０ Ｖ、恒温０ ℃条件下，进行多孔型过度阳极氧化处理，从而在Ｓｉ 基上得到包含空隙层的多孔氧化铝膜．通过对样品ＴＥＭ 平面形貌、ＳＥＭ 横断面形貌观察以及ＡＥＳ深度剖析，研究了样品的多层结构，并初步讨论了由此揭示出的硅基多孔氧化铝膜的生长过程     

Rashba electron transport in one-dimensional quantum waveguides

The properties of Rashba wave function in the planar one-dimensional waveguide are studied, and the following results are obtained. Due to the Rashba effect, the plane waves of electron with the energy E divide into two kinds of waves with the wave vectors k 1 =k 0 +k δ and k 2 =k 0 -k δ , where k δ is proportional to the Rashba coefficient, and their spin orientations are +π/2 (spin up) and -π/2 (spin down) with respect to the circuit, respectively. If there is gate or ferromagnetic contact in the circuit, the Rashba wave function becomes standing wave form exp(±ik δ l)sin[k 0 (l-L)], where L is the position coordinate of the gate or contact. Unlike the electron without considering the spin, the phase of the Rashba plane or standing wave function depends on the direction angle θ of the circuit. The travel velocity of the Rashba waves with the wave vector k 1 or k 2 are the same hk0/m * . The boundary conditions of the Rashba wave functions at the intersection of circuits are given from the continuity of wave functions and the conservation of current density. Using the boundary conditions of Rashba wave functions we study the transmission and reflection probabilities of Rashba electron moving in several structures, and find the interference effects of the two Rashba waves with different wave vectors caused by ferromagnetic contact or the gate. Lastly we derive the general theory of multiple branches structure. The theory can be used to design various spin polarized devices.