MBE生长InAs/GaSbⅡ类超晶格材料的界面控制方法分析

本文系统地介绍了MBE外延生长InAs/GaSbⅡ类超晶格材料的界面控制方法,主要包括生长中断法、表面迁移增强法、V族元素浸润法和体材料生长法.短波(中波)InAs/GaSb超晶格材料界面采用混合(mixed-like)界面,控制方法以生长中断法为主;长波(甚长波)超晶格材料界面采用InSb-like界面,控制方法采用...     

Electrolyte infiltration in phosphazene-based dye-sensitized solar cells

We report here a study of phosphazene polymer and oligomer electrolyte infiltration into high surface area titanium dioxide electrodes and its effect on the performance of dye-sensitized solar cells. The effects of different cell assembly procedures on the electrochemical properties are examined, as well as the infiltration of electrolytes based on poly[bis(2-(2-methoxyethoxy)ethoxy)phosphazene] (MEEP), hexakis(2-(2-methoxyethoxy)ethoxy)cyclotriphosphazene (MEE trimer), and a linear short chain analogue into conventional titanium dioxide electrode mesoporous (nanosphere) films, microcolumns and nanowires. The effects of temperature, co-solvents, and the order of addition of the electroactive components are found to affect both the conductivity of the electrolytes and the electrochemical performance of the cells. Cross-sectional scanning electron microscopy (SEM) imaging is employed to examine the degree of electrolyte infiltration into the nanostructured electrodes as a function of filling conditions. Using these techniques, conditions are identified for achieving a high degree of pore filling by the three electrolyte systems. Increased power conversion efficiency is obtained when iodine is introduced after the heating and evacuation procedures required for maximum infiltration.     

Modeling,Reachability and Controllability of Bounded Petri Nets Based on Semi‐Tensor Product of Matrices

In this paper, we present a comprehensive modeling technique for bounded Petri net systems (BPNSs) in the framework of the semi‐tensor product (STP) of matrices. The two dynamic properties of BPNSs, namely, reachability and controllability, are investigated systematacially. First, the dynamics of a bounded Petri net system (BPNS), by resorting to the STP of matrices, are expressed in the form of a discrete‐time bilinear equation, which is called the marking evolution equation (MEE) of BPNSs. Second, controllability and transition‐marking adjacency matrix (TMAM) of BPNSs are defined, respectively. Further, several necessary and sufficient conditions for reachability and controllability of BPNSs are given in terms of the MEE and TMAM. Third, an efficient algorithm to verify reachability property of BPNSs, in this paper, is provided, as well as its computational complexity. Finally, an example is presented to illustrate the theoretical results in this paper. The main contribution of this paper is the presentation of a precise mathematical model for BPNSs. The main advantage of the proposed approach is that not only it can be applied to verify whether or not any given marking is reachable from the other in state space, but also it is very convenient to find all firing sequences between any two reachable markings.     

电磁弹性板中的Lamb波传播特性分析

用状态空间方法将电磁弹性材料中质点运动的广义位移和应力作为状态变量，结合本构方程和平衡方程，得到质点运动的状态方程；获得状态方程的通解后，利用Lamb波存在的边界条件，求出波传播的频散曲线及模态参数。所提方法推导过程简单直观，程序编制方便。以双层电磁弹性板为对象，计算了其频散曲线及模态，结果表明，电磁弹性耦合影响电势与磁势分布，而对频散特征和弹性位移影响很小。     

Transient thermal fracture analysis of a penny-shaped magnetic and dielectric crack in a magnetoelectroelastic cylinder

The problem of penny-shaped magnetic and dielectric crack in a magnetoelectroelastic cylinder is investigated under thermal shock load. The problem is reduced to solve three coupled Fredholm integral equations. The field intensity factors are derived. Numerical results of crack opening displacement intensity factors are presented, and the effects of thermal shock time, crack configuration, and magnetoelectrical crack surface conditions on crack propagation and growth are evaluated. Among others, the larger cylinder's radius, the easier to propagate the crack is. For a fixed crack configuration, magnetoelectrical crack surface conditions have different effects on crack propagation as well.     

迁移增强外延GaAs／Al／GaAs材料生长及其俄歇分析

在配有液Ｎ２冷却Ａｓ快门的分子束外延设备中利用迁殉增强外延（ＭＥＥ）方法于低温下生长了ＧａＡｓ／Ａｌ／ＧａＡｓ结构材料。俄歇测量结果表明：用ＭＥＥ方法生长 材料中Ａｌ和ＧａＡｓ之间的互扩散大大减小，在５００℃热处理后也没有引起多大的互扩散。我们还发现在高指数ＧａＡｓ（１１３）Ｂ面上用ＭＥＥ方法生长ＧａＡｓ薄膜效果更好。     

Low threading dislocation density GaAs on Si(100) with InGaAs/GaAs strained-layer superlattice grown by migration-enhanced epitaxy

This paper reports a promising approach for reducing the density of threading dislocations in GaAs on Si. In _x Ga_1-x As/GaAs strained-layer superlattices (SLSs) grown by migration-enhanced epitaxy at 300° C on GaAs/Si acted as barriers to threading dislocations. Unlike conventional high-temperature-grown SLSs, the low-temperature-grown SLSs were hardly relaxed by the formation of misfit dislocations at GaAs/SLS interfaces, and this allowed them to accumulate considerable strain. New threading dislocation generation due to the misfit dislocation was also suppressed. These factors caused effective bending of threading dislocations and significantly reduced the dislocation density. For the samples that had an SLS withx = 0.3, the average etch-pit density was 7 × 10⁴ cm^-2, which is comparable to that of GaAs substrates.