Systematic characterization of Cl2 reactive ion etchingfor improved ohmics in AlGaN/GaN HEMTs

Pre-metal-deposition reactive ion etching (RIE) was performed on an Al_0.3Ga_0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs     

用化学腐蚀制备多孔硅太阳电池减反射膜的研究

采用HF HNO3溶液化学腐蚀 ,在硅片上制备减反射效果优良的多孔硅太阳电池减反射膜 ,借助原子力显微镜 (AFM)和X光电子谱 (XPS)对其表面形貌和成分进行观察 ,发现该膜与电化学阳极腐蚀得到的多孔硅具有相似性 ,其主要成分为非化学配比的硅的氧化物SiOx(X <2 )。采用带积分球的光度分光计 ,测得形成多孔硅减反射膜后 ,硅片表面反射率大大下降 ,,在波长 330～ 80 0nm范围反射率只有 1 5～ 2 9%。研究指出这种强减反射作用 ,与多孔硅具有合适的折射率及其多孔特性的光陷阱作用有关     

机载相控阵天线辐射方向图的分析

采用一致性几何绕射理论分析了某型预警机机体对其上安装的大型相控阵天线辐射方向图的影响，计算了天线经机体散射后的场，优化了大型相控阵天线安装的最佳位置，为天线装机后辐射性能预测与布局优化提供了理论依据。     

金刚石膜的计算机虚拟制备技术中的分子动力学模拟

综述了近年来金刚石薄膜形成过程的分子动力学（Molecular Dynamics，简称MD）模拟研究，详细地阐述了原子间相互作用势的选取，总结了不同沉积条件下MD的计算模型和几种典型情况下的模拟结果。研究表明：在原子尺度上，MD方法能较全面地提供有关膜生长的信息，对进一步了解金刚石膜形成的微观机制以及为细观层次仿真提供基本信息均具有重要意义。     

均匀设计法在烷基糖苷合成中的应用

在烷基糖苷的合成反应中，影响糖苷得率的因素很多，且各因素之间又存在着相互牵制作用。为了探索合成的最佳条件，我们采用了均匀实验设计法。实验证明：它特别适用于多因素多水平的实验设计，同时减少了实验的次数，降低了实验的费用，提高了工作效率。     

Discrete singular convolution and its application to the analysis of plates with internal supports. Part 2: Applications

Part 2 of this series of two papers presents the applications of the discrete singular convolution (DSC) algorithm. The main purpose of this paper is to explore the utility, test the accuracy and examine the convergence of the proposed approach for the vibration analysis of rectangular plates with internal supports. Both partial internal line supports and complex internal supports are considered for 21 square plates of various combinations of edge support conditions. The effects of different size, shape and topology of the internal supports and different boundary conditions on the vibration response of plates are investigated. The partial internal line supports may vary from a central point support to a full range of cross or diagonal line supports. Several closed‐loop supports, such as ring, square and rhombus, and their combinations are studied for complex internal supports. Convergence and comparison studies are carried out to establish the correctness and accuracy of the DSC algorithm. The DSC results are compared with those in the available literature obtained by using other methods. Numerical results indicate that the DSC algorithm exhibits controllable accuracy for plate analysis and shows excellent flexibility in handling complex geometries, boundary conditions and support conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

马家河水电站的设计

马家河水电站通过在马家河和毛家河上游分别建底栏栅坝和低拱坝 ,经各自的引水系统将水引至两河口汇合流入前池发电。本文介绍了电站的开发方案 ,厂区、引水工程和取水枢纽的布置和设计     

High-resolution electron microscopy of the twinning and intergrowth in Ca4Al6SO16 and Ca3SrAl6SO16

The microstructures of unhydrated calcium aluminosulphate Ca₄Al₆SO₁₆ and Ca₃SrAl₆SO₁₆ have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca₃SrAl₆SO₁₆ and another phase, possibly Sr₃Al₂O₆ existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced.     

A Note on PIN Polynomials and PRIN Rational Functions

This brief presents a necessary and sufficient condition for testing positive, real, imaginary, and negative rational functions. A related term, the positive, imaginary, and negative polynomial, is defined and two necessary and sufficient conditions for testing it are given.     

煤层物性测井评价方法初探

依据煤岩的赋存方式和结构特点，利用电阻率和井径测井资料在不同煤质结构的煤层所表现的差异性，建立了2个指标(即深侧向电阻率与微球电阻率之间的比值，井径与钻头之间的比值)对煤质结构进行了准确的识别。用多元回归的概率模型建立了煤岩镜质反射率的测井计算模式，其结果与已有的煤心分析数据对比，两者具有较好的一致性。在综合分析的基础上，对煤层的重要物性参数煤阶、煤质结构进行了测井评价。