Hole capture barrier of self-organized InAs quantum dots

Deep level transient spectroscopy (DLTS) technique was successfully applied to characterize the electric properties of p type self-organized InAs quantum dots. The ground state energy and capture barrier energy of hole of quantum dots were measured for the first time. The energy of ground state of 2.5ML InAs quantum dots with respect to the valence band of bulk GaAs was obtained being about 0.09eV, and there was a barrier associated to the change of charge state of quantum dots. The capture barrier energy of such dots for hole was about 0.26eV. The work is very meaningful for further understanding the intrinsic properties of quantum dots.

A study of the interface of CeO2/Si heterostructure grown by ion beam deposition

Epitaxial cerium dioxide films on single-crystal silicon substrates (CeO2/Si) have been grown by a dual mass-analyzed low-energy ion beam deposition (IBD) system. By double-crystal X-ray diffraction (XRD), Full Width at Half Maximum (FWHM) are 23' and 33' in the rocking curves for (222) and (111) faces of the CeO2 film, respectively, and the lattice-mismatch Delta a/a with the substrate is about - 0.123%. The results show that the CeO2/Si grown by IBD is of high crystalline quality. In this work, the CeO2/Si heterostructure were investigated by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements. Especially, XPS and AES depth profiling was used to analyze the compositions and structures in the interface regions of the as-grown and post-annealed CeO2/Si. It was found that there was no silicon oxide in the interface region of the as-grown sample but silicon oxide in the post-annealed sample. The reason for obtaining such high quality heterostructure mainly depends on the absence of silicon oxide in the surface at the beginning of the deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.

基于GIS的区域土壤侵蚀模型设计

区域土壤侵蚀模型是国家和区域土壤侵蚀调查、水土保持宏观规划的支持工具。借鉴国外区域土壤侵蚀模型,以DEM栅格为空间单元,对区域土壤侵蚀的单元模型进行定量表达,包括降雨、植被截留、入渗,微地形填洼等,并利用GIS功能完成径流传递和汇集部分的计算,建立了区域土壤侵蚀模型。所建立模型在延河流域的试运算,结果接近现实,能反映土壤侵蚀时空分布趋势。模型的建立可为水土保持的宏观决策提供支持。

分光光度法测定单一稀土元素的研究

“分光光度法测定单一稀土元素的研究”论文包括三部分内容：一、用导数分光光度法测定单一稀土元素。研究了稀土离子－钛铁试剂水溶液体系的三阶及四阶导数吸收光谱。在0.05-0.3N的NaOH溶液中，Pr、Nd、Sm、Eu、Dy、Ho、Er、Tm与钛铁试剂形成具有f-f跃迁吸收光谱的络合物。在350-810nm波长区间它们有各自的特征吸收峰。其高阶导数光谱不仅灵敏度增大了许多倍，且选择性也有较大的提高。如对钕的测定是特效的，而其它稀土之间虽然存在着程度不同的干扰，但用校正系数法均可方便地扣除这些干扰。本体系的常规吸收光谱的灵敏度是高氯酸体系的1.5-19.5倍，三阶导数（半峰）灵敏度是高氯酸盐的常规吸收光谱法的6-166倍，四阶导数则为其的22-401倍。如以峰－峰法测量四阶导数光谱，铒的导数摩尔吸光系数已达3.62 * 10~3。温度对导数光谱略有影响，但可以通过简单方法校正。本文拟定了用稀土－钛铁试剂的高阶导数光度法测定混合稀土中Pr、Nd、Sm、Dy、Ho、Er、Tm的方法，和文献报导的导数光度法相比，本法具有灵敏度高、分析的元素多，不用有机溶剂等优点，适合于各种混合稀土氧化物中Pr、Nd、Sm、Dy、Ho、Er、Tm的准确快速测定。二、钸－钛铁试剂显色反应机理的探讨及混合稀土中钸和铕的测定。钛铁试剂与钸、铕有形成在可见光谱区域具有光谱吸收的络合物。铕的络合物在420nm处的摩尔吸光系数为75。本文着重对于钸和钛试剂的显色反应机理进行了探讨。通过各种实验证实只有四阶钸和钛铁试剂形成红色络合物（其最大吸收峰位于500nm，摩尔吸光系数为4128）。而三阶钸与钛铁试剂仅能形成无色络合物。但在碱性介质中， 空气或浓度中的氧可将三阶钸的络合物迅速氧化为四价钸的红色络合物。因此，不需要预先将三价钸氧化后再进行显色，可直接在形成三价钸的络合物后，再通过空气氧化来显色。从而提出了分光光度法准确快速测定混合稀土中百分之十到万分之几的钸的简便方法。此外，拟定了在微酸性溶液中分光光度法测定混合稀土中铕的分析方法，除大量的钸和镱外，其它稀土对铕的测定无干扰。三、计算光度分析法测定单一稀土元素的探讨。本工作采用三个显色体系（二甲酚橙、偶氮氯膦III、均三氯偶氮胂），达到了用计算光度分析法同时测定多个单一稀土元素的目的。比较了全主元高斯消长法、求病态方程组解的方法、抛物线拟合法，黄金分割法，BFS变R度法，布罗伊佥变R度法，梯度牛顿法、PRP其轭梯度法、FR共轭梯度法、包维尔算法、可变多面体方法，线性规划改进的单纯形法，可变误差多面体方法，网格法，复合形法等十七个计算方法的结果，着重探扩充了测定点数、波长位置、目标函数、约束条件、组分数目、组分含量范围及实验误差、一个体系和多个体系对结果的影响。获得了一些有指导意义的经验规律。其中以抛物线拟合、黄金分割、可变误差多面体等方法较为优越。合成样品五组分和八组分混合稀土氧化物分析获得较为满意的结果。