CsI:Tl晶体对高能X光照射量的响应关系研究

在X光探伤系统中使用效率较高的CsI：Tl晶体作为X光转换体。CsI：Tl晶体对X光的响应关系是精密图像处理、定量测量所需的一项重要参量。理论上已经推导了CsI：Tl晶体对X光的响应呈现线性关系,并针对性地设计了在^60Co放射源上的定量测量实验,所获数据不仅充分证明了理论推导的正确性,还证明了相应系统的这种线性关系的线性度非常好。     

Growth behavior of high k LaAlO3 films on Si by metalorganic chemical vapor deposition for alternative gate dielectric application

LaAlO₃ (LAO) is explored in this work to replace SiO₂ as the gate dielectric material in metal–oxide–semiconductor field effect transistor. Amorphous LAO gate dielectric films were deposited on Si (0 0 1) substrates by low pressure metalorganic chemical vapor deposition using La(dpm)₃ and Al(acac)₃ sources. The effect of processing parameters such as deposition temperature and precursor vapor flux on growth, structure, morphology, and composition of LAO films has been investigated by various analytical methods deeply. The film growth mechanism on Si is reaction limiting instead of mass transport control. The reaction is thermally activated with activation energy of 37 kJ/mol. In the initial growth stage, Al element is deficient due to higher nucleation barrier on Si. The LAO films show a smooth surface and good thermal stability and remain amorphous up to a high temperature of 850 °C. The electrical properties of amorphous LAO ultrathin films on Si have also been evaluated, indicating LAO is suitable for high k gate dielectric applications.     

Photoelectron spectroscopic study of Li oxides on Li over-deposited V2O5 thin film surfaces

The Li oxides species formed on Li over-deposited V₂O₅ thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V₂O₅ system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li₂O and Li₂O₂ compounds on the surface. The formation of Li₂O₂ causes to arise an emission line at about 11.3 eV in the valence band spectra.     

Interfacial structure and electrical properties of LaAlO3 gate dielectric films on Si by metalorganic chemical vapor deposition

LaAlO₃ (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO₂ layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p     

周期轨迹与不可积体系的量子化：Henon-Heiles体系的一个研究例子

研究了两个振子耦合的Henon-Heiles体系的周期轨迹与量子化问题.结果表明，周期轨迹的 作用量积分与体系的能量有着简单的线性关系.可以利用那些是整数值的周期轨迹的作用量 积分对不可积体系进行半经典量子化.由周期轨迹的物理内涵出发，揭示混沌体系的残余周 期轨迹具有与量子化有关的性质.这对于认识和理解经典力学与量子体系的联系关系及其物 理内涵有着深刻而重要的意义. 关键词： 周期轨迹 半经典量子化 混沌     

钚体源样品γ能谱计算的蒙特卡罗方法

提出了钚体源样品γ能谱分步计算的蒙特卡罗模型和方法.采用分步和直接计算两种方法对球壳形钚体源样品的γ能谱进行了模拟计算.用实验测量的γ能谱验证了计算结果的可靠性，计算结果与实验测量值在10%的误差范围符合.通过对Steve Fetter模型的模拟计算表明：对于外面包有若干屏蔽层的钚体源样品大系统，采用分步方法进行能谱计算，可以使结果快速收敛.     

x射线在毛细导管中传输的模拟计算

阐述了x射线在毛细导管中传输的基本理论，根据光线追迹原理建立了x射线在毛细导管中传输的计算模型.在此基础上使用MATLAB编写程序，实现了对x光经过x光单导管的传输效率和光强分布的模拟计算.计算结果和实验数据进行比较，得到了很好的符合. 关键词： 模拟计算 毛细导管 光线追迹 传输效率 光强分布     

超大规模集成电路互连电迁移自由体积电阻模型

将晶核析出的Avrami 方程应用于描述超大规模集成电路中金属Al薄膜互连电迁移过程中电阻的演变. 根据电子散射理论，晶界电阻主要起源于晶界处空位或者空洞对电子的散射. 为了描述这些离子的特征，引入了自由体积的概念，将晶界处电子散射这个复杂的过程简化用自由体积的有效散射截面来描述，从而建立了自由体积与电阻变化的定量关系，统一描述了电迁移过程中不同阶段的电阻变化. 数值模拟结果表明，在第一个空洞成核时刻电阻会发生急剧变化，这一结果已被实验所证实. 关键词： 电迁移 Al互连 电阻变化     

Visualization and characterization of small-scale spanwise vortices in turbulent channel flow

High-resolution particle-image velocimetry (PIV) measurements are made in the streamwise-wall-normal plane of turbulent channel flow at Re_τ=566, 1184 and 1759, facilitating documentation of the population trends and core diameters of small-scale spanwise vortices. Swirling strength, an unambiguous vortex-identification criterion and hence a local marker of rotation, is used to extract small-scale spanwise vortex cores from the instantaneous velocity fields. Once the small-scale vortices are properly extracted from the PIV realizations, their characteristics are studied in detail. The present results indicate that the very-near-wall region (y < 0.1h) is densely populated by spanwise vortices with clockwise (negative) rotation. This behavior supports the notion that hairpin-like vortices are generated very close to the wall and grow into the outer layer as they advect downstream. In contrast, counterclockwise (positive) spanwise vortices are scarce in the very-near-wall region, but their presence steadily increases within the logarithmic layer presumably due to a localized generation mechanism. The average core diameter of negative spanwise vortices is found to be larger than the average diameter of positive vortices, with few positive vortices having core diameters exceeding 80y.