Localized deep levels in AlxGa1-xN epitaxial films with various Al compositions

By using high-temperature deep-level transient spectroscopy(HT-DLTS) and other electrical measurement techniques,localized deep levels in n-type AlxGa1-xN epitaxial films with various Al compositions(x = 0, 0.14, 0.24, 0.33, and 0.43)have been investigated. It is found that there are three distinct deep levels in AlxGa1-xN films, whose level position with respect to the conduction band increases as Al composition increases. The dominant defect level with the activation energy deeper than 1.0 eV below the conduction band closely follows the Fermi level stabilization energy, indicating that its origin may be related to the defect complex, including the anti-site defects and divacancies in AlxGa1-xN films.     

The improved genetic algorithms for digital image correlation method

We present a global optimization method, called the genetic algorithms (GAs), for digital image/speckle correlation (DISC). The new algorithms do not involve reasonable initial guess of displacement and deformation gradient and the calculation of second-order spatial derivatives of the digital images, which are important challenges in practical implementation of DISC. The performance of a GA depends largely on the selection of the genetic operators. We test various operators and propose optimal operators. The algorithms are then verified using simulated images and experimental speckle images.     

多导体传输线高频场线耦合模型的研究综述

场线耦合模型的研究是电磁兼容分析和电磁效应评估的重要组成部分。低频时,可以使用基于准TEM波近似的经典场线耦合模型来计算外场激励下的传输线沿线电流电压响应,然而,当入射波频率增加到对应波长与传输线横向尺寸可比拟时,经典模型将产生不可接受的模型误差,因而需要发展高频情况下的场线耦合模型。介绍了国内外多导体传输线高频场线耦合模型的研究进展,详细分析和比较了两个主流分支：TRI模型和TLST模型;之后简要介绍了传输线超理论TLST模型并以算例说明了该模型的准确性和有效性;最后对高频场线耦合模型的研究内容和研究目标进行了总结和展望。     

Influences of annealing on structural and compositional properties of Al_2O_3 thin films grown on 4H–SiC by atomic layer deposition

Annealing effects on structural and compositional performances of Al_2O_3 thin films on 4H–Si C substrates are studied comprehensively. The Al_2O_3 films are grown by atomic layer deposition through using trimethylaluminum and H_2 O as precursors at 300?C, and annealed at various temperatures in ambient N_2 for 1 min. The Al_2O_3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750?C to 768?C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy(XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar.     

金属光栅表面增强拉曼散射的偏振依赖性研究

表面增强拉曼散射的机理主要来源于金属表面等离子体共振所产生的电磁场增强,因而基底的电磁特性决定了其增强的性能。本文以干涉光刻方法制作的大面积均匀性一维纳米光栅为增强基底,从实验和理论上探究其表面增强拉曼散射的偏振依赖特性。本文使用苯硫酚作为探针分子,并采用633nm和785nm两种波长作为激发光源,开展了等离子体共振与非共振状态下金属光栅表面增强拉曼光谱的偏振依赖特性实验研究,并通过时域有限差分法对光栅电磁特性进行分析。研究发现,光栅表面的电场无论是否激发表面等离子体共振,其电场随入射光偏振方向都会呈现出sin函数的规律性变化,拉曼光谱的峰值强度则呈sin2函数的变化规律;此外,表面等离子体共振会进一步加大拉曼光谱的偏振依赖性。     

电解精炼制备太阳级硅杂质行为研究

在氟化物电解质体系下,把Cu与冶金级多晶硅熔配成合金作为阳极,利用杂质与硅析出电位的差别,通过控制电解工艺条件和参数,对冶金硅进行了电解精炼提纯研究.结果表明,阳极铜硅合金对硅中的杂质有滞留作用,且在大电流密度下Cu不会随着合金中硅的减少而溶解到电解质中;预电解对电解质净化效果明显,XRF分析表明P含量从10降为1ppmw;阴极电沉积的硅呈颗粒状,并与电解质混杂,随着电解时间的延长,分散的硅的颗粒聚集成1—2cm直径的大尺寸硅球.ICP-AES分析表明,最后得到的产物硅与冶金级硅相比,硼含量由12·7降低到2·2ppmw,磷含量由98·6减少到4·1ppmw,说明电解精炼除杂进行多晶硅的提纯是有效和可行的.     

超相对论激光和稠密等离子体作用产生阿秒脉冲的优化

利用一维粒子模拟程序研究了超相对论激光脉冲与稠密等离子体相互作用得到的阿秒脉冲.从超相对论近似的角度分析了电子运动行为和高次谐波的产生,发现当等离子体密度一定时,随着无量纲相似参数S的减小,阿秒脉冲的转换效率呈先增大后减小的趋势,因此选择适当的光强就可以得到转换效率较高的阿秒脉冲.当S一定时,随着等离子体密度的增加,阿秒脉冲转换效率有增大的趋势.这说明用适当的光强照射更稠密度的等离子体靶面,可以产生更强的阿秒脉冲.     

脉冲γ射线对光纤的辐射效应

介绍了光纤的损耗机制和γ射线对光纤的辐射效应,设计了针对脉冲γ射线作用于光纤而产生辐射感生损耗的实验测量系统。利用平均光子能量为0.3 MeV、脉冲宽度25 ns、剂量率2.03×107Gy.s-1,和平均光子能量为1.0 MeV、脉冲宽度25 ns、剂量率5.32×109Gy.s-1的2种脉冲γ射线分别作用于多模和单模光纤,分别采用波长为405,660,850,1 310和1 550 nm的激光光纤传输系统对辐射感生损耗进行了测量。获得了光纤辐射感生损耗和辐射剂量的关系,并对实验结果进行分析。从实验结果可以看出:在近红外到可见光范围内,脉冲γ射线对光纤作用产生的辐射感生损耗随探测波长减小而增大;在0.1~3.5 Gy剂量范围内,多模光纤辐射感生损耗和辐射剂量呈线性关系。分析辐射对光纤的作用机制和实验结果后得出:光纤基质原子的电子能级对传输光子的共振吸收而造成吸收损耗增加;光纤折射率分布的改变从而导致波导损耗增加。     

一种同时测量平行偏差、倾斜偏差的方法

提出了一种仅由接收物镜和CCD构成的接收器,通过物镜位置的调整,可以同时完成平行偏差（平偏）和倾斜偏差（角偏）这两个参量的测量.通过对系统像差的分析,提出了可显著降低物镜像差对测量结果影响的算法.理论和实验数据表明,对于平偏测量范围为±10 mm、角偏测量范围为±2°、接收物镜焦距为50 mm、CCD尺寸为1/1.6 inch的系统,平偏测量准确度可达0.02 mm,角偏测量准确度可达9.5″.