金属纳米线应力分布特征的原子级模拟研究

运用分子静力学方法结合量子修正Sutten-Chen多体力场研究了Ni纳米线在平衡状态下的应力分布特征,考虑了三种不同取向的纳米线,即轴线方向分别沿［100］,［110］和［111］方向的纳米线.计算的结果表明：由于表面张应力的作用,纳米线在弛豫过程中沿轴线方向长度发生收缩;纳米线从表面向中心区域呈现出由张应力向压应力连续分布的特征.随着纳米线直径的增加,纳米线的表面区域的张应力先上升,然后略有下降,并趋向一个非零的常值;而中心区域的应力则属于压应力,其值随着直径的增加显著地减小,并趋向于零值.无论是轴向 关键词： 纳米线 应力分布 分子静力学     

回流扩散燃烧火焰湍流结构特性的PIV测量

利用粒子图像速度场测量(PIV)技术对不同燃空速度比下的钝体回流扩散燃烧流场进行了测量,考察不同火焰的湍流结构特性.结果表明,流场中轴向脉动速度沿钝体中心轴线成对称分布,轴向脉动速度最大值出现在钝体中心轴线处,流场切向雷诺应力以饨体轴线呈中心对称,在中心轴线处切向雷诺应力值为0,随燃空速度比的增大,轴向脉动速度和切向雷诺应力不断增大,随着与钝体表面的距离增加,流场截面上最大轴向脉动速度不断减小,最大切向雷诺应力先增大,后减小.     

tetracene 分子在Ru(1010)表面的吸附结构及其电子态研究

利用紫外光电子能谱(UPS)、角分辨紫外光电子能谱(ARUPS)和扫描隧道显微镜(STM)等方法研究了tetracene分子在Ru(1010)表面上吸附的电子态，吸附位置和吸附取向.UPS实验显示，与tetracene分子有关的光电子谱峰在费米能级以下2.1, 3.5, 4.8, 6.0, 7.1和9.2 eV处；ARUPS 结果表明，tetracene分子的分子平面基本平行于衬底表面；从STM图像中可以看到tetracene分子的长轴沿［0001］和［1210］两个晶向.基于密度泛函理论的从头算计算证实了上述结论.当分子长轴沿［0001］晶向时，分子中心位置在衬底表面的“短桥位”上，当分子长轴沿［1210］晶向时，分子中心位置在衬底表面的“四原子中心空位”上. 关键词： tetracene分子 Ru(1010)表面 吸附结构 吸附电子态     

冲击加载下孔洞诱导相变形核分析

用分子动力学方法模拟了冲击加载(沿［001］向)下单晶Fe中孔洞诱导相变形核及生长过程，并分析了初始温度对这一生长过程的影响.数值模拟显示：1) 相变形核首先出现在孔洞周围的(110)和(110)面上,并分别沿［110］，［110］向和［110］，［110］向生长成片状，之后核的生长方向则变为沿〈111〉向，形成“V”形板条状新相颗粒；2) 在相同冲击压力下，初始温度为300 K时在新相晶核边缘出现许多核胚，生成的新相颗粒比60 K时明显减小.这些现象表明，孔洞诱导相变形核及生长过程沿着特定晶向进行，而初     

Ni,Pd和Pt的表面应力

半经验的修正嵌入原子方法用于Ni，Pd和Pt的低指数面的表面应力计算，得到了与第一原理计算相符合的结果．给出了（110）表面［110］方向的应力是［001］方向应力的两倍左右；阐明了应力各向异性是所有fc金属（110）面的一般特性．预言了Pd和Pt（100）的表面应力的大小． 关键词：     

基于表面等离子体耦合的高密度金纳米线阵列

利用电化学沉积法在阳极氧化铝模板中制备了高长径比(20—100)金纳米线阵列,并用扫描俄歇电子显微镜对其结构进行了表征.紫外可见吸收光谱显示金纳米线的表面等离子共振包含横向吸收峰(transverse mode)和纵向吸收峰(longitudinal mode),具有很强的各向异性特征.纵向吸收峰的强度与入射光的偏振方向和入射角度有关,随着长径比的增加纵向吸收峰位置向高能方向移动.将纳米线之间的表面等离子体能量耦合与分子H聚合体的吸收光谱行为做了比较,认为相邻纳米线间的多重耦合使纵向吸收峰出现蓝移.利用有限元分析法模拟了电场在纳米线阵列和单根纳米线表面的不同分布.     

GaAs均匀点状结构的分子束外延图形生长

报道了在(311)A腐蚀图形衬底上，用分子束外延(MBE)生长高度规则的三种点状结构的实验研究.样品表面的原子力显微镜和剖面的扫描电子显微镜测试结果表明，在不同尺寸的方形凹面腐蚀图形区域，原凹面之间形成了沿［233］晶向不完全和完全收缩的尖角形点状外延结构；而在方形台面腐蚀图形区域，台顶面之间形成了沿［233］方向收缩的脊形点状结构.分析认为这些均匀有序的三角形点状结构的形成是由非平面(311)A衬底上生长各向异性导致的必然结果，而构成这些点结构的晶面取向与原图形的取向相关.低温阴极荧光谱测试结果清晰地表 关键词：     

电化学沉积Fe单晶纳米线生长中的取向控制

利用电化学沉积方法，发现了一种能够动态地控制铁纳米线生长方向的沉积方法，利用该方法沉积了包括［110］取向，［200］取向及非晶态三种结构和取向的一维Fe纳米线阵列.对于三种纳米线阵列，测量了它们的磁特性，分析发现具有[200]择优取向纳米线阵列的方形度，各向异性特性和矫顽力都比[110]取向阵列有很大的改善. 关键词： 磁性纳米线 电化学沉积 取向控制     

玻璃包覆铜丝快速凝固感应加热磁场数值模拟

 建立了玻璃包覆铜丝快速凝固感应加热电磁场计算模型，借助MATLAB软件描述了圆柱形导体内电磁场分布规律。研究了感应线圈直径、锥度和匝数等参数对感应线圈内磁场分布的影响。结果表明: 随着感应线圈直径的增大，最大磁场强度降低；随着锥度的增大，线圈中最大磁场强度降低；随着感应线圈匝数增加，线圈中的最大磁场强度增加。扫描电镜和X射线衍射仪分析表明，实验制备的玻璃包覆铜丝的直径为18 mm、铜丝的直径为3.3 mm，玻璃包覆铜丝的表面质量及直径均匀性较好，铜以晶态形式存在，在［200］晶向具有明显的择优取向。     

分子动力学研究表面缺陷对硅纳米线杨氏模量的影响

硅纳米线因受量子尺寸效应与表面效应的影响而具有奇特的力、电及其耦合特性,成为了纳米电子器件的核心构件.然而在硅纳米线的制备过程中,表面产生缺陷不可避免.因此本文采用分子动力学方法着重研究了表面缺陷浓度对不同横截面形状(正方形、六角形和三角形)的[110]晶向和[111]晶向硅纳米线杨氏模量的影响.研究结果表明,当硅纳米线仅有单一表面缺陷时,不同晶向硅纳米线的杨氏模量均随表面缺陷浓度增加而迅速单调减小.当表面缺陷浓度为10%时,杨氏模量的减小幅度在10%-20%之间,减小幅度的差异与硅纳米线的晶向以及横截面形状密切相关.当存在多个表面缺陷时,杨氏模量随着缺陷浓度的增加表现出了不同程度的波动趋势.三角形截面硅纳米线的杨氏模量波动幅度最大,正方形截面的波动较小,即表面缺陷分布的不同对正方形截面硅纳米线的杨氏模量影响较小,这表明表面缺陷的影响与其分布及硅纳米线的横截面形状密切相关.通过与实验结果对比,本文的研究结果揭示了表面缺陷是导致硅纳米线杨氏模量实验值变小的重要因素,因此在表征硅纳米线的力学性能时,需要考虑表面缺陷的影响.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.