KDP晶体台阶生长动力学的激光干涉实验研究

采用迈克尔逊干涉技术 ,通过测量KDP晶体生长的法向速率和台阶斜率来研究其台阶生长的动力学系数、台阶自由能、溶质在边界层内的扩散特征以及激发晶体生长台阶的位错活性 .实验表明 ,KDP中不同活性位错的台阶动力学系数差异较大 ,例如高活性和低活性台阶动力学系数分别为 10 .3× 10 -2 和 5 .2 1× 10 -2 cm/s,位错源在晶体表面的形状、面积的变化 ,以及Burgers矢量的变化是造成晶体生长动力学测量数据重复性差的主要原因     

刃位错可以作为晶体生长的台阶源吗?

在回答刃位错是否可以作为晶体生长的台阶源的问题之前,有必要简单回顾一下关于晶体生长机制的某些论点. 晶体(确切地说是晶面)要生长,要求在晶面上存在有生长台阶.对于粗糙面(按照晶体生长的现代理论[1-9],此时该晶面的粗糙化相变温度Tr低于晶体生长温度T),这是不成问题的,因为在它上面有着大量可供生长单元结合在其上的生长坐位(扭折位置,或称半晶体位置).而在平坦面(或称奇异面,对于这类晶面Tr>T)上则缺少这样的生长位置.因而一般需要靠二维成核或螺位错的露头点来提供晶体生长的台阶.所以,二维核和螺位错可以充当晶体生长的台阶源. 最…     

分子束外延生长GaN薄膜中的一种早期位错结构

利用高分辨电子显微术，对在GaP基体上由分子束外延生长六角GaN晶体薄膜中的晶体缺陷结构进行了研究．实验中发现了GaN薄膜外延生长过程中产生的一种典型早期刃型位错结构．此晶体缺陷位于一大块GaN晶粒内部，其外观类似于一段（1120）晶界．它由一条（1120）高能孤立晶界段及其两端的两个1/6［1120］不完全刃型位错组成．从大晶格失配材料之间分子束外延生长的机理上对这种缺陷结构的形成进行了解释． 关键词：     

晶体生长角和凝固速率对贵金属电子束区域熔炼晶体生长的作用

基于电子束区域熔炼中熔区上力的平衡关系式, 计算获得了基座法、等径区熔法两种工艺下稳定成形熔区高度的表达式, 探讨了试样尺寸、晶体生长角和凝固速率等参数对六种贵金属稳定成形熔区高度的影响. 结果发现, 区熔相同尺寸试样时, 六种贵金属能够稳定成形熔区高度大小依次排序为 Ru> Pd> Ir> Pt> Ag> Au. 同时获得了这六种贵金属的晶体生长角在8.4°-10.7°之间, 而实际的晶体生长角与界面生长机制有关. 在基座法中, 连续生长机制所能支撑的熔区高度最小, 而等径区熔法中连续生长机制支撑的熔区高度大于位错生长机制和小面生长机制. 这三种晶体界面生长机制中连续生长方式对晶体生长角和区熔熔区高度影响较小, 有利于贵金属区熔单晶制备. 另外当凝固速率达到2.4 mm·min^-1, 位错和小面生长机制对区熔熔区高度的影响也变得很小, 预测的工艺参数与Ir和Ru单晶区熔实验报道结果基本符合.     

晶体生长的层错机制及其生长动力学

面心立方晶体中层错矢量为1/6<112>和1/3<111>的堆垛层错在生长面{111}上的露头处产生了亚台阶(sub-step)。基于亚台阶的原子图象的分析,本文讨论了层错生长机制及其生长动力学,证明了亚台阶处的成核势垒总是小于二维成核势垒,解释了近年来所观察到的堆垛层错作为生长台阶源的实验事实。 关键词：     

理想的胰岛素晶体

在自然界或实验室内 ,“理想化”总是一个难以实现的概念 .但最近美国休斯顿大学的P .Vekilov教授及其同事们发现 ,他们常常可以将胰岛素晶体生长成理想的晶体形式 .他们让胰岛素蛋白质在一个已有的胰岛素晶体的螺旋位错缺陷处进行生长 ,蛋白质将绕着这个缺陷发生晶化并形成一个理想晶状胰岛素 .这是因为螺旋位错常常使晶层间产生一个微小的角度偏差 .对于大多数的晶体来说 ,晶层间的相互作用能促进晶体生长时界面间的配置 ,并导致晶层阶跃发生束缚和形成一个有条纹的晶体 .除此之外 ,在溶液中输入被溶解物质也能引起晶层阶跃的约束 .胰岛…     

基于蒙特卡罗方法的4H-SiC(0001)面聚并台阶形貌演化机理

针对SiC外延生长中微观原子动力学过程,建立了一个三维蒙特卡罗模型来研究偏向■或■方向4H-SiC(0001)邻晶面上台阶形貌演化过程,并且利用Burton-Cabera-Frank理论分析了其形成机理.在蒙特卡罗模型中,首先建立了一个计算4H-SiC晶体生长过程的晶格网格,用来确定Si原子和C原子晶格坐标以及联系它们之间的化学键;其次,考虑了原子在台阶面上的吸附、扩散,原子在台阶边上的附着、分离以及传输等过程;最后,为了更加详细地捕捉微观原子在晶体表面的动力学过程信息,该模型把Si原子和C原子分别对待,同时还考虑了能量势垒对吸附原子影响.模拟结果表明:在偏向■方向的4H-SiC(0001)邻晶面,有一个晶胞高度的聚并台阶形貌形成,而对于偏向■方向的邻晶面,出现了半个晶胞高度的聚并台阶形貌,该模拟结果与实验中观察到的结果相符合.最后,利用Burton-Cabera-Frank理论对聚并台阶形貌演化机理进行了讨论.     

单粒子瞬变中的双极放大效应研究

采用三维数值模拟的方法对比研究了单个NMOS晶体管和反相器链中的单粒子瞬变（single event transient,SET）电流脉冲,发现深亚微米工艺下双极放大电流在单管的SET电流脉冲中占主要成分,而在反相器链的SET模拟中不明显,分析二者的区别解释了源/体结偏压的形成过程和放大机理,并证明了双极放大效应受源/体结偏压影响的结论.在此基础上分析了NMOS管中源极的正向电流及其机理,发现台阶区的源极正向电流主要是由扩散作用形成的. 关键词： 单粒子瞬变 双极放大 混合模拟 台阶区电流     

用x射线形貌研究半绝缘砷化镓单晶胞状结构

通过x射线异常透射形貌（XRT），化学腐蚀显微观察和电子显微技术（TEM）研究了液封直拉（LEC）法生长的半绝缘砷化镓（SI-GaAs）单晶中蜂窝状胞状结构，从晶体生长和冷却过程的热应力、弹性形变引起位错的运动和反应考虑，分析了该结构的形成机理与过程.认为这是由高密度位错（EPD）运动和反应所形成的小角度晶界的集合群. 关键词： SI-GaAs 小角度晶界 胞状结构     

不同衬底上制备YBa2Cu3O7-δ超导薄膜的微结构研究

采用大直径中空柱状阴极直流磁控制溅射装置，在LaAlO3和Zr(Y)O2衬底上制备YBCO超导薄膜。用透射电镜（TEM）、扫描隧道显微镜（SIM）和原子力显微镜（AFM）对薄膜和衬底间的界面，薄膜的螺旋生长结构，YBCO薄膜及其相应衬底的表面形貌进行了观察和测量。分析了基片表面形貌及表层内缺陷对界面附近薄膜组织结构的影响。研究了不同衬底沉积的超导薄膜具有不同表面形貌的原因。从生长机理角度对表面形貌、缺陷和位错的形成机制进行讨论。     

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.     

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.     

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.     

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.     

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.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.