直拉法生长Y_3Al_5O_(12)(YAG)单晶体中的位错和包裹物

通过光双折射貌相法研究了YAG单晶体中位错、包裹物以及生长层间的关系,结果表明,包裹物优先吸附于固液界面上的位错露头点,而包裹物的大小与该处生长台阶的大小有关。     

LiNbO3晶体中包裹物和位错的X射线形貌研究

用X射线透射扫描形貌方法研究了LiNb0₃晶体中的包裹物和位错。在实验中发现了包裹物的相应于不同衍射矢量的X射线形貌与基于各向同性理论预言的形貌之间存在分歧,这被解释为弹性各向异性效应。同时还观察到Burgers矢量为最短点阵平移矢量1/3的纯刃型位错和次短点阵平移矢量1/3<0111>的纯螺型位错,以及由该螺型位错组成的纯扭转晶界。 关键词：     

BeAl_2O_4:Cr晶体的缺陷研究

用化学腐蚀、光学显微镜、X射线形貌术以及电子显微分析等方法研究了引上法生长的BeAl_2O_4:Cr晶体中的缺陷.其结果如下:1)获得了对低指数面(100)、(010)及(001)面位错的理想腐蚀剂,2)晶体中的位错分布不均匀,位错产生的来源有二:一是从晶种中,另一是由包裹物引起.大多数位错是刃型位错,其柏格氏矢量为〈100〉方向、滑移面为(010)面.3)在晶体中常出现的包裹物如气泡,管状物及第二相沉积物,它们是由于原料中的杂质及生长过程中的组分过冷引起的.     

二元晶体中缺陷所引起的位移畴

借助于应变晶体的弹性偶极子模型,把二元晶体中的每一个原子都视为一弹性偶极子。它们有不同的等效偶极矩,在晶体内其他强内应力源,如位错、包裹物等所产生的应力场中受到不同的作用力,因而产生不同的位移,形成了不同形状的畴。它决定于永久偶极矩及感生偶极矩的相对大小和内应力源所产生的应力场的分布。本文分别给出了二元晶体中在刃位错、螺位错、包裹物和挤列等的应力场作用下出现的畴图样。它们呈各种形式排列的花瓣状图形。在适当的条件下,它们可以被观察到。结果还表明了压力对相变的影响。 关键词：     

PbFe12O19单晶体中的位错蚀斑研究

应用50％HCl作为浸蚀剂,对助熔法生长的PbFe₁₂O₁₉单晶体的(0001)解理面进行了浸蚀,以显示位错蚀斑。根据蚀斑所具有的形态,将其进行了分类,并确定了各自对应的位错类型。应用Mathews等人提出的机制,解释了在(0001)基面上所观察到的位错蚀斑阵列。 关键词：     

LiNbO_3晶体中包裹物和位错的X射线形貌研究

用X射线透射扫描形貌方法研究了LiNb0_3晶体中的包裹物和位错。在实验中发现了包裹物的相应于不同衍射矢量的X射线形貌与基于各向同性理论预言的形貌之间存在分歧,这被解释为弹性各向异性效应。同时还观察到Burgers矢量为最短点阵平移矢量1/3的纯刃型位错和次短点阵平移矢量1/3<0111>的纯螺型位错,以及由该螺型位错组成的纯扭转晶界。     

外延PbZr0.4Ti0.6O3薄膜厚度对其铁电性能的影响

从Landau-Devonshire唯象理论出发，考虑到晶格失配导致的NFDA3位错应力场与极化场的耦合，研究了在SrTiO₃衬底上外延生长的PbZr_0.4Ti_0.6O₃薄膜厚度对其自发极化强度、电滞回线的影响. 结果表明，产生刃位错的PbZr_0.4Ti_0.6O₃薄膜临界厚度为～1.27nm，当薄膜厚度大于临界厚度时，在所形成的位错附近，极化强度出现急剧变化，形成自发极化强度明显减弱的“死层”；随着薄膜厚度的减小，位错间距增大，“死层”厚度与薄膜总厚度之比增加. 由薄膜电滞回线的变化情况可知，其剩余极化强度随着薄膜厚度的减小而逐渐减小. 关键词： 铁电薄膜 自发极化强度 电滞回线 位错     

磷酸铝(AlPO4)晶体中缺陷的X射线形貌研究

用X射线衍射形貌法研究了AlPO₄晶体中的微观缺陷。在所研究的晶体中,主要晶体缺陷是生长层,沉淀物和位错。位错密度在晶体表面附近最大,晶体中部较低。位错主要起源于热应力和由沉淀物或生长层所造成的晶格畸变。多数位错的柏氏矢量是b=(a+c)<1123>型,部分的是b=a[2110]。分析了晶体缺陷与生长条件之间的关系。控制生长过程中的温度波动,特别是晶体出炉时的冷却速度,对提高晶体完美性是重要的。 关键词：     

GaN外延衬底LiGaO2晶体的生长和缺陷

ＬｉＧａＯ２与ＧａＮ的晶格失配率只有０．２％，是一种很有潜力的蓝光衬底材料。通过多次实验，用提拉法生长了尺寸为１５×６０ｍｍ的高质量ＬｉＧａＯ２单晶。利用化学侵蚀、光学显微镜、透射电子显微镜对晶体中的缺陷进行了分析，研究了生长参数、原料化学配比对晶体质量的影响。ＬｉＧａＯ２晶体在〈１００〉方向生长速率最快，在〈００１〉方向上生长较慢。由于原料按非化学计量比挥发致使组份偏离，容易产生γ－Ｇａ２Ｏ３包裹物。包裹物和位错的形成具有一定的相互促进作用，往往形成平行于（００１）面的亚晶界。通过调整原料配比、生长工艺参数可克服上述问题。     

冲击条件下含纳米空洞的单晶铜的塌缩

利用分子动力学方法研究了单晶铜中不同大小的球形空洞在冲击波下的演化过程.模拟结果表明不同大小空洞的塌缩过程不同.模拟中冲击波由空洞左边扫向空洞右边.在较大尺寸的空洞塌缩过程中会产生系列的位错环.当空洞半径较小时,先在空洞的右侧形成位错环,当空洞半径增大到某一临界大小时,在空洞左右两侧同时产生位错环,当空洞半径较大时,先在空洞左侧形成位错环.当空洞左右两侧的位错环均形成以后,其右侧位错环前端的生长速度大于其左侧的.空洞半径增大,相应的位错环前端的生长速度变化不大.当空洞半径增大时,空洞中心指向位错源的矢量方 关键词： 纳米空洞 位错环 冲击波 塑性变形     

Defect structure in EuS single crystals grown from the melt

The defect structure in EuS single crystals grown form the melt is studied by etch pitting, scanning and high-voltage electron microscopy. Circular and square etch pits and a second phase in the shape of thin hexagonal platelets are observed by etching. Microprobe analysis indicates the platelets to consist of Eu metal. In the transmission electron microscope, smoothly curved dislocations and helical dislocations, small dislocation loops and inclusions associated with dislocations are observed. The possible origin of the detected dislocation structure is considered with reference to climb and glide processes occurring during cooling down the grown crystals. The results corroborate the glide geometry of the NaCl lattice for EuS. On leave from Institute of Physics, Academic Sinica, Peking, VR China     

A general model for hydrogen trapping at the inclusion-matrix interface and its relation to crack initiation

Abstract

The role of non-metallic inclusions in hydrogen-induced failure of structural materials has been a controversial topic for many years. In this paper, hydrogen trapping and its relation to the crack initiation at the inclusion-matrix interfaces are studied by considering the interfacial structure and the interaction between the dissolved hydrogen atoms and the elastic strains produced by lattice matching and misfit dislocations. A model is proposed to analyse the change of interfacial structure with inclusion size and its relation to hydrogen trapping. Hydrogen accumulation at the interfaces is quantitatively analysed. The obtained results are in good agreement with the experimental observations. The multiple factors, such as interfacial structure, chemical composition, elastic properties of matrix and inclusions, crystallographic relationship between inclusions and matrix, inclusion morphology and size, simultaneously control hydrogen trapping. In addition, the mechanism of hydrogen-induced crack initiation at the interface is investigated. A criterion is proposed to determine critical conditions for crack initiation. For the first time, the inherent relationship between hydrogen trapping and hydrogen-induced cracking at the interface is clarified. This work paves a way for an in-depth understanding of the effects of inclusions on hydrogen-induced degradation of mechanical properties.     

Structural defects in germanium single crystals

The origin and distribution of structural defects (dislocations, small angle grain boundaries, slip lines, polycrystalline inclusions) is studied in large single crystals of germanium applied in manufacturing optical elements.     

The coalescence of silicon layers grown over SiO2 by liquid-phase epitaxy

The coalescence of epitaxial silicon layers which are grown laterally over oxidized and patterned Si substrates is studied using various techniques of transmission electron microscopy (TEM). The epitaxial layers, the seam of coalescence and lattice defects formed by the coalescence are characterized. The epitaxial layer as a whole is found to be bent with respect to the substrate. Such misorientations, together with facetting of the growth fronts of the coalescing layers, may lead to the formation of solvent inclusions, dislocations and stacking faults at the seam of coalescence. However, under favourable conditions, the seam is found to be entirely defect-free.     

X-ray measurement of a microdistortion tensor and its application in an analysis of the dislocation structure of thick GaN layers obtained by hydrochloride gaseous-phase epitaxy

The method of two-and three-crystal x-ray diffractometry (TCD) is used for studying the dislocation structure of thick GaN layers grown by chloride gaseous-phase epitaxy (CGE) on sapphire, as well as on a thin GaN layer, which is grown by the metalloorganic synthesis (MOS) method. Five components of the microdistortion tensor 〈?_ij〉 and the sizes of the coherent scattering regions along the sample surface and along the normal to it are obtained from the measurements of diffracted intensity in the Bragg and Laue geometries. These quantities are used to analyze the type and geometry of the dislocation arrangement and to calculate the density of the main types of dislocations. The density of the vertical screw dislocations, as well as of the edge dislocations, decreases (by a factor of 1.5 to 3) during growth on a thin GaN layer. The diffraction parameters of the thick layer on the MOS-GaN substrate suggest that it has a monocrystalline structure with inclusions of microcrystalline regions.     

High-resolution transmission and scanning electron microscopy of boride-nitride nanostructured films

The results of electron-microscopic studies of grain boundaries and the structure of fractures of titanium boride-and nitride-based films obtained by nonreactive magnetron sputtering are considered. The chemical and phase composition of the films is analyzed with the help of Auger electron spectroscopy and microscopic electron diffraction analysis. The structure of boundaries and the presence of amorphous inclusions, dislocations, and other structural distortions are discussed and the nature of the deformation under indentation is considered.     

Influence of coherent nanoinclusions on stress-driven migration of low-angle grain boundaries in nanocomposites

A theoretical model that effectively describes stress-driven migration of low-angle tilt grain boundaries in nanocomposites with nanocrystalline or ultrafine-grained metallic matrices containing ensembles of coherent nanoinclusions has been developed. Within this model, low-angle tilt boundaries have been considered as walls of edge dislocations that, under the influence of stress, slip in the metallic matrix and can penetrate into nanoinclusions. The dislocation dynamics simulation has revealed three main regimes of the stress-driven migration of low-angle grain boundaries. In the first regime, migrating grain boundaries are completely retarded by nanoinclusions and their migration is quickly terminated, while dislocations forming grain boundaries reach equilibrium positions. In the second regime, some segments of the migrating grain boundaries are pinned by nanoinclusions, whereas the other segments continue to migrate over long distances. In the third regime, all segments of grain boundaries (except for the segments located at the boundaries of inclusions) migrate over long distances. The characteristics of these regimes have been investigated, and the critical shear stresses for transitions between the regimes have been calculated.     

三羟甲基甲胺单晶缺陷的X射线衍射形貌研究

三羟甲基甲胺(Trihydroxymethylaminomethane,缩写为TAM)是一种新型的X射线分光晶体,综合分光性能优于季戍四醇(PET)。X射线形貌鉴定结果表明,除了宏观包裹物和包裹列外,主要是门类繁多的位错,还有面缺陷干涉条纹。文中扼要讨论了缺陷形成的结构影响因素。 关键词：     

钼单晶体中亚晶界位错结构的研究

本文应用蚀象法对电子束浮区区熔法制得的原生态钼单晶体中的亚晶界位错结构进行了直接观测。对于实验结果进行了细致的分析,并与亚晶界的Frank公式的一些预期结果比较,全面地证实了理论预测。对(111)面上平行蚀线方向的测量表明,它们大体沿着1/2〈111〉刃型位错的滑移面及攀移面的交线,从而证实了它们是这种位错所组成的一组位错倾侧型晶界。通过对蚀斑三叉亚晶界的分析,检验了推广后的Read-Shockley公式,同时表明存在着两组位错的倾侧晶界。对于(111)面上观察到的15组蚀线网络进行了分析,结果表明其中5组是1/2〈111〉/〈100〉网络,9组是〈100〉/〈110〉网络。分析中,除去应用Carrington等所发展的极图分析法以外,我们还根据Frank公式所规定的网线间距的关系式,提出了进一步定量检验的分析方法。实践证明,当极图分析不能获得唯一的结果时,这种定量检验法可以有效地确定位错网络的Burgers矢量。此外,我们还观察到奇位错和亚晶界交互作用的事例,特别是奇位错在亚晶界上引起“台阶”以及夹杂物和亚晶界交互作用的迹象。不同类型的亚晶界交接以及非平衡态的亚晶界也是经常可以观察到的。以上结果表明,蚀象法对于定量地研究原生态晶体中的亚晶界位错结构是极其有效的,其能力并不亚于电子显微镜薄膜透射法。