人造石英单晶中位错双折射像的反衬

考虑了光弹系数的各向异性,对石英晶体中位错双折射象的反衬进行了计算。在实验上采用反射偏光法抵消旋光后沿光轴观察获得了位错双折射象,并和计算结果进行了比较。 关键词：     

直拉法生长的GGG和YAG单晶体中螺型位错的双折射像

在直拉法生长的GGG和YAG单晶体中,从实验上首次获得了沿位错线观察的(viewed end-on)螺型位错的双折射像,确立了沿位错线观察和垂直于位错线观察(viewed from the side)的双折射像间的一一对应关系,以及与蚀斑间的一一对应关系,并基于石榴石晶体弹-光性质的各向异性,给出了沿位错线观察的螺型位错双折射像的成像规律,得到了理论与实验一致的结果。 关键词：     

六角片状包裹体双折射象与计算机模拟象

在钆镓石榴石(GGG)晶体中观察到六角片状大包裹体的应力双折射象,对其应变场进行了分析,并计算双折射象的反衬和作出相应的数值模拟象,实验与理论计算结果符合得较好。     

在具有长程应变场的GGG晶体中螺型位错的应力双折射像

基于弹性各向同性和弹光各向异性的考虑,获得了长程应变场中沿位错线观察的螺型位错双折射像的解析表达式以及其计算机模拟像,成功地解释了GGG晶体中实验观察到的螺型位错像所具有的两瓣一黑一白的衬度特征。 关键词：     

在具有长程应变场的GGG晶体中螺型位错的应力双折射像

基于弹性各向同性和弹光各向异性的考虑, 获得了长程应变场中沿位错线观察的螺型位错双折射像的解析表达式以及其计算机模拟像, 成功地解释了G G G 晶体中实验观察到的螺型位错像所具有的两瓣一黑一白的衬度特征. 关键词：     

钾矾晶体中螺位错的双折射端点像

考虑了弹性各向异性和弹光各向异性,得到了含有长程应力场的钾矾KAl(SO_4)_2·12H_2O单晶体中a<111>螺位错的双折射端点像的强度分布,其结果与实验相符。据此,给出了估计晶体中内应力场的主应力大小和方向的方法。 关键词：     

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。     

晶体中滑移的位错机构研究

在研究岩盐型晶体的塑性变形中,用偏振光方法观察晶体中在塑性变形时出现的双折射光带,并结合用显微干涉仪对晶体表面的研究,观察到晶体中发生滑移时滑移带两端所发生的滑移距离恆不相等。根据这一结果,用腐蚀方法观察晶体中的位错排列,并和双折射光带及表面干涉图形的研究对比,全面地验证了离子型晶体中滑移过程的位错机构。此外,还证明了腐蚀坑和位错之间的一一对应的关系,并用实验方法证明了晶体滑移面内存在着符号不同的位错。     

直拉法生长Y3Al5O12(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。 关键词：     

在YAG:Nd晶体中位错对激光特性的影响

本文用双折射貌相法和化学腐蚀法测定了六根晶体棒中的位错分布和位错密度,用光学方法检验了晶体的光学质量,晶体的激光性能是在一台Q开关YAG激光装置上测定的。实验表明当位错密度增加到一定程度时,位错形成的应力场会引起明显的双折射,以致探测光通过晶体时波面会发生畸变。在干涉仪上可观察到干涉条纹的增加。同样,在位错应力场区消光比亦下降。因此,作为结构缺陷的位错也是晶体光学不均匀的来源之一。晶体激光性能的实验结果指出:位错对激光输出特性有很大的影响,从激光近场光斑图看出,在位错应力场区,因为高的激光阈值而不能产生激光振荡,并且由于应力双折射效应产生光的退偏性。由于存在高位错密度,晶体的激光发散度增加,倍频效率下降。当晶体中存在缀饰位错(decorated dislocation)时,激光输出特性的变化尤为明显.     

Analysis of dislocation images in X-ray topography of protein crystals: tetragonal hen egg-white lysozyme crystals

Dislocation images in X-ray topography of protein crystals such as tetragonal hen egg-white lysozyme crystals were analyzed. Not only extinction but also double contrast of dislocation images are clearly observed on the X-ray topographs. It should be noted that the observed image widths of the dislocation contrasts are much less than those calculated on the basis of the kinematical theory in X-ray topography, which has been successfully applied for inorganic crystals and organic crystals of small molecules so far. Moreover, in tetragonal HEW lysozyme crystals, the rocking curve widths of the perfect crystal related to the kinematical theory are less than the measured ones by two orders of magnitude. This discrepancy is consistent with that in the image width of the dislocation contrast. From this correlation, it is suggested that the larger rocking curve width, or higher mosaicity, is mainly responsible for the observed image width in the grown crystals.     

Formation and nature of swirl defects in silicon

Point defect agglomerates in dislocation-free silicon crystals, usually called “swirls”, have been investigated by means of high-voltage electron microscopy. It was found that a single swirl defect consists of a dislocation loop or a cluster of dislocation loops. By contrast experiments it could be shown that these loops are formed by agglomeration of self-interstitial atoms. Generally the loops have a/2〈110〉 Burgers vectors, but in specimens with high concentrations of carbon (～10¹⁷ cm^?3) and oxygen (～10¹⁶ cm^?3) also dislocation loops including a stacking fault were observed. In crystals grown at growth rates higher thanv=4 mm/min no swirls are observed; lower growth rates do not markedly affect the size and shape of the dislocation loops. With decreasing impurity content (particulary of oxygen and carbon) the swirl density decreases, whereas the dislocation loop clusters become larger and more complex. A model is presented which describes the formation of swirls in terms of agglomeration of silicon self-interstitials and impurity atoms.     

Multiphysical simulation analysis of the dislocation structure in germanium single crystals

To grow high-quality germanium crystals is one of the most important problems of growth industry. The dislocation density is an important parameter of the quality of single crystals. The dislocation densities in germanium crystals 100 mm in diameter, which have various shapes of the side surface and are grown by the Czochralski technique, are experimentally measured. The crystal growth is numerically simulated using heat-transfer and hydrodynamics models and the Alexander–Haasen dislocation model in terms of the CGSim software package. A comparison of the experimental and calculated dislocation densities shows that the dislocation model can be applied to study lattice defects in germanium crystals and to improve their quality.     

Features of X-ray diffraction at elastic deformations near the dislocation axis in section topography techniques

Features of the formation of an x-ray diffraction image by x-ray section topography are considered for a strongly distorted region near the dislocation axis in silicon single crystals. The results of experimental investigations and numerical calculations of the diffraction contrast and section topographs of rectilinear dislocations are presented for their different orientations and positions in the scattering triangle in silicon single crystals. A comparison and an analysis of the experimental topographs and the simulated images lead to the conclusion that the structure of the image of a dislocation strongly depends on its position and orientation in the scattering triangle. It has been found that each point of the strongly distorted region of the elastic field of a dislocation becomes a source of a new wave field propagating under the dislocation in a new scattering triangle. This new field interferes with the primary wave field forming the observed diffraction image of a dislocation. The addition of these waves with regard to their amplitudes and phases results in a large variety of images of defects. A comparison of different dislocation orientations in the Borrmann triangle allowed us to evaluate the role of different effects determined by the interference of the initial and newly formed wave fields, to determine on this basis the main dislocation parameters, and to optimize the diffraction conditions of the topographic measurement for the investigation of elastic-field characteristics.     

位错的会聚束电子衍射研究

从硅位错附近得到的会聚束电子衍射图样表明高阶劳厄带线和菊池线分裂,晶体学等效的衍射显示不同的分裂或不分裂,这些结果可以用晶体缺陷的衍衬理论来解释,不分裂的衍射相当于位错的不可见,即g·b=0,会聚束电子衍射提供了强有力的研究缺陷的高空间分辨率手段。 关键词：     

Defocus convergent beam electron diffraction determination of Burgers vectors of dislocations in quasicrystals

Principles, method and some application examples of determining Burgers vectors of dislocations in crystals and quasicrystals by means of defocus convergent-beam electron diffraction (CBED) technique are described and reviewed and compared with contrast experiment techniques. By using defocus CBED technique, dislocation reactions during high-temperature plastic deformation of face-centered icosahedral quasicrystals have been studied. These studies lead to a preliminary understanding to the micromechanism of high-temperature plastic deformation of quasicrystals.     

Formation of a disordered (Glassy) phase in deformed solid <Superscript>4</Superscript>He in the region of supersolid state

A method has been proposed to create disorder in helium crystals by their deformation immediately during the experiment. Precise measurements of the pressure have been performed at a constant volume in samples of various qualities. It has been revealed that excess pressure, which is characterized by the quadratic temperature dependence typical of the disordered glassy phase and of the dislocation contribution to the pressure, is observed in the deformed crystals along with the phonon contribution to the pressure. The effect is observed in the supersolid-state region and disappears after the careful annealing of the crystals. The ultraslow relaxation of the pressure also characteristic of the glassy phase has been observed in the process of annealing of the crystals. The obtained experimental results have been analyzed in the framework of the dislocation model and the model of two-level tunneling states.     

Anomalous elastic response of silicon to uniaxial shock compression on nanosecond time scales

We have used x-ray diffraction with subnanosecond temporal resolution to measure the lattice parameters of orthogonal planes in shock compressed single crystals of silicon (Si) and copper (Cu). Despite uniaxial compression along the (400) direction of Si reducing the lattice spacing by nearly 11%, no observable changes occur in planes with normals orthogonal to the shock propagation direction. In contrast, shocked Cu shows prompt hydrostaticlike compression. These results are consistent with simple estimates of plastic strain rates based on dislocation velocity data.     

Dislocation models of mechanoluminescence in γ- and X-irradiated alkali halides crystals

The mechanoluminescence appears in the elastic, plastic and fracture regions of γ- and X-irradiated KCl and NaCl crystals. A linear relation is found between the mechanoluminescence intensity and the newly created dislocations. Four models are proposed for the mechanoluminescence excitation during the movement of dislocations. These models are: dislocation unpinning model, dislocation interaction model, dislocation defect stripping model, and dislocation innihilation model. The dislocation annihilation model seems to be a dominating process for the M.L. excitation in γ- and X-irradiated alkali halide crystals.     

Influence of a weak magnetic field on microplasticity of silicon crystals

The possibility of magnetic ordering at dangling bonds in dislocation cores has been investigated theoretically. It has been experimentally shown that magnetic ordering in dislocations affects the spin-dependent effects occurring in dislocation crystals of silicon. It has been found that preliminary magnetic treatment of silicon crystals in a weak magnetic field leads to the suppression of the electroplastic effect induced in silicon crystals excited by an electric current. It has been assumed that a change in the microplasticity under the combined action of a magnetic field and an electric current is caused by a weakening of spin-dependent recombination at dislocation dangling bonds.