共查询到19条相似文献,搜索用时 218 毫秒
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用会聚束电子衍射得到了石墨和辉钼矿的底面横向层错的带轴图样。带轴图样显示了层错引起的变化,对称性降低和部分衍射分裂,本文首先指出衍射分裂或不分裂可以用晶体缺陷衍射衬度理论来解释,这对应于缺陷的可见和不可见,这结果对缺陷的研究有普遍性意义。这方法为研究晶体缺陷提供了强有力的手段。
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会聚束电子衍射是测定晶体点群、空间群的有效方法。要清楚地判断会聚束电子衍射图样的对称性,电子束的会聚角要大,但衍射盘不能重叠。本文提出了一种新方法来获得不重叠的大角度会聚束电子衍射。新方法是使电子束离焦,固定样品,从而保留了样品的同心倾动位置,作大角度倾动时不会失去原来感兴趣的区域。新方法在原理上和田中等人提出的方法相同,但优越性更大。同时也研究了大束斑(≥2μm)大角度会聚束电子衍射。
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引 言 会聚束电子衍射(CBED)技术是由Kossel和 Mollenstedt[1]在1939年首创.到六十年代,Goodman等[2]改装了电子显微镜,用较小的电子束斑得到了一些有意义的结果[3].样品的厚度和取向是电子衍射中两个十分关键的参数,厚度和取向的变化导致等厚条纹和等倾条纹(所谓摆动曲线).会聚束衍射最大的好处是束斑很小(<100nm),这样由厚度和取向而引起的变化可以减到最小,结果高阶劳厄带效应不但不可以忽视,而且成为十分重要的信息.在七十年代,Steeds[4]及同事很系统地研究和发展了CBED,并且把这技术应用于各种材料研究中[5].随着扫描透射电子显微… 相似文献
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基于双光栅的马赫-曾德尔干涉仪的初步研制 总被引:1,自引:1,他引:0
设计和初步制备了基于双光栅的等臂和不等臂马赫-曾德尔干涉仪,两个衍射光栅分别用作光束分裂器和光束复合器.来自激光器的平行光束透过第一光栅后产生多柬衍射光,等臂干涉仪使用两个平面反射镜反射两束对称衍射光至第二光栅的同一位置并产生完全重合的衍射条纹,即每束衍射光包含两个成分.利用光探测器监测任一束重合的衍射光束,该光束两成分之间的相位差随时间的变化就能够被准确测定.而不等臂干涉仪仅使用一个反射镜反射某一束衍射光并使之与零级光束透过第二光栅后产生完全重合的衍射条纹.通过使用一个厚度为50μm的玻璃片来改变相位差,对不等臂干涉仪的干涉效果进行了测试,得到了与理论值相符的实验结果. 相似文献
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T. M. Poletika S. L. Girsova A. N. Shmakov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(3):408-412
Synchrotron radiation X-ray diffraction has been applied for the precision study of the micro-structure evolution of a Zr-1% Nb alloy deformed by uniaxial tension. A nonmonotonic pattern of the integral width of X-ray lines as a function of in situ deformation and acting stress has been revealed, which is in agreement with intensity fluctuations of reflections and elastic microdistortions related to structural imperfection. The obtained results correlate with transmission electron microscopy data on the cyclicity of dislocation transformations during necking. 相似文献
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The types of diffraction effects which may be expected from secondary relaxations in high-Σ [001] twist boundaries are calculated and discussed. An idealized two-plane model is used which incorporates secondary relaxations by rotating patches of boundary about coincident site lattice elements normal to the boundary. Local relaxations within the patches are also employed using rotational relaxations about local O-lattice elements in a manner consistent with earlier results. The main effect of secondary relaxations is the splitting of grain boundary reflections into small clusters which fall on a “grain boundary dislocation lattice”. This localized splitting is significant only when the deviation of the boundary from a nearby low-Σ misorientation becomes sufficiently large. Under these circumstances a noticeable distortion of the diffraction pattern can also occur. The results are compared with some X-ray diffraction observations from twist boundaries in gold. 相似文献
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Abstract Energy-dispersive x-ray diffraction using synchrotron radiation was carried out on α-cristobalite to 3 GPa and 350°C in a cubic anvil press. A cascading structural phase transition occurred beyond 0.61 GPa at room temperature. The transition was accompanied by a splitting of most of the a-cristobalite reflections: the (111) reflection at 0.61 GPa through the (211) reflections at 2.13 GPa, with many other lines between. The pressure of this transition decreased with increasing temperature. 相似文献
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AbstractDislocations in shock loaded tantalum single crystals were imaged using both transmission electron microscope (TEM) and electron channelling contrast image (ECCI) in a scanning electron microscope with a conventional backscattered electron detector. The results were compared with backscattered electron intensity profiles across dislocations calculated via the dynamic theory of electron diffraction. A one-to-one correspondence between ECCI and TEM is established. High voltage and low index reflections should be used to obtain the highest dislocation contrast and greatest imaging depth. 相似文献
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K. B. Samusev M. V. Rybin S. Yu. Lukashenko P. A. Belov M. F. Limonov 《Physics of the Solid State》2016,58(7):1412-1419
Photonic structures with hexagonal symmetry have been prepared by the additive technology of two-photon laser lithography, and their optical properties have been investigated. The structure of the samples has been examined using scanning electron microscopy. The calculations have been performed for the optical diffraction in the Born approximation of the scattering theory for structures with a limited number of scatterers. The images formed in the monochromatic light on a flat screen located behind the sample have been calculated. The diffraction patterns on the screen have C6v symmetry and consist of three straight lines intersecting at an angle of 120° and hyperbolas, the number of which is a multiple of six. An important feature of these diffraction patterns is the superstructure, i.e., the partition of straight lines and hyperbolas into individual diffraction reflections, the number of which is determined by the number of scatterers of a particular sample. The results of the experimental investigation of the diffraction patterns completely coincide with the calculated data, including the number and arrangement of the superstructure reflections. 相似文献
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We present a fast algorithm to accelerate geometric sound propagation in complex 3D scenes. Our approach computes propagation paths from each source to the listener by taking into account specular reflections and higher-order edge diffractions around finite edges in the scene. We use the well known Biot–Tolstoy–Medwin (BTM) diffraction model along with efficient algorithms for region-based visibility to cull away primitives and significantly reduce the number of edge pairs that need to be processed. The performance of region-based visibility computation is improved by using a fast occluder selection algorithm that can combine small, connected triangles to form large occluders and perform conservative computations at object-space precision. We show that our approach is able to reduce the number of visible primitives considered for sound propagation by a factor of 2–4 for second order edge diffraction as compared to prior propagation algorithms. We demonstrate and analyze its performance on multiple benchmarks. To the best of our knowledge, this is the first algorithm that uses object-space visibility algorithms to improve the performance of finite-edge diffraction computation for geometric sound propagation. 相似文献
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The specific features of the formation of a diffraction image of a single edge dislocation in the case where the defect region can be located at different points of the scattering triangle are investigated by computer simlation and experimentally. The dislocation images are experimentally obtained at different wavelengths and for different reflections. The diffraction geometry in which the dislocation line is perpendicular to the sample surface and the Burgers vector is parallel or perpendicular to the reciprocal lattice vector is studied. From analysis of the experimental and theoretical images, inferences are made regarding the image symmetry, as well as the angular resolution and the sensitivity of section topography to the formation of the dislocation image. Special attention is focused on the dependence of the image contrast and the image size on the radiation wavelength, the magnitude of the reciprocal lattice vector, and the interference absorption. 相似文献
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V. M. Silonov V. V. Chubarov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2014,8(3):509-512
In addition to reflections of the hexagonal phase of ice I h, the intense diffuse scattering of X-rays mainly due to the amorphization of ice is revealed on the X-ray diffraction patterns of water ice samples prepared at liquid nitrogen (studied by the authors earlier) and samples prepared at T = ?10°C (this work). The measurements are performed in the temperature range from ?25 to 0°C. The existence of reflections of the crystalline phase and intense diffuse scattering on the X-ray diffraction patterns makes it possible make a conclusion about the coexistence of crystalline and amorphous structures of ice. Splitting of the first maximum on the electron-density radial distribution function is detected on the basis of an X-ray diffraction pattern recorded at T = ?3°C. This splitting is explained by an increase in the interatomic distances between the nearest-neighbor atoms located at different levels. Similar splitting was also detected on a radial distribution function constructed using an X-ray diffraction pattern recorded at ?10°C. 相似文献
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Samples of Ti–6?wt%?Al–4?wt%?V and Timet 550 (Ti–4?wt%?Al–4?wt%?Mo–2?wt%?Sn–0.5?wt%?Si?wt%), which have been deformed at a strain rate of 5?s?1, were annealed after thinning so that the visibility of dislocations in transmission electron microscopy could be compared before and after annealing. It has been found that imaging with g?=?0002 produces clear images of dislocations before and after annealing, but that imaging with other diffracting vectors gives reasonable dislocation images only after annealing to at least 700°C. The sharpness of Kikuchi lines in diffraction patterns obtained from fully annealed samples, deformed at 10?1 and 5?s?1, has been examined. The lines are sharp for all planes in the fully annealed samples, but become more diffuse in samples deformed at 10?1?s?1. However, in samples deformed at 5?s?1 the Kikuchi lines from (0002) planes are sharp but the lines from all other planes are diffuse. These observations are interpreted in terms of the presence of a high density of defects, which do not distort the elastically strong (0002) planes as significantly as they distort all other planes. These observations are discussed with respect to the recent claim that a particular Ti alloy deforms by a mechanism that does not involve dislocations. 相似文献