Development of a nm-scale crystal structure refinement method

在当今材料科学中，如何控制材料的纳米级结构是最重要的研究主题。要解决这一问题，纳米级的晶体结构分析是必不可少的。本研究的目的是建立一种利用会聚束电子衍射(CBED)对纳米级样品区域进行精确的晶体结构精细化的方法，并将该方法应用于实际准晶的详细结构的测定。为了实现这种方法，研制了一种新型电子显微镜，它配备了场发射枪、用于去除非弹性散射电子的omega型滤光片、成像板和CCD电子探测系统。这台显微镜向前迈出了划时代的一步，允许远程计算机控制，并使用互联网系统同时观察不同地点的电子显微镜图像。我们开发了一个完全基于电子衍射动力学理论的结构求精软件，使…S更有可能对CBED模式进行二维拟合。我们对非中心对称材料CdS进行了结构修正，测得硫的位置参数u为0.378，镉和硫的两个德拜-沃勒因子B(Cd)和B(S)分别为1.35和1.14。这些值与X射线的u=0.3771，B(Cd)=1.4B(S)=1.1值很好地吻合。Cd S结构精细化的成功证明了CBED精确的结构精细化在材料科学中具有实用价值。我们发现了十方准晶的新结构特征，修正了已被接受的结果。也就是说，被认为是十方准晶基本单元的2 nm团簇可以分解成直径约为0.4 nm的两个较小的团簇。这两个碎屑与存在于近似晶体中的碎屑非常相似。这提供了指导原则，即可以根据近似物的晶体结构来考虑准晶。我们正在应用高维结晶学进行结构分析。较少

In materials science at the present time, how to control nm-scale structures of materials is the most important research theme. Crystal structure analysis in nm-scale is indispensable to solve the question. The aim of the present research is to develop an accurate crystalstructure refinement method for nm-diameter specimen areas using convergent-beam electron diffraction (CBED), and to apply using method to the determination of detailed structures of real quasicrystals. To rearize the method, a new electron microscope equipped with a field-emission gun, an omega type filter to remove inelastically scattered electrons, an imaging plate and a CCD electron detection system was developed. This microscope took an epoch-making step forward to allow remote computer control and simultaneous observation of electron microscope images at different places using an internet system. We developed a structure refinement software based fully upon the dynamical theory of electron diffraction, which make … More s possible two dimensional fitting of CBED patterns. We performed a structure refinement of a noncentrosymmetric material CdS.We determined the positional parameter of sulfur u to be 0.378 and two Debye-Waller factors of cadmium and sulfur B(Cd) and B(S) respectively to be 1.35 and 1.14. These values well agree with X-ray values of u=0.3771, B(Cd)=1.4 and B(S)=1.1. The success of the structure refinement of Cd S proved that the accurate structure refinement by CBED is practically useful for materials science. We discovered new structural features of decagonal quasicrystals which correct the results already accepted. That is, the 2nm-cluster, which was considered to be a basic unit of the decagonal quasicrystal, can be decomposed into two smaller clusters of about a 0.4nm diameter. These two clasters are very similar to those existing in the approximant crystal. This provided the guiding principle that the quasicrystal can be considered on the basis of the crystal structure of the approximant. We are in the course of structure analysis by applying the high-dimensional crystallography. Less