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Development of a nm-scale crystal structure refinement method

纳米级晶体结构细化方法的开发

基本信息

批准号：
06102003
负责人：
TANAKA Michiyoshi
金额：
$ 176万
依托单位：
RESEARCH INSTITUTE FOR SCIENTIFIC MEASUREMENTS,TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Specially Promoted Research
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1997
项目状态：
已结题

项目摘要

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

在当前的材料科学中，如何控制材料的纳米级结构是最重要的研究主题。纳米尺度的晶体结构分析是解决这一问题不可或缺的手段。本研究的目的是建立一种利用会聚束电子衍射（CBED）精确测定纳米直径样品区域晶体结构的方法，并将该方法应用于实际准晶体的详细结构测定。为了实现该方法，研制了一种新型电子显微镜，该显微镜配备了场发射枪、用于去除非弹性散射电子的omega型滤波器、成像板和CCD电子检测系统。这台显微镜迈出了划时代的一步，可以通过远程计算机控制，并通过互联网系统在不同地方同时观察电子显微镜图像。我们开发了一个完全基于电子衍射动力学理论的结构优化软件，使CBED图的二维拟合成为可能。我们对非中心对称材料CdS进行了结构改进。我们确定硫u的位置参数为0.378，镉与硫B（Cd）和B(S)的两个Debye-Waller因子分别为1.35和1.14。这些值与u=0.3771、B(Cd)=1.4、B(S)=1.1的x射线值吻合较好。对Cd - S进行结构细化的成功证明了用CBED技术进行精确的结构细化在材料科学中具有实际应用价值。我们发现了十角准晶体的新结构特征，修正了已有的结果。也就是说，作为十方准晶体基本单元的2nm团簇可以分解成两个直径约为0.4nm的更小的团簇。这两种晶粒与存在于近似晶体中的晶粒非常相似。这为在近似晶体结构的基础上考虑准晶体提供了指导原则。我们正在应用高维晶体学进行结构分析。少