Development of a nm-scale crystal structure refinement method

点击翻译按钮获取中文摘要

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