Zou X
Structural Chemistry, Stockholm University, S-106 91 Stockholm, Sweden.
Microsc Res Tech. 1999 Aug 1;46(3):202-19. doi: 10.1002/(SICI)1097-0029(19990801)46:3<202::AID-JEMT4>3.0.CO;2-8.
In electron microscopy, the word phase is used for different physical phenomena, including crystallographic structure-factor phases and the electron wave phases. This has resulted in great confusion, as to whether the phase information is present or lost when an image is recorded. The aim of this paper is to solve this phase confusion problem by studying the relationships between structure factors, exit waves, and high-resolution electron microscopy (HREM) images. Three approaches are taken. First phases at different stages of the imaging processes are compared analytically for a crystal that can be considered a weak phase object (WPO). Then these different phases are calculated by the multi-slice method based on dynamical diffraction theory, and their numerical values are compared. Finally, the validity of the theoretical description is checked by comparison with experimental data on a real crystal, Ti(2)S. It is demonstrated that it is possible to obtain accurate structure factor-phases directly from HREM images by crystallographic image processing. The two major methods for structure determination from HREM images-exit wave reconstruction and crystallographic image processing-are compared. It is shown that the information utilised by the two methods as well as the results are essentially the same.
在电子显微镜中，“相位”一词用于不同的物理现象，包括晶体结构因子相位和电子波相位。这导致了很大的困惑，即记录图像时相位信息是存在还是丢失。本文的目的是通过研究结构因子、出射波和高分辨率电子显微镜（HREM）图像之间的关系来解决这个相位混淆问题。采用了三种方法。首先，对可视为弱相位物体（WPO）的晶体，在成像过程的不同阶段对相位进行分析比较。然后，基于动力学衍射理论，用多层法计算这些不同的相位，并比较它们的数值。最后，通过与真实晶体Ti(2)S的实验数据进行比较，检验理论描述的有效性。结果表明，通过晶体学图像处理可以直接从HREM图像中获得准确的结构因子相位。比较了从HREM图像确定结构的两种主要方法——出射波重建和晶体学图像处理。结果表明，这两种方法所利用的信息以及结果基本相同。
