Li F H
Institute of Physics, Chinese Academy of Sciences, Beijing, China.
Microsc Res Tech. 1998 Jan 15;40(2):86-100. doi: 10.1002/(SICI)1097-0029(19980115)40:2<86::AID-JEMT2>3.0.CO;2-R.
A method of crystal structure determination by electron crystallographic image processing based on the combination of high-resolution electron microscopy (HREM) and electron diffraction is introduced. It consists of two stages: image deconvolution and resolution enhancement. In the first stage an image taken at an arbitrary defocus condition is transformed into the structure image with the resolution depending on the resolution of the electron microscope. In the second stage the image resolution is enhanced to the diffraction resolution limit by combining the electron diffraction data and using the phase extension technique so that in the final image most unoverlapped atoms can be resolved individually. The experimental diffraction intensities are corrected for approximating to square structure factors. The principle of the image processing and the procedure of diffraction intensity correction are briefly described and the results of applications are illustrated. Since the method is based on the weak phase object approximation (WPOA), the validity of WPOA is discussed by introducing an approximate image contrast theory named pseudo weak phase object approximation (PWPOA) to demonstrate the image contrast change with the crystal thickness for very thin crystals.
介绍了一种基于高分辨电子显微镜（HREM）与电子衍射相结合的电子晶体学图像处理晶体结构测定方法。它包括两个阶段：图像去卷积和分辨率增强。在第一阶段，将在任意散焦条件下拍摄的图像转换为结构图像，其分辨率取决于电子显微镜的分辨率。在第二阶段，通过结合电子衍射数据并使用相位扩展技术将图像分辨率提高到衍射分辨率极限，以便在最终图像中大多数不重叠的原子能够被单独分辨出来。对实验衍射强度进行校正以近似方形结构因子。简要描述了图像处理原理和衍射强度校正过程，并举例说明了应用结果。由于该方法基于弱相位物体近似（WPOA），通过引入一种近似图像对比度理论——伪弱相位物体近似（PWPOA）来讨论WPOA的有效性，以证明非常薄晶体的图像对比度随晶体厚度的变化。
