Accurate crystal structure analysis by quantitative high-resolution electron microscopy

我们尝试建立了用高分辨电子显微镜和电子衍射进行晶体结构分析的过程。高分辨电子显微照片和电子衍射图作为定量数据用慢扫描CCD(电荷耦合器件)相机和IP(成像板)固定在分辨率为0.17 nm的400千伏透射电子显微镜(JEM-4000EX)上。这项工作的主要目的是开发一种用计算机处理高分辨率显微照片和电子衍射图的定量数据的晶体结构分析程序。我们的研究结果总结如下。为了准确分析Tl_2Ba2CuO_y超导氧化物的晶体结构，引入了定量观测图像与模拟图像之间的残差指数。通过对剩余折射率取厚度和离焦值等参数的最小化，可以定量地评价金属原子的部分占有率，从而可以检测出缺氧原子的位置。利用CCD相机的高灵敏度特性，我们观测到了掺镍沸石的高分辨率电子显微镜图像，这些沸石对电子束的作用非常弱。通过对高分辨率电子显微照片的图像处理和图像分析，可以对镍原子的结构进行准确的分析。在这里，我们展示了应用慢扫描CCD相机来提高合成沸石结构ZSM-5(MFI)对比度细节的实验分辨率。通过与使用观测到的电子衍射强度的傅里叶合成进行比较，也表明了通过使用ccd相机在结构细节的数量和质量上的改进。基于归一化衍射光强的R因子被用来评价结构分析的结果。

We have tried to establish the process of crystal structure analysis with high-resolution electron microscopy and electron diffraction. High-resolution electron micrographs and electron diffraction patterns are measured as quantitative data by a slow-scan CCD (charge-coupled device) camera and IP (imaging-plate) attached to a 400 kV transmission electron microscope (JEM-4000EX) having a resolution of 0.17nm. The main purpose of this work has been to develop a procedure of crystal structure analysis with computer work of the quantitative data of high-resolution micrographs and electron diffraction patterns. Our results are summarized as the follows.1. In order to try accurate crystal structure analysis of a Tl_2Ba_2CuO_y superconducting oxide, a residual index between observed quantitative images and simulated images was introduced. From minimizing the residual index with some parameters of thickness and defocus values, partial occupancy of metal atoms can be quantitatively evaluated and deficient oxygen atom positions can be detected.2. By using high-sensitive properties of the CCD camera, we observed high-resolution electron microscopic images of zeorites introduced with Ni, which are extremely weak for electron beam. From image processing and image analysis of the high-resolution electron micrographs, accurate structure analysis of Ni atoms can be evaluated.3. We demonstrate herein the application of a slow-scan CCD camera for improvement in the experimental resolution of contrast details in the synthetic zeorite structure ZSM-5 (MFI). The improvement in the amount and quality of structural detail through the use of the CCD camera is also shown by a comparison of a Fourier synthesis, made by using the observed electron diffraction intensities. R-factors based on the normalized diffraction intensities have been employed to evaluate the result of the structure analysis.