Dorset D L, McCourt M P
Electron Diffraction Department, Hauptman-Woodward Medical Research Institute, Inc., Buffalo, New York 14203-1196, USA.
Microsc Res Tech. 1997 Feb 1;36(3):212-23. doi: 10.1002/(SICI)1097-0029(19970201)36:3<212::AID-JEMT9>3.0.CO;2-Q.
Recently two successful zeolite structures based on experimental electron crystallographic data have been published. Diffraction and image data based on the silicate portion of the zeolite, mordenite, which are perturbed by dynamical (as well as secondary) scattering, have been simulated by a multiple-beam dynamical scattering program. Structure analyses with these data show that the above claims are not unreasonable, given a high enough accelerating voltage for the electron beam. If, for example, 2.9 A resolution micrographs are taken from a 120 A thick crystal in a 200 or 400 kV electron microscope, the crystallographic phases found by image analysis (Fourier filtration) are accurate enough to be extended by the Sayre equation to the (atomic) resolution limit of the electron diffraction pattern (for example from a 105 A thick crystal illuminated by a 1,200 kV electron source). The resultant potential map can be interpreted to find most of the atomic positions and the remaining ones will appear during the progress of a Fourier refinement.
最近，基于实验电子晶体学数据的两种成功的沸石结构已被发表。基于沸石丝光沸石硅酸盐部分的衍射和图像数据，受到动态（以及二次）散射的干扰，已通过多束动态散射程序进行了模拟。利用这些数据进行的结构分析表明，考虑到电子束足够高的加速电压，上述说法并非不合理。例如，如果在200或400 kV电子显微镜中从120 Å厚的晶体拍摄2.9 Å分辨率的显微照片，通过图像分析（傅里叶滤波）找到的晶体学相位足够精确，可以通过塞尔方程扩展到电子衍射图的（原子）分辨率极限（例如由1200 kV电子源照射的105 Å厚的晶体）。由此产生的电势图可以进行解释以找到大多数原子位置，其余的原子位置将在傅里叶精修过程中出现。
