Crystal Structure Analysis of Zeolites by Quantitative HRTEM Study

我们应用高分辨电子显微镜(HRTEM)定量技术对几种沸石晶体和微孔内掺入的分子进行了结构分析。首先，我们在400kVHRTEM上安装了一台慢扫描CCD相机，以提高合成沸石结构MFI对比度细节的实验分辨率。额外分辨的对比度特征表明，有机TPA+(四丙基铵)离子存在于该材料的原子骨架的结构笼子(通道)中。通过使用CCD相机在结构细节的数量和质量方面的改进，也可以通过比较使用观察到的电子衍射强度进行的傅里叶合成和使用基于X射线测量的结构模型计算的另一种傅立叶合成来显示。根据X射线数据计算了两个傅里叶图的位相。虽然绕射强度的计算是基于运动学近似，但两种傅里叶计算的结果很好地吻合。基于归一化衍射强度的R因子也被用来评价结构分析的结果。为了进行更详细的结构分析，我们利用FAU沸石的骨架结构进行了计算，评价了电子的动态散射效应。FAU沸石是最受欢迎的低原子堆积密度的沸石结构类型之一。计算结果表明，运动学近似可应用于厚度约为30 nm的样品，特别适用于客体材料的结构分析。

We have applied a quantitative high-resolution transmission electron microscopy (HRTEM) technique to the structure analysis for several kinds of zeolite crystals and incorporated molecules inside micropores. First, we applied a slow-scan CCD camera attached to a 400kV HRTEM for improvement in the experimental resolution of contrast details in the synthetic zeolite structure MFI.The additionally resolved contrast features are shown to be due to the presence of organic TPA+(tetrapropylammonium) ions in the structural cage (Channels) of atomic framework of this material. The improvement in the amount and quality of strucutural 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, with another one calculated by using a structure model based on X-ray measurements. The phases for both Fourier maps were calculated from the X-ray data. A comparison of the two Fourier calculations results in a good agreement, although the calculation of the diffraction intensities are based on the kinematical approximation. Rfactors based on the normalized diffraction intensities have also been employed to evaluate the results of the structure analysis. For more detailed structure analysis, we have evaluated an effect of dinamical scattering of electrons by the calculation using the framework structure of zeolite FAU,which is one of the best popular zeolite structure type having a low atomic packing density. The results of calculations indicated that the kinematical approximation can be applied up to the specimen thickness of about 30 nm, and is useful especially for the structure analysis of incorporated guest materials.