Study On The Influence Of Thickness In High-resolution Imaging Of Transmission Electron Microscope

Nowadays,high-resolution electron microscopy is widely used in the research of various materials,thanks to its powerful evaluation and analysis of materials at the atomic scale.However,due to factors such as sample thickness and aberrations in the TEM imaging process,high-resolution images may not necessarily reflect the true structural information,that gives huge difficult to scholars in analyzing the structure of material.So,it is necessary to perform image processing on the high-resolution images taken by the electron microscope to obtain information reflecting the structure or further improve the resolution of the image,and finally determine the material structure.In this paper,aiming at the influence of sample thickness on high-resolution imaging,the simulation experimental environment is used to further study the practicability of the existing methods of linear and nonlinear separation of high-resolution images,and also use this method to study the influence of the thickness of amorphous ice on high-resolution images.The main details of this thesis are as follows:1.Linear and nonlinear separation methods have been proposed for a long time,but the two positive and negative Cs-corrected HRTEM images used in the separation process only consider the ideal situation,that is,the spherical aberration coefficient and the effective defocus amount are opposite to each other.However,in actual experiments,the situation will going to complicated,and there may be factors such as offset of positive and negative Cs-corrected HRTEM images pixels,inaccurate measurement of defocus,and adding high-order astigmatism.Therefore,some complex experimental environments will be simulated to study the applicable range and tolerance of the separation method.2.The effect of the thickness of amorphous ice on the high resolution image is studied by using the linear and nonlinear separation methods.First,through image processing methods,it is verified that the diffraction pattern after the amorphous Fourier transform has a corresponding relationship with the contrast transfer function of the corresponding condition,and the relationship can be used to obtain the approximate value of the defocus amount of the amorphous high resolution image with unknown defocus amount(other conditions are constant).Secondly,use simulation software to simulate the positive and negative Cs-corrected HRTEM images of amorphous ice with different thicknesses and also meet Scherzer's focusing conditions,and combine the above-mentioned separation methods to observe its influence on imaging.