| The results of electron microscopic imaging are sometimes not so intuitive.More information can be obtained from the limited results through simulation research.In my thesis,the imaging simulation method of transmission electron microscope is introduced,and the imaging of electron microscope under defocus and astigmatism is studied.In addition,the multi-slice method based full-space mechanical analysis is developed and applied to the study of the mechanical effect of electron beam on samples.Firstly,the imaging mechanism of charged nanowires under large defocus is present.In electron microscope,the sample is sometimes charged when irradiated by an electron beam.The charge will affect the imaging quality and can also reflect the electrical properties of the sample,which has attracted people’s attention.By using electron off-axis holography,one can obtain the charge distribution of the sample through a series of defocused images.However,it requires good coherence of the electron beam.For defocused images,the coherence loss caused by sample scattering is creatively proposed,and the simulation method is given.It is concluded that when there is a large amount of charge,the scattering of nanowires and the resulting partial coherence can have a negligible impact on the defocus image.Secondly,the imaging mechanism of magnetic needle under large astigmatism is explained,and its application prospect is discussed.Vortex electron beam is a new kind of electron beam with angular momentum.It has application prospects in the measurement of material magnetism,chirality and dichroism.The magnetic needle method can produce vortex electron beam efficiently,but the magnetization of the magnetic needle is often not ideal.It is found that under large astigmatism,the morphology of vortex selfcoherent fringes and magnetic needle can be observed at the same time.By simulating astigmatic images,the distortion of self-coherent fringes and the distortion of Fresnel fringes of magnetic needle are analyzed.In my thesis,a multi magnetic monopoles model is proposed,and the simulation results are consistent with the experiment.It is proposed that the magnetic flux leakage and the inclination of the magnetization direction can be judged by observing the fringe distortion period on both sides of the magnetic needle.This study provides a simple and effective method to determine the magnetization of magnetic needle in magnetic needle method,which is also a potential magnetic domain observation technology.Thirdly,for the mechanical action between sample and electron beam,a full space mechanical analysis theory and a set of mechanical analysis tools are developed in the thesis.It provides a powerful analysis tool for the developing electron beam manipulation technology.This method is based on the multi-slice method,and has the same advantages of high efficiency,high accuracy,highly customized samples and beams,and strong expression ability.In the thesis,the force and torque of vortex beam on nanoparticles are studied.The mechanism that electron beam intensity gradient and phase gradient can drive the movement of nanoparticles is proposed,which is verified by force vector diagram.In the study of the depth dependent mechanical action of vortex electron beam on the sample,the accuracy advantage of our method is demonstrated,and the phenomenon of angular momentum oscillating with depth is analyzed.To sum up,the effects of charge,nonuniform magnetization and aberration on transmission electron microscope imaging are studied.The result provides theoretical support for the application of electron in-line holography in charge measurement and the optimization of vortex electron beam generated by magnetic needle method.In addition,a method for analysis of the mechanical interaction between electron beam and nano materials is proposed.The mechanical interaction between vortex electron beam and nano particles are studied.The mechanism of electron beam manipulation is proposed. |
