| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 93 === Transmission electron microscopy (TEM) is a modern instrument for analyzing materials, including the imaging, structure and element analysis. However, as the diffraction patterns and images are recorded, the phase of the electronic waves is lost that the half information is unknown at the same time. Besides, as the electronic waves pass through the magnetic lens system, the unavoidable lens aberrations blur the images that it is not actually reflect the specimen when the images are recorded.
The phase in reciprocal space reveals the relative position of the atoms. From the phase retrieval the recovered image will not contain the aberrations because the lens aberrations do not affect the intensity of diffraction beam. To be brief, the goal in the thesis is to solve the phase problem and lens aberrations in TEM at the same time.
The oversampling method is still in the early stage in the phase retrieval for TEM, although the some simulations and experimental cases for x-ray are discussed in recent years. In the thesis we take MgO for example because its simple structure and light mass. Some limitation for overampling method will be discussed, and after overcome the difficulties of limitations, the experimental data will be shown and discussed. To do the comparison, not only the experimental but the simulation case will be discussed. After recovering the images of two-dimensions, it is further to do the three-dimensional reconstruction. That is, in the thesis we will discuss from several diffraction patterns in different directions, the diffraction tomography can be done and the 3-D image can be recovered in the simulation case.
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