Study On X-ray Fluorescence Holography And Atomic-resolution 3-D Reconstruction

X-ray fluorescence holography based on inside reference points is a new structure-determination method developed in the middle of the 1990s, which combines X-ray detection and holography imaging techniques. Different from the conventional holography imaging, it directly uses atoms in solids as sources or detectors, and is thus able to attain atomic resolution and an immediate picture of the 3D arrangements of atoms in solids. It will provide a new imaging method of microscopic structure for the development of physics, chemistry, biology, material science and high technique manufacturing. Hence a thorough study into the theory and method of X-ray fluorescence holography is of great value.Drawing on physical concepts and optical principles, this thesis presents the mathematic description of X-ray fluorescence holography, including the imaging and reconstruction processes. With the modification of the reconstruction algorithm, discrete Fourier transform is used to speed up the reconstruction and 3D atomic arrangement is obtained by utilizing the idea of CT. As the twin images disturbance is inevitable in holography methods, the reason for their formation and the condition of their cancellation are given in the thesis. In order to suppress the twin images, the widely used Barton's multiple-energy algorithm is introduced and a modified two-energy algorithm is proposed. Compared with Nishino's method, the modified algorithm fully makes use of the information of two different holograms. The simulation calculation shows that the valid modified algorithm is easier than Barton's and more convenient for experiments.The thesis also investigates the factors which influence the quality of reconstruction, including energy, completeness of data, and collection step, and obtains some suggesting results for experiments. The major hologram pretreatments, including background subtraction, absorption correction and low-pass filter, are also studied as they are necessary and important for the extraction of holographic information. As no related experiments have been carried out in our country, experiment data provided by foreign fellow researchers have been processed and the results are in accordance.In most reported experiments, holograms are collected point by point. This method requires expensive equipments with high precision and complexity, which impedes its own popularization. In the end of the thesis, an experimental configuration based on plan detector for hologram collection is introduced. Besides the simplicity of the setup, it also has the advantage of fast holographic imaging with high precision and angular resolution of data. Apparently, the given method is favorable and feasible for laboratory study in this field.