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Quantitative Electron Crystallography

Author: CaiCanYing
Tutor: YangQiBin;WangYanGuo
School: Xiangtan University
Course: Condensed Matter Physics
Keywords: Electron crystallography Electronic power diffraction Exit surface wave function
CLC: O73
Type: Master's thesis
Year: 2004
Downloads: 68
Quote: 0
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Abstract


Today has the unique advantages of X-ray crystallography unmatched by electron crystallography has become increasingly active. However, due to the strong dynamic interactions between the electrons and crystal, making the complicated structure analysis using an electron microscope method. In order to solve the problem of power diffraction, for many years the electronic crystal scientists have developed a numerical simulation method. These methods do not reveal the intuitive relationship between the simulation results with the crystal structure, and only on the known crystal structure of the proposed simulation confirmed, and to the analysis of unknown structure, the development of electronic power diffraction analytical formulas. So far, has not been able to describe a good electronic power diffraction analytical expression. The electron crystallography scientists are able to do is to find the approximate formula from a different perspective. 2001, Yang Qibin et al. Based Schr? Dinger equation, an analytical expression is derived: In this paper, the derivation of the electron dynamics diffraction analytical formulas Schr? Dinger equation in consideration of the second-order differential term, and to get a more accurate analysis expression; analyzed in some cases, corrected to the formula is necessary. Generally, the wave function of the exit surface is mainly determined by the zero-order Laue zone, but in some cases, the senior Laue band effect also must be considered. Relative to the zero-order Laue with effect senior Lloyd with a study of the impact of the exit surface wave function is more difficult (This is because despite the down easy space zero-order Laue band effect with senior Lloyd with The effect is to separate, but both in the HREM image is often superimposed on the a). We first take the same approach to study the effect of the zero-order Laue zone study senior Lloyd with effect the senior Lloyd with effect in two ways (numerical methods and analytical formulas) to calculate; then according to the analytical expression from theoretically analyzed composition sample atomic weight, the thickness of the sample, the incident electron beam wavelengths, and perpendicular to the incoming beam direction of the lattice plane spacing, and the distribution of the atoms in the atomic columns factors Sr Laue band effect; Finally calculation results show that the above conclusion. correctness. The analytical formula is a universal formula, in principle, it can be used for the beam inclination, the sample inclination calculated under a variety of imaging conditions. We put this electronic dynamics the diffraction theory formulas and LT; WP = 4 GT; multilayer method control, the simulated distribution of the phase of the wave function of the electron beam along the zone axis direction deviation of the different incident angles when the exit surface. Confirmed the analytical expression indeed be applied to the beam tilt situation. The actual operation of the electron microscope, the incident beam and the sample crystal zone axis, there is always a certain deviation, so this analysis makes sense.

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CLC: > Mathematical sciences and chemical > Crystallography > Crystal physics
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