Comparision And Simulation Of Dynamical Electron Diffraction Method

The history of electron crystallography is much shorter than that of X-ray crystallography. However, electron crystallography becomes more and more remarkable due to the outstanding advantages, which X-ray crystallography does not have. The dynamical electron diffraction(DED) calculation of the interaction between electron beams and the sample, is one of the most important approach to determine the crystal structure in the electron crystallography field. There are various algorithms for simulation of DED. However, the most popular ones among them are the multislice(MS) method and the Bloch wave(BW) method. Sometimes the MS method is also called the conventional multislice(CMS) method. The real space(RS) method and the revised real space multislice(RRS) method are seldom adopted owing to some complex factors. In this thesis, we compared the RS method, MS method and BW method, and found some unique advantages about the RS method. Then, we simulated and compared the reflection high-energy electron diffraction(RHEED) patterns using the CMS method and RRS method, respectively. Finally, the convergent beam electron d iffraction(C BED) patterns were simulated using the RS method for the first time due to its advantaages. The main study contents of this thesis are listed as following.(1) A uniform expression was derived from the CMS method, the RS method and the BW method. The only difference among them is the implementation of the algorithm. The BW method is performed in reciprocal space, and the RS method is performed in real space, and the CMS method is alternatively performed in real and reciprocal space. Accuracy, calculation speed and application flexibility of these three simulation methods have been compared by means of quantitative numerical calculations. It was fo und that the RS method is advantageous with respect to accuracy, calculation speed and application flexibility among the three methods.(2) CMS method, one of the most popular dynamical electron diffraction calculation procedures in transmission electron microscopy(TEM), was introduced to calculate reflection high-energy electron diffraction(RHEED) as it is well adapted to deal with the deviations from the periodicity in the direction parallel to the surface. However, in the present work, we showed that t he CMS method is no longer sufficiently accurate for simulating RHEED with the accelerating voltage 3-100 kV because of the high-energy approximation in the solution process. RRS method can be an alternative for more accurate RHEED calculations with reasonable computing time. A detailed comparison of the numerical calculation of the RRS method and the CMS method was carried out with respect to different accelerating voltages, surface structure models, Debye-Waller factors and glancing angles.(3) Convergent beam electron diffraction(C BED) is a significant technique widely used for the characterization of materials microstructure in TEM. It is used to determinate crystal structures, crystal symmetries and atom positions in a crystal as small as several angstroms in size. Rich information about crystal structures are included in the CBED patterns. In order to obtain as many as possible information from the experimental CBED patterns, it is necessary to carry out dynamical simulation of CBED. In this thesis, we simulated the CBED patterns using the RS method for the first time. The effect of the accelerating voltages, the thickness of samples, the size of apertures and the Debye-Waller factors on the CBED patterns are analyzed.