研究晶體的原子結構,一直是一個很重要的研究課題,方法也很多種,像吸收光譜或兩光繞射(Diffraction Anomalous fine structure)而本論文是用多光繞射(MDAFS)(000,222,33-1)研究GaAs的異常精細結構然後和EXAFS及兩光繞射(DAFS)比較。利用同步輻射光源的可調性,在光束線17B把能量調至Ga的K吸收邊(10.369KeV)然後改變入射光能量,作三光複繞射並量測強度再藉由動力繞射的理論計算配合由實驗數據得知的Rv值求出異常散射因子的實部,進而求出精細結構項,再利用傅利葉轉換得到GaAs晶體內的原子間間距。

The research of the structure of a crystal is always a very popular and important issue. There are many
methods which can be used to study the structure of the crystal such as X-ray diffraction, X-ray absorption, DAFS(Diffraction Anomalous Fine Structure) and EXAFS
(Extended X-ray Anomalous Fine Structure). DAFS is an x-ray spectroscopic, structural and crystallographic method which
combines the benefit of x-ray diffraction and x-ray absorption by measuring the elastic Bragg reflection intensities versus photon energy. However, we cannot calculate the real part of anomalous scattering factor directly. We have to find out the imaginary part of anomalous scattering factor first, then use the KKR relation to calculate the real part of anomalous scattering factor. The main topic of my thesis is the use of MDAFS(Multiple Diffraction Anomalous Fine Structure) to find out
the real part of anomalous scattering factor of GaAS directly. This method does not need to go through the complex procedure, KKR transformations, and provide a
quick way to analyze the data collected. By the combining the intensity ratios value Rv, both experimental and theoretical based on the dynamical theory, the the real part of anomalous scattering factor can be determined easily from intensity measurement. Furthermore, we can obtain the fine structure, thus leading to the determination of the distances between Ga and its neighboring atoms.

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