鉍薄膜的結構特性研究

Abstract

本論文利用X光繞射、X光吸收光譜、電子背向散射繞射量測分析以分子束磊晶法成長於矽基板上的鉍薄膜結構。X光繞射初步分析下的結果顯示成長之鉍薄膜主要有兩種晶向，分別為(003)以及(012)。 於國家同步輻射中心量測鉍薄膜延伸X光吸收精細結構，透過Athena與Artemis軟體分析擬合，得到鍵長及德拜-沃勒因子，分別由電子背向散射繞射、X光繞射得到鉍(012)的面積比例與強度比例，並與德拜-沃勒因子比較，發現薄膜中(012)成分比例越高，德拜-沃勒因子越大。 利用六方晶晶體結構模型計算出鉍的結構因子，分別討論在X光繞射中的偏振因子、角速度因子、吸收因子，將這些因素考慮進去X光繞射強度公式，並藉由公式與鉍薄膜對稱面(006)與(009)的變溫X光繞射量測得到不同溫度下的原子偏差，估算電子背向散射繞射圖上的晶粒直徑大小，判斷原子偏差較大的樣品是由於晶向較為雜亂所致，且由搖擺曲線印證結果。鉍晶體結構中存在雙層結構，其層與層之間會存在不同的鍵結，分別為共價鍵以及凡德瓦鍵，鍵結強度的不同導致不同的對稱面面間距膨脹程度出現差異，引起原子偏差的增加。

The purpose of this thesis is measuring and analyzing the bismuth thin films grown on silicon substrates via molecular beam epitaxy by using X-ray diffraction, X-ray absorption spectroscopy, and electron backscatter diffraction. The preliminary analysis of X-ray diffraction shows that the grown bismuth film has two lattice orientations, namely (003) and (012). The extended X-ray absorption fine structure of bismuth thin films were measured at NSRRC, the bond lengths and Debye-Waller factor were obtained by fitting using Athena and Artemis software analysis fitting. We obtain the area ratio and intensity ratio of bismuth (012) via electron backscatter diffraction and X-ray diffraction, and compared with the Debye-Waller factor, it shows that the higher the proportion of bismuth (012) in the film, the greater the Debye-Waller factor. We calculate the structure factor of bismuth using the hexagonal crystal structure model, discuss the polarization factor, angular velocity factor, and absorption factor in X-ray diffraction, and take these factors into consideration in the X-ray diffraction intensity formula, by using the formula and the temperature-dependent X-ray diffraction measurement of the bismuth film symmetry planes (006) and (009) to obtain the atomic deviation at different temperatures. Estimating the diameter of the grains by EBSD chart, judging that the sample with larger atomic deviation is caused by the disordered lattice orientation, and the result is confirmed by the rocking curve. There is a bilayer structure in bismuth crystal structure, bonds between layers are different, which are covalent bonds and van der Waals bonds. The difference in bonding strength leads to differences in the expansion of different symmetry planes, causing an increase in atomic deviation.