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HAADF-STEM成像:从原子分辨率HAADF-STEM图像的定性到定量解释

HAADF-STEM imaging: from qualitative to quantitative interpretation of atomic resolution HAADF-STEM images
课程网址: http://videolectures.net/slonano07_ceh_hsi/  
主讲教师: Miran Čeh
开课单位: 约瑟夫·斯特凡学院
开课时间: 2008-01-18
课程语种: 英语
中文简介:
在我们的演讲中,将给出定性和定量HAADF STEM技术的概述,并通过各种无机陶瓷材料的表征示例进行举例说明,例如CaTiO3 La(Mg,Ti)O3固溶体,GaN蓝色激光二极管,块状CaTiO3和AO掺杂SrTiO3(A = Sr,Ca,Ba)。用于HAADF STEM观察的样品是通过高能和/或低能离子铣削制备的,并在FEG JEOL 2010F(Cs = 0.48 mm)中进行观察。探针半角为10毫弧度。 HAADF检测器的内环形角和外环形角分别为100和220 mrad。使用渡边开发的计算方案进行了HAADF STEM图像模拟。我们的结果表明,可以通过HAADF STEM成像轻松检测出平均原子序数Z仅有2%的差异。在对原子分辨率HAADF STEM图像进行定性解释时,我们比较了不同原子列之间的强度比或使用强度分布图来显示各个原子列之间化学成分的差异。这样,我们可以定性地解释散装材料中溶质原子的有序和/或部分有序,评估特殊结构中原子柱的占有率,并研究沿晶界的杂质偏析。定量解释需要图像模拟,并将处理后的实验图像与计算出的图像进行匹配。然而,为了计算HAADF STEM图像,应该知道所观察到的结构现象的确切结构,即原子的位置,以便创建用于计算的适当的超级单元。计算中也应使用Debye Waller因子的实际值。在图像计算之后,应用与实验图像的适当匹配算法,以便确定计算图像与实验图像之间的最佳拟合。
课程简介: In our presentation an overview on qualitative and quantitative HAADF-STEM technique will be given and illustrated by examples of characterization of various inorganic ceramic materials, such as CaTiO3-La(Mg,Ti)O3 solid solution, GaN blue laser diode, bulk CaTiO3 and AO-doped SrTiO3 (A=Sr,Ca,Ba). The specimens for the HAADF-STEM observations were prepared by high-energy and/or low-energy ion milling and were observed in a FEG JEOL-2010F (Cs=0.48 mm). The probe semi-angle was 10 mrad. The inner and outer annular angles of the HAADF detector were 100 and 220 mrad, respectively. The HAADF-STEM image simulations were carried out using a calculation scheme developed by Watanabe. Our results showed that differences as small as 2% in the average atomic number Z can readily be detected by HAADF-STEM imaging. In qualitative interpretation of atomic-resolution HAADF-STEM images we compared intensity ratios between different atom columns or used intensity profiles to show the difference in the chemical composition between individual atom columns. In this way we could qualitatively interpret the ordering and/or partial ordering of solute atoms in bulk materials, evaluate the occupancy of atom columns in special structures and study the segregation of impurities along grain boundaries. Quantitative interpretation required image simulations and matching of the processed experimental images with the calculated ones. However, in order to calculate HAADF-STEM images the exact structure of the observed structural phenomena should be known, i.e., the positions of the atoms, in order to create proper supercells for calculations. The realistic values of the Debye-Waller factor should also be used in calculations. After image calculations appropriate matching algorithms with the experimental images were applied in order to determine the best fit between calculated and experimental image.
关 键 词: 原子; 图像; 离子
课程来源: 视频讲座网
入库时间: 2019-09-25
最后编审: 2019-09-25:yuh
阅读次数: 482