Establishment of new analytical technique applicable for local atomic arrangements in various multi-component materials

本研究旨在建立一种适用于氧化铝或氧化物等多种多元体系的局域原子排布定量分析的新的电子显微镜技术。从实验和理论上研究了B_2和L_0型有序铝化物的沟道增强微量分析原子定位的最佳实验条件和配方。用几种不同的方法测量了铝化物中超晶格反射的结构因子，并对这些方法的准确性和适用性进行了检验。主要结论如下：1.本文的主要结论如下。对于含有大量轻元素的合金和化合物，如Al或O，ALCHEMI的结果强烈地依赖于衍射条件。如果为沟道条件设置了正激发误差，则特征X射线强度可能给出不正确的组成元素的占据概率。The…更多的事实主要是由于样品内部X射线发射和吸收的内壳层电离的离域。对于具有相当小的超晶格反射结构因子的合金和化合物，如B2有序的Ti-Al-Mo2，占据几率的实验值与校正值之间的差异变大。提出了一种新的ALCHEMI方法，为此类铝化物提供了可靠的数据：(1)将晶体取向设置为系统的行激发。(2)用倾斜入射电子束的方法测量组成元素的特征X射线强度，得到“衍射条件-特征X射线强度”的轮廓，以及箔的厚度。(3)通过ALCHEMI计算机模拟对剖面进行拟合，确定各组成元素的占据概率，给出最佳的拟合结果。ALCHEMI的模拟必须考虑(I)被非弹性散射衰减的弹性散射电子的动态衍射，(Ii)弹性和非弹性散射电子的特征X射线发射，(Iii)内壳层电离的离域和(Iv)样品内X射线的吸收。对于具有较小超晶格反射结构因子的合金，如B2有序的Ti-Al-Mo，用多光束动力学衍射理论进行定量电子衍射及其拟合模拟，给出了比相交Kikuchi线法和厚度条纹法更可靠的结构因子值。较少

This study aims at establishing a new TEM (transmission electron microscope) techique to analyze local atomic arrangements quantitatively which is applicable for various multi-component systems, such as aluminides or oxides. The optimum experimental conditions and formulations of ALCHEMI (atom location by channelling enhanced microanalysis) for B2 or L1_0 type-ordered aluminides were investigated experimentally and theoretically. The structure factors of superlattice reflections in the aluminides were measured by some different methods, and the preciseness and applicability of the methods were examined. The main conclusions are drawn as follows.1. In case of alloys and compounds containing a large amount of light elements, such as Al or O, the result of ALCHEMI depends strongly on the diffraction condition. If a positive excitation error is set for the channelling condition, the characteristic X-ray intensity may give incorrect occupation probabilities of the constituent elements. The … More fact is mainly due to delocalization of the inner-shell ionization for the X-ray emission and absorption of the X-rays within the specimen. The differences between the experimental values of occupation probabilities and the correct ones become large for alloys and compounds which have considerable small structure factors of superlattice reflections, such as B2-ordered Ti-Al-Mo.2. A new procedure of ALCHEMI which gives reliable data for such aluminides are proposed as follows : (1) set the crystal orientation into the systematic row excitation. (2) measure the characteristic X-ray intensity of constituent elements with tilting the incident electron beam to obtain a "diffraction condition-characteristic X-ray intensity" profile, as well as the foil thickness. (3) fit the profile by the computer simulation of ALCHEMI to determine the occupation probabilities of the constituent elements which give the best fitting result.3. The simulation of ALCHEMI must consider (i) dynamical diffraction of elastic-scattered electrons attenuated by inelastic scattering, (ii) characteristic X-ray emission by the elastic- and inelastic-scattered electrons, (iii) delocalization of the inner-shell ionization and (iv) absorption of the X-rays within the specimen.4. For alloys which have small structure factors of superlattice reflections, such as B2-ordered Ti-Al-Mo, the quantitative electron diffraction and its fitting-simulation using the many-beam dynamical diffraction theory give much reliable values of the structure factors than the intersecting Kikuchi-line method and the thickness-fringe one. Less