Haruta M, Kurata H, Komatsu H, Shimakawa Y, Isoda S
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
Ultramicroscopy. 2009 Mar;109(4):361-7. doi: 10.1016/j.ultramic.2009.01.004. Epub 2009 Jan 14.
Atomic resolution imaging using the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) can be applied to analyze the atomic structures of materials directly. This technique provides incoherent Z-contrast with the atomic number of the constituent elements. In the present work, unique contrasts that make intuitively interpreting the HAADF-STEM image in double perovskite oxide La(2)CuSnO(6) difficult were observed. Multislice simulation confirmed that this occurred as an effect of the channeling process of electrons in combination with the effect of Debye-Waller factors. This was confirmed because in the La(2)CuSnO(6) crystal, two independent Sn atoms and four independent La atoms in the unit cell had different Debye-Waller factors, and the La columns consisted of pairs of columns with a small separation, whereas the Sn atoms were arranged straight. Furthermore, the image contrast was examined by mutislice simulation, and two atomic La columns were separated in a projected plane and appeared as one column contrast using multislice simulation. As a result, the HAADF intensity did not decrease constantly with the increase in column separation, with the exception of a very thin sample, which could be interpreted by the specific change in the electron-channeling process.
使用高角度环形暗场扫描透射电子显微镜（HAADF-STEM）进行原子分辨率成像可直接用于分析材料的原子结构。该技术提供与组成元素原子序数相关的非相干Z衬度。在本工作中，观察到在双钙钛矿氧化物La₂CuSnO₆中直观解释HAADF-STEM图像存在困难的独特衬度。多层模拟证实，这是电子沟道效应与德拜-瓦勒因子效应共同作用的结果。这一点得到了证实，因为在La₂CuSnO₆晶体中，晶胞内两个独立的Sn原子和四个独立的La原子具有不同的德拜-瓦勒因子，La柱由间距较小的成对柱组成，而Sn原子是直线排列的。此外，通过多层模拟检查了图像衬度，在投影平面中两个原子La柱是分开的，但使用多层模拟时却显示为一个柱衬度。结果表明，除了非常薄的样品外，HAADF强度并不随柱间距增加而持续降低，这可通过电子沟道过程的特定变化来解释。
