Effects of Electron channeling in HAADF-STEM intensity in La2CuSnO6

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 La2CuSnO6 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 La2CuSnO6 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. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.