Ultimate observation of tungsten atoms and clusters adsorbed on single crystalline MgO films

作者:Tanaka, N.; Kimata, H.; Takashima, T.; Kizuka, T. 刊名:Microscopy Research and Technique 上传者:杨海艳


Ultimate Observation of Tungsten Atoms and Clusters Adsorbed on Single Crystalline MgO Films N. TANAKA,* H. KIMATA, T. TAKASHIMA, AND T. KIZUKA Department of Applied Physics, School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan KEY WORDS tungsten atoms; clusters of four and five atoms; multislice image simulation; determination of atomic configuration; adsorption sites; lattice-mismatch; magne-sium oxide ABSTRACT Tungsten single atoms and clusters composed of four and five atoms deposited on MgO (001) thin films were observed by high-resolution transmission electron microscopy at R.T. The observation was realized by optimizing the thickness of the MgO films and by using special imaging techniques such as an off-Bragg HREM method. The multislice simulation for the interpretation of the image contrast showed a possibility of discrimination of the atomic configuration of clusters, such as ‘‘b.c.c.,’’ ‘‘on-top,’’ or ‘‘f.c.c.’’ type clusters, from details of the image-contrast. The image intensity at the center of the clusters with the b.c.c. configuration was evidently smaller than that of the clusters with the f.c.c. configuration. The reason for the difference was clarified through the multislice image simulation, suggesting that the lattice mismatch between the clusters and the MgO lattice was a key factor in determining the intensity of the center of the clusters. Microsc. Res. Tech. 40:265–276, 1998. r 1998 Wiley-Liss, Inc. INTRODUCTION Observation of single ato