Direct Methods Solution of the Si(111)-4x1 Surface Structure Using Electron Diffraction Data. C. Collazo-Davila*, L. D. Marks*, K. Nishii_, and Y. Tanishiro1 *Dept. of Materials Science and Engineering, Northwestern University Evanston, IL 60208 _Physiscs Dept., Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152, Japan
Direct methods were applied to transmission electron diffraction data to solve the unknown In on Si(111)4x1 surface structure. While direct methods are well-established and common in bulk structure analysis, their application to two-dimensional surface diffraction data is new. This study represents one of the first surface structure determinations based on direct methods. The structure analysis is straight-forward and a model consisting of a zig-zag chain of In atoms and a region of silicon including a dimer chain is proposed. As a final step, atomic positions were refined using a conventional [chi]2 minimization approach to fit diffraction intensities.
Several stable surface structures are formed with increasing In coverages on the Si(111) surface. The Ö3xÖ3 structure consists of 1/3 of a monolayer of In, the Ö31xÖ31 occurs at a slightly higher coverage, and the 4x1 structure appears before the formation of In islands on the surface. Knowledge of the atomic positions in the 4x1 structure is an important step in understanding metal/semiconductor epitaxy and interface formation. The model found by direct methods in this study is similar to recently proposed models for other nx1 metal-induced structures on the Si(111) surface [Marks and Plass 1995, Erwin 1995] allowing some preliminary generalizations to be made.
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