A THEORETICAL-STUDY OF THE INITIAL-STAGES OF SI(111)-7X7 OXIDATION .1. THE MOLECULAR PRECURSOR

We have studied the initial stages of the oxidation of the Si (111) surface using extended Huckel tight-binding calculations. Due to the different dangling bond sites present on the reconstructed Si(111)-7 X 7 surface, one may expect more than one molecular precursor or dissociated Si-O configuration to be formed. As candidates for the main and kinetically most stable molecular precursor, structures involving O2 associated with a single Si adatom site are proposed. Bridge structures are found to be less stable. However, dissociated species derived from bridge structures play an important role in the oxidation process. In this paper we introduce the computational approach used, and discuss the nature of the molecular precursors. In a second paper the nature of the atomic oxygen containing products and the mechanism of SiO4 formation are discussed.