OXIDATION OF SILICON SURFACES.

The authors have carried out theoretical studies (generalized valence bond) for chemisorbed O atom and O//2 molecule on Si(111) surfaces using clusters of atoms to model the surface. For the perfect surface the authors find that O//2 molecule binds to a single surface Si with an Si-O bond length of 1. 68 Angstrom (bulk SiO//2R//S//i//- //O equals 1. 61 A), an Si-O-O angle of 116 degree , and an O-O bond distance of 1. 32 Angtrom. The authors have also calculated the shifts in the Si(2p) and O(1s) core level energies for chemisorbed O and O//2 on the surface. The Si(2p) shift is plus 1. 1 ev (higher binding energy) for the O atom and plus 1. 5 ev for O//2, in agreement with the shifts observed for low oxygen exposure by W. E. Spicer and co-workers.