Ab initio periodic pseudopotential Hartree-Fock calculations of O 2 dissociation on perfect Si(100) surface

Abstract

This paper investigates the cleavage of O 2 adsorbed on clean Si(100) surfaces with ab initio periodic pseudopotential Hartree-Fock calculations. For the adsorption of the O 2 molecular precursors at coverage ϑ = 1 (one O 2 per dimer), the Si(100) surface remains reconstructed and O 2 are adsorbed on the dimers, parallel to the surface; the sites between the dimers are vacant. For the atomic adsorption at the same coverage (representing then one O per surface Si) the surface reconstruction nearly disappears; the oxygen atoms are adsorbed over the successive spaces between adjacent surface Si atoms along the (110) directions (those of the elongated dimers and those between them) in asymmetric fashion. The dissociation of O 2 requires the breaking of two bonds, the SiSi and OO bonds and the migration of an oxygen atom. It therefore implies the presence of a high activation energy. Two paths are investigated for the O 2 dissociation and the migration of an atomic oxygen on the surface. The migration of O 2 from the best adsorption mode to least favourable one where the dissociation is easier is also discussed.