Ab initio study of incorporation of O₂ molecules into Si(001) surfaces: Oxidation by Si ejection

By carrying out ab initio total-energy calculations on incorporation of O₂ into Si(001), we have reinvestigated possible initial oxidation structures and processes at the Si(001) surfaces. We found a new oxidation structure that is more stable than previously proposed backbond-oxidation models. The new structure is achieved by the oxidation process of ejecting Si atoms onto surfaces as observed in experiments. The atomic structure after the Si ejection is characterized by the O₂-incorporated single dimer-vacancy (O2/1-DV) structure. In particular, our finding indicates that the Si ejection also occurs at surfaces during initial stages of oxidation, in contrast to hitherto proposed Si ejection at SiO₂/Si interfaces.