Backbond oxidation of the Si(001) surface: Narrow channel of barrierless oxidation

Oxidation of the Si(001) surface was studied by the first principles calculation technique with spin-polarized gradient approximation, We have clarified, the apparent barrierless reaction mechanism of the backbond oxidation of the surface Si by incoming O-2 molecules. An O-2 molecule does not attack directly the backbond but the oxidation occurs via metastable chemisorption states on the Si surface. We have also found that the triplet-to-singlet spin conversion is crucial in explaining the incident energy dependence of the sticking probability of O-2 molecules. [S0031-9007(98)05462-3].