Chemisorption of a single oxygen molecule on the Si(100) surface: Initial oxidation mechanisms

Chemisorption of an O₂ molecule from the topmost layer to deeper subsurface layers on the Si(100) surface is studied by employing the spin-polarized generalized-gradient approximation. The calculated results reveal that an O₂ molecule is weakly adsorbed on a clean Si(100) surface with an initial spin-triplet state, but is adiabatically chemisorbed with a spin-state conversion, when an O₂ molecule arrives at the surface with a low incident energy. Barrierless back-bond oxidation has been found to occur through dissociative chemisorption with a spin-orbit interaction followed by O-atom migration to back-bond centers. According to the depth from the surface, energy barriers are found to be increasingly necessary for chemisorption of an O₂ molecule in subsurface layers.