Identification of the Initial-Stage Oxidation Products on Si(111)-(7×7)

Density functional theory calculations are used to study the initial-stage adsorption of O₂ molecules on the Si(111)-(7×7) surface. Contrary to experimental suggestions, we find no evidence of metastable O₂ molecular states on this surface, i.e., O₂ molecules dissociate spontaneously without any barrier. Our electronic and vibrational analysis reveals that the resulting atomic-oxygen products can explain the ``molecular'' features reported in previous experiments.