Identification of the Initial-Stage Oxidation Products on $\mathrm{Si}\left(111\right)-(7\times 7)$

Density functional theory calculations are used to study the initial-stage adsorption of ${\mathrm{O}}_2$ molecules on the $\mathrm{Si}\left(111\right)-(7\times 7)$ surface. Contrary to experimental suggestions, we find no evidence of metastable ${\mathrm{O}}_2$ molecular states on this surface, i.e., ${\mathrm{O}}_2$ 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.