Based on real-space multigrid electronic structure calculations, we find that a double Si-O-Si bridge structure is the lowest energy configuration of interstitial oxygen ions ( ${\mathrm{O}}^{-}$ and ${\mathrm{O}}^{2-}$) in ${\mathrm{SiO}}_2$, where two additional Si-O bonds are formed with almost no interaction between the interstitial and host O atoms, while the peroxy linkage is the most stable structure for neutral interstitial O. We propose a diffusion mechanism of interstitial O ions generated from molecular ${\mathrm{O}}_2$ under UV radiation, and find extremely low energy barriers of 0.11–0.27 eV for migration in the form of the double-bridge structure, in good agreement with enhanced oxidation experiments.

• Received 23 June 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.1793