It was recalled that interstitial water and O molecules were common impurities, and participated in various defect formation processes in thermally grown SiO2 films and synthetic silica glass. Using the results of first-principles calculations, a study was made of the types of defect (including different possible charge states) that H2O and O2 molecules could form in bulk amorphous SiO2. Their formation energies were calculated and, in the most interesting cases, the energy barriers were used to map out the most likely defect formation scenarios. It was shown that water molecules could form double silanol groups (Si-OH) as well as H3O+ and OH– ions at a low energy cost; with a barrier of about 1.5eV. The formation energies of other defects emanating from H2O interstitials were too high to be thermally activated. It was found that O2 molecules could form ozonyl (Si-O-O-O-Si) linkages, with an energy barrier of ~2.4eV. An explanation for the O isotope exchange observed in thin SiO2 films, near to the Si/SiO2 and SiO2/vacuum interfaces was suggested; based upon the energy barrier for ozonyl formation being commensurate with the O2 diffusion barrier close to the Si/SiO2 interface and the O2 incorporation energy from vacuum. The differing creation rates of E’ centers in wet and dry oxides were explained by studying the annihilation mechanism of neutral and charged O vacancies.

H2O and O2 Molecules in Amorphous SiO2 - Defect Formation and Annihilation Mechanisms. T.Bakos, S.N.Rashkeev, S.T.Pantelides: Physical Review B, 2004, 69[19], 195206 (9pp)