Affiliation: | aSandia National Labs, MS 1110, P.O. Box 5800, Albuquerque, NM 87185, United States bAir Force Research Labs, Albuquerque, NM 87117, United States cPenn State Erie, Erie, PA 16563, United States |
Abstract: | We investigate molecular scale mechanisms for radiation-induced release of hydrogen from precursor sites using density functional theory applied to a fully periodic model of SiO2. We focus on proton release from H-decorated oxygen vacancies in the bulk oxide. After hole-capture at the vacancy, a proton can hop to an energetically favorable bound state at a neighboring oxygen atom. In -quartz, this release mechanism has an activation energy of about 1.2 eV. In amorphous silica, this hop has a range of low barriers, from 0.1 to 0.5 eV. Furthermore, another proton release mechanism involves cracking of H2 molecules by a reaction with an isolated, positively charged Si-dangling bond. |