Synchrotron-radiation-stimulated evaporation and defect formation in a-${\mathrm{SiO}}_2$

The vacuum ultraviolet-stimulated evaporation of a-${\mathrm{SiO}}_2$ and formation of oxygen vacancy defects in a-${\mathrm{SiO}}_2$ was found to be temperature dependent. Below a 500 °C surface oxygen atoms are depleted, a ${\mathrm{SiO}}_{\mathit{x}}$ layer is formed, and the a-${\mathrm{SiO}}_2$ is etched at a constant rate by photon-stimulated desorption of constituent atoms. Between 500 and 700 °C the a-${\mathrm{SiO}}_2$ itself decomposes and evaporates by forming SiO molecules and a thick layer that did not evaporate accumulates on the surface and reduces the rate of evaporation. Above 700 °C evaporation of a-${\mathrm{SiO}}_2$ proceeds at a constant rate, keeping the surface stoichiometry as ${\mathrm{SiO}}_2$; any ${\mathrm{SiO}}_{\mathit{x}}$ layer created vanishes instantly.