Cathodoluminescence microcharacterization of the defect structure of irradiated hydrated and anhydrous fused silicon dioxide

The irradiation-sensitive defect structure of pure anhydrous and hydrated fused amorphous silicon dioxide $(a-{\mathrm{SiO}}_2)$ has been investigated using cathodoluminescence (CL) microanalysis. Irradiation of ${\mathrm{SiO}}_2$ by a continuous stationary electron beam results in a subsurface, trapped-charge-induced electric field that causes the electromigration of mobile charged defect species within the volume of irradiated specimen. CL emissions, observed between 300–900 nm at specimen temperatures between 5 and 295 K are identified with particular defect centers including the nonbridging oxygen-hole centers with strained bond and/or nonbridging hydroxyl precursors (hydrated specimen only), the self-trapped exciton, oxygen-deficient centers such as the neutral oxygen vacancy and/or the twofold coordinated silicon defect, and the charge-compensated substitutional aluminum center.