Non-Crystalline SiO2: Processing Induced Pre-Existing Defects Associated with Vacated O-Atom Intrinsic Bonding Sites

The electron spin resonance studies by Galeener et al. on bulk-quenched non-crystalline (nc-) silica glasses, nc-SiO2 have distinguished between pre-existing defects formed during quenching and annealing of glasses, and X-ray and g- ray radiation induced defects. This article shows similar defects in plasma-deposited thin films and thermally-grown nc-SiO2 and nc-GeO2. Pre-existing defect densities increase exponentially with increasing quenching and annealing temperatures and in “dry silicas” with no detectable Si-OH vibrations are assigned to\E’ centers or singly occupied Si atom dangling bonds. Non-bonding O-hole centers, or NBOHCs are also detected in dry silicas, but only after significant X-ray or γ-ray irradiation. Pre-existing defect are also detected by 2nd derivative O K pre-edge X-ray absorption spectroscopy in remote plasma deposited/thermally grown nc-SiO2 and nc-GeO2 thin films. These spectra display singlet and triplet features labeled according to Tanabe-Sugano (T-S) diagrams. It is demonstrated by ab initio theory and experiment that pre-existing defects in thin film nc-SiO2 and nc-GeO2 are vacated O-atom sites in which an O-atom has never resided.