Defects in SiO2 glass irradiated with high energy Ar ions

SiO2 glass specimens are irradiated at room temperature with 560 MeV and 1.15 GeV Ar ions. Defect production is investigated by positron lifetime spectra, EPR and UV absorption measurements. Free volumes of about 0.065 nm(3) in size are found to be present in the virgin specimen from the corresponding Ortho-Positronium lifetimes. With increasing dose the intensity of the component corresponding to positronium decreases sharply. This is attributed to the preferred annihilation of positrons with the radiation-ionized-electrons wandering in free volumes of the material. Optical absorption bands are induced at about 5.8, 5 and 4.5 eV by the irradiations and the absorption coefficients increase gradually with increasing dose. The EPR spectra of the irradiated specimens show the occurrence of the E' center, the number density of which reveals two distinct regimes according to its dependence on dose. In the low dose range the number density of E' center follows a 0.23 power law dose dependence whereas at high dose it increases linearly with dose. Furthermore the EPR spectra show fine structure which changes with dose. (C) 1998 Elsevier Science B.V. All rights reserved.