Annealing studies of irradiation effects in vitreous silica

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Abstract
This paper describes a series of annealing experiments devoted to the study of the thermal behaviour of B2 and E' centres produced by heavy-ion irradiations in v-SiO2. Thermal bleaching of the B2 component is shown to be complete and irreversible at relatively low temperatures (⩽500°C). On the other hand, bleaching of E' in the same range is reversible and the corresponding absorption band can be entirely recovered in subsequent electron irradiations, suggesting the existence of a stable precursor defect for this centre. By alternating isochronal annealing cycles with electron re-irradiations, the annealing of such defects was investigated up to 1000°C, taking care to compare the behaviour of the heavy-ion damaged material with that of undamaged material. The results seem to suggest a structural difference between pre-existing E' precursors of normal SiO2 and those produced in excess by displacing radiation, the latter being characterized by a distinct process of destruction with an activation energy Q ≳0.6 eV.