DEFECT STRUCTURE OF ION-IRRADIATED AMORPHOUS SIO2

Uniformly enhanced small-angle X-ray scattering intensities of amorpho us SiO2, measured following irradiation with 320 keV H+ and He+ beams, are shown to be correlated, irrespective of the incident ion, with th e O and Si cumulative displacement yields. Damage by both beams origin ated primarily from nuclear stopping but, under H+-ion irradiation, co ntributions from ionization processes were significant as well. At low beam fluences, the irradiated structure is compatible with the presen ce of stable radiation-induced interstitial-like O and Si atoms and co mplementary O and Si vacancy-like sites. There is no evidence for reco very near room temperature of the modified structure to the pre-irradi ated state or for formation of colloidal-size scattering centers, such as gas bubbles or voids. Thus, ion-irradiation-induced changes in phy sical and chemical properties of silica seem to be due to the effect o f the preserved primary atomic displacement damage.