Structure of latent tracks created by swift heavy-ion bombardment of amorphous SiO2

The defect structure of ion irradiation damage localized in latent tracks i n amorphous SiO2 and their role in the chemical etch rate of such tracks ha s been studied. A variety of light and heavy ions were used with energies r anging from 4 to 127 MeV. It was found that the frequency of the infrared a bsorption associated with the asymmetric stretch vibration of Si-O was sign ificantly reduced following swift heavy-ion bombardment and that the shift correlated with the enhancement of the etching rate. In contrast, no correl ation between the etching rate and either the E' center or the oxygen defic ient center was observed. The IR peak shift has been related to the transit ion of ordinal six rings of SiO4 tetrahedra to planar three- and four-membe r rings, which were generated in the latent track due to the flash heating and quenching by bombardment. We propose that large numbers of planar three - and four-member rings in the latent track are responsible for the fast ch emical etching rate.