ESR Studies of Paramagnetic Defects formed in Amorphous SiO2 by High Energy Heavy Ions

High energy heavy ions in insulators induce the formation of defects which have been studied by track etching methods and small angle X-ray scattering1-3. These previous studies have shown that the formation of defects is linked to electronic energy losses. However, the processes which result in lattice defects following such interactions are not well understood. In order to characterize the defects formed and their lattice environment, we studied amorphous SiO₂ (dry Tetrasil SE) irradiated by heavy ions using Electron Spin Resonance (ESR). The paramagnetic defects formed in this material by γ-ray, X-ray and electron irradiation have already been extensively studied4–7. After such irradiation, two major types of defects have been observed: the E₁′ center8 (hole trapped by an oxygen vacancy) and the oxygen hole center 9 (or OHC, associated with a peroxy radical). The density of defects observed was closely related to the total energy deposited in the sample. We previously showed 10 that high energy heavy ions also induce the formation of E₁′ centers and OHC’s. However, the ion irradiated samples present specific characteristics, which are linked to the very high density of energy deposited near the path of heavy ions11. We present here a study of the dependence of the defects on the residual energy, the atomic number and the fluence of the incident ions. We show that, in contrast to γ-ray irradiations, the total energy deposited is not the single parameter controlling the formation of paramagnetic defects by high energy heavy ions.