Synergy of nuclear and electronic energy losses in ion-irradiation processes: The case of vitreous silicon dioxide

Structural modification of vitreous SiO₂ by Au ion irradiation is investigated over an energy regime (∼0.3-15 MeV) in which the decrease of the nuclear energy loss with increasing energy is compensated by the increase of the electronic energy loss, leading to a nearly constant total energy loss of ∼4 keV/nm. The radii of damaged zones resulting from the ion impact, deduced from changes in infrared bands as a function of ion fluence, decrease from 4.9 nm at 0.3 MeV to 2.5 and 2.6 nm at 9.8 and 14.8 MeV, respectively. Based on previous data where vitreous SiO₂ was irradiated with much higher energy Au ions, the damage zone radius increases from 2.4 nm at 22.7 MeV to 5.4 nm at 168 MeV, and a U-shaped dependence on energy is observed is observed in the energy region from 0.3 to 168 MeV. The current results demonstrate that large damage radii at low and high ion energy can be explained by the elastic or inelastic thermal spike model, respectively. In the transition regime where both nuclear and electronic energy loss are significant, a unified thermal spike model consisting of a coherent synergy of the elastic collision spike model with the inelastic thermal spike model is suggested to interpret and describe the radius evolution from the nuclear to the electronic energy regime.