Synergy between thermal spike and exciton decay mechanisms for ion damage and amorphization by electronic excitation

A theoretical model is proposed to account for the damage and amorphization induced in LiNbO₃ by ion bombardment in the electronic energy-loss regime. It relies on the synergy between the thermal spike generated by electron-phonon interaction and the nonradiative decay of localized (self-trapped) excitons. Calculations have been carried out to describe the effect of single impact as well as multiple impact (high fluence) irradiations. In the first case, the defect concentration profile and the radius of the amorphous tracks have been theoretically predicted and they are in good accordance with those experimentally determined. For high fluence irradiations (≥10¹³0.3em0excm^-2) the model predicts the formation of homogeneous amorphous surface layers whose thickness increases with fluence. The propagation of the crystalline-amorphous boundary has been determined as a function of irradiation fluence. Theoretical predictions are also in good agreement with experimental data on Si-irradiated (7.5 and 50.3em0exMeV) LiNbO₃ outside the region of nuclear collision damage.