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

Abstract

A theoretical model is proposed to account for the damage and amorphization induced in LiNbO 3 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-trapped͒ excitons. Calculations have been carried out to describe the effect of single impact as well as multiple impact ͑high fluence͒ 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 ͑Ն10 13 cm −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 5 MeV͒ LiNbO 3 outside the region of nuclear collision damage.

Kinetics of amorphization induced by swift heavy ions in α-quartz

“…When the defect concentration reaches a certain threshold value the lattice collapses into an amorphous phase. Several specific models for defect creation have been proposed, including thermally-assisted bond breaking [19] and non-radiative exciton decay [20,21]. We consider that these models appear better suited to account for the structure and morphology of the damage tracks consisting of an amorphous core surrounded by a halo of point (and maybe extended) defects.…”

Femtosecond laser and swift-ion damage in lithium niobate: A comparative analysis

“…The most recent version couples the thermal spike to nonradiative exciton decay to determine the generated point defect concentration. 38,39 At this stage, we are going to use for this comparative analysis the simplest idea behind all those models; namely, the defect concentration generated by irradiation is exclusively a function of the local deposited energy, although the dependence is strongly superlinear ͑thresholding͒. It is to be remarked that the different distribution of the energy between the exciton plasma and the phonon system ͑i.e., the g factor͒ can also have significant implications on the amount of damage depending on the particular mechanism.…”

“…A number of proposals and strategies have been advanced to understand the damage effects of ion irradiation, namely, thermal spike models 15,25 followed by melting and/or ablation, exciton models, 38,39 and molecular dynamics calculations. 40,41 For femtosecond-laser pulse irradiation, a variety of models have also been invoked.…”

Stopping power dependence of nitrogen sputtering yields in copper nitride films under swift-ion irradiation: Exciton model approach

“…This feature cannot be properly explained on the basis of the thermal spike model [19] since it would predict an enhancement of the damage track radius produced by each impact with temperature and thus, an increase in the overall sputtering yield. Therefore, we propose here to discuss the electronic sputtering process in terms of an alternative excitonic model [37,38], initially suggested by Itoh et al [39], and satisfactorily applied to describe many damage features in LiNb0 3 [37][38][39][40][41][42], as well as in alkali halides [43]. It assumes that the bond-breaking and nitrogen release from their lattice sites is caused by non-radiative decay of localized excitons.…”

“…In other words, the bond-breaking efficiency is roughly proportional to the number of excitons generated by the ion impact and is independent of the temperature reached in the spike, provided that the temperature is high enough to promote nonradiative decay of excitons. The excitonic model [37,38] assumes that the concentration profile of excitons around the ion trajectory (radial concentration) is coupled to the initial temperature profile and can be written as:…”