The concept of effective electronic stopping power for modelling the damage cross-section in refractory oxides irradiated by GeV ions or MeV clusters

Single crystals of Al(2)0\O-3 and LiNbO3 were bombarded at room temperature with either GeV ions (up to U-238) or MeV carbon clusters (up to C-60) Depending on the irradiation conditions, the electronic stopping power S-e ranged from 3 to 76 keV nm(-1). Rutherford Backscattering Spectrometry in Channeling geometry (RBS-C) evidenced lattice disorder at the sample surface which was ascribed to the high density of electronic energy deposited by the incident projectile. The damage cross-sections A(d) varied from 3 to 350 nm(2), the highest values being obtained, at a given S-e, in LiNbO3 irradiated with C-60 clusters. For each target, A(d) was found to depend on both S-e and the projectile velocity. In this paper, we propose a modelling of A(d) based on the new concept of effective electronic stopping power S-e*. In our approach, the target is characterized by two parameters: a diffusion length L and a critical density of energy W-c. The calculation of S-e* takes into account L, W-c and the radial distribution of energy deposited by the projectile. Provided a correct choice of L and W-c, this model predicts a linear law between A(d) and S-e*, and consequently unifies the results obtained from both ion and cluster irradiations. This was confirmed by fitting the A(d) measurements in Al2O3 and LiNbO3. According to our calculations, the different damage sensitivities between these two materials are mainly ascribable to the diffusion length, which is higher in Al2O3 (L = 5.2 nm) than in LiNbO3 (L = 1.5 nm).