Three-dimensional thermal-spike modeling of ion charge-state dependence on sputtering yield in silicon dioxide thin films under MeV heavy-ion irradiation

Abstract

The influence of ion charge-state effects on the induced sputtering in silicon dioxide (SiO₂) thin films irradiated by 30 MeV Cl^q+, 40 MeV Au^q+ and 50 MeV Cu^q+ heavy ions was investigated numerically using the inelastic thermal spike (i-TS) model extended to 3-dimensions. An improved numerical approach using a cylindrical geometry was used to simulate the heat transfer from electronic to lattice subsystems by varying the ion charge-state. The obtained numerical profiles of electronic and atomic temperatures revealed more significant ion charge-state effects close to the center of the formed latent-track and near the surface up to deeper depths of 25 nm. The extracted numerical track-radii revealed small variations (of ∼1.9 to ∼9.9 %) for lower depths up to 25 nm. Then, they reached a mean track-value (around ∼3.9 nm in case of 40 MeV Au^q+ ions) corresponding to charge equilibrium, for which, a good agreement was found with the available experimental track-data. The obtained numerical sputtering yields versus penetration depth were finally found to predict better the non-equilibrium to equilibrium sputtering yield ratios, when they were compared to the available experimental data. Adequate mean depths (of ∼10 to ∼15 nm) corresponding to depth at origin of sputtered particles were estimated via i-TS calculation, equivalent to that (of ∼17 nm) previously evaluated from empirical scaling laws of ion mean-charge.