Influence of the projectile charge state on the ionization probability of sputtered particles

Abstract

We present a computational study of the effect of the projectile charge state on secondary ion formation in sputtering. A molecular dynamics simulation of an atomic collision cascade is combined with a kinetic excitation model including electronic friction and electron promotion in close atomic collisions. The model is extended to account for potential excitation following the bombardment with a highly charged ion (HCI). The spatial spreading of the excitation generated in the cascade is treated in an diffusive approach. The excitation energy density profile obtained this way is parametrized via an effective electron temperature, which is then used to calculate the ionization probability of each sputtered atom in terms of a simple charge exchange model. The results obtained for the impact of a 5 keV Ag atom onto a solid silver surface show that the average ionization probability increases from 4.7 × 10 - 4 for a neutral projectile to 5.4 × 10 - 4 for a highly charged projectile ion with a total ionization energy of 576 eV.