The influence of crater formation for electron excitation processes in cluster induced collision cascades

The interplay between electronic energy loss and the excitation of electronic degrees of freedom accompanying the bombardment of a silver crystal with 7-keV Ag and 20-keV Ag3 particles is investigated by molecular dynamics simulation. Two kinetic excitation processes – the friction of moving atoms in a free electron gas and autoionization in close, binary collisions – are considered, as to describe the electronic stopping. In order to accommodate the massive transient morphology changes following a cluster impact, the electronic friction is described by a modified Lindhard/Scharff model, where the friction coefficient is scaled to the local environment of a moving atom. It is shown that this approach is capable of reproducing both the measured sputter yields and the degree of electronic excitation as manifested by measured electron and secondary ion yields.