Critical ion velocities for nanostructure formation on metal surfaces by slow highly charged ions at arbitrary incidence angles

Surface nanostructuring of metal targets induced by irradiation with slow, highly charged ions at various incidence angles is investigated. We extend our recently developed cohesive energy model to analyze the influence of impact geometry. At low ion energies, both the neutralization energy and the deposited kinetic energy, resulting from processes occurring above and below the surface, contribute to changes in the material's morphology. We define the critical ion velocity as a key parameter that characterizes the interplay between these two energy contributions and determines which mechanism predominantly drives nano-sized object formation. Based on the critical velocity definition, hillocks formation indicates that the neutralization energy is a dominant energy source, whereas craters formation implies that the deposited kinetic energy plays a significant role for a given collision geometry. The effect of the incidence angle on the critical ion velocity is examined in detail. The model predictions for angular effects are applied to a system consisting of slow, highly charged [Formula: see text] ions interacting with a gold target.