Electronic sputtering: angular distributions of (LiF)nLi+ clusters emitted in collisions of Kr (10.1 MeV/u) with LiF single crystals

Abstract

A combination of imaging techniques (XY) and time-of-flight (TOF) spectroscopy was used to measure the complete velocity vector of sputtered positive secondary ions in collisions of Kr33+ (10.1 MeV/u) with well prepared LiF single crystals in the electronic stopping regime. The angular distributions of (LiF) n Li+ clusters become broader with increasing cluster size n. This could be an indication of contributions from different ejection mechanisms. The experimental secondary ion angular distributions can be fitted by a simple cosine function of the type N(θ) = A cos m (θ), but it does not reproduce the shape of the jet-like structure observed for the emission of neutral LiF particles perpendicular to the ion beam. Therefore, the cluster emission hypothesis does not explain in a simple way the observed narrow jet.