Electron emission induced by cluster impact on a clean metal surface

Abstract

Atomically clean polycrystalline gold was bombarded under UHV conditions by slow cluster ions (N 2) n ( n ≤ 100), Ne n +(n ≤ 100) and C 60,70 q ( q ≤ 4+) at impact energies from the apparent electron emission thresholds up to 6 kV times the cluster charge ( qe). The resulting total electron emission yields were determined from the corresponding electron emission statistics, i.e. the distributions of probabilities, W n , for emission of given numbers of electrons, n, due to single cluster ion impacts. Grossly different electron yields were found for different cluster species of similar velocity and mass, which is attributed to different partitioning of the initial cluster kinetic energy into kinetic electron emission and internal excitation, respectively. For impact of Ne n + cluster ions, approximately linear relationships of the total electron yields with, respectively, impact velocity and cluster size indicate a more or less complete desintegration upon surface impact, whereby all cluster constituents should contribute nearly independently to the observed kinetic electron emission. For (N 2) n + cluster ions, with growing cluster size an increasing contribution per cluster constituent to the total electron yield was observed, and for C 60,70 + cluster ions the impact-velocity dependence of the total electron yields was strongly nonlinear. The present results are relevant for quantitative detection of slow large cluster ions and give some hints on processes involved during and after slow cluster ion impact on a clean metal surface.