The manipulation of Cu cluster dimensions on highly oriented pyrolytic graphite surfaces by low energy ion beam irradiation

Low energy Ar+ and Ne+ beams have been used to treat isolated Cu clusters deposited onto HOPG surfaces by evaporation. Following such treatment, cluster size and number density changes, as functions of treatment time, have been evaluated by using in situ X-ray photoelectron spectroscopy (XPS). Both Cu mass thickness and surface cluster density decrease with treatment time, as the clusters are sputtered, while weak interaction between the cluster and the treated HOPG surface permits cluster coalescence through surface diffusion, even at room temperature. We discuss the effect of both on the decrease in cluster size, which ultimately stabilizes, depending on the ion beam current density at the kinetic energy used. Further, short bursts of Ar+ or Ne+ treatment are not masked by such sputtering effects, and are found to lead to an enhancement of surface coalescence, as kinetic energy is transferred from the primary ion to the cluster.