Mechanism for ion beam passivation of copper surfaces

Abstract

Irradiation by energetic ion beams has been observed to produce resistance to oxidation of the surface of copper and other metals. The effect was initially assumed to derive from a carbonaceous buildup produced when the surface was irradiated in a poor vacuum. However, we have found substantial protection of copper surfaces to be associated with a surprisingly thin surface layer containing carbon and having a thickness less than 30 Å. The evidence suggests that the ion beam serves to dissociate the contaminant layer of hydrocarbon adsorbates found on metal surfaces exposed to room atmosphere prior to implantation, leading to blocking of sites on the copper surface where oxygen would otherwise be adsorbed. In this experiment, the role of carbon in copper passivation has been tested by comparing the effect of ion bombardment of a copper surface during which carbon is totally excluded. The resulting lack of passivation leads to the conclusion that sub-monolayer ion bombarded carbon plays a critical role in ion beam passivation of copper surfaces. A model for the process is proposed in terms of graphitic carbon lodged at preferred sites on the copper surface.