Contamination layers formed by argon ion bombardment

Contamination layers formed on an aluminium substrate by 5-35 keV argon ion bombardment have been studied at various ion bombarding times, current densities, ion energies and substrate temperatures. The results are compared with a simple theory which takes sputtering into account and good qualitative agreement is obtained. According to this theory, the higher contamination growth by ion bombardment than by electron bombardment can be explained by the large cross section for polymerization of organic molecules adsorbed on the surface. Furthermore, it is ascertained that heating the substrate or using a cold trap surrounding the substrate can effectively reduce the contamination growth.