High energy ion irradiation induced surface roughening in Ag and Cu films

Ag/Fe and Cu/Fe bilayers were deposited onto Si substrates and irradiated at room temperature with 2 MeV Cu and 2.5 MeV Au ions in order to study the ion beam induced surface roughening. We have used contact atomic force microscopy (AFM) to study the surface topography and observed that film grains grow slowly, in a uniform way, but simultaneously, individual grains aggregate to each other to form complex structures. This suggests that two different mechanisms take place during ion bombardment contributing to surface roughening. One is a thermally activated mechanism, while the second is a non-uniform process that might be related with the fractal nature of ion bombardment. The former predominates at temperatures where surface defects are mobile across grain boundaries and produces uniform spherical grains, whereas the latter is always present and produces non-uniform structures that give evidence of fractal aggregation patterns. No roughness increase due to surface sputtering was observed.