Surface morphology of ion-irradiated Fe films

The surface morphology of thin (60 nm) Fe films irradiated with 243 MeV Au ions has been investigated using atomic force microscopy (AFM). The surface roughness was increased by the ion irradiation. The changes in the Fe content during ion irradiation were monitored by ERDA. A large area position-sensitive telescope detector with kinematic correction was used. The measurement showed that there was no change in the film thickness. This rules out the possibility of sputtering from the surface, within the sensitivity of the detection setup. Moreover, from the calculated sputter yield less than one monolayer sputtering can be expected for the applied dose. Therefore the present work shows that the increased surface roughness is due to the rearrangement of the atoms on the surface of the film. The reordering of the atoms at the surface is more likely associated with electronic excitation by the incident ions, as the energy deposition by elastic collision process is two orders of magnitude smaller than the process of electronic excitation generated by inelastic collisions.