SHI induced surface modifications of immiscible Fe/Bi bilayer system

Topographical evolution of immiscible Fe/Bi bilayer systems irradiated with 120 MeV Au ions was studied using atomic force microscopy (AFM). Bilayer films of Fe–Bi were prepared by thermal evaporation on Si <100> substrate. The grain size of the films was estimated by glancing angle X-ray diffraction. The surface roughness of the as-deposited films has been found to be 23.6 nm from AFM analysis. The roughness of the sample is found to be decreased at lower fluences due to the strain relaxation between Fe and Bi by energy deposition. However, at higher fluences, beyond the 6 × 1012 ions cm− 2, the agglomeration of smaller grains has been observed due to the shear flow induced by the formation of dangling bonds by SHI irradiation, which results in the surface roughening. The observed behavior of surface smoothening and roughening under SHI irradiation may be explained on the basis of thermal spike model.