Dewetting of nickel oxide-films on silicon under swift heavy ion irradiation

Dewetting, occurring when a thin film on a non-wettable substrate turns into its liquid state, has gained strong interest during the last decade, since it results in nano-scale, large-area covering pattern formation. Recently we found that swift heavy ion (SHI) irradiation of thin NiO films on Si substrates at 80 K results in similar dewetting pattern, although in this case the coating has never reached its melting point. Careful inspection of the SEM images clearly revealed that the same nucleation mechanisms as observed for molten polymer films on Si (heterogeneous and homogeneous nucleation) were active. AFM shows that the circular holes formed in the early stages of the dewetting process exhibit a high and asymmetric rim-structure. RBS analysis was used to measure the coverage of the surface by the oxide films and revealed that the holes grow at constant velocity. This, and the shape of the rims, indicate that the material removed from the substrate surface piles up by plastic deformation, which points at a balance of the capillary driving forces and the hindered material dissipation.