Effects of ion irradiation on metallic nanocrystals formed by ion beam synthesis in SiO2

Au nanocrystals (NCs) fabricated by ion implantation into thin SiO2 and annealing were irradiated with 2.3 MeV Sn ions at -180 oC. The NCs were investigated using cross-section transmission electron microscopy (TEM) as a function of irradiation dose. We observe nucleation of new nanocrystals as a consequence of collisional mixing and their growth at the expense of the larger ones upon further irradiation. These observations are consistent with the process of inverse Ostwald ripening, although thermally activated diffusion can be neglected due to the low irradiation temperature. Concomitant with the change in size distribution is a change in NC morphology caused by the anisotropic distribution of recoils during collisions