Ion Irradiation Induced Effects in Metal Nanostructures

High resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectrometry (RBS) are used to study the ion induced effects in Au, Ag nanostructures grown on Si and thermally grown SiO2 substrates. Au and Ag films (~2 nm) are prepared by thermal evaporation under high vacuum condition at room temperature (RT). These films were irradiated with MeV Au ions also at RT. Very thin films of Au and Ag deposited on silicon substrates (with native oxide) form isolated nano-island structures due to the non-wetting nature of Au and Ag. Ion irradiation causes embedding of these nanoislands into the substrate. For Ag nanoislands with diameter 15 - 45 nm, the depth of the embedding increases with ion fluence and the nano particles are fully submerged into Si and SiO$_2$ substrate at a fluence of 5*10^14 ions /cm^2 without any mixing. Au nanoparticles (diameter 6 - 20 nm), upon ion irradiation, forms embedded gold-silicide in the case of Si substrate and show lack of mixing and silicide formation in the case of SiO2 substrate system.