  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.
