Swift Heavy Ion Irradiation Induced Surface Sputtering And Micro Structural Modification Of Gold Thin Films

Abstract

Two sets of gold thin films of thickness of about 20 and 50 nm, grown by thermal evaporation method on (100) silicon wafers were irradiated by 197 MeV Au ions. Grazing incidence X-Ray diffraction (GIXRD) study has been revealed lattice expansion on decreasing the film thickness. 197 MeV Au ion irradiation was not affect either the cubic crystal structure of gold or its lattice parameter. Atomic force microscopy (AFM) study indicated that the evolution of the surface morphology with ion fluence crucially depended on the film thickness, the thinner film being more sensitive than the thicker one. Irradiation led to nanoparticles formation on the surface of the films. This observation is in contrast to the generally perceived damaging role of swift heavy ion (SHI) irradiation. Power spectral density analysis of the roughness along both the lateral and vertical directions demonstrated dominance of surface diffusion over volume diffusion induced by SHI irradiation. A comparison of the sputtering yield obtained from Rutherford back scattering (RBS) spectra of the irradiated films and transmission electron microscopy (TEM) of the particles sputtered from the films and collected by a catcher grid during irradiation indicated that more than the surface and volume diffusion processes, it is the irradiation induced sputtering that controls the overall surface morphology of the films. The surface roughness increase with ion fluence and the irradiation induced sputtering yield was found to be larger in thinner films. Film thickness dependence of the evolution of surface morphology and sputtering yield with 197 MeV Au ion irradiation clearly indicates the dominance of the electronic energy loss over the nuclear energy loss of the projectiles ions in the target medium and opens up the ways for examining the applicability of different models of ion-matter interaction in systems with reduced dimensions.