Co-sputtered Au-Ni thin films having thickness of 30 nm were deposited on Si(1 0 0) substrates and irradiated with 160 keV Ar-40(+) under ambient condition at a number of fluences and analyzed using Rutherford backscattering spectrometry (RBS). The variation of Au signal counts in the RBS spectra with ion fluence has been investigated. The distribution of Au, Ni and Si atoms over various depths within the as deposited and irradiated samples have been computed using the backscattering data by means of a direct analytical method. Au and Si profiles have been fitted with error function and the relative changes in variance for various ion fluences compared to that of as deposited profiles have been studied. The spreading rates of different constituents across the interface due to Ar ion impact have also been discussed. (C) 2008 Elsevier B. V. All rights reserved.