Monodisperse tin oxide nanocrystalline thin films are grown on silicon substrates by electron beam evaporation method followed by 100 MeV silver ion bombardment with varying ion fluence from 5x10(11) ions cm(-2) to 1 x 10(13) ions cm(-2) at constant ion flux. Enhancement of crystallinity of thin films with fluence is observed from glancing angle X-ray diffraction studies. Morphological studies by atomic force microscopy reveal the changes in grain size from 25 nm to 44 nm with variation in ion fluence. The effect of initial surface roughness and adatom mobility on topography is reported. In this work correlation between ion beam induced defect concentration with topography and grain size distribution is emphasized. (C) 2012 Elsevier B.V. All rights reserved.