NiO nanoparticle thin films grown on Si substrates were irradiated by 107 MeV Ag8+ ions. The films were characterized by glancing angle X-ray diffraction and atomic force microscopy. Ag ion irradiation was found to influence the shape and size of the nanoparticles. The pristine NiO film consisted of uniform size (similar to 100 nm along major axis and similar to 55 nm along minor axis) elliptical particles, which changed to also of uniform size (similar to 63 nm) circular shape particles on irradiation at a fluence of 3 x 10(13) ions cm (2). Comparison of XRD line width analysis and AFM data revealed that the particles in the pristine films are single crystalline, which turn to polycrystalline on irradiation with 107 MeV Ag ions. (C) 2009 Elsevier B.V. All rights reserved.