CuInS2 thin films were prepared by a two-stage ion layer gas reaction (ILGAR) process in which the Cu and In precursors were deposited on glass substrate by using a simple and low-cost dip coating technique and annealed in H2S atmosphere at different temperatures. The influence of the annealing temperature (250-450 degrees C) on the particle size, crystal structure and optical properties of the CuInS2 thin films was studied. Transmission electron microscopy revealed that the particle radii varied in the range 6-21 nm with annealing. XRD and SAED patterns indicated polycrystalline nature of the nanoparticles. The optical band gap (E-g) varied from 1.48 to 1.56 eV with variation of particle size. The variation of Urbach tail with temperature indicated higher density of the defects for the films annealed at lower temperature. From the Raman study, it was observed that the FWHM of the A(1) mode at similar to 292 cm(-1) corresponding to the chalcopyrite phase of CuInS2 decreased with increasing annealing temperature. (c) 2006 Elsevier B.V. All rights reserved.