Thin ZrNx films have been prepared by reactive radio frequency magnetron sputtering. The radio frequency power has been chosen as a sputtering parameter and the effect on the compositional and optical properties of the films was systematically studied. The films have been analyzed by X-ray photoelectron spectroscopy. The reflectance and transmittance of the samples have been recorded by a spectrophotometer in the UV-Vis-IR range. The effects of the different powers (in the range 100-400 W) on the stoichiometry of ZrNx films have been studied. The components revealed on N 1s photoelectron peaks were correlated with different bounding states for the zirconium nitride. The threshold power value between N-rich ZrNx films and Zr-rich ZrNx ones is 270 W. A correlation has been observed between the optical properties and the stoichiometry of the films. In fact, the samples catalogued as N-rich by X-ray photoelectron spectroscopy analyses are optically insulating and the Zr-rich ones show a metallic behaviour. A simple growth model has been set up in order to explain the different chemical states detected from the compositional measurements. (c) 2006 Elsevier B.V. All rights reserved.