SiNx thin films were prepared by the RF plasma-enhanced chemical vapor deposition method. Composition, structure, surface morphology and optical properties of the thin films were analyzed by X-ray fluorescence, IR transmittance, IR reflectance and SEM. The results show that the composition of the films is SiN0.35. Nitrogen atoms take part in the reaction with silicon atoms and Si-N bonds are formed. There are also some Si-H and N-H bonds in the films. The films have very low hemispherical IR reflectance across the full 8-13 mum band and high hemispherical reflectance elsewhere, which indicates that silicon nitride films can be used as good radiative cooling materials. The surface morphology and growth mechanisms of the films were also explained. (C) 2002 Elsevier Science Ltd. All rights reserved.