The effects of thermal annealing on the component and microstructure of carbon nitride films deposited by vacuum cathodic arc method are reported. The bonding structure of the films is investigated by Raman spectroscopy, FTIR, XPS and valence band XPS. Upon annealing, the N content of the film drops gradually from original 31.0 to 17.0 at.% at 600 degreesC. The results of Raman spectroscopy, FTIR and valence XPS demonstrate that the films below 500 degreesC mainly consist of aromatic cluster component and polymeric component, which is rather stable upon the increasing of anealing temperatures. With the further increasing of the annealing temperatures from 400 to 600 degreesC, the fraction of polymeric component decreases and the aromatic component develops greatly. Meanwhile the films tend to transform towards the fullerene-like microstructure, which can be seen from the. large separation of the N is peaks (>2.0 eV). As a result the N spa C bonds increase due to the rising of cross-linking between, the graphite plane. (C) 2003 Elsevier Science B.V. All rights reserved.