Carbon nitride films were successfully prepared by ion beam synthesis method. 100 keV N+ions at a dosage of 1.2×1018cm−2were implanted into carbon thin films at different temperatures. The samples were evaluated by x‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, cross‐sectional transmission electron microscopy (XTEM), Rutherford backscattering spectroscopy (RBS), x‐ray diffraction analysis (XRD), and Vickers microhardness measurement. XPS results show that most of the implanted nitrogen atoms are free state. Most of the carbon atoms have C–C bonding and a little of them form a C–N bond. It also can be clearly seen that the content of the C–N covalent bonding state in the samples is increased by raising the implanting temperature of the samples. Raman spectrum indicates that there is a Raman band near 2300 cm−1corresponding to carbon‐nitrogen stretching. XTEM and RBS studies show that there is a buried layer of carbon nitride. XRD and TEM analyses reveal that the buried carbon nitride is predominantly amorphous with a small volume fraction of nanocrystallites. The sample has a higher hardness than that of a carbon thin film. ©1996 American Institute of Physics.