Three series of CNx films were prepared by ion beam sputtering : (i) in N-2 ambient (N-2-series), (ii) with N-2(+) ion assist (N-2(+)-series), and (iii) with Ar+ ion assist in N-2 ambient (Ar+-series). The substrate temperature T-s was varied from 28 to 337 degrees C. Structural analyses by X-ray photoelectron spectroscopy (XPS) and infrared absorption show that the films of the N-2(+)-series have the highest N content (20-23 at.%). All the films are composed of six-membered ring structures and groups containing C-N, C=N and C=N bonds. As T-s increases, the fraction of the six-membered rings increases, and some groups containing C-N, C=N and C=N bonds become volatile and are detached from the film, such that the film structure becomes more graphitic. This leads to an overlap between the conduction band and the valence band, and hence, a higher electrical conductivity sigma(room). At any given T-s, the films of the Ar+-series have the highest sigma(room), because they have the highest level of graphitization among the three series. sigma(room) of the N-2-series and the N-2(+)-series are lower because the former experiences less graphitization, while the latter contains more N, thus resulting in a lower carrier drift mobility.