Relationship between the structure and the optical and electrical properties of ion beam deposited CN_xfilms

Three series of CNxfilms were prepared by ion beam sputtering: (i) in N2ambient (N2-series), (ii) with N2+ion assist (N2+-series), and (iii) with Ar+ion assist in N2ambient (Ar+-series). The substrate temperature Tswas varied from 28 to 337°C. Structural analyses by X-ray photoelectron spectroscopy (XPS) and infrared absorption show that the films of the N2+-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 Tsincreases, 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 σroom. At any given Ts, the films of the Ar+-series have the highest σroom, because they have the highest level of graphitization among the three series. σroomof the N2-series and the N2+-series are lower because the former experiences less graphitization, while the latter contains more N, thus resulting in a lower carrier drift mobility.