XPS, XANES and ToF-SIMS Characterization of Reactively Magnetron-sputtered Carbon Nitride Films

The existence of β-C3N4 with hardness characteristics similar or better than diamond was predicted in 1990 by Liu and Cohen. Many studies have since been devoted to the synthesis of this compound. In the present work, carbon nitride films were deposited by various reactive magnetron sputtering processes of graphite targets in pure nitrogen and characterized by AES, XPS, x-ray adsorption near-edge structure (XANES) and static time-of-flight SIMS (ToF-SIMS). Various bonding states (single and double bond) are observed between carbon and nitrogen atoms and between carbon atoms but there is no evidence in the XANES results for either the presence of carbon–nitrogen triple bonds or a pyridine-like ring structure. Surface N/C ratios were estimated to be close to 0.3. Carbon K-edge XANES lineshapes, the C 1s plasmon-loss structure and the calculated density (2.2 g cm-3) indicate that the films are similar to diamond-like carbon without long-range ordering. The presence of CxNy fragments with 1⩽y<4 and the low abundance of CHx and CHxNy fragments in ToF-SIMS spectra further confirm that the carbon atoms do not adopt a graphite or pyridine-like cyclic two-dimensional structure and that the films are not significantly hydrogenated. A three-phase solid solution model is proposed for the composition of the films: a ‘free’ carbon phase, an sp3—carbon-nitrided phase and an sp2—carbon-nitrided phase. The relative proportion of these phases is influenced by the deposition conditions. Enhanced plasma ionization reactive magnetron sputtering leads to higher density and to a higher fraction of the sp3 carbon phase.