Heat-induced transformation of nickel-coated polycrystalline diamond film studied in situ by XPS and NEXAFS

Controlling the high-temperature graphitization of diamond surface is important for many applications that require the formation of thin conductive electrodes on dielectric substrate. Transition metal catalysts can facilitate the graphitization process. In this work, a polycrystalline diamond films with mixed grain orientation, as well as a synthetic single crystal diamond with a polished (110) face, were covered with a nickel thin film deposited by thermal evaporation method. The effect of nickel on the chemical state of diamond surfaces after high vacuum annealing at a temperature of about 1100 °C has been studied in situ using synchrotron based X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Differences in the morphology and structure of annealed polycrystalline diamond films with and without nickel were evidenced using scanning electron microscopy and Raman spectroscopy. Nickel-coated polycrystalline and single crystal diamond surfaces were found to be more prone to transformation into sp ² -hybridized carbon compared to their nickel-free counterparts. XPS data revealed the formation of a thin graphite-like film with low-ordered atomic structure on the surface of the nickel-coated polycrystalline film. The chemical state of sp ² -hybridized carbon atoms was found to be insensitive to the face orientation of the diamond micro-sized crystallites; however, the layer defectiveness increased in areas with fine-dispersed crystallites. The angular dependence of NEXAFS spectra at the C K-edge of annealed nickel-coated (110) face of single crystal diamond discovered the vertical orientation of sp ² -hybridized carbon layers relative to the diamond surface.