Properties of amorphous a-CH(:N) films synthesized by direct ion beam deposition and plasma-assisted chemical vapour deposition

Abstract

Abstract Hydrogenated carbon films and hydrogenated carbon films containing nitrogen have been synthesized by direct ion beam deposition (IBD) using cyclohexane and methane as precursors and by plasma-assisted chemical vapour deposition (PACVD) using cyclohexane and acetylene as precursors. The elemental composition has been assessed by gas chromatography. The films' structure has been analysed by FTIR, Raman, NEXAFS spectroscopy and X-ray reflectivity. The hardness has been determined by nanoindentation and microhardness measurements, and the stress by optical profilometry. FTIR measurements reveal an increasing nitrile and amine group absorption with a corresponding decrease of C–H stretching modes as the nitrogen concentration in the film increases. The nitrogen-containing functional groups are proposed to be at peripheral positions of graphitic domains. The corresponding reduction of the domain size is detected in the Raman data, and the increase of delocalized bonding in a-CH(:N) films with respect to a-CH films is confirmed by the NEXAFS results. In the carbon K-edge spectra, the intensity of the π* CC resonance at ≃285.3 eV has been found to increase as a function of N content. This indicates principally an increment of the sp2 hybridization. Such a structural change leads to a decrease in the hardness and the internal compressive stress with respect to a-CH films. In a film containing 15 at% N, the hardness is reduced to 44% and the stress to 36% of that for a-CH.