Effect of nitrogen flow on the properties of carbon nitride films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition

Abstract Amorphous hydrogenated carbon nitride (a-CNx:H) films were fabricated via electron cyclotron resonance microwave plasma-enhanced chemical vapor deposition technology using N2 and C2H2 as nitrogen and carbon sources, respectively. The effects of the N2/C2H2 gas flow ratio on the composition, bond structure, scratch resistance, and optical properties of the a-CNx:H films were investigated. X-ray photoluminescence spectroscopy and Raman spectroscopy results indicated that the N/C atomic ratio, carbon 1s sp3/sp2 ratio, and nitrogen 1s sp3/sp2 ratio increased with increasing N2/C2H2 gas ratio. Pin-on-disk wear tests conducted with a pin made of ultrahigh-molecular weight polyethylene indicated that all the a-CNx:H films exhibited good scratch resistance; however, rubbing with a stainless-steel ball weakened the wear resistance of the a-CNx:H films as the N2/C2H2 gas ratio changed from 5/30 to 30/30. The measured transmittance spectra showed that nitrogen incorporation into the carbon films increased their transmittance in the visible to near-infrared regions. The optical bandgap of the a-CNx:H films was obtained by the Tauc method, which demonstrated that when the N2/C2H2 gas flow ratio changed from 0/30 to 30/30, the optical bandgap increased from 1.18 to 1.86 eV. Our results suggest that a-CNx:H films can be used as optical and protective coatings.