Effect of C2H4/N2 Ratio in an Atmospheric Pressure Dielectric Barrier Discharge on the Plasma Deposition of Hydrogenated Amorphous Carbon-Nitride Films (a-C:N:H)

The goal of this study was to investigate the properties and growth mechanisms of nitrogen-containing carbon-based coatings obtained with an atmospheric pressure dielectric barrier discharge in an N₂-C₂H₄ atmosphere. Radically different chemical compositions were observed depending on C₂H₄/N₂ ratio. With a low C₂H₄ concentration (<400 ppm) as a function of the residence time in the discharge, two different growth mechanisms were observed consisting of a highly nitrogenated coating (N/C > 0.8) and low hydrogen content. At the short residence time, growth was due to mobile small radicals that procured a smooth yet soluble coating, while at the longer residence time, diffusion-limited aggregation of high sticking N-containing radicals produced a cauliflower-like structure. With a high C₂H₄ concentration (≥2,000 ppm), a polymer-like coating with relatively lower nitrogen content (N/C ~ 0.2) was observed with a cauliflower morphology for the entire coating. Nanoindentation measurements revealed very different physical properties in the two types of coatings.