Deposition and characterization of a-C:H coatings using a glow discharge

A range of amorphous hydrogenated carbon (a-C:H) coatings was synthesized using CH4 or C2H2 as the working gas in a modified physical vapour deposition (PVD) procedure based on a glow discharge plasma technique. The values of elastic moduli (E) for these coatings span from 57 to 137 GPa, and hardness (H) values are in the range 6–16 GPa. Coating thickness is of the order of 30–500 nm, and the compressive stresses in the coatings are between 0.2 and approximately 2 GPa. The procedure used to deposit these coatings is described with emphasis on the way process parameters can be altered to affect the resultant coating properties. Selected coatings have been characterized further using spectroscopic techniques such as Raman and IR. Three distinct Raman spectra have been noted and correlated with the original plasma composition. Elastic Recoil Detection measurements determined that the coatings contain between 22 and 32% hydrogen and that the process allows for 2–3 at.% nitrogen incorporation. AFM and TEM have been used to assess the surface roughness and coating morphology.