Hydrogenated amorphous carbon (a-C:H)-based films were synthesized by the dielectric barrier discharge-based plasma deposition at atmospheric pressure from C2H2 diluted with He or N2 gas with varying dilution ratios (R) and their hardness, surface roughness and chemical composition were analyzed. The films deposited from C2H 2/N2 contained nitrogen elements and they were softer with rougher surface compared with the a-C:H films deposited from C 2H2/He. Additionally the amount of nitrogen incorporation increased as the ratio R decreased, which led to deterioration of hardness and surface smoothness. As for C2H2/He, the film hardness slightly increased by decreasing the ratio R and the a-C:H (R = 1%) showed a maximum hardness of 1.1 GPa. © 2012 Elsevier B.V.