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 N-2 gas with varying dilution ratios (R) and their hardness, surface roughness and chemical composition were analyzed. The films deposited from C2H2/N-2 contained nitrogen elements and they were softer with rougher surface compared with the a-C: H films deposited from C2H2/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. (C) 2012 Elsevier B. V. All rights reserved.