Hydrogenated amorphous carbon (a-C:H) films were formed by atmospheric dielectric barrier discharge-chemical vapor deposition (DBD-CVD), and the functional groups substituted at the film surface were characterized. It was found that the CH3/(CH + CH2) ratio in the a-C:H films formed by DBD-CVD was higher than in other carbon films formed by different methods, and a high density of carboxyl group was introduced on the film surface due to oxidation and dry etching reactions by ultraviolet irradiation. The result was consistent with the zeta potential measurements as well as the analysis of the surface atomic structures using discrete variational X alpha (DV-X alpha) calculations. (c) 2006 The Electrochemical Society.