A dielectric barrier discharge (DBD) in Ar/CH4 gas mixtures used for amorphous hydrogenated carbon (a-C:H) film deposition was investigated. It was found that the a-C:H film properties (the ratios of sp(3)/Isp(2) and CH3/CH2, the number density of hydrogen atoms in the film and the energy band gap) correlate with the number densities of Ar(I-S5) atom and CH(chi(2) Pi) radical. A high value of the energy band gap, which corresponds to a high content of sp(3) fraction in the film was obtained, when the CH radical number density in the plasma was relatively small (similar to 10(8) cm(-3)). The DBD breakdown voltage decreased when the a-C:H film was deposited on the dielectric surface of the electrode. (c) 2005 Published by Elsevier B.V.