Abstract The a-C:H and a-C:N X :H films were deposited onto silicon wafers using radio frequency (rf) plasma enhanced chemical vapor deposition (PECVD) and pulsed-dc glow discharge plasma CVD, respectively. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize chemical nature and bond types of the films. The results demonstrated that the a-C:H film prepared by rf-CVD (rf C:H) has lower I D / I G ratio, indicating smaller sp 2 cluster size in an amorphous carbon matrix. The nitrogen concentrations of 2.9 at.% and 7.9 at.% correspond to carbon nitride films prepared with rf and pulse power, respectively. Electrochemical corrosion performances of the carbon films were investigated by potentiodynamic polarization test. The electrolyte used in this work was a 0.89% NaCl solution. The corrosion test showed that the rf C:H film exhibited excellent anti-corrosion performance with a corrosion rate of 2 nA cm −2 , while the carbon nitride films prepared by rf technique and pulse technique showed a corrosion rate of 6 nA cm −2 and 235 nA cm −2 , respectively. It is reasonable to conclude that the smaller sp 2 cluster size of rf C:H film restrained the electron transfer velocity and then avoids detriment from the exchange of electrons.