The authors synthesized carbon nitride films on chromium steel substrate under various conditions by unbalanced magnetron sputtering method. As a result of changing the flow rate of N2 gas and Ar gas during deposition, it was found that the film thickness and the amount of nitrogen inside the film increased with the increase in nitrogen gas. Further, in the plasma during synthesis, an increase in CN emitting species could be also confirmed by the increase in gas flow rate. In addition, when the substrate bias voltage was -100 V or less, it was found that the film thickness decreased and the chemical bonding state changed, but the hardness of the film was constant at 10 to 15 GPa. However, when the substrate bias voltage was not applied, the film hardness was constant at 6 to 10 GPa. The nitrogen concentration in the films was 25atom% at the maximum. As a result of a friction test, the friction coefficient of a carbon nitride film was equal to or less than that of a DLC film under machine oil condition.
