An investigation of carbon nitride films deposited at various N2/Ar ratios by the vacuum cathodic arc deposition method

Carbon nitride films have been prepared by the vacuum cathodic arc method at various N2/Ar ratios, while the total deposition pressure was kept at 4.0 and 8.0 Pa, respectively. The films were characterized by Raman spectroscopy and XPS. The maximum N concentration was up to 32 at.%. The properties of the films changed according to the total pressure and N2/Ar ratio in the mixture. At 4.0 Pa, with increasing N2/Ar ratio the N concentration rose quickly to a stable value in the initial stages; further increase in the N2 content in the mixture led to only a small variation in the N concentration. Raman spectra indicated that the sp2 carbon phase in the films increased at first. The sp2 phase then tended to decrease, accompanied by an increase in the sp3 CN bond relative ratio. On the other hand, at 8.0 Pa the N concentration remained at approximately 30 at.%. Upon increasing the N2 relative ratio, the films showed a decrease in sp2 carbon phase at first, accompanied by an increase in the sp3 CN bond relative ratio. The sp2 carbon phase then increased, which corresponded to a fall in the sp3 CN relative ratio. During the process, the nanohardness was in the range of 3.5–11 GPa; the maximum corresponded to the optimum N2/Ar ratio at which the variation of both sp3 CN bonds and sp2 phase changed. The increasing sp2 carbon phase in the initial stages at 4 Pa resulted from the increasing N concentration in the films, while the variation of sp2 carbon phase for stable N concentrations is attributed to the modification of CN bonds. The variation in hardness was affected by both sp2 carbon phase and CN bonds. The reasons for the variation of the microstructure of the films with N2/Ar ratio are discussed.