Investigating the structural and physical properties of hydrogenated amorphous carbon films fabricated by middle frequency pulsed unbalanced magnetron sputtering

Hydrogenated amorphous carbon (a-C:H) films were deposited by the middle frequency pulsed magnetron sputtering method using a graphite target in a mixed methane and argon plasma. The effects of substrate bias on the microstructure, surface morphology, mechanical, electrical and optical properties of the a-C:H films were investigated. It has been found that the sp3 fraction in the a-C:H films increases with increasing substrate bias from 0 to 150 V. AFM measurements show that the RMS surface roughness of the films decreases with increasing substrate bias from 0 to 150 V. The correlation between the sp3 fraction and surface roughness of the a-C:H films is revealed, and the mechanism on it is suggested in this paper. Nanoindentation, electrical and optical measurements indicate that the nanohardness, electrical resistivity and optical band gap increase with increasing substrate bias from 0 to 150 V. The results above are useful for the practical application of a-C:H films.