The effect of duty cycle on the microstructure and properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering

The effect of duty cycle on the microstructure and properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering was investigated. The structure of the resultant carbon film is amorphous, as shown by high-resolution transmission electron microscopy. Raman analysis shows that the studied films are dominated by sp(2) sites, and the intensity ratio of the D and G peaks ranges from 4.0 at a duty cycle of 20% to 6.0 at 50%, which is one order of magnitude larger than that of diamond-like carbon films, indicating an obvious increase in sp2 sites with duty cycle. The surface morphology was investigated by atomic force microscopy. The images show that the as-deposited carbon films have a very rough surface, and the maximum granular structure size is up to 180 nm in diameter and 50 nm in height. The hardness and internal stress of the resultant carbon films increase with increasing duty cycle, accompanied by an increase in sp2 fraction in the films, which is different from the diamond-like carbon films. In addition, the resultant carbon films show superior tribological properties with high load-bearing capacity and excellent wear resistance. The influence of duty cycle on the microstructure and properties is discussed in detail.