Microstructure, mechanical and tribological properties of Si and Al co-doped hydrogenated amorphous carbon films deposited at various bias voltages

Hydrogenated amorphous carbon films containing Si and Al (a-C:H/(Si, Al)) were deposited on Si(100) substrates at different negative bias voltages, by radio frequency (RF, 13.56MHz) magnetron sputtering. The chemical composition and structure were detected by means of X-ray photoelectron spectroscopy (XPS) and Raman spectra, respectively. It was found from the results of Raman spectra that the film deposited at zero negative bias voltage was highly hydrogenated, but significant graphitization happened to the films when high bias voltages were applied. The results of atomic force microscope (AFM) showed that the films deposited at moderate negative bias voltage had ultra-smooth surface. The mechanical and tribological properties of the films were measured by nano-indentation test and tribo-meter in ball-on-disk mode, respectively. It was revealed that the negative bias voltage had great impacts on the mechanical properties of the films. The tribological properties of the films were significantly improved when bias voltages were applied on substrates. Particularly, the film deposited at -200V performed a super-low friction behavior (0.0085) and long wear life (>10 ⁵ revolutions) in ambient air under high Hertz contact stress (as high as 1.6GPa) though it showed a relatively low hardness.