Effects of bias voltage on the microstructure and properties of Al-doped hydrogenated amorphous carbon films synthesized by a hybrid deposition technique

Al-doped hydrogenated amorphous carbon films were deposited by a hybrid deposition technique combining middle-frequency magnetron sputtering and anode layer ion source. The evolution of chemical composition, surface morphology and chemical bonding state of the resultant films were investigated using XPS, SEM, TEM and Raman spectroscopy, respectively. It was found that the surface morphology of as-deposited films evolved from a rough surface with quasi-columnar characteristic to an ultra-smooth surface with the increasing of applied bias voltage from 0 V to −400 V. At the low bias voltage of 0 V to −50 V, a polymer-like structure was mainly formed. A diamond-like structure is dominated at the moderate bias voltage of −100 V to −300 V, while it transforms to graphite-like after a further increase of the applied bias voltage up to −400 V. The residual stresses and tribological behavior were characterized by stress-tester and ball-on-disk tribo-meter, respectively. The results suggested that tensile stress or compressive stress of the a-C:H(Al) film can be tailored by modifying the applied bias voltage. Particularly, the film deposited at −150 V exhibited a combination of superior properties, including low residual stress, high hardness, a low steady-state friction coefficient of 0.045 and wear rate of 2.7 × 10−7 mm3 N-1·m-1.