Microstructure, mechanical, and wettability properties of Al-doped diamond-like films deposited using a hybrid deposition technique: Bias voltage effects

In this study, Al-doped diamond-like carbon (DLC) films were prepared using a hybrid deposition technique combining high-power impulse magnetron sputtering and pulsed direct current magnetron sputtering. The influence of bias voltage effects on the microstructure and properties of films were investigated. The results showed that the deposition rate of the films decreased after increasing the bias voltage, and the Al content also slightly decreased in the films. All films exhibited a cauliflower-like surface morphology, which was independent of the bias voltage. The maximum values of sp(2)/sp(3) and ID/IG were achieved without bias voltage; the ratios then monotonously decreased with an increase in the bias voltage from-100 V to-400 V, which indicates that the content of sp(3)-C bonds has improved in films. The mechanical properties and the wettability of the films were also evaluated. The results revealed that the hardness, elastic modulus and residual stress of the films increased with increasing bias voltage. The highest hardness occurred at-400 V, and the high sp3-C fraction and residual stress were beneficial to the hardness enhancement. All films exhibited a water contact angle greater than 100, implying that the film possessed good hydrophobic performance. Specifically, when deposited at-300 V, the film presented a combination of superior properties, namely, a relatively high hardness and strong hydrophobic behavior.