Pulsed DC sputtered DLC based nanocomposite films:Controlling growth dynamics, microstructure and frictional properties

Surface smoothness of diamond-like carbon based thin films becomes a crucial property for developing nearly frictionless protective coatings. Surface roughness and the dynamic growth behaviour of TiC/a-C nanocomposite films, deposited by non-reactive pulsed DC (p-DC) sputtering of graphite targets, were studied using atomic force microscopy and cross-sectional scanning electron microscopy. Upon increasing the intensity of concurrent ion impingement by raising the frequency of p-DC sputtering, a transition from dynamic roughening to dynamic smoothing was revealed, leading to a transition from a strong columnar to a columnar free microstructure. It was shown that smooth films can be deposited on initial rough surfaces at a higher pulse frequency (350 kHz). Also dense, tough, ultrasmooth and ultralow friction TiC/a-C: H nanocomposite films were successfully deposited on industrial polished steel substrates by reactive p-DC sputtering of Ti targets at 350 kHz frequency in an argon/acetylene atmosphere.