On the dynamic roughening transition in nanocomposite film growth

Surface roughness and dynamic growth behavior of TiC/a-C nanocomposite films deposited by nonreactive pulsed-dc (p-dc) magnetron sputtering were studied using atomic force microscopy, cross-sectional scanning, and transmission electron microscopy. From detailed analyses of surface morphology and growth conditions, it is concluded that a transition in growth mechanisms occurs, i.e., a mechanism dominated by geometric shadowing at a p-dc frequency of 100 kHz evolving to a surface diffusion mechanism driven by impact-induced atomistic downhill flow process by Ar+ ions at a p-dc frequency of 350 kHz. It is shown that rapid smoothening of initially rough surfaces with rms roughness from ∼6 to <1 nm can be effectively achieved with p-dc sputtering at 350 kHz pulse frequency, leading to a transition from a strong columnar to a columnar-free microstructure.