Growth of nanocomposite films: From dynamic roughening to dynamic smoothening

This paper reports several new findings on the breakdown of dynamic roughening in thin film growth. With increasing energy flux of concurrent ion impingement during pulsed DC sputtering, a transition from dynamic roughening to dynamic smoothening is observed in the growth behavior of TiC/a-C nanocomposite films. The nanocomposite films show a negative growth exponent and ultra-smoothness (RMS roughness ∼0.2 nm at a film thickness of 1.5 μm). Based on high-resolution cross-sectional transmission electron microscopy observations we conclude that during growth an amorphous front layer of 2 nm covers the nanocomposite film and suppresses the influence of nanocrystallites on the roughness evolution of the nanocomposite films. We were able to predict the evolution of surface roughness based on a linear equation of surface growth which contains two diffusivity parameters that control the atomic mobility along the growing outer surface. The model is in good agreement with atomic force microscopy measurements of roughness evolution.