DLC coating roughness as a function of film thickness

We have investigated the evolution of surfaces roughness of DLC-coated substrates as a function of film thickness. This is important for DLC applications having to do with friction and wear. We used substrates with three different roughnesses between several nanometers and hundreds of nanometers. The substrates were cut into a number pieces and each piece coated with a different DLC thickness. The coated samples were characterized by atomic force microscopy. The results show that the surface roughness changes with DLC coating thickness. For substrates with original roughness 393 and 278 nm, the coating roughness increased with DLC thickness up to a maximum and then decreased. For the substrate with original roughness around 4 nm, the coating roughness showed no systematic tendency to decrease or increase. These results are interpreted using our previous results and taking into account the thin film growth dynamics.