Roughness evolution during growth of hydrogenated tetrahedral amorphous carbon

Hydrogenated tetrahedral amorphous carbon (ta-C:H) is advantageous as coating material for high-density magnetic and optical storage devices, due to its favorable combination of density and smoothness. An advantage of ta-C:H over tetrahedral amorphous carbon (ta-C) is the absence of macroparticles, often found in cathodic arc deposition of ta-C, and the hydrogen rich surface, compatible with the lubricant. As for ta-C, in order to increase the magnetic storage density, the ta-C:H thickness needs to be decreased. It is thus necessary to determine the minimum thickness for continuous and pin-hole free films. Here we investigate the roughness evolution of ta-C:H by atomic force microscopy and determine the roughness and growth exponents α and β. We find a very similar behaviour to ta-C, with the ta-C:H roughness slightly higher than the ta-C one for any given thickness. This confirms the smoothing effect of impinging ions during ta-C:H deposition.