Surface roughness of diamond-like carbon films prepared using various techniques

Diamond-like carbon (DLC) films have been deposited onto mirror-finish sili con surfaces using three different techniques: (a) RF glow discharge from m ethane, (b) DC magnetron sputtering from a graphite target, with substrate RF bias; and (c) an ion beam generated from a cathodic are discharge. Nanos cale atomic force microscopy (AFM) (tapping mode) surface roughness analysi s has been carried out on as-deposited and post-deposition treated DLC film s. It was found that, in terms of the effect on surface roughness, there is a threshold value of the ion impingement energy. Below this ion energy, wh ich has a value of approximately 50 eV for each of the three techniques stu died, the DLC surface is very rough on a nanoscale, while above it the roug hness drops sharply. This threshold is close to previously reported atomic displacement threshold energies for graphite and diamond. These observation s have been explained in terms of the tendency for surface diffusion to gen erate sp(2)-rich surface clusters which roughen the surface, whereas high i mpingement energies lead to ion implantation, and hence less efficient surf ace diffusion, and to preferential sputter removal of protruding regions, w hich also favours low roughness. Observed effects of substrate temperature and exposure to atomic hydrogen have also been explained in terms of these mechanisms of roughening and smoothing. (C) 2001 Elsevier Science B.V. All rights reserved.