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.