In order to determine the mechanism of diamond-like film deposition in
a r.f. discharge in methane, a tiny glass fiber was spanned along the
discharge axis and perpendicular to the parallel-plate electrodes. Th
e discharge was operated in a symmetric and slightly asymmetric regime
. The film thickness and its surface topography were analyzed by means
of scanning electron microscopy. Across the interelectrode space a no
n-uniform film thickness distribution on the fiber was observed. The f
ilms up to 15 mu m were deposited with excellent coverage uniformity a
nd time stability on a 40 mu m diameter glass fiber substrate. The fil
m thickness distribution along the fiber is the result of the space-de
pendent density profile of methyl CH3 radicals which contribute mostly
to the film formation. It was concluded that the diffusion of methyl
radicals in the discharge is responsible for the observed film thickne
ss profile along the fiber.