Amorphous hydrogenated carbon a-C:H films were deposited on silicon and quartz substrates in a parallel plate reactor by radio frequency (rf) plasma-enhanced chemical vapor deposition. The deposition rates of the films have been studied in the low-frequency region of the electric field. The Si and quartz substrates of different thickness have been used. The rf and substrate thickness dependencies of the deposition rates are discussed in terms of a theory of ion bombardment. (C) 1999 American Institute of Physics. [S0021-8979(99)07506-4].85633453347