  By molecular dynamics simulation, the chemical vapor deposition of amorphous
carbon onto graphite and diamond surfaces was studied. In particular, we
investigated the effect of source H/C ratio, which is the ratio of the number
of hydrogen atoms to the number of carbon atoms in a source gas, on the
deposition process. In the present simulation, the following two source gas
conditions were tested: one was that the source gas was injected as isolated
carbon and hydrogen atoms, and the other was that the source gas was injected
as hydrocarbon molecules. Under the former condition, we found that as the
source H/C ratio increases, the deposition rate of carbon atoms decreases
exponentially. This exponential decrease in the deposition rate with increasing
source H/C ratio agrees with experimental data. However, under the latter
molecular source condition, the deposition rate did not decrease exponentially
because of a chemical reaction peculiar to the type of hydrocarbon in the
source gas.
