The depth profiles of the elemental composition were obtained from ToF-ERDA measurements, see Fig. . The films deposited in hydrogen ambient at 450 °C consist of 82.5 at.% B, 15.6 at.% C, 1.3 at.% O and 0.6 at.% H, corresponding to a composition of about B5C. It can be observed from the depth profiles (Fig. ) that the substrate-film interface is very sharp. It is interesting to note the very low amount of hydrogen, which is opposite to our previous results on CVD of B-C films from TEB. We explain this difference in hydrogen content in the films to the difference in gas flow velocities. While maintaining the same total reactor pressure, we reduced the flow velocity through the reactor by adjusting the gas flow in the vent line (bypass line to the throttle valve inlet).