A low temperature process(350 °C<T<500 °C) for nanocrystalline diamond film growth by microwave plasma-enhanced chemical vapor deposition has been developed that yields high rates (up to 2.5&mgr;m/h) at relatively low plasma powers (0.5 kW). In contrast to the widely used H2-rich mixtures of CH4or CO and H2that exhibit monotonic decreases in the diamond growth rate asTis reduced from 800 to400 °C, CO-rich mixtures of CO and H2exhibit an increase and sharp maximum asTis reduced. The results suggest a different diamond growth mechanism from the CO-rich mixtures. ©1997 American Institute of Physics.