Method to grow pure nanocrystalline diamond films at low temperatures and high deposition rates

A method of depositing nanocrystalline diamond film on a substrate at a rate of not less than about 0.2 microns/hour at a substrate temperature less than about 500° C. The method includes seeding the substrate surface with nanocrystalline diamond powder to an areal density of not less than about 10<10>sites/cm<2>, and contacting the seeded substrate surface with a gas of about 99% by volume of an inert gas other than helium and about 1% by volume of methane or hydrogen and one or more of acetylene, fullerene and anthracene in the presence of a microwave induced plasma while maintaining the substrate temperature less than about 500° C. to deposit nanocrystalline diamond on the seeded substrate surface at a rate not less than about 0.2 microns/hour. Coatings of nanocrystalline diamond with average particle diameters of less than about 20 nanometers can be deposited with thermal budgets of 500° C.-4 hours or less onto a variety of substrates such as MEMS devices.