A continuous, adhering film of polycrystalline diamond is grown on a grape substrate from diamond crystallites nucleated at a metal layer on the substrate when subjected to a microwave activated plasma of hydrogen and a carbon containing gas. Pyrolytic graphite and cured graphite adhesive are effective and other forms of graphite may be effective. Effective metals are chromium, nickel, and titanium. Diamond nucleation apparently occurs at crystallites of metal carbides nucleated by carbon from the plasma so that other carbide forming metals may be effective. Metal not nucleated as the carbide is, apparently, etched away by the plasma; and the diamond film is effectively deposited directly on the graphite since the diamond film is not contaminated by the metal even at the graphite interface where carbide contamination was less than 0.2 percent from a 2500 .ANG. chromium film. The diamond film deposition occurs at substrate temperatures as low as 650.degree. C. and may be facilitated by a positive voltage bias of the substrate relative to an enclosing vacuum chamber wall. Partial coating of a graphite surface with the metal results in diamond deposition only at the coated portion. A grid of diamond film has thus been deposited on graphite by application of a nickel screen to the graphite, and diamond film may be deposited in a desired pattern by masking the substrate to deposit the metal at selected substrate portions.