DIAMOND DEPOSITION ON CHROMIUM, COBALT AND NICKEL SUBSTRATES BY MICROWAVE PLASMA CHEMICAL-VAPOR-DEPOSITION

Only after a relatively long incubation time (which is necessary to sa turate the substrate and its surface with carbon by diffusion or forma tion of an intermediate layer) did diamond nucleation and deposition o ccur on Cr, Co and Ni. Also, prior to the onset of the diamond formati on, non-diamond carbon layers can be formed with too high a concentrat ion of CH4. However, most of the experimental facts observed during th e diamond depositions on Cr, Co and Ni surfaces can be explained by in teractions occurring between the reaction gases and the substrates. Ch romium substrates form an intermediate carbide layer prior to diamond deposition. Diamond nucleation did not occur readily. Cobalt has only a low solubility for C. At low CH4 concentrations, diamond was deposit ed on pure Co. No deposition of amorphous carbon was observed. Nickel has a certain C solubility. Diamond nucleation occurred only after the substrate and its surface had been carbon saturated. The length of th e interval until saturation was reached depended on the substrate thic kness. During the time needed to cover the substrate fully with a diam ond layer, the metal vapour from substrate interacted with the diamond growth. Large growth steps developed on the diamond crystal facets. A lso refractory metal substrates placed near to the Cr, Co or Ni substr ates were contaminated and their diamond coatings exhibited the same g rowth step features.