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 saturate the substrate and its surface with carbon by diffusion or formation of an intermediate layer) did diamond nucleation and deposition occur on Cr, Co and Ni. Also, prior to the onset of the diamond formation, non-diamond carbon layers can be formed with too high a concentration of CH4. However, most of the experimental facts observed during the diamond depositions on Cr, Co and Ni surfaces can be explained by interactions occurring between the reaction gases and the substrates. Chromium 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 deposited 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 the interval until saturation was reached depended on the substrate thickness. During the time needed to cover the substrate fully with a diamond layer, the metal vapour from substrate interacted with the diamond growth. Large growth steps developed on the diamond crystal facets. Also refractory metal substrates placed near to the Cr, Co or Ni substrates were contaminated and their diamond coatings exhibited the same growth step features.