Simultaneous growth of diamond and nickel carbide on a graphite substr
ate was observed. Nickel carbide appeared as a non-stoichiometric inte
rstitial solid solution possessing the NaCl-type structure. The nuclea
tion and growth of diamond was conducted by microwave plasma chemical
vapor deposition. The CH4-H-2 plasma produces intensive mass transport
in the separate nickel carbide crystals resulting in coalescence. A h
ypothesis of the formation of gaseous organometallic molecules is desc
ribed and the role of atomic hydrogen which alters the Ni-C-H equilibr
ia is discussed.