MECHANISMS IN ION-ASSISTED DEPOSITION OF SUPERHARD COATINGS - CUBIC BORON-NITRIDE TETRAHEDRAL AMORPHOUS-CARBON

Ion-assisted deposition of tetrahedral amorphous carbon (ta-C) and cub ic boron nitride (c-BN) is compared with existing models (subplantatio n, stress model, sputter model). None of the models is found to descri be all aspects of a certain deposition process; nevertheless, some gen eral tendencies can be outlined: whereas for ta-C deposition local pen etration processes play a role, c-BN grows via attachment of atoms to c-BN crystals. The most important differences exist with respect to re laxation processes: during thermal activation ta-C relaxes towards the sp(2) structure, whereas in case of c-BN the crystalline sp(3) lattic e is even improved. Also, the problems concerning the adhesion of ta-C and c-BN are different: in the case of ta-C the main problem is the h igh stress which is a consequence of the over-constrained network, whe reas the adhesion of c-BN seems to be limited by the mechanical streng th of the interface (h-BN nucleation layer). (C) 1997 Elsevier Science S.A.