Mechanisms in ion-assisted deposition of superhard coatings: cubic boron nitride–tetrahedral amorphous carbon

Abstract Ion-assisted deposition of tetrahedral amorphous carbon (ta-C) and cubic boron nitride (c-BN) is compared with existing models (subplantation, stress model, sputter model). None of the models is found to describe all aspects of a certain deposition process; nevertheless, some general tendencies can be outlined: whereas for ta-C deposition local penetration processes play a role, c-BN grows via attachment of atoms to c-BN crystals. The most important differences exist with respect to relaxation processes: during thermal activation ta-C relaxes towards the sp 2 structure, whereas in case of c-BN the crystalline sp 3 lattice 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 high stress which is a consequence of the over-constrained network, whereas the adhesion of c-BN seems to be limited by the mechanical strength of the interface (h-BN nucleation layer).