Reactivity of different tBN environments serving as reaction sites in cBN film deposition

Experimental observation of cubic boron nitride (cBN) growth on most substrates showed that cBN nucleated and grew on turbostratic boron nitride (tBN) layers. TEM study of BN films deposited by both PVD and CVD methods revealed three major types of tBN environments in the tBN layer [tBN with its (0002) planes parallel to the growth direction (I), perpendicular to the growth direction (II) and with its (0002) planes forming curvatures in random directions (III)]. In accord with these tBN environments observed by TEM, the corresponding structural models were designed via theoretical studies. The theoretical studies used frontier orbital theory based on ab initio Hartee-Fock calculations to compare the reactivity of the tBN environments serving as further reaction sites for the cBN growth. Both B and N were chosen as reactants. The type I tBN showed the highest reactivity, while the type II tBN exhibited the lowest reactivity. The type III tBN yielded different reactivity levels, which varied upon the curvature of the tBN (0002) planes. In terms of analyzing the nucleation sites on tBN planes, possible cBN nucleation mechanisms are also discussed. These results are consistent with the current experimental observations and data previously published.