Study of the surface layer in cBN growth by PVD techniques

A sp2 bonded boron nitride (sp2 BN) surface layer is sometimes observed on top of cubic boron nitride (cBN) grains for BN films deposited using ion-assisted PVD techniques. Understanding the formation of such surface layer gives a clue to the cBN growth mechanisms. In the current study, the microstructure and phase composition near the top surface of several BN films were investigated in order to clarify the formation mechanism of such a surface layer. All the films investigated were synthesized using ion-assisted PVD techniques, but with different deposition parameters. It was found that such a surface layer is not necessarily present in some of the cBN growth, and its presence depends on the bombardment of ion energy during deposition. The cBN growth mechanisms are discussed based on these observations.