ON THE LOW-TEMPERATURE THRESHOLD FOR CUBIC BORON-NITRIDE FORMATION INENERGETIC FILM DEPOSITION

The sharp threshold in substrate temperature below which cubic boron n itride (cBN) cannot be formed in energetic film-deposition processes w as investigated. We found that cBN could be synthesized below the thre shold temperature on top of cBN that had been previously formed above the threshold temperature. That the initial nucleation of cBN is more strongly dependent on temperature than its subsequent growth is sugges ted. How the structure of the sp(2)-bonded BN that accompanied cBN gro wth changed with temperature was also investigated. Lowering the subst rate temperature decreased the local ordering within the graphitic pla nes, and below the threshold temperature the separation of the graphit ic planes increased dramatically. How these structural changes may inf luence the nucleation of cBN is discussed.