Atomic-scale structure at the nucleation site of cubic boron nitride deposited from the vapor phase

Cross-sectional transmission electron microscopy, two-dimensional Fourier analysis, and electron energy loss spectroscopy were applied to sputter-deposited cubic boron nitride (cBN) films in order to investigate the structural evolution during cBN film growth, especially cBN nucleation on the initial sp²-bonded BN layer adjacent to the substrate. The difference in the bonding state of each layer and the existence of rhombohedral BN (rBN)-like structure in the turbostratic BN (tBN) layer at the cBN nucleation sites were clearly ascertained. In addition, strong correlations between rBN003 and cBN111, and between rBN101 and cBN111, similar to those predicted for pressure-induced direct diffusionless conversion of rBN to cBN, were also confirmed.