Formation of cBN nanocrystals by He+ implantations of hBN

The structural modifications of polycrystalline hexagonal boron nitride implanted with He+ ion beams at energies between 200 keV and 1.2 MeV to fluences of 1.0 \times 1017 ions \cdot cm-2 were investigated using micro-Raman spectroscopy. The measured Raman spectra show evidence of implantation-induced structural transformations from the hexagonal phase to nanocrystalline cubic boron nitride, rhombohedral boron nitride and amorphous boron nitride phases. The first-order Longitudinal-Optical cBN phonon was observed to be downshifted and asymmetrically broadened and this was explained using the spatial correlation model coupled with the high ion implantation-induced defect density.