Formation of cBN nanocrystals by He+ implantations of hBN

TL;DR

This study investigates how He+ ion implantation transforms polycrystalline hexagonal boron nitride into nanocrystalline cubic and rhombohedral phases, revealing structural changes via micro-Raman spectroscopy.

Contribution

It demonstrates the formation of cBN nanocrystals from hBN through ion implantation, providing insights into the structural transformation mechanisms.

Findings

Evidence of phase transformation from hBN to cBN, rBN, and amorphous BN.

Downshift and broadening of the cBN phonon mode observed.

Implantation-induced defects influence the Raman spectral features.

Abstract

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.