Formation of c-BN nanoparticles by helium, lithium and boron ion implantation

Ion induced phase transformation from the soft graphitic hexagonal boron nitride (h-BN) to ultrahard cubic boron nitride (c-BN) nanoparticles is presented in the work herein. Ion implantation was used as a technique to introduce boron lithium and helium ions, at the energy of 150 keV and fluences ranging from 1 × 10 ¹⁴ to 1 × 10 ¹⁶ ions/cm ², into hot pressed, polycrystalline h-BN. Analyses using Raman Spectroscopy showed that He ⁺, Li ⁺ and B ⁺ led to a h-BN to c-BN phase transition, evident from the longitudinal optical (LO) Raman phonon features occurring in the implanted samples' spectra. The nature of these phonon peaks and their downshifting is explained using the spatial phonon correlation model.