On the origin of fivefold multiply twinned nanoparticles in chemically vapour-deposited hexagonal boron nitride

Abstract The influence of different sample treatments on the formation of particles exhibiting fivefold symmetry in chemically vapour-deposited hexagonal boron nitride is reported. Particles with an average lateral dimension of 150nm were observed by transmission electron microscopy after mechanical thinning of polycrystalline hexagonal boron nitride at room temperature. Such particles have not been found in freshly cleaved samples, samples annealed at 1100°C, and samples prepared from the same material but in the form of a powder. The electron microscopy results are supported by X-ray powder diffraction data showing a corresponding anisotropic increase in the mean correlation length of ordered domains from an initial size below 10 nm in as-deposited samples to about 45 nm in the mechanically thinned specimens. It is suggested that micromechanical twinning contributes to the formation of fivefold particles.