Mg-Facilitated Growth of Cubic Boron Nitride by Ion Beam-Assisted Molecular Beam Epitaxy

Trace amounts of Mg deposited on a diamond (100) substrate surface facilitate the growth of cubic boron nitride (c-BN) by ion beam-assisted molecular beam epitaxy. Fourier transform infrared spectroscopy indicates that films grown with Mg are cubic, while those without Mg are either hexagonal BN or lacking measurable cubic or hexagonal signatures. Initiating the growth with 0.005 monolayer equivalent of Mg is sufficient to yield epitaxial films with >99% c-BN. Reflection high energy electron diffraction, electron energy loss spectroscopy, and X-Ray photoelectron spectroscopy indicate the surface of the film to be sp(2)-bonded BN, consistent with the results of other groups. High-resolution scanning transmission electron microscopy reveals c-BN with a high density of stacking faults and twinning. A model is proposed by which Mg locally diminishes the energy barrier to dissociation of the as-deposited sp(2)-bonded BN, facilitating the nucleation of c-BN.