Na: A New Flux for Growing Hexagonal Boron Nitride Crystals at Low Temperature

The 2075°C melting temperature of boron has hindered the growth of hexagonal boron nitride (h-BN) crystal. The use of Si flux was reported to decrease the growth temperature to 1850°C. In this work, we discovered Na as a new flux for the growth of h-BN crystals at a temperature as low as 700°C. The growth of h-BN detected by X-ray diffraction (XRD) was consistent with the hexagonal features observed by scanning electron microscopy (SEM). Absorption at ∼1372 cm -1 was indicated by Fourier transform infrared (FTIR) spectroscopy. This absorption was attributed to the in-plane B-N stretching mode of h-BN. Emissions at photon energies as high as ∼5.6 eV are observed from cathodoluminescence (CL) spectra, indicating an optical band gap of at least 5.6 eV.