Single Crystal Growth of Millimeter-Sized Monoisotopic Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) with a single boron isotope have many enhanced physical, thermal and optical properties compared to the most common hBN with the natural distribution of boron (19.9 at. % ¹⁰B and 80.1 at. % ¹¹B). These property differences can significantly improve the device performance in applications, such as neutron detectors, nanoscale electronics, and optical components. In this study, a new method for the growth of large-scale, high-quality monoisotopic hBN single crystals, i.e., h¹⁰BN and h¹¹BN, was developed. hBN single crystals were grown using a nickel-chromium solvent and pure boron and nitrogen sources at atmospheric pressure. The clear and colorless crystals have a maximum domain size of around 1 mm. Raman measurements demonstrate that the crystals produced with this method are pure hBN phase with low defect density, and the spectral peaks vary with the boron isotope concentrations. X-ray photoelectron spectroscopy spectra show that the B-N bond in h¹¹BN is slightly stronger than that in h¹⁰BN. The ability to produce crystals in this manner opens the door to isotopically engineering the properties and performance of hBN devices.