The 2D electrically insulating material hexagonal boron nitride (hBN) is being developed for a broad range of applications including infrared chemical sensors, ultraviolet emitters, quantum communications, neutron detectors, membrane separation of isotopes, and as a substrate and dielectric for 2D electronics and optoelectronics. These applications require hBN with a high degree of crystal perfection and controlled impurity concentrations. Such crystal are being grown a metal flux. Molten mixtures of nickel and chromium or iron and chromium were used to grow crystals over 1 cm2 in area and up to 200 µm thick. These crystals, produced in a simple, atmospheric pressure process, match the quality of the best hBN crystals reported in the literature. They have narrow Raman peak widths and room temperature phonon-assisted photoluminescence peaks above 5.7 eV. The properties of hBN are further enhanced by using isotopically pure boron sources, to produce monoisotopic hBN, made with either pure 10B or 11B isotopes. For example, the elimination of isotopic disorder in monoisotopic hBN increases its room temperature thermal conductivity by 40% and increase the phonon lifetimes by a factor of three compared to hBN with the natural (20% 10B and 80% 11B) distribution of boron isotopes. This seminar will describe both the process for growing hBN crystals and the characterization of their properties.
