Single crystal growth of monoisotopic hexagonal boron nitride from a Fe-Cr flux

Hexagonal boron nitride (hBN) is an important insulator that is incorporated into numerous 2D electronic, optoelectronic, and photonic devices, whereas natural hBN is a mixture of 20%B-10 and 80%B-11 isotopes, and monoisotopic hBN is a variant with just a single boron isotope, either(10)B or(11)B. Consequently, monoisotopic hBN has a higher thermal conductivity and a stronger neutron absorption (in the case of h(10)BN), making it superior for neutron detectors, heat management materials in nano flexible electronic devices, and phonon polariton-based nanophotonics. Here we synthesized approximately monoisotopic hBN using boron powder containing a single boron isotope and nitrogen, and grew single crystals from a Fe-Cr metal flux at atmospheric pressure. Narrow Raman peaks from the shear (<= 1.3 cm(-1)) and intralayer (<= 3.3 cm(-1)) modes demonstrate that the crystals are highly ordered. In the photoluminescence spectra, the presence of phonon-assistant transition peaks is also indicative of the high-quality of the crystals. This growth protocol permits us to get rid of the emission at 4.1 eV. This work provides a novel material for studying the fundamental properties of isotopic effects and the high-performance hBN device.