Low-cost growth of high-quality monoisotopic hexagonal boron nitride single crystals using a boric acid precursor†

Monoisotopic-boron-enriched hexagonal boron nitride (hBN) has a higher thermal conductivity (¹⁰B- or ¹¹B-enriched), larger phonon lifetime (¹⁰B- or ¹¹B-enriched) and stronger neutron absorption cross-section (¹⁰B-enriched) than the natural, non-isotopic-enriched hBN counterpart. These features make monoisotopic hBN highly desirable for application in neutron detectors, nanoscale electronics, and optical components. Herein, we synthesized monoisotopic hBN single crystals (SCs) using isotope-enriched boric acid based on the atmospheric-pressure high-temperature (APHT) method. X-ray diffraction measurements indicated that the monoisotopic hBN SCs were well-crystallized. Detailed Raman measurements verified the high crystal quality and uniformity. The dependency of the Raman peak position and peak width on the isotope content was also observed, matching well with theoretical calculations. In the cathodoluminescence spectra, the presence of a longitudinal optical (LO) phonon-related emission at around 5.75 eV was also indicative of the high quality of the crystals. Thus, our results present a low-cost route for the synthesis of high-quality monoisotope-enriched hBN single crystals.