Growth of hBN crystals under high pressure N2
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The well-known, graphite-like hexagonal boron nitride (hBN) is currently experiencing a major renaissance as an essential material in 2D electronics, an extremely efficient UV emitter, and an excellent neutron detector. To fully explore and exploit the potential of hBN, a top-quality material is required, preferably in the form of a single crystal of a size suitable for research and applications.
At our Institute, we are working on the crystallization of hBN under high pressure. Recent results have been just published in the paper Crystal Growth of hBN from Ni and Ni–Cr Solutions at High N2 pressure, B. Sadovyi, P. Sadovyi, A. Nikolenko, V. Strelchuk, B. Turko, Y. Eliyashevskyy, I. Yahniuk, M. Marocko, J. Eroms, I. Petrusha, S. Krukowski, S. Porowski, and I. Grzegory, ACS Applied Materials & Interfaces 17, 63610 (2025). We describe there the processes and results of hBN crystal growth from B and N solutions in liquid nickel and a Ni-Cr mixture, under a nitrogen pressure of 1000-1500 bar.
The transparent, colorless hBN crystals showed excellent structural quality and homogeneity, confirmed by Raman spectrum mapping. The width of the E2g Raman peak corresponding to the vibrations of atoms in the plane of the hBN layer did not exceed 8 cm-1, which is evidence of the very high crystalline quality of the obtained hBN. Analysis of optical absorption spectra confirmed that hBN is a crystal with a skewed energy gap. Increased by a factor of 30-40 as a result of compression, the solubility of nitrogen in metal allowed for the production of crystals significantly thicker (up to 30 μm) than at atmospheric pressure.
In order to further verify the quality of the obtained single crystals, our collaborators from the University of Regensburg exfoliated thin hBN flakes and used these flakes to construct graphene devices. In graphene layers surrounded by hBN layers, spectacularly high mobility of both electrons and holes was obtained, exceeding 21.2 m²·V–1·s–1 at 230 K.
The paper summarizes part of the results of the research project “Long-term program of support of the Ukrainian research teams at the Polish Academy of Sciences carried out in collaboration with the U.S. National Academy of Sciences with the financial support of external partners” Grant No. PAN. BFB.S.BWZ.369.022.2023, entitled “Influence of high N2 gas pressure on crystallization mechanisms and physical properties of h-BN”.
