Boron and Nitrogen Isotope Effects on Hexagonal Boron Nitride Properties

Abstract

The unique physical, mechanical, chemical, optical, and electronic properties of hexagonal boron nitride (hBN) make it a promising 2D material for electronic, optoelectronic, nanophotonic, and quantum devices. Here, the changes in hBN's properties induced by isotopic purification in both boron and nitrogen are reported. Previous studies on isotopically pure hBN have focused on purifying the boron isotope concentration in hBN from its natural concentration (≈20 at% ¹⁰ B, 80 at% ¹¹ B) while using naturally abundant nitrogen (99.6 at% ¹⁴ N, 0.4 at% ¹⁵ N), that is, almost pure ¹⁴ N. In this study, the class of isotopically purified hBN crystals to ¹⁵ N is extended. Crystals in the four configurations, namely h¹⁰ B¹⁴ N, h¹¹ B¹⁴ N, h¹⁰ B¹⁵ N, and h¹¹ B¹⁵ N, are grown by the metal flux method using boron and nitrogen single isotope (> 99%) enriched sources, with nickel plus chromium as the solvent. In-depth Raman and photoluminescence spectroscopies demonstrate the high quality of the monoisotopic hBN crystals with vibrational and optical properties of the ¹⁵ N-purified crystals at the state-of-the-art of currently available ¹⁴ N-purified hBN. The growth of high-quality h¹⁰ B¹⁴ N, h¹¹ B¹⁴ N, h¹⁰ B¹⁵ N, and h¹¹ B¹⁵ N opens exciting perspectives for thermal conductivity control in heat management, as well as for advanced functionalities in quantum technologies.

Keywords: Raman spectroscopy; hexagonal boron nitride; isotopes; photoluminescence.