Selective Synthesis of Isotopically Enriched Hexagonal Boron Nitride

Seth Eckels
Kansas State University, Manhattan, Kansas, USA _______________________________________

Hexagonal boron nitride (hBN) is a promising material for several novel devices such as quantum sensors, spintronic memory, and photonic devices. These applications require high quality crystals with application-specific defects and negligible concentrations of residual impurities. To meet these needs, the metal flux method of hBN crystal growth was developed. Boron, from either elemental boron or hBN powder, is first dissolved in a liquid metal flux (Ni + Cr) at high temperatures (1550 °C). The environment is kept slightly above atmospheric pressure with a constant controlled flowrate of nitrogen and hydrogen. The metal flux is then cooled to precipitate a layer of hBN crystals on the resulting ingot. Isotopically enriched sources for boron, ¹⁰B & ¹¹B, and nitrogen, ¹⁴N & ¹⁵N, were used to prepare four different combinations of isotopes: h¹⁰B¹⁴N, h¹¹B¹⁴N, h¹⁰B¹⁵N, and h¹¹B¹⁵N. These combinations are advantageous for specific applications, such as h10B14N for nanophotonics and h¹⁰B¹⁵N for quantum sensing. By adding graphite to the source materials, carbon-doped hBN crystals were also produced. Several spectroscopic techniques show that the metal flux method is capable of producing large area, low defect density, and versatile selectively enriched crystals for device applications.

Email: sethe44@ksu.edu