Tuning Phonon Propertiesof Isotopically EnrichedHexagonal Boron Nitride

Hexagonal boron nitride (hBN) is a two-dimensional material with prominent applications in quantum devices. The phonon properties of hBN, including the phonon velocity and lifetime, are critical for a complete understanding of the material’s elasticity and loss mechanisms in charge-carrier and heat diffusion. Recently, isotopically enriched hBN crystals have been produced, offering a tuning mechanism for the material’s chemical and physical properties, albeit the low-frequency acoustic phonon properties of these isotopes are yet to be characterized. Here, we report the experimental characterization of enriched hBN bulk crystals by using Raman and Brillouin spectroscopies across four compositions (h10B14N, h10B15N, h11B14N, and h11B15N) and compare their acoustic and optical phonon properties to those of a natural hBN. Both techniques indicate a common trend: as atomic mass increases, the vibrational frequency decreases in accordance with the elastic model. These findings reinforce motivation for further developments in fabrication and optimization of isotopically enriched 2D materials as a means to fine-tune material stiffness and enhance optoelectronic performance.