Acoustic Phonons of Chemically Tunable 2D Hexagonal Boron Nitride from Brillouin Spectroscopy

We use Brillouin light scattering spectroscopy to measure the acoustic phonons of 2D layered hexagonal boron nitride at GHz frequencies. Measurements provide longitudinal and transverse sound velocities, nearly complete elastic stiffnesses, refractive indices, and acoustic attenuations. Further, we chemically intercalate noble metals of Au, Ag, and Cu into the van der Waals gap of layered hBN to achieve chemical tunability of the acoustic phonon properties. This work establishes unique chemical control of acoustic phonons in hBN.