Determining the Out-of-Plane Longitudinal Sound Speed in GeS by Broadband Time-Domain Brillouin Scattering.

Over the past decade, two-dimensional (2D) layered semiconducting materials, with their distinctive structures and unique physicochemical properties, have attracted attention for potential applications in photonics and optoelectronics. In this study, we utilized time-domain broadband Brillouin scattering on a single germanium monosulfide (GeS) crystal to determine the out-of-plane longitudinal sound speed, evaluated at v L = (4035 ± 200) m/s. The reported results demonstrate the effectiveness of this nondestructive, all-optical technique for measuring the elastic properties in fragile 2D layered materials and provide the value of the out-of-plane compressive elastic constant, C = (69 ± 7) GPa.