Dynamic Mechanical Modulation of WS2 Monolayer by Standing Surface Acoustic Waves

Abstract

Surface acoustic waves (SAWs) propagating on piezoelectric materials carry large out-of-plane mechanical strain and strong in-plane electromagnetic fields, providing a fascinating hybrid platform for the manipulation of excitons in active media. The interaction of SAWs with two-dimensional (2D) semiconducting transition-metal dichalcogenide (TMD) monolayers has recently garnered significant attention due to their extreme sensitivity to strain and electromagnetic near-fields, resulting in exciton ionization in lithium niobate (LiNbO₃) based delay lines. In this study, we demonstrate an innovative approach to manipulate the optomechanical properties of a tungsten disulfide (WS₂) monolayer, based on the excitation of standing SAWs in an acoustic resonator defined on gallium arsenide (GaAs), a weak piezoelectric material. In contrast to previous reports on LiNbO₃ delay lines, our platform exhibits a resonant enhancement of the monolayer’s photoemission together with the imprinting of a discernible spatial structuring of the WS₂ luminescence in a one-dimensional (1D) periodic pattern. By imaging a large monolayer flake driven at the resonator frequency, we demonstrate that this optical modulation arises from a periodic detachment of the monolayer from the substrate surface due to the robust mechanical oscillations induced by the standing SAW pattern in high quality factor resonators. Our work establishes SAW resonators as an alternative paradigm to locally and reversibly tuning the optical and structural properties of TMD monolayers at room temperature by micro/nanoscale control of mechanical fields. This approach holds substantial potential for applications in the field of optics and nanophotonics with tunable light-matter interactions.