Enhanced Electromechanical Response Due to Inhomogeneous Strain in Monolayer MoS2.

ABSTRACT

2D transition metal dichalcogenides (TMDs) exhibit exceptional resilience to mechanical deformation. Applied strain can have pronounced effects on properties such as the bandgaps and exciton dynamics of TMDs, via deformation potentials and electromechanical coupling. In this work, we use piezoresponse force microscopy to show that the inhomogeneous strain from nanobubbles produces dramatic, localized enhancements of the electromechanical response of monolayer MoS2. Nanobubbles with diameters under 100 nm consistently produce an increased piezoresponse that follows the features' topography, while larger bubbles exhibit a halo-like profile, with maximum piezoresponse near the periphery. We show that spatial filtering enables these effects to be eliminated in the quantitative determination of effective piezoelectric or flexoelectric coefficients. Numerical strain modeling reveals a correlation between the hydrostatic strain gradient and the effective piezoelectric coefficient in large MoS2 nanobubbles, suggesting a localized variation in electromechanical coupling due to symmetry reduction induced by inhomogeneous strain.