Strongly enhanced electromechanical coupling in atomically thin transition metal dichalcogenides

Abstract: Flexoelectricity in thin films has emerged as an effective electromechanical response owing to appealing scaling law and universal existence. However, current studies show limited out-of-plane converse flexoelectric effect (CFE) of ultra-thin transition metal dichalcogenides (TMDs) when compared to their conventional in-plane piezoresponse. Here, we report converse flexoresponse of atomically thin TMDs such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) which exceeds their intrinsic in-plane piezoresponses. Our piezoresponse force microscopy (PFM) measurements revealed strongly enhanced CFE of the atomically thin MoS2 and WSe2 than their bulk counterpart (∼700% enhancement in MoS2, ∼400% enhancement in WSe2). We observed an anomalous reduction in converse flexoresponse in the monolayer structure attributed to a puckering deformation. By inducing a built-in in-plane tension to reduce puckering, we estimated the CFE of monolayer WSe2 to be 8.14?pm/V, the highest among the atomically thin TMDs.