Thinner Is Not Always Better: Nonmonotonic Flexoelectric Scaling in Suspended MoS2 Semiconductor Membranes

Flexoelectricity is generally expected to strengthen as material dimensions shrink, because strain gradients are amplified at small length scales. Here, we reveal a nonmonotonic thickness dependence of the flexoelectric response in suspended semiconducting MoS2 membranes. Combining atomic force microscopy, piezoelectric force microscopy, scanning microwave impedance microscopy, and nonlinear finite element modeling, we identify a maximum flexoelectric response at ∼42 nm. Carrier redistribution increasingly screens the flexoelectric field with increasing thickness, reaching ∼16% at 80 nm, but it does not determine the optimal thickness. Instead, the optimum thickness is governed primarily by the coupled balance among bending deformation, strain-gradient elasticity, dielectric response, and flexoelectric polarization. Its independence from loading force and suspended radius further indicates a material-parameter-governed characteristic length. These findings uncover an anomalous size effect in layered semiconductors and provide design insight for high-performance 2D material-based electromechanical devices.