Flexoelectric Polarization in Wrinkled Janus Transition-Metal Dichalcogenide Monolayers

Abstract

Strain-gradient engineering via out-of-plane wrinkling offers a powerful route to tune electronic and electromechanical properties in two-dimensional (2D) materials. Here, we systematically investigate the electronic and flexoelectric response of wrinkled Janus MoSSe/MoSeS monolayers using density functional theory (DFT) calculations coupled with continuum elastica modeling. Exploring varying wrinkle sizes and compressive strain levels ($5\%-20\%$), we show that the global out-of-plane polarization follows a linear behavior when parameterized by the projected aspect ratio of the nanowrinkles. On this basis, we develop a physically grounded geometric model incorporating an effective 2D flexoelectric coefficient, which accurately predicts DFT polarizations without requiring higher-order nonlinear parameters. Atom- and orbital-resolved charge density analyses reveal the microscopic origin of this behavior: while the central Mo $4d$-orbital manifold acts as a robust, linear flexoelectric core, local curvature drives continuous, chemically asymmetric charge transfer between the S $3p$ and Se $4p$ sublayer manifolds. Our findings establish clear geometric design rules for harnessing Janus-based flexoelectricity for flexible nanoelectronics and optoelectronics.