Large-Scale Domain Engineering in Two-Dimensional FerroelectricCuInP2S6 via Giant Flexoelectric Effect

Room-temperature ferroelectricity in two-dimen-sional (2D) materials is a potential for developing atomic-scalefunctional devices. However, as a key step for the technologyimplementations of 2D ferroelectrics in electronics, the control-lable generation of uniform domains remains challenging at thecurrent stage because domain engineering through an externalelectricfield at the 2D limit inevitably leads to large leakagecurrents and material breakdown. Here, we demonstrate a voltage-free method, theflexoelectric effect, to artificially generate large-scale stripe domains in 2D ferroelectric CuInP2S6with singledomain lateral size at the scale of several hundred microns. Withgiant strain gradients (similar to 106m-1), we mechanically switch the out-of-plane polarization in ultrathin CuInP2S6. Theflexoelectric control of polarization is understood with a distorted Landau-Ginzburg-Devonshire double well model. Through substrate strain engineering, the stripe domain density is controllable. Ourresults highlight the potential of developing van der Waals ferroelectrics-basedflexible electronics.

Automated summary

Room-temperature ferroelectricity in two-dimensional materials has the potential for developing atomic-scale functional devices. However, the controllable generation of uniform domains in 2D ferroelectrics remains challenging. In this study, we demonstrate the artificial generation of large-scale stripe domains using the flexoelectric effect in 2D ferroelectric CuInP2S6. We mechanically switch the out-of-plane polarization in ultrathin CuInP2S6 with giant strain gradients. The density of stripe domains can be controlled through substrate strain engineering.