Formation of polar topological domains in wrinkled bulges in freestanding BiFeO₃ thin films

Abstract

This work presents a voltage-free strategy for creating and manipulating topological domains in freestanding BiFeO₃ films via the flexoelectric effect. By introducing bulge-like surface wrinkles into freestanding films, complexed polarization topological textures can be formed, i.e., center-type domain state with a cylinder bubble domain pattern along the vertical direction. This can be interpreted by the flexoelectric effect arising from the bulge topology, as verified by the phase-field simulation results. The observed center topological texture can also allow reversible switching between the center divergent state and the mosaic-like state driven by applying an electric field. The results provide a good example for the construction of topological domains via flexoelectric engineering, and offer opportunities for on-demand design of polar topological structures for certain nanoelectronics applications.