Atomic imaging of electrically switchable striped domains in β′-In2Se3

Abstract

2D ferroelectricity in van-der-Waals-stacked materials such as indium selenide (In2Se3) has attracted interests because the ferroelectricity is robust even in ultrathin layers, which is useful for the miniaturization of ferroelectric field effect transistors. To implement In2Se3 in nanoscale ferroelectric devices, an understanding of the domain structure and switching dynamics in the 2D limit is essential. In this study, a biased scanning tunnelling microscopy (STM) tip is used to locally switch polarized domains in β′-In2Se3, and the reconfiguration of these domains are directly visualized using STM. The room-temperature surface of β′-In2Se3 breaks into 1D nanostriped domains, which changes into a zig-zag striped domains of β″ phase at low temperatures. These two types of domains can coexist, and by applying a tip-sample bias, they can be interchangeably switched locally, showing volatile or nonvolatile like behavior depending on the threshold voltage applied. An atomic model is proposed to explain the switching mechanism based on tip-induced flexoelectric effect and the ferroelastic switching between β′ and β″ phases.