Atomic-resolution imaging and characterization of ferroelectric domain walls in two-dimensional In₂Se₃

Two-dimensional (2D) ferroelectric materials have garnered interest for their applications in nanoscale electronics and memory storage devices [1]. α-In₂Se₃ was recently discovered to exhibit strong out-of-plane ferroelectricity [2], ideal for these next-generation devices. In our work, we study the atomic structure and electronic properties of domain walls in α-In₂Se₃ using scanning transmission electron microscopy (STEM), piezoelectric force microscopy (PFM), and density functional theory (DFT). We identify two main types of ferroelectric domain boundaries in α-In₂Se₃: transverse and lateral domain walls, which respectively are perpendicular and parallel to the basal plane. By creating buckled structures, we find that we can induce polarization switching via mechanical deformation, forming transverse domain walls at highly localized bends. Using 4D-STEM, we measure the charge density and width of the domain walls, and we show that lateral domain walls are strongly charged. Finally, we also show that the lateral domain wall can readily travel between the In₂Se₃ layers to tune the overall polarization of a multilayer flake.

[1] Z. Guan, et al. Adv. Electr. Mat. 6, 1900818 (2020).

[2] Y. Zhou, et al. Nano Lett. 17, 5508-5513 (2017).