Atomic and Electronic Structure of Strongly Charged Domain Walls in van der Waals {\alpha}-In$_2$Se$_3$

TL;DR

This study combines advanced microscopy and first principles calculations to reveal the atomic and electronic structures of charged domain walls in Se in a van der Waals ferroelectric, highlighting their potential for electronic applications.

Contribution

It provides detailed atomic and electronic characterization of charged domain walls in Se, including their complex 3D structures and localized conducting states, advancing domain wall engineering.

Findings

Charged domain walls contain nonpolar Se layers or are atomically abrupt.

Nearly 180b0 domain walls have complex 3D curved structures.

Localized conducting states exist within 1 nm at the domain walls.

Abstract

Here, we use atomic resolution scanning transmission electron microscopy (STEM) and first principles calculations to study the atomic and electronic structure of strongly charged domain walls in $\alpha$-In$_2$Se$_3$. STEM imaging and density functional theory (DFT) show that head-to-head (HH) domain walls contain a layer of nonpolar $\beta$-In$_2$Se$_3$, whereas tail-to-tail (TT) domain walls are atomically abrupt. We apply 4D STEM and multislice electron ptychography to map ferroelectric domains in 2D and 3D, showing that nearly $180^\circ$ domain walls exhibit complex, curved 3D structures that differ from ideal $180^\circ$ structures. Band structure calculations show localized conducting states within a $\sim$ 1 nm thick layer at both HH and TT domain walls, such as a midgap state at the $\beta$ layer of the HH domain wall. These properties make strongly charged domain walls in $\alpha$-In$_2$Se$_3$ excellent candidates for realizing 2D electron or hole gases and domain wall engineering in van der Waals ferroelectrics.