Atomic and Electronic Structure of Strongly Charged Domain Walls in van der Waals α-In2Se3.

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 α-In2Se3. STEM imaging and density functional theory (DFT) show that head-to-head (HH) domain walls contain a layer of β/β'-In2Se3, 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° domain walls exhibit complex, curved 3D structures that differ from ideal 180° structures. First-principles simulations predict localized conducting states within an ∼1 nm thick layer at both HH and TT domain walls, such as a midgap state at the β layer of the HH domain wall. These properties make strongly charged domain walls in α-In2Se3 excellent candidates for realizing 2D electron or hole gases and domain wall engineering in van der Waals ferroelectrics.