Bend-Induced Ferroelectric Domain Walls in α-In<sub>2</sub>Se<sub>3</sub>
Edmund Han, Shahriar Muhammad Nahid, Tawfiqur Rakib, Gillian Nolan, Paolo F. Ferrari, M. Abir Hossain, André Schleife, SungWoo Nam, Elif Ertekin, Arend M. van der Zande, Pinshane Y. Huang
Abstract
The low bending stiffness of atomic membranes from van der Waals ferroelectrics such as α-In 2 Se 3 allow access to a regime of strong coupling between electrical polarization and mechanical deformation at extremely high strain gradients and nanoscale curvatures. Here, we investigate the atomic structure and polarization at bends in multilayer α-In 2 Se 3 at high curvatures down to 0.3 nm utilizing atomic-resolution scanning transmission electron microscopy, density functional theory, and piezoelectric force microscopy. We find that bent α-In 2 Se 3 produces two classes of structures: arcs, which form at bending angles below ∼33°, and kinks, which form above ∼33°. While arcs preserve the original polarization of the material, kinks contain ferroelectric domain walls that reverse the out-of-plane polarization. We show that these kinks stabilize ferroelectric domains that can be extremely small, down to 2 atoms or ∼4 Å wide at their narrowest point. Using DFT modeling and the theory of geometrically necessary disclinations, we derive conditions for the formation of kink-induced ferroelectric domain boundaries. Finally, we demonstrate direct control over the ferroelectric polarization using templated substrates to induce patterned micro- and nanoscale ferroelectric domains with alternating polarization. Our results describe the electromechanical coupling of α-In 2 Se 3 at the highest limits of curvature and demonstrate a strategy for nanoscale ferroelectric domain patterning.