Manipulating Charged Domain Wall Arrays in BiFeO Films by Asymmetric Electrical Boundary Conditions.

Charged domain walls (CDWs) in ferroelectric thin films have been identified as reconfigurable functional elements for advanced nanoelectronics, owing to their enhanced electrical conductivity and field-tunable topology. Deterministic control of stable CDWs remains a critical challenge due to insufficient understanding of their atomic-scale mechanisms. Here, we present a method for controllable introduction of CDWs in BiFeO thin films. By making use of atom resolved scanning transmission electron microscopy (STEM), we specified the stabilization principle of head-to-head and tail-to-tail CDW arrays in ultrathin BiFeO epitaxial films governed by asymmetric electrical boundary conditions, which were grown on SrTiO substrates. Atomic scale analysis of the lattice parameters and Fe ion displacements show distinct structural responses at head-to-head and tail-to-tail CDWs. Specifically, a reduction of in-plane lattice constant was observed at head-to-head CDWs, whereas an increase of in-plane lattice constant was identified at tail-to-tail CDWs. Moreover, the in-plane Fe ion displacements exhibit a continuous and periodic variation along the alternating head-to-head and tail-to-tail CDWs. These phenomena are governed by interfacial screening charge asymmetry, which plays a crucial role in stabilizing CDW arrays in dimensionally confined ferroelectrics. Our study advances the manipulation of interfacial screening and polarizations of ferroelectric films, facilitating the development of domain-wall-based nanoelectronic devices.