Stabilization of ferroelastic charged domain walls in self-assembled BiFeO₃nanoislands

Understanding the microscopic origin of exotic domain configurations and emergent properties in charged domain walls is essential for both fundamental physics and applications in next-generation nanoelectronics. In self-assembled BiFeO3 nanoislands, 71° ferroelastic charged domain walls were spontaneously formed, which were traditionally regarded as unstable architectures. Here, by combining scanning transmission electron microscopy, geometric phase analysis, and energy dispersion spectrum, we explored the microscopic mechanism of stabilizing the tail-to-tail charged domain walls with upward center-divergent quad-domain structures in BiFeO3 nanoislands. The comprehensive factors include the fully relaxed rhombohedral phase in nanoislands, negative surface screening charges, and upward built-in bias at the BiFeO3-(La,Sr)MnO3 interface, which are respectively induced by interfacial periodic dislocations, surface reconstructions, and interfacial terminations. Moreover, the unusual polarization state and domain-wall arrangement in the nanoislands were also proved to be stable even at an elevated temperature.