Shape and Surface Charge Modulation of Topological Domains in Oxide Multiferroics

Topological defects showing exotic properties and diverse functionalities provide us a potential utilization in nanoscale electronic devices. However, the formation mechanism and density manipulation of topological defects such as center-type domains which are crucial for applications remain elusive. Usually, these center-type domains are generated by applying external electric fields in ferroelectrics. In contrast, here we have prepared high-density center-divergent domains in BiFeO₃ as self-assembled nanoislands deposited on both Nb- and Fe-doped SrTiO₃ substrates. The size and density of these domains can be easily manipulated by varying doping level in substrates. The panorama polar configurations of the center-divergent domains are revealed by piezoresponse force microscopy and Cs-corrected scanning transmission electron microscopy. Phase-field simulations prove that both the surface charge accumulation and the shape of the nanoislands take great effect in the formation of center-type domains. The controllable growth of the nanoislands offers us a promising way to acquire high-density nanoscale nonvolatile memories.