Exotic Quad-Domain Textures and Transport Characteristics of Self-Assembled BiFeO Nanoislands on Nb-Doped SrTiO.

Topological quad-domain textures with interesting cross-shaped buffer domains (walls) have been recently observed in BiFeO (BFO) nanoislands, indicating a new platform for exploring topological defects and multilevel memories. Such domain textures have nevertheless only been limited in BFO nanoislands grown on LaAlO substrates with a large lattice mismatch of ∼-4.4%. Here, we report that such exotic domain textures could also form in BFO nanoislands directly grown on a conductive substrate with a much smaller lattice mismatch and the local transport characteristics of the BFO nanoislands are distinct from the previously reported ones. The angle-resolved piezoresponse force images verify that the domain textures consist of center-divergent quad-domains with upward polarizations and cross-shaped buffer domains with downward polarizations. Interestingly, textures with multiple crosses are also observed in nanoislands of larger sizes, besides the previously reported ones with a single cross. The nanoislands exhibit strong diodelike rectifying characteristics and the quad-domains show a higher average conductance than the cross-shaped buffer domains, indicating that there is a certain correlation between the local conductance of the nanoislands and the domain textures. This transport behavior is attributed to the effect of the depolarization field on the Schottky barriers at both the substrate/BFO interface and the tip/BFO junction. Our findings extend the current understanding of the exotic quad-domain textures of ferroelectric nanoislands and shed light on their potential applications for configurable electronic devices.