From Thin Films to Nanodots: Bottom-Up Integration of Fe3O4 on Nb:STO for Functional Oxide Nanostructures.

Epitaxial heterostructures of iron oxide thin films on oxide substrates are promising for spintronic applications. Scaling down such heterostructures into ordered nanostructures enables integration into functional devices. However, fabricating well-ordered nanostructures while retaining their structural and functional integrity remains challenging. A bottom-up approach is used to grow epitaxial Fe3O4 nanodot arrays on Nb-doped SrTiO3(Nb:STO) substrates integrating anodic aluminum oxide (AAO) templates combined with pulsed laser deposition. Following this method, the lateral confinement of Fe3O4 into 30 and 70 nm nanodots with 3D long-range ordering is then confirmed by grazing-incidence small-angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM). Building on this structural evidence, the Verwey transition is found to be retained, as observed in the continuous film. To explore its applicability in nanoelectronics, conductive atomic force microscopy (c-AFM) is used to probe local electrical behavior, and reveals bipolar resistive switching at room temperature in individual nanodots, consistent with behavior observed in thin films. Together, these results establish the first demonstration of ordered epitaxial Fe3O4/Nb:STO nanodots with preserved structural, magnetic, and electrical functionalities, providing a generalizable route for nanoscale integration of complex oxides.