Directed Self-Assembly of Oxide Nanocomposites by Ion-Beam Lithography

Vertically aligned self-assembled nanocomposite films have provided a unique platform to study magnetoelectric effects and other forms of coupling between complex oxides. However, the distribution in the locations and sizes of the phase-separated nanostructures limits their utility. In this work, we demonstrate a process to template the locations of the self-assembled structure using ion lithography, which is effective for general insulating substrates. This process was used to produce a nanocomposite consisting of fin-shaped vertical nanostructures of ferroelectric BiFeO₃ and ferrimagnetic CoFe₂O₄ with a feature size of 100 nm on (111)-oriented SrTiO₃ substrates. Cross-sectional imaging of the three-phase perovskite-spinel-substrate epitaxial interface reveals the selective nucleation of CoFe₂O₄ in the trenches of the patterned substrate, and the magnetic domains of CoFe₂O₄ were manipulated by applying an external magnetic field.