Three-dimensional heteroepitaxy in self-assembled $BaTiO3–CoFe2O4$ nanostructures

Self-assembled $BaTiO3–CoFe2O4$ complex oxide nanostructures have been synthesized by pulsed laser deposition. A single ceramic target with a molar ratio of $0.62BaTiO3–0.38CoFe2O4$ was used. Spinel $CoFe2O4$ and perovskite $BaTiO3$ phases spontaneously separated during heteroepitaxial growth on a single-crystal $SrTiO3(001)$ substrate. The nanostructures are epitaxial in-plane as well as out-of-plane, with $CoFe2O4$ nanopillar arrays embedded in a $BaTiO3$ matrix. The $CoFe2O4$ nanopillars have uniform size and spacing and nearly circular cross section. As the substrate temperature increases from 750 to $950°C$⁠, the average diameter of the pillars increases from $∼9$ to $∼70nm$⁠.