Orientation-tuning in self-assembled heterostructures induced by a buffer layer

Abstract

Anisotropic nano-plate structures in self-assembled perovskite–spinel thin films, BiFeO₃–NiFe₂O₄ and BiFeO₃–CoFe₂O₄, which were deposited on (001)_c SrRuO₃/SrTiO₃ and DyScO₃ substrates, respectively, have been demonstrated using transmission electron microscopy combined with strain analysis. Unlike the unitary cube-on-cube orientation relationship reported widely, the growth direction of the CoFe₂O₄ and NiFe₂O₄ plates was tuned to [011]_c while the BiFeO₃ matrix kept [001]_c in both systems. In particular, a thin stress-sensitive BiFeO₃ buffer layer between the spinel nanostructure and the substrate was introduced for providing a complex strain state in both film systems. The novel orientation tuning and the pattern configuration of the heterostructures are mainly attributed to the strain imposed on the films and the anisotropic ledge growth mechanism of spinels.