Atomic Scale Understanding of the Epitaxy of Perovskite Oxides on Flexible Mica Substrate

The excellent functionalities of perovskite oxides and the growing demands for flexible devices lead to great interests on epitaxial growth of functional oxide films on flexible mica substrates. Understanding the film epitaxy on the substrate with a very different crystal structure is a key issue for the optimization of the film growth and hence properties. Such understanding largely depends on knowing the atomic structure of the interfaces between the films and the substrates. Here, the interface between the epitaxial films of SrTiO₃ on the fluorophlogopite mica substrate is studied in detail. Two types of interfaces, clean or with secondary phase, exist in this system, leading to two types of crystallographic orientation relationships. Atomic-resolution scanning transmission electron microscopy images reveal that at the clean interface the (111) Sr–O₃ atomic plane of SrTiO₃ interacts with the (001) (SiAl)₂–O₃ plane of mica. This interface structure and thus the epitaxy of the film are understood in light of the strong similarity of the oxygen sublattices in these two atomic planes. First-principles calculations demonstrate strong bonding of the atoms at the interface, which is also corroborated by the observation of misfit dislocations at the interfaces.