Interface matching in oxides of rocksalt/rocksalt(001) and rocksalt/perovskite(001)

The matching configuration in an ionic interface is more stringent relative to metallic systems due to the polarity concern. This configuration has to satisfy both geometric and electrostatic requirements. We study the growth of several different thin films, including MgO, SrO, NiO, and Fe3O4 on single crystalline MgO(001) and SrTiO3(001) substrates by molecular beam epitaxy. These oxides have different structures (rocksalt, perovskite, and spinel) and lattice misfits (small, ∼1%, and large, ∼23%). Using high energy electron diffraction, we observed some specific orientation relations between these structures. The interface of a rocksalt/rocksalt only shows a direct matching configuration. However, the interface of rocksalt/perovskite shows two different matching configurations, direct on and 45° rotation of the film relative to the substrate. This difference results from the relative ionic arrangements of these materials. It further implies that a more general matching rule may exist in other ionic interfaces depending on the relative ionic symmetry. A calculation based on Ewald sum is also included.