High-Quality Heteroepitaxial Growth of Thin Films of the Perovskite Oxynitride CaTaO₂N: Importance of Interfacial Symmetry Matching between Films and Substrates.

ABSTRACT: Perovskite oxynitrides have been studied with regard to their visible light-driven photocatalytic activity and novel electronic functionalities. The assessment of the intrinsic physical and/or electrochemical properties of oxynitrides requires the epitaxial growth of single-crystalline films. However, the heteroepitaxy of perovskite oxynitrides has not yet matured compared to the progress realized in work with perovskite oxides. Herein, we report the heteroepitaxial growth of CaTaO₂N thin films with (100)_pc, (110)_pc, and (111)_pc crystallographic surface orientations (where the subscript pc denotes a pseudocubic cell) on SrTiO₃ substrates using reactive radio frequency magnetron sputtering, along with investigations of crystallinity and surface morphology. Irrespective of surface orientation, stoichiometric CaTaO₂N epitaxial thin films were grown coherently on SrTiO₃ substrates and showed clear step and terrace surfaces in the case of low values of film thickness of approximately 20 nm. A (110)_pc-oriented film was also more highly crystalline than (100)_pc- and (111)_pc-oriented specimens. This relationship between crystallinity and surface orientation is ascribed to the number of inequivalent in-plane rotational domains, which stems from the symmetry mismatch between the orthorhombic CaTaO₂N and cubic SrTiO₃. A CaTaO₂N thin film grown on a lattice- and symmetry-matched orthorhombic DyScO₃ substrate exhibited a significant crystallinity and a clear step and terrace surface even though the film was thick (?190 nm). These results are expected to assist in developing the heteroepitaxial growth of high-quality perovskite oxynitride thin films.

SUBMITTER: Wakasugi T 

PROVIDER: S-EPMC7288696 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature