Effects of the Heterointerface on the Growth Characteristics of a Brownmillerite SrFeO 2.5 Thin Film Grown on SrRuO 3 and SrTiO 3 Perovskites

Manipulation of the heterointerfacial structure and/or chemistry of transition metal oxides is of great interest for the development of novel properties. However, few studies have focused on heterointerfacial effects on the growth characteristics of oxide thin films, although such interfacial engineering is crucial to determine the growth dynamics and physical properties of oxide heterostructures. Herein, we show that heterointerfacial effects play key roles in determining the growth process of oxide thin films by overcoming the simple epitaxial strain energy. Brownmillerite (SrFeO 2.5 ; BM-SFO) thin films are epitaxially grown along the b -axis on both SrTiO 3 (001) and SrRuO 3 /SrTiO 3 (001) substrates, whereas growth along the a -axis is expected from conventional epitaxial strain effects originating from lattice mismatch with the substrates. Scanning transmission electron microscopy measurements and first principles calculations reveal that these peculiar growth characteristics of BM-SFO thin films originate from the heterointerfacial effects governed by their distinct interfacial structures. These include octahedral connectivity between dissimilar oxides containing different chemical species and a peculiar transition layer for BM-SFO/SrRuO 3 /SrTiO 3 (001) and BM-SFO/SrTiO 3 (001) heterostructures, respectively. These effects enable subtle control of the growth process of oxide thin films and could facilitate the fabrication of novel functional devices.