Abstract
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 (SrFeO2.5; BM-SFO) thin films are epitaxially grown along the b-axis on both SrTiO3(001) and SrRuO3/SrTiO3(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/SrRuO3/SrTiO3(001) and BM-SFO/SrTiO3(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.
Highlights
Manipulation of the heterointerfacial structure and/or chemistry of transition metal oxides is of great interest for the development of novel properties
We investigated the microstructures of Brownmillerite oxides such as SrFeO2.5 (BM-SFO) thin films grown on SrTiO3(STO)(001) and SrRuO3(SRO)/STO(001) substrates using transmission electron microscopy (TEM) and first principles calculations
Even though the two substrates have the same in-plane lattice parameters, the thin films grown on both substrates displayed very different heterointerfacial structures and growth processes, suggesting additional key factors that control the growth behaviour of the thin films. We found that these differences in the growth processes of the thin films are attributed to interfacial effects determined by the heterointerfacial structures such as the peculiar transition layer, the different chemical species, and octahedral connectivity
Summary
Manipulation of the heterointerfacial structure and/or chemistry of transition metal oxides is of great interest for the development of novel properties. In recent years, manipulating the heterointerface of transition metal oxides has enabled the development of novel phenomena such as two-dimensional free electron gases[3,4,5,6,7], interfacial charge transfer[8,9], high-Tc superconductors[10], and colossal magnetoresistance[11]; these have never been available in bulk equilibrium phases These new phenomena emerged through controlling the interface, which essentially modify the degree of orbital hybridization[12,13,14]. Accurate determination of the oxide heterointerfacial structure is essential to understand the growth characteristics of oxide thin films and fabricate functional devices with desired physical properties Brownmillerite oxides such as SrFeO2.5 (BM-SFO) are of particular interest due to their wide range of physical properties including thermoelectricity, fast oxygen-ion transport, catalysis, and topotactic phase transformation at low temperatures[15,16]. These effects have been rarely reported, despite their great potential for manipulating the growth dynamics and consequential physical properties of oxide thin films
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