Effects of the Heterointerface on the Growth Characteristics of a Brownmillerite SrFeO2.5 Thin Film Grown on SrRuO3 and SrTiO3 Perovskites

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 (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.

Analog memristive synapse based on topotactic phase transition for high-performance neuromorphic computing and neural network pruning

“…The metallic SRO was used as the BE, enabling an atomically clean epitaxial interface without misfit dislocations (fig. S2) ( 35 ). After the film growth, a 20-nm-thick Al 2 O 3 capping layer was deposited on top to protect the SCO layer.…”

Interfacial stabilization for epitaxial CuCrO2 delafossites

“…Meanwhile, the Cu– L 2,3 edge was not detected on the substrate side, verifying that Al atoms were intermixed with the B -site Cr atoms not Cu atoms. In general, the O– K edge in transition metal oxides has been used for the investigation of the individual electronic structure of materials, since the 1s core states have a relatively small exchange interaction with the final states, resulting in no visible multiplet effects 27 – 29 . The O– K edge spectra profile across the interface confirms that one ML above the interface and two MLs below the interface exhibits the characteristic electronic structures from those of the CuCrO 2 thin film and Al 2 O 3 substrate, respectively.…”

Atomic Structure of the Initial Nucleation Layer in Hexagonal Perovskite BaRuO3 Thin Films

“…Because the growth of epitaxial thin film is predominantly determined at the nucleation stage, it is critical to characterize the atomic structures at the interface between the thin film and substrate. [ 24,25 ] Figure a shows a typical high‐magnification HAADF STEM image for the interfacial region between 9R BRO thin film and (111) STO substrate (several other HAADF STEM images for the interfacial regions are displayed in Figure S1 in the Supporting Information). The image shows that an intermediate layer is formed between the bulk film and substrate denoted by white dashed lines in Figure 2a, where the atomic structure is different from that of nominal 9R BRO.…”

“…face-and corner-sharing, can be analyzed by HAADF STEM. The face-sharing of RuO 6 octahedra corresponds to Ru atomic columns aligned along the c-axis, while the corner-sharing corresponds to Ru atomic columns lying aslant from that axis.Because the growth of epitaxial thin film is predominantly determined at the nucleation stage, it is critical to characterize the atomic structures of the interface between the thin film and the substrate 25,26. Fig.…”