Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

Abstract

The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=Ca, Sr, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for SrSnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices.

Enhanced Stability and Thickness‐Independent Oxygen Evolution Electrocatalysis of Heterostructured Anodes with Buried Epitaxial Bilayers

“…Energy Mater. [19] A discontinuity in the conduction band edge at the NSTO/BLSO interface as schematically shown in the lower panel of (c) is supported by hard X-ray photoemission measurements. The capacitance was determined by fitting the impedance data from 0.1 Hz to 20 kHz to a Randles circuit.…”

“…[19,22] Films were grown at 760 °C /0.1 mTorr O 2 , 740 °C/10 −6 Torr vacuum, and 650 °C/500 mTorr O 2 for BLSO, LSTO, and LSCO, respectively, which yielded deposition rates of 1.72 nm min −1 (BLSO), 2.14 nm min −1 (LSTO), and 1.15 nm min −1 (LSCO). Ba 0.97 La 0.03 SnO 3 and La 0.7 Sr 0.3 CoO 3−δ films were deposited using polycrystalline Ba 0.95 La 0.05 Sn 1.1 O 3 and La 0.7 Sr 0.3 CoO 3 targets, respectively, while La 0.04 Sr 0.96 TiO 3 films were deposited using La 0.05 Sr 0.95 TiO 3 single crystal targets.…”

“…[19] Cs-corrected (CEOS, Germany) high-resolution HAADF-STEM images were acquired with a JEM-2100F (JEOL, Japan) operated at 200 kV with a Cs estimated by probe tableau calculation to be less than 1 mm. Structural characterization by X-ray diffraction was carried out using a Philips X'Pert Pro thin film diffractometer.…”

“…Figure 1c presents schematic diagrams of the trends of depletion layer thickness based on the Mott-Schottky analysis with band alignments deduced from photoemission measurements [19,20] revealing that we have succeeded in reducing the depletion layer width x d of the support structure and potentially enabling low cross plane transport resistance upon subsequent catalyst deposition. For the NSTO surface coated with a 10 nm thick epitaxial BLSO layer, these values are reduced to 26ε o and 3.0 nm, respectively, with the extracted BLSO permittivity close to bulk value.…”

Wide Bandgap Perovskite Oxides with High Room‐Temperature Electron Mobility

“…81 SrSnO 3 , another candidate in the family of alkaline-earth stannates, has a wider indirect bandgap with experimental and theoretical values ranging between 4.0 eV -5.0 eV. [82][83][84][85][86] The wider bandgap in SrSnO 3 is argued to be a result of smaller Sn-O-Sn bond angle (< 180 ° as in BaSnO 3 ), which causes a larger overlap between Sn 5s and O 2p orbitals. The bandgap can, therefore, be tuned between that of BaSnO 3 and SrSnO 3 by alloying.…”