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Title: Probing the Origin of Interfacial Carriers in SrTiO 3$-$LaCrO 3 Superlattices

Abstract

Emergent phenomena at complex oxide interfaces could provide the basis for a wide variety of next-generation devices, including photovoltaics and spintronics. To date, detailed characterization and computational modeling of interfacial defects, cation intermixing, and film stoichiometry have helped to explain many of the novel behaviors observed at a single heterojunction. Unfortunately, many of the techniques employed to characterize a single heterojunction are less effective for a superlattice made up of a repeating series of interfaces that induce collective interfacial phenomena throughout a film. These repeating interfaces present an untapped opportunity to introduce an additional degree of complexity, such as confined electric fields, that cannot be realized in a single heterojunction. In this work, we explore the properties of SrTiO 3–LaCrO 3 superlattices to understand the role of defects, including variations in cation stoichiometry of individual layers of the superlattice, intermixing across interfaces, and interfacial oxygen vacancies. Using X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS), we quantify the stoichiometry of individual layers of the superlattice and determine the degree of intermixing in these materials. By comparing these results to both density functional theory (DFT) models and STEM-EELS measurements of the Ti and Cr valence inmore » each layer of the superlattice, we correlate different types of defects with the associated materials properties of the superlattice. In conclusion, we show that a combination of ab initio modeling and complementary structural characterization methods can offer unique insight into structure–property relationships in many oxide superlattice systems.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3];  [4]; ORCiD logo [4];  [2];  [3];  [2];  [2]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Auburn Univ., AL (United States). Dept. of Physics
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. SuperSTEM, Daresbury (United Kingdom). SciTech Daresbury Campus
  4. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1340608
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 3; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
97 MATHEMATICS AND COMPUTING; 36 MATERIALS SCIENCE; Complex oxides; superlattices; x-ray photoelectron spectroscopy; x-ray absorption spectroscopy; scanning transmission electron microscopy

Citation Formats

Comes, Ryan B., Spurgeon, Steven R., Kepaptsoglou, Despoina M., Engelhard, Mark H., Perea, Daniel E., Kaspar, Tiffany C., Ramasse, Quentin M., Sushko, Peter V., and Chambers, Scott A. Probing the Origin of Interfacial Carriers in SrTiO3$-$LaCrO3 Superlattices. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.6b04329.
Comes, Ryan B., Spurgeon, Steven R., Kepaptsoglou, Despoina M., Engelhard, Mark H., Perea, Daniel E., Kaspar, Tiffany C., Ramasse, Quentin M., Sushko, Peter V., & Chambers, Scott A. Probing the Origin of Interfacial Carriers in SrTiO3$-$LaCrO3 Superlattices. United States. doi:10.1021/acs.chemmater.6b04329.
Comes, Ryan B., Spurgeon, Steven R., Kepaptsoglou, Despoina M., Engelhard, Mark H., Perea, Daniel E., Kaspar, Tiffany C., Ramasse, Quentin M., Sushko, Peter V., and Chambers, Scott A. Fri . "Probing the Origin of Interfacial Carriers in SrTiO3$-$LaCrO3 Superlattices". United States. doi:10.1021/acs.chemmater.6b04329. https://www.osti.gov/servlets/purl/1340608.
@article{osti_1340608,
title = {Probing the Origin of Interfacial Carriers in SrTiO3$-$LaCrO3 Superlattices},
author = {Comes, Ryan B. and Spurgeon, Steven R. and Kepaptsoglou, Despoina M. and Engelhard, Mark H. and Perea, Daniel E. and Kaspar, Tiffany C. and Ramasse, Quentin M. and Sushko, Peter V. and Chambers, Scott A.},
abstractNote = {Emergent phenomena at complex oxide interfaces could provide the basis for a wide variety of next-generation devices, including photovoltaics and spintronics. To date, detailed characterization and computational modeling of interfacial defects, cation intermixing, and film stoichiometry have helped to explain many of the novel behaviors observed at a single heterojunction. Unfortunately, many of the techniques employed to characterize a single heterojunction are less effective for a superlattice made up of a repeating series of interfaces that induce collective interfacial phenomena throughout a film. These repeating interfaces present an untapped opportunity to introduce an additional degree of complexity, such as confined electric fields, that cannot be realized in a single heterojunction. In this work, we explore the properties of SrTiO3–LaCrO3 superlattices to understand the role of defects, including variations in cation stoichiometry of individual layers of the superlattice, intermixing across interfaces, and interfacial oxygen vacancies. Using X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS), we quantify the stoichiometry of individual layers of the superlattice and determine the degree of intermixing in these materials. By comparing these results to both density functional theory (DFT) models and STEM-EELS measurements of the Ti and Cr valence in each layer of the superlattice, we correlate different types of defects with the associated materials properties of the superlattice. In conclusion, we show that a combination of ab initio modeling and complementary structural characterization methods can offer unique insight into structure–property relationships in many oxide superlattice systems.},
doi = {10.1021/acs.chemmater.6b04329},
journal = {Chemistry of Materials},
number = 3,
volume = 29,
place = {United States},
year = {Fri Jan 13 00:00:00 EST 2017},
month = {Fri Jan 13 00:00:00 EST 2017}
}

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  • Emergent phenomena at complex oxide interfaces could provide the basis for a wide variety of next-generation devices, including photovoltaics and spintronics. To date, detailed characterization and computational modeling of interfacial defects, cation intermixing, and film stoichiometry have helped to explain many of the novel behaviors observed at a single heterojunction. Unfortunately, many of the techniques employed to characterize a single heterojunction are less effective for a superlattice made up of a repeating series of interfaces that induce collective interfacial phenomena throughout a film. However, these repeating interfaces present an untapped opportunity to introduce an additional degree of complexity, such asmore » confined electric fields, that cannot be studied in a single heterojunction. In this work, we explore the properties of SrTiO3-LaCrO3 superlattices to understand the role of defects, including variations in cation stoichiometry of individual layers of the superlattice, intermixing across interfaces, and interfacial oxygen vacancies. Using x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS), we quantify the stoichiometry of individual layers of the superlattice and determine the degree of intermixing in these materials. By comparing these results to both density functional theory (DFT) models and STEM-EELS measurements of the Ti and Cr valence in each layer of the superlattice, we correlate different types of defects with the associated materials properties of the superlattice. We show that a combination of ab initio modeling and complementary structural characterization methods can offer unique insight into structure-property relationships in many oxide superlattice systems.« less
  • The interfacial electronic structure characterization of a m x (LaMnO{sub 3})/n x (SrTiO{sub 3}) superlattice based on scanning transmission electron microscopy and electron energy loss spectroscopy. Evidence of interfacial band alignment and electron transfer are presented based on the observation of O K edge of individual transition metal and oxygen atomic columns. Electron probe aberration correction was essential for the high spatial resolution mapping of interfacial electronic states.
  • Epitaxial interfaces and superlattices comprised of polar and non-polar perovskite oxides have generated a good deal of interest because of the variety of novel properties they possess. In this work, we examine superlattices comprised of SrTiO3 (STO) and LaCrO3 (LCO) layers; we demonstrate that the differing band alignment of the polar LCO layer and the non-polar STO layer produces a ferroelectric phase transition throughout the STO layers of the superlattice. Through x-ray absorption near edge spectroscopy and aberration-corrected scanning transmission electron microscopy we show that the Ti cations are displaced off-center in the TiO6 octahedra along the superlattice growth direction.more » We also demonstrate that a built-in potential gradient exists within the STO and LCO layers via in situ x-ray photoelectron spectroscopy measurements. Density functional theory models of the system are in excellent agreement with these results, predicting both the ferroelectric octahedral distortion and the built-in electric field. These results represent a new avenue for research in perovskite superlattices, as two non-ferroelectric phases are shown to induce a bulk ferroelectric response due to interfacial phenomena.« less
  • Epitaxial interfaces and superlattices comprised of polar and non-polar perovskite oxides have generated a good deal of interest because of the variety of novel properties they possess. In this work, we examine superlattices comprised of SrTiO3 (STO) and LaCrO3 (LCO) layers; we demonstrate that the differing band alignment of the polar LCO layer and the non-polar STO layer produces a ferroelectric phase transition throughout the STO layers of the superlattice. Through x-ray absorption near edge spectroscopy and aberration-corrected scanning transmission electron microscopy we show that the Ti cations are displaced off-center in the TiO6 octahedra along the superlattice growth direction.more » We also demonstrate that a built-in potential gradient exists within the STO and LCO layers via in situ x-ray photoelectron spectroscopy measurements. Density functional theory models of the system are in excellent agreement with these results, predicting both the ferroelectric octahedral distortion and the built-in electric field. These results represent a new avenue for research in perovskite superlattices, as two non-ferroelectric phases are shown to induce a bulk ferroelectric response due to interfacial phenomena.« less
  • Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO 3 or STO) substrates have recently shown superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 K), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature T c, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO 3 substrate. Here we report high-resolution angle-resolved photoemission spectroscopy resultsmore » that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO 3 system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO 3, which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO 3.« less