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Seo J, Lee H, Eom K, Byun J, Min T, Lee J, Lee K, Eom CB, Oh SH. Feld-induced modulation of two-dimensional electron gas at LaAlO 3/SrTiO 3 interface by polar distortion of LaAlO 3. Nat Commun 2024; 15:5268. [PMID: 38902225 PMCID: PMC11189907 DOI: 10.1038/s41467-024-48946-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 05/19/2024] [Indexed: 06/22/2024] Open
Abstract
Since the discovery of two-dimensional electron gas at the LaAlO3/SrTiO3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO3/SrTiO3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO3.
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Affiliation(s)
- Jinsol Seo
- Department of Energy Engineering, KENTECH Institute for Energy Materials and Devices, Korea Institute of Energy Technology (KENTECH), Naju, Republic of Korea
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Department of Energy Systems Research and Department of Physics, Ajou University, Suwon, Republic of Korea
| | - Kitae Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Jinho Byun
- Department of Energy Engineering, KENTECH Institute for Energy Materials and Devices, Korea Institute of Energy Technology (KENTECH), Naju, Republic of Korea
| | - Taewon Min
- Department of Physics, Pusan National University, Busan, Republic of Korea
| | - Jaekwang Lee
- Department of Physics, Pusan National University, Busan, Republic of Korea
| | - Kyoungjun Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Sang Ho Oh
- Department of Energy Engineering, KENTECH Institute for Energy Materials and Devices, Korea Institute of Energy Technology (KENTECH), Naju, Republic of Korea.
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2
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Marelli E, Lyu J, Morin M, Leménager M, Shang T, Yüzbasi NS, Aegerter D, Huang J, Daffé ND, Clark AH, Sheptyakov D, Graule T, Nachtegaal M, Pomjakushina E, Schmidt TJ, Krack M, Fabbri E, Medarde M. Cobalt-free layered perovskites RBaCuFeO 5+δ (R = 4f lanthanide) as electrocatalysts for the oxygen evolution reaction. EES CATALYSIS 2024; 2:335-350. [PMID: 38222064 PMCID: PMC10782807 DOI: 10.1039/d3ey00142c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 10/30/2023] [Indexed: 01/16/2024]
Abstract
Co-based perovskite oxides are intensively studied as promising catalysts for electrochemical water splitting in an alkaline environment. However, the increasing Co demand by the battery industry is pushing the search for Co-free alternatives. Here we report a systematic study of the Co-free layered perovskite family RBaCuFeO5+δ (R = 4f lanthanide), where we uncover the existence of clear correlations between electrochemical properties and several physicochemical descriptors. Using a combination of advanced neutron and X-ray synchrotron techniques with ab initio DFT calculations we demonstrate and rationalize the positive impact of a large R ionic radius in their oxygen evolution reaction (OER) activity. We also reveal that, in these materials, Fe3+ is the transition metal cation the most prone to donate electrons. We also show that similar R3+/Ba2+ ionic radii favor the incorporation and mobility of oxygen in the layered perovskite structure and increase the number of available O diffusion paths, which have an additional, positive impact on both, the electric conductivity and the OER process. An unexpected result is the observation of a clear surface reconstruction exclusively in oxygen-rich samples (δ > 0), a fact that could be related to their superior OER activity. The encouraging intrinsic OER values obtained for the most active electrocatalyst (LaBaCuFeO5.49), together with the possibility of industrially producing this material in nanocrystalline form should inspire the design of other Co-free oxide catalysts with optimal properties for electrochemical water splitting.
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Affiliation(s)
- Elena Marelli
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
- Electrochemistry Laboratory, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Jike Lyu
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Mickaël Morin
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
- Excelsus Structural Solutions (Swiss) AG, PARK InnovAARE CH-5234 Villigen PSI Switzerland
| | - Maxime Leménager
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Tian Shang
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
- Key Laboratory of Polar Materials and Devices (MOE), School of Physics and Electronic Science, East China Normal University Shanghai China
| | - N Sena Yüzbasi
- High Performance Ceramics, EMPA, Swiss Federal Laboratories for Materials Science and Technology CH-8600 Dübendorf Switzerland
| | - Dino Aegerter
- Electrochemistry Laboratory, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Jinzhen Huang
- Electrochemistry Laboratory, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Niéli D Daffé
- Laboratory for Condensed Matter, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Adam H Clark
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Denis Sheptyakov
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Thomas Graule
- High Performance Ceramics, EMPA, Swiss Federal Laboratories for Materials Science and Technology CH-8600 Dübendorf Switzerland
| | - Maarten Nachtegaal
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Ekaterina Pomjakushina
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Thomas J Schmidt
- Electrochemistry Laboratory, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
- Laboratory of Physical Chemistry, ETH Zürich CH-8093 Zürich Switzerland
| | - Matthias Krack
- Laboratory for Materials Simulations, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Emiliana Fabbri
- Electrochemistry Laboratory, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
| | - Marisa Medarde
- Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut CH-5232 Villigen PSI Switzerland
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3
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Gradauskaite E, Meier QN, Gray N, Sarott MF, Scharsach T, Campanini M, Moran T, Vogel A, Del Cid-Ledezma K, Huey BD, Rossell MD, Fiebig M, Trassin M. Defeating depolarizing fields with artificial flux closure in ultrathin ferroelectrics. NATURE MATERIALS 2023; 22:1492-1498. [PMID: 37783942 PMCID: PMC10713449 DOI: 10.1038/s41563-023-01674-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Accepted: 08/25/2023] [Indexed: 10/04/2023]
Abstract
Material surfaces encompass structural and chemical discontinuities that often lead to the loss of the property of interest in so-called dead layers. It is particularly problematic in nanoscale oxide electronics, where the integration of strongly correlated materials into devices is obstructed by the thickness threshold required for the emergence of their functionality. Here we report the stabilization of ultrathin out-of-plane ferroelectricity in oxide heterostructures through the design of an artificial flux-closure architecture. Inserting an in-plane-polarized ferroelectric epitaxial buffer provides the continuity of polarization at the interface; despite its insulating nature, we observe the emergence of polarization in our out-of-plane-polarized model of ferroelectric BaTiO3 from the very first unit cell. In BiFeO3, the flux-closure approach stabilizes a 251° domain wall. Its unusual chirality is probably associated with the ferroelectric analogue to the Dzyaloshinskii-Moriya interaction. We, thus, see that in an adaptively engineered geometry, the depolarizing-field-screening properties of an insulator can even surpass those of a metal and be a source of functionality. This could be a useful insight on the road towards the next generation of oxide electronics.
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Affiliation(s)
| | | | - Natascha Gray
- Department of Materials, ETH Zurich, Zurich, Switzerland
| | | | | | | | - Thomas Moran
- Department of Materials Science and Engineering, University of Connecticut, Storrs, CT, USA
| | | | - Karla Del Cid-Ledezma
- Department of Materials Science and Engineering, University of Connecticut, Storrs, CT, USA
| | - Bryan D Huey
- Department of Materials Science and Engineering, University of Connecticut, Storrs, CT, USA
| | | | - Manfred Fiebig
- Department of Materials, ETH Zurich, Zurich, Switzerland
| | - Morgan Trassin
- Department of Materials, ETH Zurich, Zurich, Switzerland.
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4
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Du C, Guzman F, Yang H, Waqar M, Pan X. Observation of Polarization Enhancement at BiFeO3/ La0.7Sr0.3MnO3 Interface. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2023; 29:1651-1652. [PMID: 37613912 DOI: 10.1093/micmic/ozad067.850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Affiliation(s)
- Chaojie Du
- Department of Materials Science and Engineering, University of California-Irvine, Irvine, CA, United States
| | - Francisco Guzman
- Department of Materials Science and Engineering, University of California-Irvine, Irvine, CA, United States
| | - Hongbin Yang
- Department of Materials Science and Engineering, University of California-Irvine, Irvine, CA, United States
| | - Moaz Waqar
- Department of Materials Science and Engineering, University of California-Irvine, Irvine, CA, United States
| | - Xiaoqing Pan
- Department of Materials Science and Engineering, University of California-Irvine, Irvine, CA, United States
- Irvine Materials Research Institute, University of California-Irvine, Irvine, CA, United States
- Department of Physics and Astronomy, University of California-Irvine, Irvine, CA, United States
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5
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Vogel A, Ruiz Caridad A, Nordlander J, Sarott MF, Meier QN, Erni R, Spaldin NA, Trassin M, Rossell MD. Origin of the Critical Thickness in Improper Ferroelectric Thin Films. ACS APPLIED MATERIALS & INTERFACES 2023; 15:18482-18492. [PMID: 36996320 DOI: 10.1021/acsami.3c00412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Improper ferroelectrics are expected to be more robust than conventional ferroelectrics against depolarizing field effects and to exhibit a much-desired absence of critical thickness. Recent studies, however, revealed the loss of ferroelectric response in epitaxial improper ferroelectric thin films. Here, we investigate improper ferroelectric hexagonal YMnO3 thin films and find that the polarization suppression, and hence functionality, in the thinner films is due to oxygen off-stoichiometry. We demonstrate that oxygen vacancies form on the film surfaces to provide the necessary charge to screen the large internal electric field resulting from the positively charged YMnO3 surface layers. Additionally, we show that by modifying the oxygen concentration of the films, the phase transition temperatures can be substantially tuned. We anticipate that our findings are also valid for other ferroelectric oxide films and emphasize the importance of controlling the oxygen content and cation oxidation states in ferroelectrics for their successful integration in nanoscale applications.
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Affiliation(s)
- Alexander Vogel
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
- Department of Materials, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland
| | - Alicia Ruiz Caridad
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
| | - Johanna Nordlander
- Department of Materials, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Martin F Sarott
- Department of Materials, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland
| | - Quintin N Meier
- Université Grenoble Alpes, CNRS, Institut Néel, 38042 Grenoble, France
| | - Rolf Erni
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
| | - Nicola A Spaldin
- Department of Materials, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland
| | - Morgan Trassin
- Department of Materials, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland
| | - Marta D Rossell
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
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6
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Kim D, Efe I, Torlakcik H, Terzopoulou A, Veciana A, Siringil E, Mushtaq F, Franco C, von Arx D, Sevim S, Puigmartí-Luis J, Nelson B, Spaldin NA, Gattinoni C, Chen XZ, Pané S. Magnetoelectric Effect in Hydrogen Harvesting: Magnetic Field as a Trigger of Catalytic Reactions. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2110612. [PMID: 35276030 DOI: 10.1002/adma.202110612] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 02/12/2022] [Indexed: 06/14/2023]
Abstract
Magnetic fields have been regarded as an additional stimulus for electro- and photocatalytic reactions, but not as a direct trigger for catalytic processes. Multiferroic/magnetoelectric materials, whose electrical polarization and surface charges can be magnetically altered, are especially suitable for triggering and control of catalytic reactions solely with magnetic fields. Here, it is demonstrated that magnetic fields can be employed as an independent input energy source for hydrogen harvesting by means of the magnetoelectric effect. Composite multiferroic CoFe2 O4 -BiFeO3 core-shell nanoparticles act as catalysts for the hydrogen evolution reaction (HER), which is triggered when an alternating magnetic field is applied to an aqueous dispersion of the magnetoelectric nanocatalysts. Based on density functional calculations, it is proposed that the hydrogen evolution is driven by changes in the ferroelectric polarization direction of BiFeO3 caused by the magnetoelectric coupling. It is believed that the findings will open new avenues toward magnetically induced renewable energy harvesting.
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Affiliation(s)
- Donghoon Kim
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Ipek Efe
- Materials Theory, Department of Materials, ETH Zürich, Wolfgang-Pauli-Strasse 27, Zürich, 8093, Switzerland
| | - Harun Torlakcik
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Anastasia Terzopoulou
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Andrea Veciana
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Erdem Siringil
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Fajer Mushtaq
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Carlos Franco
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Denis von Arx
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Semih Sevim
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Josep Puigmartí-Luis
- Departament de Ciència dels Materials i Química Física, Institut de Química Teòrica i Computacional, University of Barcelona (UB), Barcelona, 08028, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, Barcelona, 08010, Spain
| | - Bradley Nelson
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Nicola A Spaldin
- Materials Theory, Department of Materials, ETH Zürich, Wolfgang-Pauli-Strasse 27, Zürich, 8093, Switzerland
| | - Chiara Gattinoni
- Materials Theory, Department of Materials, ETH Zürich, Wolfgang-Pauli-Strasse 27, Zürich, 8093, Switzerland
- Department of Chemical and Energy Engineering, London South Bank University, 103 Borough Rd, London, SE1 0AA, UK
| | - Xiang-Zhong Chen
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
| | - Salvador Pané
- Multi-Scale Robotics Lab, Institute of Robotics and Intelligence Systems, ETH Zürich, Tannenstrasse 3, Zürich, CH-8092, Switzerland
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7
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Mundy JA, Grosso BF, Heikes CA, Ferenc Segedin D, Wang Z, Shao YT, Dai C, Goodge BH, Meier QN, Nelson CT, Prasad B, Xue F, Ganschow S, Muller DA, Kourkoutis LF, Chen LQ, Ratcliff WD, Spaldin NA, Ramesh R, Schlom DG. Liberating a hidden antiferroelectric phase with interfacial electrostatic engineering. SCIENCE ADVANCES 2022; 8:eabg5860. [PMID: 35108054 PMCID: PMC8809685 DOI: 10.1126/sciadv.abg5860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Antiferroelectric materials have seen a resurgence of interest because of proposed applications in a number of energy-efficient technologies. Unfortunately, relatively few families of antiferroelectric materials have been identified, precluding many proposed applications. Here, we propose a design strategy for the construction of antiferroelectric materials using interfacial electrostatic engineering. We begin with a ferroelectric material with one of the highest known bulk polarizations, BiFeO3. By confining thin layers of BiFeO3 in a dielectric matrix, we show that a metastable antiferroelectric structure can be induced. Application of an electric field reversibly switches between this new phase and a ferroelectric state. The use of electrostatic confinement provides an untapped pathway for the design of engineered antiferroelectric materials with large and potentially coupled responses.
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Affiliation(s)
- Julia A. Mundy
- Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | | | - Colin A. Heikes
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20878, USA
| | - Dan Ferenc Segedin
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
- Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Zhe Wang
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | - Yu-Tsun Shao
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
| | - Cheng Dai
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
| | - Berit H. Goodge
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
| | - Quintin N. Meier
- Department of Materials, ETH Zürich, Zürich CH-8093, Switzerland
| | - Christopher T. Nelson
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Bhagwati Prasad
- Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Fei Xue
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
| | | | - David A. Muller
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
| | - Lena F. Kourkoutis
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
| | - Long-Qing Chen
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
| | - William D. Ratcliff
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20878, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA
| | | | - Ramamoorthy Ramesh
- Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
- Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Darrell G. Schlom
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
- Leibniz-Institut für Kristallzüchtung, 12489 Berlin, Germany
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853, USA
- Corresponding author.
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