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Yang C, Pons R, Sigle W, Wang H, Benckiser E, Logvenov G, Keimer B, van Aken PA. Direct observation of strong surface reconstruction in partially reduced nickelate films. Nat Commun 2024; 15:378. [PMID: 38191551 PMCID: PMC10774438 DOI: 10.1038/s41467-023-44616-x] [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: 08/15/2023] [Accepted: 12/22/2023] [Indexed: 01/10/2024] Open
Abstract
The polarity of a surface can affect the electronic and structural properties of oxide thin films through electrostatic effects. Understanding the mechanism behind these effects requires knowledge of the atomic structure and electrostatic characteristics at the surface. In this study, we use annular bright-field imaging to investigate the surface structure of a Pr0.8Sr0.2NiO2+x (0 < x < 1) film. We observe a polar distortion coupled with octahedral rotations in a fully oxidized Pr0.8Sr0.2NiO3 sample, and a stronger polar distortion in a partially reduced sample. Its spatial depth extent is about three unit cells from the surface. Additionally, we use four-dimensional scanning transmission electron microscopy (4D-STEM) to directly image the local atomic electric field surrounding Ni atoms near the surface and discover distinct valence variations of Ni atoms, which are confirmed by atomic-resolution electron energy-loss spectroscopy (EELS). Our results suggest that the strong surface reconstruction in the reduced sample is closely related to the formation of oxygen vacancies from topochemical reduction. These findings provide insights into the understanding and evolution of surface polarity at the atomic level.
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Affiliation(s)
- Chao Yang
- Max Planck Institute for Solid State Research, Stuttgart, Germany.
| | - Rebecca Pons
- Max Planck Institute for Solid State Research, Stuttgart, Germany
| | - Wilfried Sigle
- Max Planck Institute for Solid State Research, Stuttgart, Germany
| | - Hongguang Wang
- Max Planck Institute for Solid State Research, Stuttgart, Germany
| | - Eva Benckiser
- Max Planck Institute for Solid State Research, Stuttgart, Germany
| | - Gennady Logvenov
- Max Planck Institute for Solid State Research, Stuttgart, Germany
| | - Bernhard Keimer
- Max Planck Institute for Solid State Research, Stuttgart, Germany
| | - Peter A van Aken
- Max Planck Institute for Solid State Research, Stuttgart, Germany
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Nanoscale self-templating for oxide epitaxy with large symmetry mismatch. Sci Rep 2016; 6:38168. [PMID: 27909313 PMCID: PMC5133589 DOI: 10.1038/srep38168] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 11/02/2016] [Indexed: 11/17/2022] Open
Abstract
Direct observations using scanning transmission electron microscopy unveil an intriguing interfacial bi-layer that enables epitaxial growth of a strain-free, monoclinic, bronze-phase VO2(B) thin film on a perovskite SrTiO3 (STO) substrate. We observe an ultrathin (2–3 unit cells) interlayer best described as highly strained VO2(B) nanodomains combined with an extra (Ti,V)O2 layer on the TiO2 terminated STO (001) surface. By forming a fully coherent interface with the STO substrate and a semi-coherent interface with the strain-free epitaxial VO2(B) film above, the interfacial bi-layer enables the epitaxial connection of the two materials despite their large symmetry and lattice mismatch.
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Polar Spinel-Perovskite Interfaces: an atomistic study of Fe3O4(111)/SrTiO3(111) structure and functionality. Sci Rep 2016; 6:29724. [PMID: 27411576 PMCID: PMC4944391 DOI: 10.1038/srep29724] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 06/21/2016] [Indexed: 11/09/2022] Open
Abstract
Atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy combined with ab initio electronic calculations are used to determine the structure and properties of the Fe3O4(111)/SrTiO3(111) polar interface. The interfacial structure and chemical composition are shown to be atomically sharp and of an octahedral Fe/SrO3 nature. Band alignment across the interface pins the Fermi level in the vicinity of the conduction band of SrTiO3. Density functional theory calculations demonstrate very high spin-polarization of Fe3O4 in the interface vicinity which suggests that this system may be an excellent candidate for spintronic applications.
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Hong S, Nakhmanson SM, Fong DD. Screening mechanisms at polar oxide heterointerfaces. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:076501. [PMID: 27308889 DOI: 10.1088/0034-4885/79/7/076501] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The interfaces of polar oxide heterostructures can display electronic properties unique from the oxides they border, as they require screening from either internal or external sources of charge. The screening mechanism depends on a variety of factors, including the band structure at the interface, the presence of point defects or adsorbates, whether or not the oxide is ferroelectric, and whether or not an external field is applied. In this review, we discuss both theoretical and experimental aspects of different screening mechanisms, giving special emphasis to ways in which the mechanism can be altered to provide novel or tunable functionalities. We begin with a theoretical introduction to the problem and highlight recent progress in understanding the impact of point defects on polar interfaces. Different case studies are then discussed, for both the high thickness regime, where interfaces must be screened and each interface can be considered separately, and the low thickness regime, where the degree and nature of screening can be manipulated and the interfaces are close enough to interact. We end with a brief outlook toward new developments in this rapidly progressing field.
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Affiliation(s)
- Seungbum Hong
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA. Department of Materials Science & Engineering, KAIST, Daejeon 305-701, Korea
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Gilks D, Nedelkoski Z, Lari L, Kuerbanjiang B, Matsuzaki K, Susaki T, Kepaptsoglou D, Ramasse Q, Evans R, McKenna K, Lazarov VK. Atomic and electronic structure of twin growth defects in magnetite. Sci Rep 2016; 6:20943. [PMID: 26876049 PMCID: PMC4753457 DOI: 10.1038/srep20943] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 01/14/2016] [Indexed: 12/04/2022] Open
Abstract
We report the existence of a stable twin defect in Fe3O4 thin films. By using aberration corrected scanning transmission electron microscopy and spectroscopy the atomic structure of the twin boundary has been determined. The boundary is confined to the (111) growth plane and it is non-stoichiometric due to a missing Fe octahedral plane. By first principles calculations we show that the local atomic structural configuration of the twin boundary does not change the nature of the superexchange interactions between the two Fe sublattices across the twin grain boundary. Besides decreasing the half-metallic band gap at the boundary the altered atomic stacking at the boundary does not change the overall ferromagnetic (FM) coupling between the grains.
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Affiliation(s)
- Daniel Gilks
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Zlatko Nedelkoski
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Leonardo Lari
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | | | - Kosuke Matsuzaki
- Secure Materials Centre, Materials and Structures Laboratory, Tokyo Institute for Technology, 4259 Nagatsuta, Midori-ku, Yokohama-city, Kanagawa, 226-8503, Japan
| | - Tomofumi Susaki
- Secure Materials Centre, Materials and Structures Laboratory, Tokyo Institute for Technology, 4259 Nagatsuta, Midori-ku, Yokohama-city, Kanagawa, 226-8503, Japan
| | - Demie Kepaptsoglou
- SuperSTEM, STFC Daresbury Laboratories, Keckwick Lane, Warrington, WA4 4AD, UK
| | - Quentin Ramasse
- SuperSTEM, STFC Daresbury Laboratories, Keckwick Lane, Warrington, WA4 4AD, UK
| | - Richard Evans
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Keith McKenna
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Vlado K Lazarov
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
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Gilks D, Lari L, Naughton J, Cespedes O, Cai Z, Gerber A, Thompson SM, Ziemer K, Lazarov VK. Origin of anomalous magnetite properties in crystallographic matched heterostructures: Fe3O4(111)/MgAl2O4(111). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:485004. [PMID: 24177186 DOI: 10.1088/0953-8984/25/48/485004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Magnetite films grown on crystallographically matched substrates such as MgAl2O4 are not expected to show anomalous properties such as negative magnetoresistance and high saturation fields. By atomic resolution imaging using scanning transmission electron microscopy we show direct evidence of anti-phase domain boundaries (APB) present in these heterostructures. Experimentally identified 1/4<101> shifts determine the atomic structure of the observed APBs. The dominant non-bulk superexchange interactions are between 180° octahedral-Fe/O/octahedral-Fe sites which provide strong antiferromagnetic coupling across the defect interface resulting in non-bulk magnetic and magnetotransport properties.
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Affiliation(s)
- D Gilks
- Department of Physics, University of York, Heslington, York YO10 5DD, UK
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Affiliation(s)
- Claudine Noguera
- Institut des Nanosciences de Paris, UMR 7588, CNRS, and Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France
| | - Jacek Goniakowski
- Institut des Nanosciences de Paris, UMR 7588, CNRS, and Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France
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Reconstruction of the polar interface between hexagonal LuFeO3 and intergrown Fe3O4 nanolayers. Sci Rep 2012; 2:672. [PMID: 22993697 PMCID: PMC3446212 DOI: 10.1038/srep00672] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Accepted: 08/28/2012] [Indexed: 11/10/2022] Open
Abstract
We report the observation of an unusual phase assembly behavior during the growth of hexagonal LuFeO3 thin films which resulted in the formation of epitaxial Fe3O4 nanolayers. The magnetite layers were up to 5 nm thick and grew under the conditions at which Fe2O3 is thermodynamically stable. These Fe3O4 nanolayers act as buffer layers promoting a highly epitaxial growth of the hexagonal LuFeO3 thin film up to 150 nm thick. Using scanning transmission electron microscopy, we show that the interface between (001) LuFeO3 and (111) Fe3O4 can be reconstructed in two ways depending on the sequence in which these compounds grow on each other. We suggest the polarity of the interface is the reason behind the observed interface reconstruction and epitaxial stabilization of magnetite.
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Mordehai D, Rabkin E, Srolovitz DJ. Pseudoelastic deformation during nanoscale adhesive contact formation. PHYSICAL REVIEW LETTERS 2011; 107:096101. [PMID: 21929255 DOI: 10.1103/physrevlett.107.096101] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Indexed: 05/31/2023]
Abstract
Molecular dynamics simulations are employed to demonstrate that adhesive contact formation through classical jump to contact is mediated by extensive dislocation activity in metallic nanoparticles. The dislocations generated during jump to contact are completely annihilated by the completion of the adhesive contact, leaving the nanoparticles dislocation-free. This rapid and efficient jump to contact process is pseudoelastic, rather than purely elastic or plastic.
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Affiliation(s)
- Dan Mordehai
- Department of Materials Engineering, Technion - Israel Institute of Technology, 32000 Haifa, Israel.
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Zhu K, Hu J, Kübel C, Richards R. Efficient Preparation and Catalytic Activity of MgO(111) Nanosheets. Angew Chem Int Ed Engl 2006. [DOI: 10.1002/ange.200602393] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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11
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Zhu K, Hu J, Kübel C, Richards R. Efficient Preparation and Catalytic Activity of MgO(111) Nanosheets. Angew Chem Int Ed Engl 2006; 45:7277-81. [PMID: 17024713 DOI: 10.1002/anie.200602393] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Kake Zhu
- International University Bremen, 28759 Bremen, Germany
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Lazarov VK, Zimmerman J, Cheung SH, Li L, Weinert M, Gajdardziska-Josifovska M. Selected growth of cubic and hexagonal GaN epitaxial films on polar MgO(111). PHYSICAL REVIEW LETTERS 2005; 94:216101. [PMID: 16090332 DOI: 10.1103/physrevlett.94.216101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Indexed: 05/03/2023]
Abstract
Selected molecular beam epitaxy of zinc blende (111) or wurtzite (0001) GaN films on polar MgO(111) is achieved depending on whether N or Ga is deposited first. The cubic stacking is enabled by nitrogen-induced polar surface stabilization, which yields a metallic MgO(111)-(1 x 1)-ON surface. High-resolution transmission electron microscopy and density functional theory studies indicate that the atomically abrupt semiconducting GaN(111)/MgO(111) interface has a Mg-O-N-Ga stacking, where the N atom is bonded to O at a top site. This specific atomic arrangement at the interface allows the cubic stacking to more effectively screen the substrate and film electric dipole moment than the hexagonal stacking, thus stabilizing the zinc blende phase even though the wurtzite phase is the ground state in the bulk.
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Affiliation(s)
- V K Lazarov
- Department of Physics and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201, USA
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