1
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Leermakers I, Rubi K, Yang M, Kerdi B, Goiran M, Escoffier W, Rana AS, Smink AEM, Brinkman A, Hilgenkamp H, Maan JC, Zeitler U. Quantum oscillations in an optically-illuminated two-dimensional electron system at the LaAlO 3/SrTiO 3interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:465002. [PMID: 34433152 DOI: 10.1088/1361-648x/ac211a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Accepted: 08/25/2021] [Indexed: 06/13/2023]
Abstract
We have investigated the illumination effect on the magnetotransport properties of a two-dimensional electron system at the LaAlO3/SrTiO3interface. The illumination significantly reduces the zero-field sheet resistance, eliminates the Kondo effect at low-temperature, and switches the negative magnetoresistance into the positive one. A large increase in the density of high-mobility carriers after illumination leads to quantum oscillations in the magnetoresistance originating from the Landau quantization. The carrier density (∼2 × 1012 cm-2) and effective mass (∼1.7me) estimated from the oscillations suggest that the high-mobility electrons occupy thedxz/yzsubbands of Ti:t2gorbital extending deep within the conducting sheet of SrTiO3. Our results demonstrate that the illumination which induces additional carriers at the interface can pave the way to control the Kondo-like scattering and study the quantum transport in the complex oxide heterostructures.
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Affiliation(s)
- I Leermakers
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - K Rubi
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - M Yang
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - B Kerdi
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - M Goiran
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - W Escoffier
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - A S Rana
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - A E M Smink
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - A Brinkman
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - H Hilgenkamp
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - J C Maan
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - U Zeitler
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
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2
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Rose MA, Barnett J, Wendland D, Hensling FVE, Boergers JM, Moors M, Dittmann R, Taubner T, Gunkel F. Local inhomogeneities resolved by scanning probe techniques and their impact on local 2DEG formation in oxide heterostructures. NANOSCALE ADVANCES 2021; 3:4145-4155. [PMID: 36132831 PMCID: PMC9419657 DOI: 10.1039/d1na00190f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 06/02/2021] [Indexed: 06/16/2023]
Abstract
Lateral inhomogeneities in the formation of two-dimensional electron gases (2DEG) directly influence their electronic properties. Understanding their origin is an important factor for fundamental interpretations, as well as high quality devices. Here, we studied the local formation of the buried 2DEG at LaAlO3/SrTiO3 (LAO/STO) interfaces grown on STO (100) single crystals with partial TiO2 termination, utilizing in situ conductive atomic force microscopy (c-AFM) and scattering-type scanning near-field optical microscopy (s-SNOM). Using substrates with different degrees of chemical surface termination, we can link the resulting interface chemistry to an inhomogeneous 2DEG formation. In conductivity maps recorded by c-AFM, a significant lack of conductivity is observed at topographic features, indicative of a local SrO/AlO2 interface stacking order, while significant local conductivity can be probed in regions showing TiO2/LaO interface stacking order. These results could be corroborated by s-SNOM, showing a similar contrast distribution in the optical signal which can be linked to the local electronic properties of the material. The results are further complemented by low-temperature conductivity measurements, which show an increasing residual resistance at 5 K with increasing portion of insulating SrO-terminated areas. Therefore, we can correlate the macroscopic electrical behavior of our samples to their nanoscopic structure. Using proper parameters, 2DEG mapping can be carried out without any visible alteration of sample properties, proving c-AFM and s-SNOM to be viable and destruction-free techniques for the identification of local 2DEG formation. Furthermore, applying c-AFM and s-SNOM in this manner opens the exciting prospect to link macroscopic low-temperature transport to its nanoscopic origin.
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Affiliation(s)
- M-A Rose
- Institute of Electronic Materials (IWE II), RWTH Aachen University Aachen Germany
- Peter Gruenberg Institute, JARA-FIT, Forschungszentrum Juelich GmbH Juelich Germany
| | - J Barnett
- I. Institute of Physics (IA), RWTH Aachen University Aachen Germany
| | - D Wendland
- I. Institute of Physics (IA), RWTH Aachen University Aachen Germany
| | - F V E Hensling
- Peter Gruenberg Institute, JARA-FIT, Forschungszentrum Juelich GmbH Juelich Germany
| | - J M Boergers
- Peter Gruenberg Institute, JARA-FIT, Forschungszentrum Juelich GmbH Juelich Germany
| | - M Moors
- Peter Gruenberg Institute, JARA-FIT, Forschungszentrum Juelich GmbH Juelich Germany
| | - R Dittmann
- Peter Gruenberg Institute, JARA-FIT, Forschungszentrum Juelich GmbH Juelich Germany
| | - T Taubner
- I. Institute of Physics (IA), RWTH Aachen University Aachen Germany
| | - F Gunkel
- Institute of Electronic Materials (IWE II), RWTH Aachen University Aachen Germany
- Peter Gruenberg Institute, JARA-FIT, Forschungszentrum Juelich GmbH Juelich Germany
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3
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Rose MA, Šmíd B, Vorokhta M, Slipukhina I, Andrä M, Bluhm H, Duchoň T, Ležaić M, Chambers SA, Dittmann R, Mueller DN, Gunkel F. Identifying Ionic and Electronic Charge Transfer at Oxide Heterointerfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2004132. [PMID: 33263190 DOI: 10.1002/adma.202004132] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 08/31/2020] [Indexed: 06/12/2023]
Abstract
The ability to tailor oxide heterointerfaces has led to novel properties in low-dimensional oxide systems. A fundamental understanding of these properties is based on the concept of electronic charge transfer. However, the electronic properties of oxide heterointerfaces crucially depend on their ionic constitution and defect structure: ionic charges contribute to charge transfer and screening at oxide interfaces, triggering a thermodynamic balance of ionic and electronic structures. Quantitative understanding of the electronic and ionic roles regarding charge-transfer phenomena poses a central challenge. Here, the electronic and ionic structure is simultaneously investigated at the prototypical charge-transfer heterointerface, LaAlO3 /SrTiO3 . Applying in situ photoemission spectroscopy under oxygen ambient, ionic and electronic charge transfer is deconvoluted in response to the oxygen atmosphere at elevated temperatures. In this way, both the rich and variable chemistry of complex oxides and the associated electronic properties are equally embraced. The interfacial electron gas is depleted through an ionic rearrangement in the strontium cation sublattice when oxygen is applied, resulting in an inverse and reversible balance between cation vacancies and electrons, while the mobility of ionic species is found to be considerably enhanced as compared to the bulk. Triggered by these ionic phenomena, the electronic transport and magnetic signature of the heterointerface are significantly altered.
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Affiliation(s)
- Marc-André Rose
- Institute for Electronic Materials (IWE 2), and Juelich-Aachen Research Alliance for Fundamentals on Future Information Technology (JARA-FIT), RWTH Aachen University, 52074, Aachen, Germany
- Peter Grünberg Institute 7, Forschungszentrum Jülich GmbH, and JARA-FIT, 52425, Jülich, Germany
| | - Břetislav Šmíd
- Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, Prague, 180 00, Czech Republic
| | - Mykhailo Vorokhta
- Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, Prague, 180 00, Czech Republic
| | - Ivetta Slipukhina
- Peter Grünberg Institute 1 and Institute for Advanced Simulation, Forschungszentrum Jülich GmbH and JARA-FIT, 52425, Jülich, Germany
| | - Michael Andrä
- Peter Grünberg Institute 7, Forschungszentrum Jülich GmbH, and JARA-FIT, 52425, Jülich, Germany
| | - Hendrik Bluhm
- Chemical Sciences Division, Lawrence Berkeley National Lab., Berkeley, CA, 94720, USA
- Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, 14195, Berlin, Germany
| | - Tomáš Duchoň
- Peter Grünberg Institute 6, and JARA-FIT, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany
| | - Marjana Ležaić
- Peter Grünberg Institute 1 and Institute for Advanced Simulation, Forschungszentrum Jülich GmbH and JARA-FIT, 52425, Jülich, Germany
| | - Scott A Chambers
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Regina Dittmann
- Peter Grünberg Institute 7, Forschungszentrum Jülich GmbH, and JARA-FIT, 52425, Jülich, Germany
| | - David N Mueller
- Peter Grünberg Institute 7, Forschungszentrum Jülich GmbH, and JARA-FIT, 52425, Jülich, Germany
- Peter Grünberg Institute 6, and JARA-FIT, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany
| | - Felix Gunkel
- Institute for Electronic Materials (IWE 2), and Juelich-Aachen Research Alliance for Fundamentals on Future Information Technology (JARA-FIT), RWTH Aachen University, 52074, Aachen, Germany
- Peter Grünberg Institute 7, Forschungszentrum Jülich GmbH, and JARA-FIT, 52425, Jülich, Germany
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4
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On the emergence of conductivity at SrTiO 3-based oxide interfaces - an in-situ study. Sci Rep 2019; 9:18005. [PMID: 31784583 PMCID: PMC6884556 DOI: 10.1038/s41598-019-54463-w] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 11/09/2019] [Indexed: 11/08/2022] Open
Abstract
Heterostructures and crystal interfaces play a major role in state-of-the-art semiconductor devices and play a central role in the field of oxide electronics. In oxides the link between the microscopic properties of the interfaces and bulk properties of the resulting heterostructures challenge our fundamental understanding. Insights on the early growth stage of interfaces and its influence on resulting physical properties are scarce - typically the information is inferred from post growth characterization. Here, we report on real time measurements of the transport properties of SrTiO3-based heterostructures at room temperature, while the heterostructure is forming. Surprisingly, we detect a conducting interface already at the initial growth stage, much earlier than the well-established critical thickness limit for observing conductivity ex-situ after sample growth. We investigate how the conductivity depends on various physical processes occurring during pulsed laser depositions, including light illumination, particle bombardment by the plasma plume, interactions with the atmosphere and oxygen migration from SrTiO3 to the thin films of varying compositions. We conclude that the conductivity in these room-temperature grown interfaces stem from oxygen vacancies with a concentration determined primarily by a balance between vacancy formation through particle bombardment and interfacial redox reaction and vacancy annihilation through oxidation. Using this approach, we propose a new design tool to control the electrical properties of interfaces in real time during their formation.
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5
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Hensling FVE, Keeble DJ, Zhu J, Brose S, Xu C, Gunkel F, Danylyuk S, Nonnenmann SS, Egger W, Dittmann R. UV radiation enhanced oxygen vacancy formation caused by the PLD plasma plume. Sci Rep 2018; 8:8846. [PMID: 29892095 PMCID: PMC5996021 DOI: 10.1038/s41598-018-27207-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Accepted: 05/29/2018] [Indexed: 11/08/2022] Open
Abstract
Pulsed Laser Deposition is a commonly used non-equilibrium physical deposition technique for the growth of complex oxide thin films. A wide range of parameters is known to influence the properties of the used samples and thin films, especially the oxygen-vacancy concentration. One parameter has up to this point been neglected due to the challenges of separating its influence from the influence of the impinging species during growth: the UV-radiation of the plasma plume. We here present experiments enabled by a specially designed holder to allow a separation of these two influences. The influence of the UV-irradiation during pulsed laser deposition on the formation of oxygen-vacancies is investigated for the perovskite model material SrTiO3. The carrier concentration of UV-irradiated samples is nearly constant with depth and time. By contrast samples not exposed to the radiation of the plume show a depth dependence and a decrease in concentration over time. We reveal an increase in Ti-vacancy-oxygen-vacancy-complexes for UV irradiated samples, consistent with the different carrier concentrations. We find a UV enhanced oxygen-vacancy incorporation rate as responsible mechanism. We provide a complete picture of another influence parameter to be considered during pulsed laser depositions and unravel the mechanism behind persistent-photo-conductivity in SrTiO3.
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Affiliation(s)
- F V E Hensling
- Peter Grüneberg Institut 7, Forschungszentrum Jülich, 52425, Jülich, Germany.
| | - D J Keeble
- Carnegie Laboratory of Physics, SUPA, School of Science and Engineering, University of Dundee, Dundee, DD1 4HN, United Kingdom
| | - J Zhu
- Mechanical and Industrial Enginnering, University of Massachusetts, Amherst, MA, 01003-2210, USA
| | - S Brose
- Chair for Technology of Optical Systems, RWTH Aachen University, Steinbachstr. 15, 52074, Aachen, Germany
| | - C Xu
- Peter Grüneberg Institut 7, Forschungszentrum Jülich, 52425, Jülich, Germany
| | - F Gunkel
- Institute of Electronic Materials (IWE2), RWTH Aachen University, 52074, Aachen, Germany
| | - S Danylyuk
- Chair for Technology of Optical Systems, RWTH Aachen University, Steinbachstr. 15, 52074, Aachen, Germany
| | - S S Nonnenmann
- Mechanical and Industrial Enginnering, University of Massachusetts, Amherst, MA, 01003-2210, USA
| | - W Egger
- Universität Bundeswehr München, 85577, Neubiberg, Germany
| | - R Dittmann
- Peter Grüneberg Institut 7, Forschungszentrum Jülich, 52425, Jülich, Germany
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6
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Vaz DC, Lesne E, Sander A, Naganuma H, Jacquet E, Santamaria J, Barthélémy A, Bibes M. Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures. J Vis Exp 2018. [PMID: 29553560 DOI: 10.3791/56951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.
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Affiliation(s)
| | - Edouard Lesne
- Unité Mixte de Physique CNRS/Thales, Université Paris-Saclay; Max Planck Institut für Mikrostrukturphysik
| | - Anke Sander
- Unité Mixte de Physique CNRS/Thales, Université Paris-Saclay
| | - Hiroshi Naganuma
- Unité Mixte de Physique CNRS/Thales, Université Paris-Saclay; Department of Applied Physics, Tohoku University
| | - Eric Jacquet
- Unité Mixte de Physique CNRS/Thales, Université Paris-Saclay
| | - Jacobo Santamaria
- Unité Mixte de Physique CNRS/Thales, Université Paris-Saclay; Instituto de Magnetismo Aplicado, Universidad Complutense de Madrid
| | | | - Manuel Bibes
- Unité Mixte de Physique CNRS/Thales, Université Paris-Saclay
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7
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Gunkel F, Jin L, Mueller DN, Hausner C, Bick DS, Jia CL, Schneller T, Valov I, Waser R, Dittmann R. Ordering and Phase Control in Epitaxial Double-Perovskite Catalysts for the Oxygen Evolution Reaction. ACS Catal 2017. [DOI: 10.1021/acscatal.7b02036] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Felix Gunkel
- Institute
of Electronic Materials (IWE2), RWTH Aachen University, 52074 Aachen, Germany
| | - Lei Jin
- Ernst
Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
- Peter
Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
| | - David N. Mueller
- Peter
Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
| | - Clemens Hausner
- Institute
of Electronic Materials (IWE2), RWTH Aachen University, 52074 Aachen, Germany
| | - Daniel S. Bick
- Institute
of Electronic Materials (IWE2), RWTH Aachen University, 52074 Aachen, Germany
| | - Chun-Lin Jia
- Ernst
Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
- Peter
Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
| | - Theodor Schneller
- Institute
of Electronic Materials (IWE2), RWTH Aachen University, 52074 Aachen, Germany
| | - Ilia Valov
- Peter
Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
| | - Rainer Waser
- Institute
of Electronic Materials (IWE2), RWTH Aachen University, 52074 Aachen, Germany
- Peter
Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
| | - Regina Dittmann
- Peter
Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
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8
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Gunkel F, Heinen RA, Hoffmann-Eifert S, Jin L, Jia CL, Dittmann R. Mobility Modulation and Suppression of Defect Formation in Two-Dimensional Electron Systems by Charge-Transfer Management. ACS APPLIED MATERIALS & INTERFACES 2017; 9:10888-10896. [PMID: 28262026 DOI: 10.1021/acsami.7b00905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Electron mobility is one of the most-debated key attributes of low-dimensional electron systems emerging at complex oxide heterointerfaces. However, a common understanding of how electron mobility can be optimized in these systems has not been achieved so far. Here, we discuss a novel approach for achieving a systematic increase in electron mobility in polar/nonpolar perovskite interfaces by suppressing the thermodynamically required defect formation at the nanoscale. We discuss the transport properties of electron gases established at interfaces between SrTiO3 and various polar perovskites [LaAlO3, NdGaO3, and (La,Sr)(Al,Ta)O3], allowing for the individual variation of epitaxial strain and charge transfer among these epitaxial interfaces. As we show, the reduced charge transfer at (La,Sr)(Al,Ta)O3/SrTiO3 interfaces yields a systematic increase in electron mobility, while the reduced epitaxial strain has only minor impact. As thermodynamic continuum simulations suggest, the charge transfer across these interfaces affects both the spatial distribution of electrons and the background distribution of ionic defects, acting as major scatter centers within the potential well. Easing charge transfer in (La,Sr)(Al,Ta)O3/SrTiO3 yields an enlarged spatial separation of mobile charge carriers and scattering centers, as well as a reduced driving force for the formation of ionic defects at the nanoscale. Our results suggest a general recipe for achieving electron enhancements at oxide heterostructure interfaces and provide new perspectives for atomistic understanding of electron scattering in these systems.
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Affiliation(s)
- Felix Gunkel
- Institute of Electronic Materials, RWTH Aachen University , 52062 Aachen, Germany
- Peter Grünberg Institute, Fundamentals of Future Information Technology, Jülich Aachen Research Alliance, Forschungszentrum Jülich , 52425 Jülich, Germany
| | - Ronja A Heinen
- Peter Grünberg Institute, Fundamentals of Future Information Technology, Jülich Aachen Research Alliance, Forschungszentrum Jülich , 52425 Jülich, Germany
| | - Susanne Hoffmann-Eifert
- Peter Grünberg Institute, Fundamentals of Future Information Technology, Jülich Aachen Research Alliance, Forschungszentrum Jülich , 52425 Jülich, Germany
| | - Lei Jin
- Peter Grünberg Institute, Fundamentals of Future Information Technology, Jülich Aachen Research Alliance, Forschungszentrum Jülich , 52425 Jülich, Germany
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich , 52425 Jülich, Germany
| | - Chun-Lin Jia
- Peter Grünberg Institute, Fundamentals of Future Information Technology, Jülich Aachen Research Alliance, Forschungszentrum Jülich , 52425 Jülich, Germany
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich , 52425 Jülich, Germany
| | - Regina Dittmann
- Peter Grünberg Institute, Fundamentals of Future Information Technology, Jülich Aachen Research Alliance, Forschungszentrum Jülich , 52425 Jülich, Germany
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9
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Hensling FVE, Xu C, Gunkel F, Dittmann R. Unraveling the enhanced Oxygen Vacancy Formation in Complex Oxides during Annealing and Growth. Sci Rep 2017; 7:39953. [PMID: 28091517 PMCID: PMC5238382 DOI: 10.1038/srep39953] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 11/30/2016] [Indexed: 11/26/2022] Open
Abstract
The reduction of oxides during annealing and growth in low pressure processes is a widely known problem. We hence investigate the influence of mere annealing and of growth in vacuum systems to shed light on the reasons behind the reduction of perovskites. When comparing the existing literature regarding the reduction of the perovskite model material SrTiO3 it is conspicuous that one finds different oxygen pressures required to achieve reduction for vacuum annealing and for chemically controlled reducing atmospheres. The unraveling of this discrepancy is of high interest for low pressure physical vapor depositions of thin films heterostructures to gain further understanding of the reduction of the SrTiO3. For thermal annealing, our results prove the attached measurement devices (mass spectrometer/ cold cathode gauge) to be primarily responsible for the reduction of SrTiO3 in the deposition chamber by shifting the thermodynamic equilibrium to a more reducing atmosphere. We investigated the impact of our findings on the pulsed laser deposition growth at low pressure for LaAlO3/SrTiO3. During deposition the reduction triggered by the presence of the laser plume dominates and the impact of the measurement devices plays a minor role. During post annealing a complete reoxidization of samples is inhibited by an insufficient supply of oxygen.
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Affiliation(s)
- Felix V E Hensling
- Peter Grünberg Institut 7, Forschungszentrum Jülich GmbH, Jülich, 52428, Germany
| | - Chencheng Xu
- Peter Grünberg Institut 7, Forschungszentrum Jülich GmbH, Jülich, 52428, Germany
| | - Felix Gunkel
- RWTH Aachen University, Institute of Electronic Materials (IWE 2), Aachen, 52056, Germany
| | - Regina Dittmann
- Peter Grünberg Institut 7, Forschungszentrum Jülich GmbH, Jülich, 52428, Germany
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10
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Gunkel F, Hoffmann-Eifert S, Heinen RA, Christensen DV, Chen YZ, Pryds N, Waser R, Dittmann R. Thermodynamic Ground States of Complex Oxide Heterointerfaces. ACS APPLIED MATERIALS & INTERFACES 2017; 9:1086-1092. [PMID: 27992161 DOI: 10.1021/acsami.6b12706] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The formation mechanism of 2-dimensional electron gases (2DEGs) at heterointerfaces between nominally insulating oxides is addressed with a thermodynamical approach. We provide a comprehensive analysis of the thermodynamic ground states of various 2DEG systems directly probed in high temperature equilibrium conductivity measurements. We unambiguously identify two distinct classes of oxide heterostructures: For epitaxial perovskite/perovskite heterointerfaces (LaAlO3/SrTiO3, NdGaO3/SrTiO3, and (La,Sr)(Al,Ta)O3/SrTiO3), we find the 2DEG formation being based on charge transfer into the interface, stabilized by the electric field in the space charge region. In contrast, for amorphous LaAlO3/SrTiO3 and epitaxial γ-Al2O3/SrTiO3 heterostructures, the 2DEG formation mainly relies on the formation and accumulation of oxygen vacancies. This class of 2DEG structures exhibits an unstable interface reconstruction associated with a quenched nonequilibrium state.
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Affiliation(s)
- F Gunkel
- Institute of Electronic Materials, IWE2, RWTH Aachen University , 52056 Aachen, Germany
| | - S Hoffmann-Eifert
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
| | - R A Heinen
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
| | - D V Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Y Z Chen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - N Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - R Waser
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
| | - R Dittmann
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
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Hu HL, Zeng R, Pham A, Tan TT, Chen Z, Kong C, Wang D, Li S. Subtle Interplay between Localized Magnetic Moments and Itinerant Electrons in LaAlO3/SrTiO3 Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2016; 8:13630-13636. [PMID: 27186855 DOI: 10.1021/acsami.6b01518] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Clarification of the role of magnetic ordering and scattering in two-dimensional electron gas has become increasingly important to understand the transport and magnetic behavior in the LaAlO3 (LAO)/SrTiO3 (STO) heterostructures. In this work, we report the sheet resistance of the LAO/STO heterostructures as functions of temperature, magnetic field, and field orientation. An unexpected resistance minimum was discovered at ∼10 K under a sufficiently high in-plane magnetic field. An anisotropic magnetoresistance (MR) is clearly identified, indicating the presence of magnetic scattering which may be related to the interaction between itinerant electrons and localized magnetic moments in the LaAlO3/SrTiO3 heterostructures. It is believed that the high concentration of oxygen vacancies induced by the ultralow oxygen partial pressure during the deposition process plays a predominant role in the occurrence of the anisotropic MR.
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Affiliation(s)
- Hai-Long Hu
- School of Materials Science & Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia
| | - Rong Zeng
- School of Materials Science & Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia
| | - Anh Pham
- School of Materials Science & Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia
| | - Thiam Teck Tan
- School of Materials Science & Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia
| | - Zhigang Chen
- School of Mechanical & Mining Engineering, The University of Queensland , Brisbane, Queensland 4072, Australia
| | - Charlie Kong
- Mark Wainwright Analytical Centre, The University of New South Wales , Sydney, New South Wales 2052, Australia
| | - Danyang Wang
- School of Materials Science & Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia
| | - Sean Li
- School of Materials Science & Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia
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