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Prakash DJ, Chen Y, Debasu ML, Savage DE, Tangpatjaroen C, Deneke C, Malachias A, Alfieri AD, Elleuch O, Lekhal K, Szlufarska I, Evans PG, Cavallo F. Reconfiguration of Amorphous Complex Oxides: A Route to a Broad Range of Assembly Phenomena, Hybrid Materials, and Novel Functionalities. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2105424. [PMID: 34786844 DOI: 10.1002/smll.202105424] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 10/09/2021] [Indexed: 06/13/2023]
Abstract
Reconfiguration of amorphous complex oxides provides a readily controllable source of stress that can be leveraged in nanoscale assembly to access a broad range of 3D geometries and hybrid materials. An amorphous SrTiO3 layer on a Si:B/Si1- x Gex :B heterostructure is reconfigured at the atomic scale upon heating, exhibiting a change in volume of ≈2% and accompanying biaxial stress. The Si:B/Si1- x Gex :B bilayer is fabricated by molecular beam epitaxy, followed by sputter deposition of SrTiO3 at room temperature. The processes yield a hybrid oxide/semiconductor nanomembrane. Upon release from the substrate, the nanomembrane rolls up and has a curvature determined by the stress in the epitaxially grown Si:B/Si1- x Gex :B heterostructure. Heating to 600 °C leads to a decrease of the radius of curvature consistent with the development of a large compressive biaxial stress during the reconfiguration of SrTiO3 . The control of stresses via post-deposition processing provides a new route to the assembly of complex-oxide-based heterostructures in 3D geometry. The reconfiguration of metastable mechanical stressors enables i) synthesis of various types of strained superlattice structures that cannot be fabricated by direct growth and ii) technologies based on strain engineering of complex oxides via highly scalable lithographic processes and on large-area semiconductor substrates.
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Affiliation(s)
- Divya J Prakash
- Center for High Technology Materials, University of New Mexico, Albuquerque, NM, 87106, USA
- Department of Chemical and Biological Engineering, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Yajin Chen
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Mengistie L Debasu
- Center for High Technology Materials, University of New Mexico, Albuquerque, NM, 87106, USA
| | - Donald E Savage
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Chaiyapat Tangpatjaroen
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Christoph Deneke
- Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, Campinas, SP, 13083-970, Brazil
| | - Angelo Malachias
- Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, 31270-901, Brazil
| | - Adam D Alfieri
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Omar Elleuch
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Kaddour Lekhal
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Izabela Szlufarska
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Paul G Evans
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Francesca Cavallo
- Center for High Technology Materials, University of New Mexico, Albuquerque, NM, 87106, USA
- Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM, 87131, USA
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2
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Sun Y, Liu Y, Hong S, Chen Z, Zhang M, Xie Y. Critical Thickness in Superconducting LaAlO_{3}/KTaO_{3}(111) Heterostructures. PHYSICAL REVIEW LETTERS 2021; 127:086804. [PMID: 34477422 DOI: 10.1103/physrevlett.127.086804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 07/29/2021] [Indexed: 06/13/2023]
Abstract
Recently, two-dimensional superconductivity was discovered at the oxide interface between KTaO_{3} and LaAlO_{3} (or EuO), whose superconducting transition temperature T_{c} is up to 2.2 K and exhibits strong crystalline-orientation dependence. However, the origin of the interfacial electron gas, which becomes superconducting at low temperatures, remains elusive. Taking the LaAlO_{3}/KTaO_{3}(111) interface as an example, we have demonstrated that there exists a critical LaAlO_{3} thickness of ∼3 nm. Namely, a thinner LaAlO_{3} film will give rise to an insulating but not conducting (or superconducting) interface. By in situ transport measurements during growth, we have also revealed that the critical thickness can be suppressed if exposure to oxygen is avoided. These observations, together with other control experiments, suggest strongly that the origination of the electron gas is dominated by the electron transfer that is from oxygen vacancies in the LaAlO_{3} film to the KTaO_{3} substrate.
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Affiliation(s)
- Yanqiu Sun
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, and Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Yuan Liu
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, and Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Siyuan Hong
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, and Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Zheng Chen
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, and Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Meng Zhang
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, and Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Yanwu Xie
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, and Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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Chen Z, Zhang M, Ren T, Xie Y. Unravelling oxygen-vacancy-induced electron transfer at SrTiO 3-based heterointerfaces by transport measurement during growth. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:505002. [PMID: 31499485 DOI: 10.1088/1361-648x/ab42af] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Numerous studies have shown that oxygen vacancies play an important role on the formation of two-dimensional electron gas (2DEG) at SrTiO3-based heterointerfaces. Previously, it is widely believed that the main mechanism is that the oxygen vacancies in SrTiO3 directly contribute electrons to the 2DEG. Here, we performed transport measurements during the creation of 2DEG for depositing amorphous LaAlO3 on SrTiO3 substrates and related heterostructures. Our result suggests that, unlike the previous viewpoint, in this kind of 2DEG the determinant mechanism is the electron transfer from the oxygen vacancies in the film grown on SrTiO3, rather than the oxygen vacancies in SrTiO3 themselves. This effect is so striking that an amorphous film of less than 10% monolayer coverage on SrTiO3, or equivalently 0.04 nm, can already generate a highly conducting 2DEG. The present result may have a general implication and provide a possible way to understand the long-standing debate on the origin of 2DEG at SrTiO3-based heterointerfaces.
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Affiliation(s)
- Zheng Chen
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, People's Republic of China
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Biswas A, Talha M, Kashir A, Jeong YH. A thin film perspective on quantum functional oxides. CURRENT APPLIED PHYSICS 2019; 19:207-214. [DOI: 10.1016/j.cap.2018.07.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
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Wu H, Zhao X, Guan C, Zhao LD, Wu J, Song D, Li C, Wang J, Loh KP, Venkatesan TV, Pennycook SJ. The Atomic Circus: Small Electron Beams Spotlight Advanced Materials Down to the Atomic Scale. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802402. [PMID: 30306651 DOI: 10.1002/adma.201802402] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Revised: 08/06/2018] [Indexed: 06/08/2023]
Abstract
Defects in crystalline materials have a tremendous impact on their functional behavior. Controlling and tuning of these imperfections can lead to marked improvements in their physical, electrical, magnetic, and optical properties. Thanks to the development of aberration-corrected (scanning) transmission electron microscopy (STEM/TEM), direct visualization of defects at multiple length scales has now become possible, including those critically important defects at the atomic scale. Thorough understanding of the nature and dynamics of these defects is the key to unraveling the fundamental origins of structure-property relationships. Such insight can therefore allow the creation of new materials with desired properties through appropriate defect engineering. Herein, several examples of new insights obtained from representative functional materials are shown, including piezoelectrics/ferroelectrics, oxide interfaces, thermoelectrics, electrocatalysts, and 2D materials.
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Affiliation(s)
- Haijun Wu
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
| | - Xiaoxu Zhao
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 13 Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
| | - Cao Guan
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
| | - Li-Dong Zhao
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
| | - Jiagang Wu
- Department of Materials Science, Sichuan University, Chengdu, 610064, China
| | - Dongsheng Song
- NUSNNI-NanoCore, National University of Singapore, Singapore, 117411, Singapore
| | - Changjian Li
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
| | - John Wang
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Thirumalai V Venkatesan
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
- NUSNNI-NanoCore, National University of Singapore, Singapore, 117411, Singapore
| | - Stephen J Pennycook
- Department of Materials Science and Engineering, National University of Singapore (NUS), Singapore, 117574, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 13 Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
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Wang X, Zhang M, Tian X, Zhang Y, Gong J, Rahman A, Dai R, Wang Z, Zhang Z. Strain-induced conductivity accelerated recoveries in LaAlO 3/SrTiO 3 heterostructure with millimeter scale. RSC Adv 2018; 8:37804-37810. [PMID: 35558592 PMCID: PMC9089444 DOI: 10.1039/c8ra08564a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Accepted: 11/05/2018] [Indexed: 11/21/2022] Open
Abstract
The transport and magnetic properties of LaAlO3/SrTiO3 (LAO/STO) heterostructure have been studied during cooling and warming. The strain gradient perpendicular to the surface of the heterostructure increases with the thickness of LAO film. The conductivity accelerated recoveries (CAR) are found at 80 K and 176 K in the interface of LAO/STO sample with millimeter scale, and are more obvious for thicker LAO layers during warming. These two recovering temperatures correspond to the migrating energies of oxygen single vacancy and divacancy trapped by polarized domain walls, separately. This indicated that domain walls diffuse along the longitudinal direction and expand to larger area due the strain gradient perpendicular to the interface. The stable and precise accelerating recovering temperatures make the sample at a larger scale a potential widely applied temperature standard reference. The magnetization measurements reveal the coexistence of paramagnetic and diamagnetic in the LAO/STO samples at whole temperature from 2 K to 300 K. The abnormal electric resistance rise is observed with the decreasing temperature below 25 K for the samples of 7 and 15 LAO layers. This anomaly is attributed to the Kondo effect below 25 K and weak anti-localization below 5 K due to the weightier paramagnetic content. The larger diamagnetic content suppresses these contributions in 25 LAO layers sample. This work provided an insightful view that the strain modified structure domain leads to the enhancement of CAR effect, which helps to achieve a better understanding of domain related physics in the LAO/STO system. The transport and magnetic properties of LaAlO3/SrTiO3 (LAO/STO) heterostructure have been studied during cooling and warming.![]()
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Affiliation(s)
- Xiangqi Wang
- Department of Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Min Zhang
- Department of Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Xirui Tian
- Department of Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Yinying Zhang
- Department of Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Junbo Gong
- Department of Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Azizur Rahman
- Department of Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Rucheng Dai
- The Centre for Physical Experiments
- University of Science and Technology of China
- Hefei 230026
- China
| | - Zhongping Wang
- The Centre for Physical Experiments
- University of Science and Technology of China
- Hefei 230026
- China
| | - Zengming Zhang
- The Centre for Physical Experiments
- University of Science and Technology of China
- Hefei 230026
- China
- Key Laboratory of Strongly-Coupled Quantum Matter Physics
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Wang Y, Cheng J, Behtash M, Tang W, Luo J, Yang K. First-principles studies of polar perovskite KTaO3 surfaces: structural reconstruction, charge compensation, and stability diagram. Phys Chem Chem Phys 2018; 20:18515-18527. [DOI: 10.1039/c8cp02540a] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
First-principles calculations predict a surface phase stability diagram for the polar perovskite KTaO3.
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Affiliation(s)
- Yaqin Wang
- Department of Material Science and Engineering
- Xihua University
- Chengdu
- P. R. China
- Department of NanoEngineering
| | - Jianli Cheng
- Department of NanoEngineering
- University of California
- La Jolla
- USA
| | - Maziar Behtash
- Department of NanoEngineering
- University of California
- La Jolla
- USA
| | - Wu Tang
- State Key Laboratory of Electronic Thin Films and Integrated Devices
- University of Electronic Science and Technology of China
- Chengdu 610054
- P. R. China
| | - Jian Luo
- Department of NanoEngineering
- University of California
- La Jolla
- USA
| | - Kesong Yang
- Department of NanoEngineering
- University of California
- La Jolla
- USA
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8
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Plumb NC, Radović M. Angle-resolved photoemission spectroscopy studies of metallic surface and interface states of oxide insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:433005. [PMID: 28961143 DOI: 10.1088/1361-648x/aa833f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Over the last decade, conducting states embedded in insulating transition metal oxides (TMOs) have served as gateways to discovering and probing surprising phenomena that can emerge in complex oxides, while also opening opportunities for engineering advanced devices. These states are commonly realized at thin film interfaces, such as the well-known case of LaAlO3 (LAO) grown on SrTiO3 (STO). In recent years, the use of angle-resolved photoemission spectroscopy (ARPES) to investigate the k-space electronic structure of such materials led to the discovery that metallic states can also be formed on the bare surfaces of certain TMOs. In this topical review, we report on recent studies of low-dimensional metallic states confined at insulating oxide surfaces and interfaces as seen from the perspective of ARPES, which provides a direct view of the occupied band structure. While offering a fairly broad survey of progress in the field, we draw particular attention to STO, whose surface is so far the best-studied, and whose electronic structure is probably of the most immediate interest, given the ubiquitous use of STO substrates as the basis for conducting oxide interfaces. The ARPES studies provide crucial insights into the electronic band structure, orbital character, dimensionality/confinement, spin structure, and collective excitations in STO surfaces and related oxide surface/interface systems. The obtained knowledge increases our understanding of these complex materials and gives new perspectives on how to manipulate their properties.
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Affiliation(s)
- Nicholas C Plumb
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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Mohammadi V, Nihtianov S, Fang C. A doping-less junction-formation mechanism between n-silicon and an atomically thin boron layer. Sci Rep 2017; 7:13247. [PMID: 29038490 PMCID: PMC5643333 DOI: 10.1038/s41598-017-13100-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 09/04/2017] [Indexed: 11/11/2022] Open
Abstract
The interest in nanostructures of silicon and its dopants has significantly increased. We report the creation of an ultimately-shallow junction at the surface of n-type silicon with excellent electrical and optical characteristics made by depositing an atomically thin boron layer at a relatively low temperature where no doping of silicon is expected. The presented experimental results and simulations of the ab initio quantum mechanics molecular dynamics prove that the structure of this new type of junction differs from all other known rectifying junctions at this time. An analysis of the junction formation has led to the conclusion that the chemical interaction between the surface atoms of crystalline silicon and the first atomic layer of the as-deposited amorphous boron is the dominant factor leading to the formation of a depletion zone in the crystalline silicon which originates from the surface. The simulation results show a very strong electric field across the c-Si/a-B interface systems where the charge transfer occurs mainly from the interface Si atoms to the neighboring B atoms. This electric field appears to be responsible for the creation of a depletion zone in the n-silicon resulting in a rectifying junction-formation between the n-silicon and the atomically thin boron layer.
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Affiliation(s)
- Vahid Mohammadi
- Department of Microelectronics, Delft University of Technology, 2628 CD, Delft, The Netherlands.
| | - Stoyan Nihtianov
- Department of Microelectronics, Delft University of Technology, 2628 CD, Delft, The Netherlands
| | - Changming Fang
- Brunel Centre for Advanced Solidification Technology (BCAST), Brunel University London, Uxbridge, Middlesex, UB8 3PH, UK
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10
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Gazquez J, Stengel M, Mishra R, Scigaj M, Varela M, Roldan MA, Fontcuberta J, Sánchez F, Herranz G. Competition between Polar and Nonpolar Lattice Distortions in Oxide Quantum Wells: New Critical Thickness at Polar Interfaces. PHYSICAL REVIEW LETTERS 2017; 119:106102. [PMID: 28949171 DOI: 10.1103/physrevlett.119.106102] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Indexed: 05/13/2023]
Abstract
Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO_{3}/SrTiO_{3} system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO_{3} structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO_{3}/SrTiO_{3} system and for the general quest towards nanoscale control of material properties.
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Affiliation(s)
- J Gazquez
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - M Stengel
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
- ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
| | - R Mishra
- Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - M Scigaj
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - M Varela
- Materials Science and Technology Division, Oak Ridge National Laboratory, Tennessee 37831-6071, USA
- Departamento de Física de Materiales and Instituto Pluridisciplinar, Universidad Complutense de Madrid, Madrid 28040, Spain
| | - M A Roldan
- Departamento de Física de Materiales and Instituto Pluridisciplinar, Universidad Complutense de Madrid, Madrid 28040, Spain
| | - J Fontcuberta
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - F Sánchez
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - G Herranz
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
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Dielectric collapse at the LaAlO 3/SrTiO 3 (001) heterointerface under applied electric field. Sci Rep 2017; 7:9516. [PMID: 28842643 PMCID: PMC5573322 DOI: 10.1038/s41598-017-09920-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 08/01/2017] [Indexed: 11/25/2022] Open
Abstract
The fascinating interfacial transport properties at the LaAlO3/SrTiO3 heterointerface have led to intense investigations of this oxide system. Exploiting the large dielectric constant of SrTiO3 at low temperatures, tunability in the interfacial conductivity over a wide range has been demonstrated using a back-gate device geometry. In order to understand the effect of back-gating, it is crucial to assess the interface band structure and its evolution with external bias. In this study, we report measurements of the gate-bias dependent interface band alignment, especially the confining potential profile, at the conducting LaAlO3/SrTiO3 (001) heterointerface using soft and hard x-ray photoemission spectroscopy in conjunction with detailed model simulations. Depth-profiling analysis incorporating the electric field dependent dielectric constant in SrTiO3 reveals that a significant potential drop on the SrTiO3 side of the interface occurs within ~2 nm of the interface under negative gate-bias. These results demonstrate gate control of the collapse of the dielectric permittivity at the interface, and explain the dramatic loss of electron mobility with back-gate depletion.
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12
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Prakash A, Xu P, Faghaninia A, Shukla S, Ager JW, Lo CS, Jalan B. Wide bandgap BaSnO 3 films with room temperature conductivity exceeding 10 4 S cm -1. Nat Commun 2017; 8:15167. [PMID: 28474675 PMCID: PMC5424175 DOI: 10.1038/ncomms15167] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 02/28/2017] [Indexed: 11/23/2022] Open
Abstract
Wide bandgap perovskite oxides with high room temperature conductivities and structural compatibility with a diverse family of organic/inorganic perovskite materials are of significant interest as transparent conductors and as active components in power electronics. Such materials must also possess high room temperature mobility to minimize power consumption and to enable high-frequency applications. Here, we report n-type BaSnO3 films grown using hybrid molecular beam epitaxy with room temperature conductivity exceeding 104 S cm−1. Significantly, these films show room temperature mobilities up to 120 cm2 V−1 s−1 even at carrier concentrations above 3 × 1020 cm−3 together with a wide bandgap (3 eV). We examine the mobility-limiting scattering mechanisms by calculating temperature-dependent mobility, and Seebeck coefficient using the Boltzmann transport framework and ab-initio calculations. These results place perovskite oxide semiconductors for the first time on par with the highly successful III–N system, thereby bringing all-transparent, high-power oxide electronics operating at room temperature a step closer to reality. With impressive electronic transport properties, wide bandgap perovskite oxides are promising transparent conductors. Prakash et al. report n-type BaSnO3 films with room temperature conductivity exceeding 104 S cm−1 and investigate factors limiting carrier mobility.
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Affiliation(s)
- Abhinav Prakash
- Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, Minneapolis, Minnesota 55455, USA
| | - Peng Xu
- Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, Minneapolis, Minnesota 55455, USA
| | - Alireza Faghaninia
- Department of Energy, Environmental, and Chemical Engineering, Washington University, St Louis, Missouri 63130, USA
| | - Sudhanshu Shukla
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.,Energy Research Institute, Interdisciplinary Graduate School, School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
| | - Joel W Ager
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.,Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - Cynthia S Lo
- Department of Energy, Environmental, and Chemical Engineering, Washington University, St Louis, Missouri 63130, USA
| | - Bharat Jalan
- Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, Minneapolis, Minnesota 55455, USA
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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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14
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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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15
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van der Torren AJH, van der Molen SJ, Aarts J. Imaging pulsed laser deposition growth of homo-epitaxial SrTiO 3 by low-energy electron microscopy. NANOTECHNOLOGY 2016; 27:495702. [PMID: 27827347 DOI: 10.1088/0957-4484/27/49/495702] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
By combining low-energy electron microscopy with in situ pulsed laser deposition we have developed a new technique for film growth analysis, making use of both diffraction and real-space information. Working at the growth temperature, we can use: the intensity and profile variations of the specular beam to follow the coverage in a layer-by-layer fashion; real-space microscopy to follow e.g. atomic steps at the surface; and electron reflectivity to probe the unoccupied band structure of the grown material. Here, we demonstrate our methodology for homo-epitaxial growth of SrTiO3. Interestingly, the same combination of techniques will also be applicable to hetero-epitaxial oxide growth, largely extending the scope of research possibilities.
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Affiliation(s)
- A J H van der Torren
- Huygens-Kamerlingh Onnes Laboratorium, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands
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16
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Guo H, Saidi WA, Zhao J. Tunability of the two-dimensional electron gas at the LaAlO 3/SrTiO 3 interface by strain-induced ferroelectricity. Phys Chem Chem Phys 2016; 18:28474-28484. [PMID: 27711681 DOI: 10.1039/c6cp04769f] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The two-dimensional electron gas (2DEG) formed at the interface between two insulating materials LaAlO3 (LAO) and SrTiO3 (STO) has recently generated a lot of interest. Here, based on first-principles density functional theory calculations, we investigate the existence and stability of the 2DEG under the application of a biaxial strain on the LAO/STO(001) heterostructure. The compressive strain induces ferroelectric (FE) polarization in STO, which allows for the tunability of the 2DEG by reversing the STO polarization orientation. We show that the formation of the 2DEG is unstable when LAO and STO have the same polarization direction. On the other hand, the 2DEG will always form if the two polarizations are in the opposite directions regardless of the LAO thickness, which is in contrast to the unstrained interface that has a critical thickness for stabilizing the 2DEG. We show that the underpinnings of this behavior are due to charge passivation and band gap alignment.
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Affiliation(s)
- Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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Yang K, Nazir S, Behtash M, Cheng J. High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Polar/Nonpolar Perovskite Oxide Heterostructures. Sci Rep 2016; 6:34667. [PMID: 27708415 PMCID: PMC5052574 DOI: 10.1038/srep34667] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 09/19/2016] [Indexed: 11/15/2022] Open
Abstract
The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO3 and SrTiO3 (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO3-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests. Of these, Al-, Ga-, Sc-, and Ta-based compounds can form a 2DEG with STO, while In-based compounds exhibit a strain-induced strong polarization when deposited on STO substrate. In particular, the Ta-based compounds can form 2DEG with potentially high electron mobility at (TaO2)+/(SrO)0 interface. Our approach, by defining materials descriptors solely based on the bulk materials properties, and by relying on the perovskite-oriented quantum materials repository, opens new avenues for the discovery of perovskite-oxide-based functional interface materials in a HT fashion.
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Affiliation(s)
- Kesong Yang
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, USA
| | - Safdar Nazir
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, USA
| | - Maziar Behtash
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, USA
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, USA
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18
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Xu P, Ayino Y, Cheng C, Pribiag VS, Comes RB, Sushko PV, Chambers SA, Jalan B. Predictive Control over Charge Density in the Two-Dimensional Electron Gas at the Polar-Nonpolar NdTiO_{3}/SrTiO_{3} Interface. PHYSICAL REVIEW LETTERS 2016; 117:106803. [PMID: 27636487 DOI: 10.1103/physrevlett.117.106803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Indexed: 06/06/2023]
Abstract
Through systematic control of the Nd concentration, we show that the carrier density of the two-dimensional electron gas (2DEG) in SrTiO_{3}/NdTiO_{3}/SrTiO_{3}(001) can be modulated over a wide range. We also demonstrate that the NdTiO_{3} in heterojunctions without a SrTiO_{3} cap is degraded by oxygen absorption from air, resulting in the immobilization of donor electrons that could otherwise contribute to the 2DEG. This system is, thus, an ideal model to understand and control the insulator-to-metal transition in a 2DEG based on both environmental conditions and film-growth processing parameters.
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Affiliation(s)
- Peng Xu
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Yilikal Ayino
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Christopher Cheng
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Vlad S Pribiag
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Ryan B Comes
- Physical & Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Peter V Sushko
- Physical & Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Scott A Chambers
- Physical & Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Bharat Jalan
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Moon SY, Moon CW, Chang HJ, Kim T, Kang CY, Choi HJ, Kim JS, Baek SH, Jang HW. Thermal stability of 2DEG at amorphous LaAlO 3/crystalline SrTiO 3 heterointerfaces. NANO CONVERGENCE 2016; 3:7. [PMID: 28191417 PMCID: PMC5271142 DOI: 10.1186/s40580-016-0067-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 02/10/2016] [Indexed: 06/06/2023]
Abstract
At present, the generation of heterostructures with two dimensional electron gas (2DEG) in amorphous LaAlO3 (a-LAO)/SrTiO3 (STO) has been achieved. Herein, we analysed thermal stability of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. To create 2DEG at LAO/STO interface, regardless of growing temperature from 25 to 700 °C, we found that environment with oxygen deficient during the deposition of LAO overlayer is essentially required. That indicates that the oxygen-poor condition in the system is more essential than the crystalline nature of LAO layer. 2DEG at a-LAO/STO interface is depleted upon ex situ annealing at 300 °C under 300 Torr of oxygen pressure, while that in c-LAO/STO interface is still maintained. Our result suggests that the LAO overlayer crystallinity critically affects the thermal-annealing-induced depletion of 2DEG at a-LAO/STO interface rather than the generation of 2DEG. We clearly provide that amorphous TiOx can efficiently prevent the thermal degradation of 2DEG at the a-LAO/STO interface, which gives a cornerstone for achieving thermal-stable 2DEG at a-LAO/STO interface.
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Affiliation(s)
- Seon Young Moon
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Materials Science and Engineering, Yonsei University, Seoul, 120-749 Republic of Korea
| | - Cheon Woo Moon
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 151-744 Republic of Korea
| | - Hye Jung Chang
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-350 Republic of Korea
| | - Taemin Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 151-744 Republic of Korea
| | - Chong-Yun Kang
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-350 Republic of Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 136-701 Republic of Korea
| | - Heon-Jin Choi
- Department of Materials Science and Engineering, Yonsei University, Seoul, 120-749 Republic of Korea
| | - Jin-Sang Kim
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
| | - Seung-Hyub Baek
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-350 Republic of Korea
| | - Ho Won Jang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 151-744 Republic of Korea
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20
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Guo H, Saidi WA, Yang J, Zhao J. Nano-scale polar-nonpolar oxide heterostructures for photocatalysis. NANOSCALE 2016; 8:6057-6063. [PMID: 26932200 DOI: 10.1039/c5nr08689b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates ferroelectric instability in STO. The proposed setup is ideal for tandem oxide photocatalysts especially when combined with photoactive polar materials.
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Affiliation(s)
- Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
| | - Jinlong Yang
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
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21
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Gunkel F, Wicklein S, Hoffmann-Eifert S, Meuffels P, Brinks P, Huijben M, Rijnders G, Waser R, Dittmann R. Transport limits in defect-engineered LaAlO3/SrTiO3 bilayers. NANOSCALE 2015; 7:1013-1022. [PMID: 25469599 DOI: 10.1039/c4nr06272h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The electrical properties of the metallic interface in LaAlO3/SrTiO3 (LAO/STO) bilayers are investigated with focus on the role of cationic defects in thin film STO. Systematic growth-control of the STO thin film cation stoichiometry (defect-engineering) yields a relation between cationic defects in the STO layer and electronic properties of the bilayer-interface. Hall measurements reveal a stoichiometry-effect primarily on the electron mobility. The results indicate an enhancement of scattering processes in as-grown non-stoichiometric samples indicating an increased density of defects. Furthermore, we discuss the thermodynamic processes and defect-exchange reactions at the LAO/STO-bilayer interface determined in high temperature equilibrium. By quenching defined defect states from high temperature equilibrium, we finally connect equilibrium thermodynamics with room temperature transport. The results are consistent with the defect-chemistry model suggested for LAO/STO interfaces. Moreover, they reveal an additional healing process of extended defects in thin film STO.
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Affiliation(s)
- Felix Gunkel
- Peter Grünberg Institut and Jülich Aachen Research Alliance - Fundamentals of Future Information Technology (JARA-FIT), Forschungszentrum Jülich GmbH, Jülich, Germany.
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23
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Jovanović Z, Spreitzer M, Kovač J, Klement D, Suvorov D. Silicon surface deoxidation using strontium oxide deposited with the pulsed laser deposition technique. ACS APPLIED MATERIALS & INTERFACES 2014; 6:18205-18214. [PMID: 25249034 DOI: 10.1021/am505202p] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The epitaxial growth of functional oxides on silicon substrates requires atomically defined surfaces, which are most effectively prepared using Sr-induced deoxidation. The manipulation of metallic Sr is nevertheless very delicate and requires alternative buffer materials. In the present study the applicability of the chemically much more stable SrO in the process of native-oxide removal and silicon-surface stabilization was investigated using the pulsed-laser deposition technique (PLD), while the as-derived surfaces were analyzed in situ using reflection high-energy electron diffraction and ex situ using X-ray photoelectron spectroscopy, X-ray reflectivity, and atomic force microscopy. After the deposition of the SrO over Si/SiO2, in a vacuum, different annealing conditions, with the temperature ranging up to 850 °C, were applied. Because the deposition took place in a vacuum, a multilayer composed of SrO, Sr-silicate, modified Si, and Si as a substrate was initially formed. During the subsequent annealing the topmost layer epitaxially orders in the form of islands, while a further increase in the annealing temperature induced rapid desorption and surface deoxidation, leading to a 2 × 1 Sr-reconstructed silicon surface. However, the process is accompanied by distinctive surface roughening, and therefore the experimental conditions must be carefully optimized to minimize the effect. The results of the study revealed, for the first time, an effective pathway for the preparation of a SrO-induced buffer layer on a silicon substrate using PLD, which can be subsequently utilized for the epitaxial growth of functional oxides.
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Affiliation(s)
- Zoran Jovanović
- Advanced Materials Department and ‡Department of Surface Engineering and Optoelectronics, Jožef Stefan Institute , Jamova 39, 1000 Ljubljana, Slovenia
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24
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Mohanta N, Taraphder A. Oxygen vacancy clustering and pseudogap behaviour at the LaAlO₃/SrTiO₃ interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:215703. [PMID: 24805960 DOI: 10.1088/0953-8984/26/21/215703] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The two-dimensional electron gas at the LaAlO3/SrTiO3 interface promises to add a new dimension to emerging electronic devices due to its high degree of tunability. Defects in the form of oxygen vacancies in titanate surfaces and interfaces, on the other hand, play a key role in the emergence of the ordered states and their tunability at the interface. On the basis of an effective model, we study the influence of oxygen vacancies on the superconductivity and ferromagnetism at the LaAlO3/SrTiO3 interface. Using the Bogoliubov-de Gennes formulation in conjunction with Monte Carlo simulation, we find a clustering of the oxygen vacancies at the interface that favours the formation of coexisting ferromagnetic puddles spatially separated from the superconductivity. We also find a carrier freeze-out at low temperatures, observed experimentally in a wide variety of samples. A sufficiently large amount of oxygen vacancies leads to pseudogap-like behaviour in the superconducting state.
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Affiliation(s)
- N Mohanta
- Department of Physics, Indian Institute of Technology, Kharagpur, WB 721302, India
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25
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Bristowe NC, Ghosez P, Littlewood PB, Artacho E. The origin of two-dimensional electron gases at oxide interfaces: insights from theory. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:143201. [PMID: 24637267 DOI: 10.1088/0953-8984/26/14/143201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The response of oxide thin films to polar discontinuities at interfaces and surfaces has generated enormous activity due to the variety of interesting effects that it gives rise to. A case in point is the discovery of the electron gas at the interface between LaAlO3 and SrTiO3, which has since been shown to be quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite these findings, the origin of the two-dimensional electron gas is highly debated and several possible mechanisms remain. Here we review the main proposed mechanisms and attempt to model expected effects in a quantitative way with the ambition of better constraining what effects can/cannot explain the observed phenomenology. We do it in the framework of a phenomenological model constructed to provide an understanding of the electronic and/or redox screening of the chemical charge in oxide heterostructures. We also discuss the effect of intermixing, both conserving and not conserving the total stoichiometry.
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Affiliation(s)
- N C Bristowe
- Theoretical Materials Physics, University of Liège, B-4000 Sart-Tilman, Belgium. Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
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26
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Mohanta N, Taraphder A. Phase segregation of superconductivity and ferromagnetism at the LaAlO3/SrTiO3 interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:025705. [PMID: 24316496 DOI: 10.1088/0953-8984/26/2/025705] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The highly conductive two-dimensional electron gas formed at the interface between insulating SrTiO3 and LaAlO3 shows low-temperature superconductivity coexisting with inhomogeneous ferromagnetism. The Rashba spin-orbit interaction with the in-plane Zeeman field of the system favors p(x) ± ip(y)-wave superconductivity at finite momentum. Owing to the intrinsic disorder at the interface, the role of spatial inhomogeneity in the superconducting and ferromagnetic states becomes important. We find that, for strong disorder, the system breaks up into mutually excluded regions of superconductivity and ferromagnetism. This inhomogeneity-driven electronic phase separation accounts for the unusual coexistence of superconductivity and ferromagnetism observed at the interface.
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Affiliation(s)
- N Mohanta
- Department of Physics, Indian Institute of Technology Kharagpur, W.B. 721302, India
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27
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LaAlO3 stoichiometry is key to electron liquid formation at LaAlO3/SrTiO3 interfaces. Nat Commun 2013; 4:2351. [DOI: 10.1038/ncomms3351] [Citation(s) in RCA: 185] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 07/24/2013] [Indexed: 11/08/2022] Open
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Cantoni C, Gazquez J, Miletto Granozio F, Oxley MP, Varela M, Lupini AR, Pennycook SJ, Aruta C, di Uccio US, Perna P, Maccariello D. Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: direct measurements with atomic-column spatial resolution. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:3952-3957. [PMID: 22711448 DOI: 10.1002/adma.201200667] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 03/21/2012] [Indexed: 06/01/2023]
Abstract
Using state-of-the-art, aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for an intrinsic electronic reconstruction at the LAO/STO interface is shown. Simultaneous measurements of interfacial electron density and system polarization are crucial for establishing the highly debated origin of the 2D electron gas.
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Affiliation(s)
- Claudia Cantoni
- Materials Science and Technology Division, Oak Ridge National Laboratory, TN 37831-6116, USA.
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Reinle-Schmitt M, Cancellieri C, Li D, Fontaine D, Medarde M, Pomjakushina E, Schneider C, Gariglio S, Ghosez P, Triscone JM, Willmott P. Tunable conductivity threshold at polar oxide interfaces. Nat Commun 2012; 3:932. [DOI: 10.1038/ncomms1936] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 05/30/2012] [Indexed: 11/09/2022] Open
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Kalisky B, Bert JA, Klopfer BB, Bell C, Sato HK, Hosoda M, Hikita Y, Hwang HY, Moler KA. Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures. Nat Commun 2012; 3:922. [DOI: 10.1038/ncomms1931] [Citation(s) in RCA: 170] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Accepted: 05/28/2012] [Indexed: 11/09/2022] Open
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31
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Bristowe NC, Fix T, Blamire MG, Littlewood PB, Artacho E. Proposal of a one-dimensional electron gas in the steps at the LaAlO3-SrTiO3 interface. PHYSICAL REVIEW LETTERS 2012; 108:166802. [PMID: 22680748 DOI: 10.1103/physrevlett.108.166802] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2011] [Indexed: 06/01/2023]
Abstract
The two-dimensional electron gas at the interface between LaAlO(3) and SrTiO(3) has become one of the most fascinating and highly debated oxide systems of recent times. Here we propose that a one-dimensional electron gas can be engineered at the step edges of the LaAlO(3)/SrTiO(3) interface. These predictions are supported by first-principles calculations and electrostatic modeling which elucidate the origin of the one-dimensional electron gas as an electronic reconstruction to compensate a net surface charge in the step edge. The results suggest a novel route to increasing the functional density in these electronic interfaces.
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Affiliation(s)
- N C Bristowe
- Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
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Lee M, Williams JR, Zhang S, Frisbie CD, Goldhaber-Gordon D. Electrolyte gate-controlled Kondo effect in SrTiO3. PHYSICAL REVIEW LETTERS 2011; 107:256601. [PMID: 22243097 DOI: 10.1103/physrevlett.107.256601] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Indexed: 05/31/2023]
Abstract
We report low-temperature, high-field magnetotransport measurements of SrTiO(3) gated by an ionic gel electrolyte. A saturating resistance upturn and negative magnetoresistance that signal the emergence of the Kondo effect appear for higher applied gate voltages. This observation, enabled by the wide tunability of the ionic gel-applied electric field, promotes the interpretation of the electric field-effect-induced 2D electron system in SrTiO(3) as an admixture of magnetic Ti(3+) ions, i.e., localized and unpaired electrons, and delocalized electrons that partially fill the Ti 3d conduction band.
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Affiliation(s)
- Menyoung Lee
- Department of Physics, Stanford University, Stanford, California 94305, USA
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