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Liu X, Zhou T, Qin Z, Ma C, Lu F, Liu T, Li J, Wei SH, Cheng G, Liu WT. Nonlinear optical phonon spectroscopy revealing polaronic signatures of the LaAlO 3/SrTiO 3 interface. SCIENCE ADVANCES 2023; 9:eadg7037. [PMID: 37294751 DOI: 10.1126/sciadv.adg7037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Accepted: 05/04/2023] [Indexed: 06/11/2023]
Abstract
We report the direct observation of lattice phonons confined at LaAlO3/SrTiO3 (LAO/STO) interfaces and STO surfaces using the sum-frequency phonon spectroscopy. This interface-specific nonlinear optical technique unveiled phonon modes localized within a few monolayers at the interface, with inherent sensitivity to the coupling between lattice and charge degrees of freedom. Spectral evolution across the insulator-to-metal transition at LAO/STO interface revealed an electronic reconstruction at the subcritical LAO thickness, as well as strong polaronic signatures upon formation of the two-dimensional electron gas. We further discovered a characteristic lattice mode from interfacial oxygen vacancies, enabling us to probe such important structural defects in situ. Our study provides a unique perspective on many-body interactions at the correlated oxide interfaces.
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Affiliation(s)
- Xinyi Liu
- Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China
| | - Tao Zhou
- Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China
| | - Zhiyuan Qin
- CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Changjian Ma
- CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
| | - Fanjin Lu
- Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China
| | - Tongying Liu
- Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China
| | - Jiashi Li
- Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China
| | - Su-Huai Wei
- Beijing Computational Science Research Center, Beijing 100193, China
| | - Guanglei Cheng
- CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Wei-Tao Liu
- Physics Department, State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures [Ministry of Education (MOE)], Fudan University, Shanghai 200433, China
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2
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Song K, Min T, Seo J, Ryu S, Lee H, Wang Z, Choi S, Lee J, Eom C, Oh SH. Electronic and Structural Transitions of LaAlO 3 /SrTiO 3 Heterostructure Driven by Polar Field-Assisted Oxygen Vacancy Formation at the Surface. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:e2002073. [PMID: 34029001 PMCID: PMC8292910 DOI: 10.1002/advs.202002073] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 02/22/2021] [Indexed: 05/16/2023]
Abstract
The origin of 2D electron gas (2DEG) at LaAlO3 /SrTiO3 (LAO/STO) interfaces has remained highly controversial since its discovery. Various models are proposed, which include electronic reconstruction via surface-to-interface charge transfer and defect-mediated doping involving cation intermixing or oxygen vacancy (VO ) formation. It is shown that the polar field-assisted VO formation at the LAO/STO surface plays critical roles in the 2DEG formation and concurrent structural transition. Comprehensive scanning transmission electron microscopy analyses, in conjunction with density functional theory calculations, demonstrate that VO forming at the LAO/STO surface above the critical thickness (tc ) cancels the polar field by doping the interface with 2DEG. The antiferrodistortive (AFD) octahedral rotations in LAO, which are suppressed below the tc , evolve with the formation of VO above the tc . The present study reveals that local symmetry breaking and shallow donor behavior of VO induce the AFD rotations and relieve the electrical field by electron doping the oxide heterointerface.
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Affiliation(s)
- Kyung Song
- Materials Testing and Reliability DivisionKorea Institute of Materials Science (KIMS)Changwon51508Republic of Korea
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
| | - Taewon Min
- Department of PhysicsPusan National UniversityBusan46241Republic of Korea
| | - Jinsol Seo
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Hyungwoo Lee
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Zhipeng Wang
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
| | - Si‐Young Choi
- Materials Testing and Reliability DivisionKorea Institute of Materials Science (KIMS)Changwon51508Republic of Korea
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
| | - Jaekwang Lee
- Department of PhysicsPusan National UniversityBusan46241Republic of Korea
| | - Chang‐Beom Eom
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Sang Ho Oh
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
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Sarott MF, Gradauskaite E, Nordlander J, Strkalj N, Trassin M. In situmonitoring of epitaxial ferroelectric thin-film growth. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:293001. [PMID: 33873174 DOI: 10.1088/1361-648x/abf979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 04/19/2021] [Indexed: 06/12/2023]
Abstract
In ferroelectric thin films, the polarization state and the domain configuration define the macroscopic ferroelectric properties such as the switching dynamics. Engineering of the ferroelectric domain configuration during synthesis is in permanent evolution and can be achieved by a range of approaches, extending from epitaxial strain tuning over electrostatic environment control to the influence of interface atomic termination. Exotic polar states are now designed in the technologically relevant ultrathin regime. The promise of energy-efficient devices based on ultrathin ferroelectric films depends on the ability to create, probe, and manipulate polar states in ever more complex epitaxial architectures. Because most ferroelectric oxides exhibit ferroelectricity during the epitaxial deposition process, the direct access to the polarization emergence and its evolution during the growth process, beyond the realm of existing structuralin situdiagnostic tools, is becoming of paramount importance. We review the recent progress in the field of monitoring polar states with an emphasis on the non-invasive probes allowing investigations of polarization during the thin film growth of ferroelectric oxides. A particular importance is given to optical second harmonic generationin situ. The ability to determine the net polarization and domain configuration of ultrathin films and multilayers during the growth of multilayers brings new insights towards a better understanding of the physics of ultrathin ferroelectrics and further control of ferroelectric-based heterostructures for devices.
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Affiliation(s)
- Martin F Sarott
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4, 8093 Zurich, Switzerland
| | - Elzbieta Gradauskaite
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4, 8093 Zurich, Switzerland
| | - Johanna Nordlander
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4, 8093 Zurich, Switzerland
| | - Nives Strkalj
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4, 8093 Zurich, Switzerland
| | - Morgan Trassin
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4, 8093 Zurich, Switzerland
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Min T, Choi W, Seo J, Han G, Song K, Ryu S, Lee H, Lee J, Eom K, Eom CB, Jeong HY, Kim YM, Lee J, Oh SH. Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures. SCIENCE ADVANCES 2021; 7:7/17/eabe9053. [PMID: 33883134 PMCID: PMC8059930 DOI: 10.1126/sciadv.abe9053] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Accepted: 03/05/2021] [Indexed: 05/23/2023]
Abstract
Polarity discontinuity across LaAlO3/SrTiO3 (LAO/STO) heterostructures induces electronic reconstruction involving the formation of two-dimensional electron gas (2DEG) and structural distortions characterized by antiferrodistortive (AFD) rotation and ferroelectric (FE) distortion. We show that AFD and FE modes are cooperatively coupled in LAO/STO (111) heterostructures; they coexist below the critical thickness (t c) and disappear simultaneously above t c with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy (V O) formation at the LAO (111) surface, which acts as the source of 2DEG. Tracing the AFD rotation and FE distortion of LAO reveals that their evolution is strongly correlated with V O distribution. The present study demonstrates that AFD and FE modes in oxide heterostructures emerge as a consequence of interplay between misfit strain and polar field, and further that their combination can be tuned to competitive or cooperative coupling by changing the interface orientation.
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Affiliation(s)
- Taewon Min
- Department of Physics, Pusan National University, Busan 46241, Republic of Korea
| | - Wooseon Choi
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Jinsol Seo
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Gyeongtak Han
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Kyung Song
- Materials Testing and Reliability Division, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Kitae Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hu Young Jeong
- UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Young-Min Kim
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
| | - Jaekwang Lee
- Department of Physics, Pusan National University, Busan 46241, Republic of Korea.
| | - Sang Ho Oh
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
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Analysis of Local Charges at Hetero-interfaces by Electron Holography - A Comparative Study of Different Techniques. Ultramicroscopy 2021; 231:113236. [PMID: 33676771 DOI: 10.1016/j.ultramic.2021.113236] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 02/10/2021] [Accepted: 02/20/2021] [Indexed: 11/21/2022]
Abstract
Interface charges confined within a few nanometers of hetero-interface can be characterized by measuring the phase shift of the transmitted beam using different electron holography techniques. However, reliable measurement of the electrostatic potential arising from the interface charges is challenging as the mean inner potential difference (ΔV0) between two adjoining materials as well as local variation of the sample thickness affect the phase shift. In the present study, we show how electron holography can be used to characterize the confined charges at an oxide hetero-interface and evaluate the applicability of different techniques for this purpose. The model system chosen for this study is a LaAlO3/SrTiO3 (LAO/STO) (111) hetero-interface featuring a two-dimensional electron gas (2DEG), where the ΔV0 between LAO and STO is about 2 eV, which is unignorably large and dominates the net potential variation across the interface. For transmission electron microscopy specimens prepared by focused ion beam we applied three different variants of electron holography techniques: off-axis, inline and hybrid electron holography; and compare the results obtained by these approaches in terms of the information transfer in the spatial frequency domain, and the signal-to-noise ratio of the electric field and charge density maps. To correctly assess the information pertinent to the interface-confined charges, we calculate the electrostatic potential and electric field distribution based on a charge model with taking account of the ΔV0 between LAO and STO and compared the calculated profiles with the experimental results after calibrating the local thickness variation across the LAO/STO interface. The results show that hybrid electron holography recovers the information across a wide range of spatial frequencies, and as a result, delivers the most reliable charge density information, albeit convoluted with the unavoidable effects arising from ΔV0.
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Ding J, Cheng J, Dogan F, Li Y, Lin W, Yao Y, Manchon A, Yang K, Wu T. Two-Dimensional Electron Gas at the Spinel/Perovskite Interface: Suppression of Polar Catastrophe by an Ultrathin Layer of Interfacial Defects. ACS APPLIED MATERIALS & INTERFACES 2020; 12:42982-42991. [PMID: 32829635 DOI: 10.1021/acsami.0c13337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Two-dimensional electron gas (2DEG) at the interface between two insulating perovskite oxides has attracted much interest for both fundamental physics and potential applications. Here, we report the discovery of a new 2DEG formed at the interface between spinel MgAl2O4 and perovskite SrTiO3. Transport measurements, electron microscopy imaging, and first-principles calculations reveal that the interfacial 2DEG is closely related to the symmetry breaking at the MgAl2O4/SrTiO3 interface. The critical film thickness for the insulator-to-metal transition is approximately 32 Å, which is twice as thick as that reported on the widely studied LaAlO3/SrTiO3 system. Scanning transmission electron microscopy imaging indicates the formation of interfacial Ti-Al antisite defects with a thickness of ∼4 Å. First-principles density functional theory calculations indicate that the coexistence of the antisite defects and surface oxygen vacancies may explain the formation of interfacial 2DEG as well as the observed critical film thickness. The discovery of 2DEG at the spinel/perovskite interface introduces a new material platform for designing oxide interfaces with desired characteristics.
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Affiliation(s)
- Junfeng Ding
- Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093-0448, United States
| | - Fatih Dogan
- College of Engineering and Technology, American University of the Middle East, Kuwait
| | - Yangyang Li
- Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore
| | - Weinan Lin
- Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore
| | - Yingbang Yao
- School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Aurelien Manchon
- Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
- Aix-Marseille Univ, CNRS, CINaM, Marseille 13288, France
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093-0448, United States
| | - Tom Wu
- School of Materials Science and Engineering, University of New South Wales (UNSW), Sydney, NSW 2052, Australia
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7
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Wang Y, Qian P, Liu Y, Zhang FM, Cai HL, Wu XS, Zhang GP. Modulating the electronic and optical properties for SrTiO 3/LaAlO 3 bilayers treated as the 2D materials by biaxial strains. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:215701. [PMID: 31995526 DOI: 10.1088/1361-648x/ab70c3] [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
The emerging two-dimensional (2D) materials such as graphene have opened the door to industrial applications. Here, we consider the oxide perovskite monolayer of SrTiO3 (STO), LaAlO3 (LAO) and their heterostructures as the 2D transitional metal system. Results show that a band-gap transition from indirect to direct occurs when the separated monolayer STO (indirect band gap of 3.210 eV), and LAO (indirect band gap of 4.024 eV), form the heterostructures (direct band gap of 2.976 eV). The obtained bandgap for the stable bilayers may effectively be modulated by biaxial strains from -12% to 8%. With 12% compressive biaxial strain, the band gap reduces to be 0.23 eV. The optical properties for the stable bilayers are also tuned by the biaxial strain. When the strain increases from compressive strain to tensile strain, the strongest peak of the imaginary part of dielectric function red shifts to lower energy. In comparing with the monolayer STO and LAO, the elastic property enhances obviously for the stable heterostructure, suggesting the heterostructure can be more stable freestanding or may be applied in device fabrications.
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Affiliation(s)
- Yan Wang
- Collaborative Innovation Center of Advanced Microstructures, Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing 210093, People's Republic of China
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Chi X, Wang H, Guo R, Whitcher TJ, Yu X, Yang P, Yan X, Breese MBH, Loh KP, Chen J, Rusydi A. Unusual Hole and Electron Midgap States and Orbital Reconstructions Induced Huge Ferroelectric Tunneling Electroresistance in BaTiO 3/SrTiO 3. NANO LETTERS 2020; 20:1101-1109. [PMID: 31944125 DOI: 10.1021/acs.nanolett.9b04390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Oxide heterostructures have attracted a lot of interest because of their rich exotic phenomena and potential applications. Recently, a greatly enhanced tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs) has been realized in such heterostructures. However, our understanding on the electronic structure of resistance response with polarization reversal and the origin of huge TER is still lacking. Here, we report on electronic structures, particularly at the interface and surface, and the control of the spontaneous polarization of BaTiO3 films by changing the termination of a SrTiO3 substrate. Interestingly, unusual electron and hole midgap states are concurrently formed and accompanied by orbital reconstructions, which determine the ferroelectric polarization orientation in the BaTiO3/SrTiO3. Such unusual midgap states, which yield a strong electronic screening effect, reduce the ferroelectric barrier width and height, and pin the ferroelectric polarization, lead to a dramatic enhancement of the TER effect. The midgap states are also observed in BaTiO3 films on electron-doped Nb/SrTiO3 revealing its universality. Our result provides new insight into the origin of the huge TER effect and opens a new route for designing ferroelectric tunnel junction-based devices with huge TER through interface engineering.
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Affiliation(s)
- Xiao Chi
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Department of Chemistry , National University of Singapore , 3 Science Drive 3, 117543 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
| | - Han Wang
- Department of Materials Science and Engineering , National University of Singapore , 117575 , Singapore
| | - Rui Guo
- Department of Materials Science and Engineering , National University of Singapore , 117575 , Singapore
| | - Thomas J Whitcher
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
| | - Ping Yang
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
| | - Xiaobing Yan
- Department of Materials Science and Engineering , National University of Singapore , 117575 , Singapore
| | - Mark B H Breese
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Department of Physics , National University of Singapore , 2 Science Drive 3, 117542 , Singapore
| | - Kian Ping Loh
- Department of Chemistry , National University of Singapore , 3 Science Drive 3, 117543 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
- Solar Energy Research Institute of Singapore (SERIS) , 7 Engineering Drive 1, 117574 , Singapore
| | - Jingsheng Chen
- Department of Chemistry , National University of Singapore , 3 Science Drive 3, 117543 , Singapore
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Department of Physics , National University of Singapore , 2 Science Drive 3, 117542 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
- Solar Energy Research Institute of Singapore (SERIS) , 7 Engineering Drive 1, 117574 , Singapore
- NUSSNI-NanoCore , National University of Singapore , 117576 , Singapore
- Graduate School for Integrative Sciences and Engineering (NGS) , National University of Singapore , 28 Medical Drive, 117456 , Singapore
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9
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Yin X, Yang M, Tang CS, Wang Q, Xu L, Wu J, Trevisanutto PE, Zeng S, Chin XY, Asmara TC, Feng YP, Ariando A, Chhowalla M, Wang SJ, Zhang W, Rusydi A, Wee ATS. Modulation of New Excitons in Transition Metal Dichalcogenide-Perovskite Oxide System. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2019; 6:1900446. [PMID: 31380174 PMCID: PMC6662271 DOI: 10.1002/advs.201900446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Revised: 03/31/2019] [Indexed: 06/10/2023]
Abstract
The exciton, a quasi-particle that creates a bound state of an electron and a hole, is typically found in semiconductors. It has attracted major attention in the context of both fundamental science and practical applications. Transition metal dichalcogenides (TMDs) are a new class of 2D materials that include direct band-gap semiconductors with strong spin-orbit coupling and many-body interactions. Manipulating new excitons in semiconducting TMDs could generate a novel means of application in nanodevices. Here, the observation of high-energy excitonic peaks in the monolayer-MoS2 on a SrTiO3 heterointerface generated by a new complex mechanism is reported, based on a comprehensive study that comprises temperature-dependent optical spectroscopies and first-principles calculations. The appearance of these excitons is attributed to the change in many-body interactions that occurs alongside the interfacial orbital hybridization and spin-orbit coupling brought about by the excitonic effect propagated from the substrate. This has further led to the formation of a Fermi-surface feature at the interface. The results provide an atomic-scale understanding of the heterointerface between monolayer-TMDs and perovskite oxide and highlight the importance of spin-orbit-charge-lattice coupling on the intrinsic properties of atomic-layer heterostructures, which open up a way to manipulate the excitonic effects in monolayer TMDs via an interfacial system.
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Affiliation(s)
- Xinmao Yin
- International Collaborative Laboratory of 2D Materials for Optoelectronics Science and TechnologyShenzhen UniversityShenzhen518060China
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
| | - Ming Yang
- Institute of Materials Research and EngineeringA∗STAR (Agency for Science, Technology and Research)2 Fusionopolis WaySingapore138634Singapore
| | - Chi Sin Tang
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
| | - Qixing Wang
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
| | - Lei Xu
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
| | - Jing Wu
- Institute of Materials Research and EngineeringA∗STAR (Agency for Science, Technology and Research)2 Fusionopolis WaySingapore138634Singapore
| | - Paolo Emilio Trevisanutto
- Centre for Advanced 2D Materials and Graphene Research CentreNational University of SingaporeSingapore117551Singapore
| | - Shengwei Zeng
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- NUSNNI‐NanoCoreNational University of SingaporeSingapore117576Singapore
| | - Xin Yu Chin
- Energy Research Institute @ NTU (ERI@N)Research Techno PlazaX‐Frontier Block, Level 5, 50 Nanyang DriveSingapore637553Singapore
| | - Teguh Citra Asmara
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
| | - Yuan Ping Feng
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Centre for Advanced 2D Materials and Graphene Research CentreNational University of SingaporeSingapore117551Singapore
| | - Ariando Ariando
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
- NUSNNI‐NanoCoreNational University of SingaporeSingapore117576Singapore
| | - Manish Chhowalla
- Department of Materials Science and MetallurgyUniversity of CambridgeCambridgeCB30FSUK
| | - Shi Jie Wang
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Institute of Materials Research and EngineeringA∗STAR (Agency for Science, Technology and Research)2 Fusionopolis WaySingapore138634Singapore
| | - Wenjing Zhang
- International Collaborative Laboratory of 2D Materials for Optoelectronics Science and TechnologyShenzhen UniversityShenzhen518060China
| | - Andrivo Rusydi
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
- NUSNNI‐NanoCoreNational University of SingaporeSingapore117576Singapore
| | - Andrew T. S. Wee
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
- Centre for Advanced 2D Materials and Graphene Research CentreNational University of SingaporeSingapore117551Singapore
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10
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Cook S, Letchworth-Weaver K, Tung IC, Andersen TK, Hong H, Marks LD, Fong DD. How heteroepitaxy occurs on strontium titanate. SCIENCE ADVANCES 2019; 5:eaav0764. [PMID: 30993200 PMCID: PMC6461459 DOI: 10.1126/sciadv.aav0764] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Accepted: 02/14/2019] [Indexed: 06/01/2023]
Abstract
In traditional models of heteroepitaxy, the substrate serves mainly as a crystalline template for the thin-film lattice, dictating the initial roughness of the film and the degree of coherent strain. Here, performing in situ surface x-ray diffraction during the heteroepitaxial growth of LaTiO3 on SrTiO3 (001), we find that a TiO2 adlayer composed of the ( 13 × 13 ) R33.7° and ( 2 × 2 ) R45.0° reconstructions is a highly active participant in the growth process, continually diffusing to the surface throughout deposition. The effects of the TiO2 adlayer on layer-by-layer growth are investigated using different deposition sequences and anomalous x-ray scattering, both of which permit detailed insight into the dynamic layer rearrangements that take place. Our work challenges commonly held assumptions regarding growth on TiO2-terminated SrTiO3 (001) and demonstrates the critical role of excess TiO2 surface stoichiometry on the initial stages of heteroepitaxial growth on this important perovskite oxide substrate material.
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Affiliation(s)
- Seyoung Cook
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60202, USA
| | | | - I-Cheng Tung
- X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Tassie K. Andersen
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60202, USA
| | - Hawoong Hong
- X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Laurence D. Marks
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60202, USA
| | - Dillon D. Fong
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
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11
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Yu XJ, Diao CZ, Venkatesan T, Breese MBH, Rusydi A. A soft x-ray-ultraviolet (SUV) beamline and diffractometer for resonant elastic scattering and ultraviolet-vacuum ultraviolet reflectance at the Singapore synchrotron light source. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:113113. [PMID: 30501296 DOI: 10.1063/1.5043341] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 10/23/2018] [Indexed: 05/22/2023]
Abstract
A new beamline and a six-circle UHV diffractometer have been constructed at the Singapore Synchrotron Light Source with a broad energy coverage from 3.5 to 1500 eV. The beamline is optimized for ultraviolet-vacuum-ultraviolet optical reflectivity and resonant soft X-ray scattering with medium energy resolution over a broad energy range, achieved by using a self-focusing monochromator consisting of a plane mirror and three variable line spacing gratings. The unique character of the diffractometer comprises 4-circles in the vertical plane and 2-circles in the horizontal plane. Thirteen motions are available inside the UHV chamber with a base pressure of 1 × 10-9 mbar. Two sample holders working independently over a temperature range of 37 K-400 K are controlled by a closed-cycle cryostat, while the bottom holder inside a high field compact pulsed magnet is available for measurements requiring a magnetic field.
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Affiliation(s)
- X J Yu
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - C Z Diao
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - T Venkatesan
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
| | - M B H Breese
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - A Rusydi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
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12
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Huang Z, Renshaw Wang X, Rusydi A, Chen J, Yang H, Venkatesan T. Interface Engineering and Emergent Phenomena in Oxide Heterostructures. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802439. [PMID: 30133012 DOI: 10.1002/adma.201802439] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 07/06/2018] [Indexed: 06/08/2023]
Abstract
Complex oxide interfaces have mesmerized the scientific community in the last decade due to the possibility of creating tunable novel multifunctionalities, which are possible owing to the strong interaction among charge, spin, orbital, and structural degrees of freedom. Artificial interfacial modifications, which include defects, formal polarization, structural symmetry breaking, and interlayer interaction, have led to novel properties in various complex oxide heterostructures. These emergent phenomena not only serve as a platform for investigating strong electronic correlations in low-dimensional systems but also provide potentials for exploring next-generation electronic devices with high functionality. Herein, some recently developed strategies in engineering functional oxide interfaces and their emergent properties are reviewed.
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Affiliation(s)
- Zhen Huang
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Xiao Renshaw Wang
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Andrivo Rusydi
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Jingsheng Chen
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Hyunsoo Yang
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Thirumalai Venkatesan
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
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13
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Hu HL, Pham A, Tilley R, Zeng R, Tan TT, Kong CHC, Webster R, Wang D, Li S. Largely Enhanced Mobility in Trilayered LaAlO 3/SrTiO 3/LaAlO 3 Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2018; 10:20950-20958. [PMID: 29847913 DOI: 10.1021/acsami.7b11218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
LaAlO3 (LAO)/SrTiO3 (STO)/LaAlO3 (LAO) heterostructures were epitaxially deposited on TiO2-terminated (100) SrTiO3 single-crystal substrates by laser molecular beam epitaxy. The electron Hall mobility of 1.2 × 104 cm2/V s at 2 K was obtained in our trilayered heterostructures grown under 1 × 10-5 Torr, which was significantly higher than that in single-layer 5 unit cells LAO (∼4 × 103 cm2/V s) epitaxially grown on (100) STO substrates under the same conditions. It is believed that the enhancement of dielectric permittivity in the polar insulating trilayer can screen the electric field, thus reducing the carrier effective mass of the two-dimensional electron gas formed at the TiO2 interfacial layer in the substrate, resulting in a largely enhanced mobility, as suggested by the first-principle calculation. Our results will pave the way for designing high-mobility oxide nanoelectronic devices based on LAO/STO heterostructures.
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14
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Chi X, Huang Z, Asmara TC, Han K, Yin X, Yu X, Diao C, Yang M, Schmidt D, Yang P, Trevisanutto PE, Whitcher TJ, Venkatesan T, Breese MBH, Rusydi A. Large Enhancement of 2D Electron Gases Mobility Induced by Interfacial Localized Electron Screening Effect. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1707428. [PMID: 29667241 DOI: 10.1002/adma.201707428] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 02/13/2018] [Indexed: 06/08/2023]
Abstract
The interactions between delocalized and localized charges play important roles in correlated electron systems. Here, using a combination of transport measurements, spectroscopic ellipsometry (SE), and X-ray absorption spectroscopy (XAS) supported by theoretical calculations, we reveal the important role of interfacial localized charges and their screening effects in determining the mobility of (La0.3 Sr0.7 )(Al0.65 Ta0.35 )O3 /SrTiO3 (LSAT/SrTiO3 ) interfaces. When the LSAT layer thickness reaches the critical value of 5 uc, the insulating interface abruptly becomes conducting, accompanied by the appearance of a new midgap state. This midgap state emerges at ≈1 eV below the Ti t2g band and shows a strong character of Ti 3dxy - O 2p hybridization. Increasing the LSAT layer from 5 to 18 uc, the number of localized charges increases, resulting in an enhanced screening effect and higher mobile electron mobility. This observation contradicts the traditional semiconductor interface where the localized charges always suppress the carrier mobility. These results demonstrate a new strategy to probe localized charges and mobile electrons in correlated electronic systems and highlight the important role of screening effects from localized charges in improving the mobile electron mobility at complex oxide interfaces.
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Affiliation(s)
- Xiao Chi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Zhen Huang
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - Teguh C Asmara
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - Kun Han
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - Xinmao Yin
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Caozheng Diao
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Ming Yang
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
- Institute of Materials Research and Engineering, A*-STAR, 2 Fusionopolis Way, Singapore, 138634, Singapore
| | - Daniel Schmidt
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Ping Yang
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Paolo E Trevisanutto
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - T J Whitcher
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - T Venkatesan
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
- National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore, 117456, Singapore
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117583, Singapore
| | - Mark B H Breese
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
- National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore, 117456, Singapore
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15
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Li J, Yin D, Li Q, Sun R, Huang S, Meng F. Interfacial defects induced electronic property transformation at perovskite SrVO3/SrTiO3 and LaCrO3/SrTiO3 heterointerfaces. Phys Chem Chem Phys 2017; 19:6945-6951. [DOI: 10.1039/c6cp07691b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Unravelling the atomic structure and chemical species of interfacial defects is critical to understanding the origin of interfacial properties in many heterojunctions.
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Affiliation(s)
- Junjie Li
- Engineering Research Center for Nanophotonics and Advanced Instrument
- Ministry of Education
- Department of Physics
- East China Normal University
- Shanghai 200062
| | - Deqiang Yin
- School of Manufacturing Science and Engineering
- Sichuan University
- Chengdu 610064
- China
| | - Qiang Li
- School of Mechanical Engineering
- University of Shanghai for Science and Technology
- Shanghai 200093
- China
| | - Rong Sun
- Institute of Engineering Innovation
- The University of Tokyo
- Bunkyo-ku
- Japan
| | - Sumei Huang
- Engineering Research Center for Nanophotonics and Advanced Instrument
- Ministry of Education
- Department of Physics
- East China Normal University
- Shanghai 200062
| | - Fanzhi Meng
- School of Materials Science and Engineering
- Changchun University of Science and Technology
- Changchun 130022
- China
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16
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Bel’skii AN, Vasil’ev AN, Ivanov SN, Kamenskikh IA, Kolobanov VN, Makhov VN, Spasskii DA. Optical and luminescent VUV spectroscopy using synchrotron radiation. CRYSTALLOGR REP+ 2016. [DOI: 10.1134/s1063774516060043] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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17
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Yin X, Zeng S, Das T, Baskaran G, Asmara TC, Santoso I, Yu X, Diao C, Yang P, Breese MBH, Venkatesan T, Lin H, Rusydi A. Coexistence of Midgap Antiferromagnetic and Mott States in Undoped, Hole- and Electron-Doped Ambipolar Cuprates. PHYSICAL REVIEW LETTERS 2016; 116:197002. [PMID: 27232036 DOI: 10.1103/physrevlett.116.197002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Indexed: 06/05/2023]
Abstract
We report the first observation of the coexistence of a distinct midgap state and a Mott state in undoped and their evolution in electron and hole-doped ambipolar Y_{0.38}La_{0.62}(Ba_{0.82}La_{0.18})_{2}Cu_{3}O_{y} films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L_{3,2} edges. Supported by theoretical calculations, the midgap state is shown to originate from antiferromagnetic correlation. Surprisingly, while the magnetic state collapses and its correlation strength weakens with dopings, the Mott state in contrast moves toward a higher energy and its correlation strength increases. Our result provides important clues to the mechanism of electronic correlation strengths and superconductivity in cuprates.
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Affiliation(s)
- Xinmao Yin
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
| | - Shengwei Zeng
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Tanmoy Das
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
| | - G Baskaran
- The Institute of Mathematical Sciences, Chennai 600041, India
- Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
| | - Teguh Citra Asmara
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Iman Santoso
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Caozheng Diao
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Ping Yang
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Mark B H Breese
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - T Venkatesan
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Hsin Lin
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
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18
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Palina N, Annadi A, Asmara TC, Diao C, Yu X, Breese MBH, Venkatesan T, Ariando A, Rusydi A. Electronic defect states at the LaAlO3/SrTiO3 heterointerface revealed by O K-edge X-ray absorption spectroscopy. Phys Chem Chem Phys 2016; 18:13844-51. [DOI: 10.1039/c6cp00028b] [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
Interfaces of two dissimilar complex oxides exhibit exotic physical properties that are absent in their parent compounds.
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Affiliation(s)
- Natalia Palina
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- NUSNNI-Nanocore
| | - Anil Annadi
- NUSNNI-Nanocore
- National University of Singapore
- Singapore 117411
- Singapore
- Department of Physics and Astronomy
| | - Teguh Citra Asmara
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- NUSNNI-Nanocore
| | - Caozheng Diao
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
| | - Mark B. H. Breese
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- Department of Physics
| | - T. Venkatesan
- NUSNNI-Nanocore
- National University of Singapore
- Singapore 117411
- Singapore
- Department of Physics
| | - Ariando Ariando
- NUSNNI-Nanocore
- National University of Singapore
- Singapore 117411
- Singapore
- Department of Physics
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- NUSNNI-Nanocore
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19
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Nazir S, Cheng J, Behtash M, Luo J, Yang K. Interface Energetics and Charge Carrier Density Amplification by Sn-Doping in LaAlO3/SrTiO3 Heterostructure. ACS APPLIED MATERIALS & INTERFACES 2015; 7:14294-14302. [PMID: 26062403 DOI: 10.1021/acsami.5b02770] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Tailoring the two-dimensional electron gas (2DEG) at the n-type (TiO2)(0)/(LaO)(+1) interface between the polar LaAlO3 (LAO) and nonpolar SrTiO3 (STO) insulators can potentially provide desired functionalities for next-generation low-dimensional nanoelectronic devices. Here, we propose a new approach to tune the electronic and magnetic properties in the n-type LAO/STO heterostructure (HS) system via electron doping. In this work, we modeled four types of layer doped LAO/STO HS systems with Sn dopants at different cation sites and studied their electronic structures and interface energetics by using first-principles electronic structure calculations. We identified the thermodynamic stability conditions for each of the four proposed doped configurations with respect to the undoped LAO/STO interface. We further found that the Sn-doped LAO/STO HS system with Sn at Al site (Sn@Al) is energetically most favorable with respect to decohesion, thereby strengthening the interface, while the doped HS system with Sn at La site (Sn@La) exhibits the lowest interfacial cohesion. Moreover, our results indicate that all the Sn-doped LAO/STO HS systems exhibit the n-type conductivity with the typical 2DEG characteristics except the Sn@La doped HS system, which shows p-type conductivity. In the Sn@Al doped HS model, the Sn dopant exists as a Sn(4+) ion and introduces one additional electron into the HS system, leading to a higher charge carrier density and larger magnetic moment than that of all the other doped HS systems. An enhanced charge confinement of the 2DEG along the c-axis is also found in the Sn@Al doped HS system. We hence suggest that Sn@Al doping can be an effective way to enhance the electrical conduction and magnetic moment of the 2DEG in LAO/STO HS systems in an energetically favorable manner.
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Affiliation(s)
- Safdar Nazir
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Maziar Behtash
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Jian Luo
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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20
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Mechanical writing of n-type conductive layers on the SrTiO3 surface in nanoscale. Sci Rep 2015; 5:10841. [PMID: 26042679 PMCID: PMC4455303 DOI: 10.1038/srep10841] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Accepted: 05/01/2015] [Indexed: 11/22/2022] Open
Abstract
The fabrication and control of the conductive surface and interface on insulating SrTiO3 bulk provide a pathway for oxide electronics. The controllable manipulation of local doping concentration in semiconductors is an important step for nano-electronics. Here we show that conductive patterns can be written on bare SrTiO3 surface by controllable doping in nanoscale using the mechanical interactions of atomic force microscopy tip without applying external electric field. The conductivity of the layer is n-type, oxygen sensitive, and can be effectively tuned by the gate voltage. Hence, our findings have potential applications in oxide nano-circuits and oxygen sensors.
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21
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Nazir S, Behtash M, Yang K. The role of uniaxial strain in tailoring the interfacial properties of LaAlO3/SrTiO3heterostructure. RSC Adv 2015. [DOI: 10.1039/c4ra15866k] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Applying strains on the substrate is one effective approach to optimize the interfacial electronic properties in SrTiO3-based heterostructures.
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Affiliation(s)
- Safdar Nazir
- Department of NanoEngineering
- University of California San Diego
- USA
| | - Maziar Behtash
- Department of NanoEngineering
- University of California San Diego
- USA
| | - Kesong Yang
- Department of NanoEngineering
- University of California San Diego
- USA
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22
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Debnath AK, Prasad R, Singh A, Samanta S, Kumar A, Bohra A, Bhattacharya D, Basu S, Joshi N, Aswal DK, Gupta SK. Interface mediated semiconducting to metallic like transition in ultrathin Bi 2Se 3 films on (100) SrTiO 3 grown by molecular beam epitaxy. RSC Adv 2015. [DOI: 10.1039/c5ra17949a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Compressive strains due to the structural phase transition of SrTiO3 substrate facilitate semiconductor to metal like transition in Bi2Se3 thin films.
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Affiliation(s)
- Anil K. Debnath
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - R. Prasad
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - Ajay Singh
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - Soumen Samanta
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - Ashwini Kumar
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - Anil Bohra
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | | | - Saibal Basu
- Solid State Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - Niraj Joshi
- Sahyadri College of Engineering and Management
- Mangalore-575007
- India
| | - Dinesh K. Aswal
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
| | - S. K. Gupta
- Technical Physics Division
- Bhabha Atomic Research Center
- Mumbai-400 085
- India
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23
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Nazir S, Yang K. First-principles characterization of the critical thickness for forming metallic states in strained LaAlO₃/SrTiO₃(001) heterostructure. ACS APPLIED MATERIALS & INTERFACES 2014; 6:22351-22358. [PMID: 25486683 DOI: 10.1021/am506336w] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The emerging two-dimensional electron gas (2DEG) at the interface between polar LaAlO3 (LAO) and nonpolar SrTiO3 (STO) provides potential applications in low-dimensional nanoelectronic devices because of its exceptional electron transport property. To form 2DEG in the LAO/STO heterostructure (HS), a minimum thickness of approximately 4 unit cells of LAO is necessary. Herein, we modeled the n-type (TiO2)(0)/(LaO)(+1) HS by depositing (LAO)n (n = 4, 5, and 6) thin films on the STO substrate and explored strain effects on the critical thickness for forming 2DEG in the LAO/STO HS-based slab systems using first-principles electronic structure calculations. A vacuum layer was added along the [001] direction on the LAO film to resemble the actual epitaxial growth process of the materials. An insulator-to-metal transition is predicted in unstrained (LAO)n/STO systems when n ≥ 5. Our calculations indicate that O 2px/py states give rise to the surface conductivity, while Ti 3dxy states are responsible for the interfacial conductivity. For the tensilely strained HS system, an increased film thickness of LAO (n ≥ 6) is required to form the 2DEG, and a remarkable shift of O 2p orbitals toward higher energy in LAO layers is found, which is caused by the strain-induced change of the electrostatic potential. For the compressively strained HS system, the critical thickness of LAO film for forming 2DEG is between 5 and 6 unit cells of LAO. In addition, our calculations suggest that the interfacial charge carrier density and magnetic moment can be optimized when a moderate tensile strain is applied on the STO substrate in the ab-plane.
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Affiliation(s)
- Safdar Nazir
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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24
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Asmara TC, Santoso I, Rusydi A. Self-consistent iteration procedure in analyzing reflectivity and spectroscopic ellipsometry data of multilayered materials and their interfaces. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:123116. [PMID: 25554281 DOI: 10.1063/1.4897487] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
For multilayered materials, reflectivity depends on the complex dielectric function of all the constituent layers, and a detailed analysis is required to separate them. Furthermore, for some cases, new quantum states can occur at the interface which may change the optical properties of the material. In this paper, we discuss various aspects of such analysis, and present a self-consistent iteration procedure, a versatile method to extract and separate the complex dielectric function of each individual layer of a multilayered system. As a case study, we apply this method to LaAlO3/SrTiO3 heterostructure in which we are able to separate the effects of the interface from the LaAlO3 film and the SrTiO3 substrate. Our method can be applied to other complex multilayered systems with various numbers of layers.
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Affiliation(s)
- T C Asmara
- NUSNNI-NanoCore, Singapore Synchrotron Light Source, and Department of Physics, National University of Singapore, Singapore 117576
| | - I Santoso
- NUSNNI-NanoCore, Singapore Synchrotron Light Source, and Department of Physics, National University of Singapore, Singapore 117576
| | - A Rusydi
- NUSNNI-NanoCore, Singapore Synchrotron Light Source, and Department of Physics, National University of Singapore, Singapore 117576
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Yu L, Zunger A. A polarity-induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces. Nat Commun 2014; 5:5118. [DOI: 10.1038/ncomms6118] [Citation(s) in RCA: 230] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 09/02/2014] [Indexed: 11/09/2022] Open
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