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Yokoi M, Fujiwara S, Kawamura T, Arakawa T, Aoyama K, Fukuyama H, Kobayashi K, Niimi Y. Negative resistance state in superconducting NbSe 2 induced by surface acoustic waves. SCIENCE ADVANCES 2020; 6:6/34/eaba1377. [PMID: 32937360 PMCID: PMC7442479 DOI: 10.1126/sciadv.aba1377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 07/09/2020] [Indexed: 06/11/2023]
Abstract
We report a negative resistance, namely, a voltage drop along the opposite direction of a current flow, in the superconducting gap of NbSe2 thin films under the irradiation of surface acoustic waves (SAWs). The amplitude of the negative resistance becomes larger by increasing the SAW power and decreasing temperature. As one possible scenario, we propose that soliton-antisoliton pairs in the charge density wave of NbSe2 modulated by the SAW serve as a time-dependent capacitance in the superconducting state, leading to the dc negative resistance. The present experimental result would provide a previously unexplored way to examine nonequilibrium manipulation of the superconductivity.
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Affiliation(s)
- Masahiko Yokoi
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
| | - Satoshi Fujiwara
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
| | - Tomoya Kawamura
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
| | - Tomonori Arakawa
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
- Center for Spin Research Network, Osaka University, Toyonaka 560-8531, Japan
| | - Kazushi Aoyama
- Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
| | - Hiroshi Fukuyama
- Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
- Cryogenic Research Center, The University of Tokyo, Tokyo 113-0032, Japan
| | - Kensuke Kobayashi
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
- Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
- Institute for Physics of Intelligence, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
| | - Yasuhiro Niimi
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan.
- Center for Spin Research Network, Osaka University, Toyonaka 560-8531, Japan
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52
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Yoon J, Lesne E, Sklarek K, Sheckelton J, Pasco C, Parkin SSP, McQueen TM, Ali MN. Anomalous thickness-dependent electrical conductivity in van der Waals layered transition metal halide, Nb 3Cl 8. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:304004. [PMID: 32213671 DOI: 10.1088/1361-648x/ab832b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Understanding the electronic transport properties of layered, van der Waals transition metal halides (TMHs) and chalcogenides is a highly active research topic today. Of particular interest is the evolution of those properties with changing thickness as the 2D limit is approached. Here, we present the electrical conductivity of exfoliated single crystals of the TMH, cluster magnet, Nb3Cl8, over a wide range of thicknesses both with and without hexagonal boron nitride (hBN) encapsulation. The conductivity is found to increase by more than three orders of magnitude when the thickness is decreased from 280 µm to 5 nm, at 300 K. At low temperatures and below ∼50 nm, the conductance becomes thickness independent, implying surface conduction is dominating. Temperature dependent conductivity measurements indicate Nb3Cl8 is an insulator, however, the effective activation energy decreases from a bulk value of 310 meV to 140 meV by 5 nm. X-ray photoelectron spectroscopy (XPS) shows mild surface oxidation in devices without hBN capping, however, no significant difference in transport is observed when compared to the capped devices, implying the thickness dependent transport behavior is intrinsic to the material. A conduction mechanism comprised of a higher conductivity surface channel in parallel with a lower conductivity interlayer channel is discussed.
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Affiliation(s)
- Jiho Yoon
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle 06120, Germany
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53
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Wagner B, Huttner A, Bischof D, Engel A, Witte G, Heine J. Chemical Surface Reactivity and Morphological Changes of Bismuth Triiodide (BiI 3) under Different Environmental Conditions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:6458-6464. [PMID: 32437620 DOI: 10.1021/acs.langmuir.0c00740] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Layered metal halides like BiI3 are of current interest in connection with both 2D materials and photovoltaics. Here, we present a facile new method for the preparation of millimeter-sized BiI3 single crystals. We use these crystals to study the surface reactivity of their (001) cleavage planes toward various environmental conditions by measuring morphological changes using atomic force microscopy and analyzing the formed species by means of X-ray photoelectron spectroscopy and X-ray diffraction methods. We find that freshly cleaved samples show atomically flat surface regions extending over several micrometers and reveal steps corresponding to single BiI3 layers. However, we also find that the surface deteriorates in air on a time scale of hours. By studying samples cleaved and stored under different conditions, we identify water as the agent initiating the changes in surface morphology, while under inert gas and dry oxygen, the surface stays intact. On the basis of the analysis of deteriorated long-term-stored samples we identify BiOI as the main product of hydrolysis. We also observe a second long-term decomposition route for samples stored under dynamic vacuum, where formation of BiI whiskers occurs. Overall, our findings emphasize the challenges associated with the surface reactivity of BiI3 but also demonstrate that well-ordered BiI3 surfaces can be obtained, which indicates that preparation of extended, atomically smooth BiI3 monolayers by exfoliation from bulk crystals should be possible.
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Affiliation(s)
- Bettina Wagner
- Department of Chemistry and Material Sciences Center, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35043 Marburg, Germany
| | - Andrea Huttner
- Department of Physics and Materials Sciences Center, Philipps-Universität Marburg, Renthof 7, 35032 Marburg, Germany
| | - Daniel Bischof
- Department of Physics and Materials Sciences Center, Philipps-Universität Marburg, Renthof 7, 35032 Marburg, Germany
| | - Annikka Engel
- Department of Chemistry and Material Sciences Center, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35043 Marburg, Germany
| | - Gregor Witte
- Department of Physics and Materials Sciences Center, Philipps-Universität Marburg, Renthof 7, 35032 Marburg, Germany
| | - Johanna Heine
- Department of Chemistry and Material Sciences Center, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35043 Marburg, Germany
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54
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Bekaert J, Khestanova E, Hopkinson DG, Birkbeck J, Clark N, Zhu M, Bandurin DA, Gorbachev R, Fairclough S, Zou Y, Hamer M, Terry DJ, Peters JJP, Sanchez AM, Partoens B, Haigh SJ, Milošević MV, Grigorieva IV. Enhanced Superconductivity in Few-Layer TaS 2 due to Healing by Oxygenation. NANO LETTERS 2020; 20:3808-3818. [PMID: 32310666 DOI: 10.1021/acs.nanolett.0c00871] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
When approaching the atomically thin limit, defects and disorder play an increasingly important role in the properties of two-dimensional (2D) materials. While defects are generally thought to negatively affect superconductivity in 2D materials, here we demonstrate the contrary in the case of oxygenation of ultrathin tantalum disulfide (TaS2). Our first-principles calculations show that incorporation of oxygen into the TaS2 crystal lattice is energetically favorable and effectively heals sulfur vacancies typically present in these crystals, thus restoring the electronic band structure and the carrier density to the intrinsic characteristics of TaS2. Strikingly, this leads to a strong enhancement of the electron-phonon coupling, by up to 80% in the highly oxygenated limit. Using transport measurements on fresh and aged (oxygenated) few-layer TaS2, we found a marked increase of the superconducting critical temperature (Tc) upon aging, in agreement with our theory, while concurrent electron microscopy and electron-energy loss spectroscopy confirmed the presence of sulfur vacancies in freshly prepared TaS2 and incorporation of oxygen into the crystal lattice with time. Our work thus reveals the mechanism by which certain atomic-scale defects can be beneficial to superconductivity and opens a new route to engineer Tc in ultrathin materials.
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Affiliation(s)
- Jonas Bekaert
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Ekaterina Khestanova
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - David G Hopkinson
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Materials, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - John Birkbeck
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Nick Clark
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Materials, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Mengjian Zhu
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Denis A Bandurin
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Roman Gorbachev
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Simon Fairclough
- Department of Materials, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Yichao Zou
- Department of Materials, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Matthew Hamer
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Daniel J Terry
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | | | - Ana M Sanchez
- School of Physics, University of Warwick, Coventry, United Kingdom CV4 7AL
| | - Bart Partoens
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Sarah J Haigh
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Materials, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
| | - Milorad V Milošević
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Irina V Grigorieva
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, United Kingdom M13 9PL
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55
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Control of electron-electron interaction in graphene by proximity screenings. Nat Commun 2020; 11:2339. [PMID: 32393747 PMCID: PMC7214472 DOI: 10.1038/s41467-020-15829-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 03/25/2020] [Indexed: 11/08/2022] Open
Abstract
Electron-electron interactions play a critical role in many condensed matter phenomena, and it is tempting to find a way to control them by changing the interactions' strength. One possible approach is to place a studied system in proximity of a metal, which induces additional screening and hence suppresses electron interactions. Here, using devices with atomically-thin gate dielectrics and atomically-flat metallic gates, we measure the electron-electron scattering length in graphene and report qualitative deviations from the standard behavior. The changes induced by screening become important only at gate dielectric thicknesses of a few nm, much smaller than a typical separation between electrons. Our theoretical analysis agrees well with the scattering rates extracted from measurements of electron viscosity in monolayer graphene and of umklapp electron-electron scattering in graphene superlattices. The results provide a guidance for future attempts to achieve proximity screening of many-body phenomena in two-dimensional systems.
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56
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Wakafuji Y, Moriya R, Masubuchi S, Watanabe K, Taniguchi T, Machida T. 3D Manipulation of 2D Materials Using Microdome Polymer. NANO LETTERS 2020; 20:2486-2492. [PMID: 32155082 DOI: 10.1021/acs.nanolett.9b05228] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We demonstrate 3D mechanical manipulations, such as sliding, rotating, folding, flipping, and exfoliating, of 2D materials using a microdome polymer (MDP) via in situ real-time observation with an optical microscope. A dimethylpolysiloxane (PDMS)-based MDP is covered with a poly(vinyl chloride) (PVC) adhesion layer. This PVC-MDP structure enables us to achieve small and adjustable contact areas between the PVC-MDP and a 2D-material flake, which is typically between ∼10 and ∼100 μm in diameter. The adhesion between the PVC polymer and 2D materials is fully tunable with temperature: Strong adhesion at ∼70 °C allows pick-up of the 2D material, and release occurs at ∼130 °C when the adhesion is weak. Thus the PVC-MDP functions as a point-of-contact manipulator for 2D materials, permitting the 3D manipulation of 2D-material flakes. Our method could facilitate the expansion of van der Waals heterostructure fabrication technology and the development of preparation techniques for more complex 3D structures.
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Affiliation(s)
- Yusai Wakafuji
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Rai Moriya
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Satoru Masubuchi
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Tomoki Machida
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
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57
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Poncé S, Li W, Reichardt S, Giustino F. First-principles calculations of charge carrier mobility and conductivity in bulk semiconductors and two-dimensional materials. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2020; 83:036501. [PMID: 31923906 DOI: 10.1088/1361-6633/ab6a43] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
One of the fundamental properties of semiconductors is their ability to support highly tunable electric currents in the presence of electric fields or carrier concentration gradients. These properties are described by transport coefficients such as electron and hole mobilities. Over the last decades, our understanding of carrier mobilities has largely been shaped by experimental investigations and empirical models. Recently, advances in electronic structure methods for real materials have made it possible to study these properties with predictive accuracy and without resorting to empirical parameters. These new developments are unlocking exciting new opportunities, from exploring carrier transport in quantum matter to in silico designing new semiconductors with tailored transport properties. In this article, we review the most recent developments in the area of ab initio calculations of carrier mobilities of semiconductors. Our aim is threefold: to make this rapidly-growing research area accessible to a broad community of condensed-matter theorists and materials scientists; to identify key challenges that need to be addressed in order to increase the predictive power of these methods; and to identify new opportunities for increasing the impact of these computational methods on the science and technology of advanced materials. The review is organized in three parts. In the first part, we offer a brief historical overview of approaches to the calculation of carrier mobilities, and we establish the conceptual framework underlying modern ab initio approaches. We summarize the Boltzmann theory of carrier transport and we discuss its scope of applicability, merits, and limitations in the broader context of many-body Green's function approaches. We discuss recent implementations of the Boltzmann formalism within the context of density functional theory and many-body perturbation theory calculations, placing an emphasis on the key computational challenges and suggested solutions. In the second part of the article, we review applications of these methods to materials of current interest, from three-dimensional semiconductors to layered and two-dimensional materials. In particular, we discuss in detail recent investigations of classic materials such as silicon, diamond, gallium arsenide, gallium nitride, gallium oxide, and lead halide perovskites as well as low-dimensional semiconductors such as graphene, silicene, phosphorene, molybdenum disulfide, and indium selenide. We also review recent efforts toward high-throughput calculations of carrier transport. In the last part, we identify important classes of materials for which an ab initio study of carrier mobilities is warranted. We discuss the extension of the methodology to study topological quantum matter and materials for spintronics and we comment on the possibility of incorporating Berry-phase effects and many-body correlations beyond the standard Boltzmann formalism.
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Affiliation(s)
- Samuel Poncé
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom. Theory and Simulation of Materials (THEOS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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58
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Chen C, Lu X, Deng B, Chen X, Guo Q, Li C, Ma C, Yuan S, Sung E, Watanabe K, Taniguchi T, Yang L, Xia F. Widely tunable mid-infrared light emission in thin-film black phosphorus. SCIENCE ADVANCES 2020; 6:eaay6134. [PMID: 32110733 PMCID: PMC7021507 DOI: 10.1126/sciadv.aay6134] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 11/25/2019] [Indexed: 05/20/2023]
Abstract
Thin-film black phosphorus (BP) is an attractive material for mid-infrared optoelectronic applications because of its layered nature and a moderate bandgap of around 300 meV. Previous photoconduction demonstrations show that a vertical electric field can effectively reduce the bandgap of thin-film BP, expanding the device operational wavelength range in mid-infrared. Here, we report the widely tunable mid-infrared light emission from a hexagonal boron nitride (hBN)/BP/hBN heterostructure device. With a moderate displacement field up to 0.48 V/nm, the photoluminescence (PL) peak from a ~20-layer BP flake is continuously tuned from 3.7 to 7.7 μm, spanning 4 μm in mid-infrared. The PL emission remains perfectly linear-polarized along the armchair direction regardless of the bias field. Moreover, together with theoretical analysis, we show that the radiative decay probably dominates over other nonradiative decay channels in the PL experiments. Our results reveal the great potential of thin-film BP in future widely tunable, mid-infrared light-emitting and lasing applications.
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Affiliation(s)
- Chen Chen
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Xiaobo Lu
- Department of Physics, Washington University in St. Louis, St. Louis, MO 63136, USA
| | - Bingchen Deng
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Xiaolong Chen
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Qiushi Guo
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Cheng Li
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Chao Ma
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Shaofan Yuan
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Eric Sung
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Li Yang
- Department of Physics, Washington University in St. Louis, St. Louis, MO 63136, USA
| | - Fengnian Xia
- Department of Electrical Engineering, Yale University, New Haven, CT 06511, USA
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59
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Zhou W, Chen J, Bai P, Guo S, Zhang S, Song X, Tao L, Zeng H. Two-Dimensional Pnictogen for Field-Effect Transistors. RESEARCH 2020; 2019:1046329. [PMID: 31912022 PMCID: PMC6944228 DOI: 10.34133/2019/1046329] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 09/07/2019] [Indexed: 11/06/2022]
Abstract
Two-dimensional (2D) layered materials hold great promise for various future electronic and optoelectronic devices that traditional semiconductors cannot afford. 2D pnictogen, group-VA atomic sheet (including phosphorene, arsenene, antimonene, and bismuthene) is believed to be a competitive candidate for next-generation logic devices. This is due to their intriguing physical and chemical properties, such as tunable midrange bandgap and controllable stability. Since the first black phosphorus field-effect transistor (FET) demo in 2014, there has been abundant exciting research advancement on the fundamental properties, preparation methods, and related electronic applications of 2D pnictogen. Herein, we review the recent progress in both material and device aspects of 2D pnictogen FETs. This includes a brief survey on the crystal structure, electronic properties and synthesis, or growth experiments. With more device orientation, this review emphasizes experimental fabrication, performance enhancing approaches, and configuration engineering of 2D pnictogen FETs. At the end, this review outlines current challenges and prospects for 2D pnictogen FETs as a potential platform for novel nanoelectronics.
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Affiliation(s)
- Wenhan Zhou
- Key Laboratory of Advanced Display Materials and Devices, Ministry of Industry and Information Technology, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
| | - Jiayi Chen
- Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China
| | - Pengxiang Bai
- Key Laboratory of Advanced Display Materials and Devices, Ministry of Industry and Information Technology, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
| | - Shiying Guo
- Key Laboratory of Advanced Display Materials and Devices, Ministry of Industry and Information Technology, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
| | - Shengli Zhang
- Key Laboratory of Advanced Display Materials and Devices, Ministry of Industry and Information Technology, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
| | - Xiufeng Song
- Key Laboratory of Advanced Display Materials and Devices, Ministry of Industry and Information Technology, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
| | - Li Tao
- Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China
| | - Haibo Zeng
- Key Laboratory of Advanced Display Materials and Devices, Ministry of Industry and Information Technology, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
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60
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Zultak J, Magorrian SJ, Koperski M, Garner A, Hamer MJ, Tóvári E, Novoselov KS, Zhukov AA, Zou Y, Wilson NR, Haigh SJ, Kretinin AV, Fal'ko VI, Gorbachev R. Ultra-thin van der Waals crystals as semiconductor quantum wells. Nat Commun 2020; 11:125. [PMID: 31913279 PMCID: PMC6949292 DOI: 10.1038/s41467-019-13893-w] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 11/28/2019] [Indexed: 11/09/2022] Open
Abstract
Control over the quantization of electrons in quantum wells is at the heart of the functioning of modern advanced electronics; high electron mobility transistors, semiconductor and Capasso terahertz lasers, and many others. However, this avenue has not been explored in the case of 2D materials. Here we apply this concept to van der Waals heterostructures using the thickness of exfoliated crystals to control the quantum well dimensions in few-layer semiconductor InSe. This approach realizes precise control over the energy of the subbands and their uniformity guarantees extremely high quality electronic transport in these systems. Using tunnelling and light emitting devices, we reveal the full subband structure by studying resonance features in the tunnelling current, photoabsorption and light emission spectra. In the future, these systems could enable development of elementary blocks for atomically thin infrared and THz light sources based on intersubband optical transitions in few-layer van der Waals materials.
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Affiliation(s)
- Johanna Zultak
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Samuel J Magorrian
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Maciej Koperski
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Alistair Garner
- Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Matthew J Hamer
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Endre Tóvári
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Kostya S Novoselov
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Alexander A Zhukov
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Yichao Zou
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Neil R Wilson
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - Sarah J Haigh
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Andrey V Kretinin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.,Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
| | - Vladimir I Fal'ko
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. .,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. .,Henry Royce Institute for Advanced Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
| | - Roman Gorbachev
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. .,National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. .,Henry Royce Institute for Advanced Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
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61
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Lee Y, Lee S, Yoon JY, Cheon J, Jeong HY, Kim K. Fabrication and Imaging of Monolayer Phosphorene with Preferred Edge Configurations via Graphene-Assisted Layer-by-Layer Thinning. NANO LETTERS 2020; 20:559-566. [PMID: 31790269 DOI: 10.1021/acs.nanolett.9b04292] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Phosphorene, a monolayer of black phosphorus (BP), is an elemental two-dimensional material with interesting physical properties, such as high charge carrier mobility and exotic anisotropic in-plane properties. To fundamentally understand these various physical properties, it is critically important to conduct an atomic-scale structural investigation of phosphorene, particularly regarding various defects and preferred edge configurations. However, it has been challenging to investigate mono- and few-layer phosphorene because of technical difficulties arising in the preparation of a high-quality sample and damages induced during the characterization process. Here, we successfully fabricate high-quality monolayer phosphorene using a controlled thinning process with transmission electron microscopy and subsequently perform atomic-resolution imaging. Graphene protection suppresses the e-beam-induced damage to multilayer BP and one-side graphene protection facilitates the layer-by-layer thinning of the samples, rendering high-quality monolayer and bilayer regions. We also observe the formation of atomic-scale crystalline edges predominantly aligned along the zigzag and (101) terminations, which is originated from edge kinetics under e-beam-induced sputtering process. Our study demonstrates a new method to image and precisely manipulate the thickness and edge configurations of air-sensitive two-dimensional materials.
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Affiliation(s)
- Yangjin Lee
- Department of Physics , Yonsei University , Seoul 03722 , Korea
- Center for Nanomedicine , Institute for Basic Science (IBS) , Seoul 03722 , Korea
| | - Sol Lee
- Department of Physics , Yonsei University , Seoul 03722 , Korea
- Center for Nanomedicine , Institute for Basic Science (IBS) , Seoul 03722 , Korea
| | - Jun-Yeong Yoon
- Department of Physics , Yonsei University , Seoul 03722 , Korea
- Center for Nanomedicine , Institute for Basic Science (IBS) , Seoul 03722 , Korea
| | - Jinwoo Cheon
- Center for Nanomedicine , Institute for Basic Science (IBS) , Seoul 03722 , Korea
- Graduate Program of Nano Biomedical Engineering, Yonsei-IBS Institute , Yonsei University , Seoul 03722 , Korea
- Department of Chemistry , Yonsei University , Seoul 03722 , Korea
| | - Hu Young Jeong
- UNIST Central Research Facilities (UCRF) and School of Materials Science and Engineering , Ulsan National Institute of Science and Technology (UNIST) , Ulsan 44919 , Korea
| | - Kwanpyo Kim
- Department of Physics , Yonsei University , Seoul 03722 , Korea
- Center for Nanomedicine , Institute for Basic Science (IBS) , Seoul 03722 , Korea
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62
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Wang Z, Wang YB, Yin J, Tóvári E, Yang Y, Lin L, Holwill M, Birkbeck J, Perello DJ, Xu S, Zultak J, Gorbachev RV, Kretinin AV, Taniguchi T, Watanabe K, Morozov SV, Anđelković M, Milovanović SP, Covaci L, Peeters FM, Mishchenko A, Geim AK, Novoselov KS, Fal’ko VI, Knothe A, Woods CR. Composite super-moiré lattices in double-aligned graphene heterostructures. SCIENCE ADVANCES 2019; 5:eaay8897. [PMID: 32064323 PMCID: PMC6989342 DOI: 10.1126/sciadv.aay8897] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 10/22/2019] [Indexed: 05/30/2023]
Abstract
When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moiré pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moiré patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moiré pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moiré super cell.
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Affiliation(s)
- Zihao Wang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Yi Bo Wang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Yin
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
| | - E. Tóvári
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Y. Yang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - L. Lin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - M. Holwill
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Birkbeck
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - D. J. Perello
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Shuigang Xu
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Zultak
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - R. V. Gorbachev
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Oxford Road, Manchester M13 9PL, UK
| | - A. V. Kretinin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - T. Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - K. Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - S. V. Morozov
- Institute of Microelectronics Technology RAS, Chernogolovka 142432, Russia
| | - M. Anđelković
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - S. P. Milovanović
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - L. Covaci
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - F. M. Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - A. Mishchenko
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - A. K. Geim
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - K. S. Novoselov
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore
- Chongqing 2D Materials Institute, Liangjiang New Area, Chongqing 400714, China
| | - Vladimir I. Fal’ko
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Oxford Road, Manchester M13 9PL, UK
| | - Angelika Knothe
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - C. R. Woods
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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63
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Jain A, Szabó Á, Parzefall M, Bonvin E, Taniguchi T, Watanabe K, Bharadwaj P, Luisier M, Novotny L. One-Dimensional Edge Contacts to a Monolayer Semiconductor. NANO LETTERS 2019; 19:6914-6923. [PMID: 31513426 DOI: 10.1021/acs.nanolett.9b02166] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Integration of electrical contacts into van der Waals (vdW) heterostructures is critical for realizing electronic and optoelectronic functionalities. However, to date no scalable methodology for gaining electrical access to buried monolayer two-dimensional (2D) semiconductors exists. Here we report viable edge contact formation to hexagonal boron nitride (hBN) encapsulated monolayer MoS2. By combining reactive ion etching, in situ Ar+ sputtering and annealing, we achieve a relatively low edge contact resistance, high mobility (up to ∼30 cm2 V-1 s-1) and high on-current density (>50 μA/μm at VDS = 3V), comparable to top contacts. Furthermore, the atomically smooth hBN environment also preserves the intrinsic MoS2 channel quality during fabrication, leading to a steep subthreshold swing of 116 mV/dec with a negligible hysteresis. Hence, edge contacts are highly promising for large-scale practical implementation of encapsulated heterostructure devices, especially those involving air sensitive materials, and can be arbitrarily narrow, which opens the door to further shrinkage of 2D device footprint.
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Affiliation(s)
- Achint Jain
- Photonics Laboratory , ETH Zürich , 8093 Zürich , Switzerland
| | - Áron Szabó
- Integrated Systems Laboratory , ETH Zürich , 8092 Zürich , Switzerland
| | | | - Eric Bonvin
- Photonics Laboratory , ETH Zürich , 8093 Zürich , Switzerland
| | - Takashi Taniguchi
- National Institute for Material Science , 1-1 Namiki , Tsukuba 305-0044 , Japan
| | - Kenji Watanabe
- National Institute for Material Science , 1-1 Namiki , Tsukuba 305-0044 , Japan
| | - Palash Bharadwaj
- Department of Electrical and Computer Engineering , Rice University , Houston , Texas 77005 , United States
| | - Mathieu Luisier
- Integrated Systems Laboratory , ETH Zürich , 8092 Zürich , Switzerland
| | - Lukas Novotny
- Photonics Laboratory , ETH Zürich , 8093 Zürich , Switzerland
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64
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Hall J, Ehlen N, Berges J, van Loon E, van Efferen C, Murray C, Rösner M, Li J, Senkovskiy BV, Hell M, Rolf M, Heider T, Asensio MC, Avila J, Plucinski L, Wehling T, Grüneis A, Michely T. Environmental Control of Charge Density Wave Order in Monolayer 2H-TaS 2. ACS NANO 2019; 13:10210-10220. [PMID: 31442021 DOI: 10.1021/acsnano.9b03419] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
For quasi-freestanding 2H-TaS2 in monolayer thickness grown by in situ molecular beam epitaxy on graphene on Ir(111), we find unambiguous evidence for a charge density wave close to a 3 × 3 periodicity. Using scanning tunneling spectroscopy, we determine the magnitude of the partial charge density wave gap. Angle-resolved photoemission spectroscopy, complemented by scanning tunneling spectroscopy for the unoccupied states, makes a tight-binding fit for the band structure of the TaS2 monolayer possible. As hybridization with substrate bands is absent, the fit yields a precise value for the doping of the TaS2 layer. Additional Li doping shifts the charge density wave to a 2 × 2 periodicity. Unexpectedly, the bilayer of TaS2 also displays a disordered 2 × 2 charge density wave. Calculations of the phonon dispersions based on a combination of density-functional theory, density-functional perturbation theory, and many-body perturbation theory enable us to provide phase diagrams for the TaS2 charge density wave as functions of doping, hybridization, and interlayer potentials, and offer insight into how they affect lattice dynamics and stability. Our theoretical considerations are consistent with the experimental work presented and shed light on previous experimental and theoretical investigations of related systems.
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Affiliation(s)
- Joshua Hall
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Niels Ehlen
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Jan Berges
- Institut für Theoretische Physik, Bremen Center for Computational Materials Science , Universität Bremen , Otto-Hahn-Allee 1 , 28359 Bremen , Germany
| | - Erik van Loon
- Institut für Theoretische Physik, Bremen Center for Computational Materials Science , Universität Bremen , Otto-Hahn-Allee 1 , 28359 Bremen , Germany
| | - Camiel van Efferen
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Clifford Murray
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Malte Rösner
- Institute for Molecules and Materials , Radboud University , 6525 AJ Nijmegen , The Netherlands
| | - Jun Li
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Boris V Senkovskiy
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Martin Hell
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Matthias Rolf
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Tristan Heider
- Peter Grünberg Institut (PGI-6) , Forschungszentrum Jülich GmbH , 52425 Jülich , Germany
| | - María C Asensio
- ANTARES Beamline , Synchrotron SOLEIL and Universite Paris-Saclay , L' Orme des Merisiers, Saint Aubin-BP 48 , 91192 Gif sur Yvette Cedex , France
| | - José Avila
- ANTARES Beamline , Synchrotron SOLEIL and Universite Paris-Saclay , L' Orme des Merisiers, Saint Aubin-BP 48 , 91192 Gif sur Yvette Cedex , France
| | - Lukasz Plucinski
- Peter Grünberg Institut (PGI-6) , Forschungszentrum Jülich GmbH , 52425 Jülich , Germany
| | - Tim Wehling
- Institut für Theoretische Physik, Bremen Center for Computational Materials Science , Universität Bremen , Otto-Hahn-Allee 1 , 28359 Bremen , Germany
| | - Alexander Grüneis
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
| | - Thomas Michely
- II. Physikalisches Institut , Universität zu Köln , Zülpicher Straße 77 , 50937 Köln , Germany
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65
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Chen ZY, Qin R. Strong-field nonlinear optical properties of monolayer black phosphorus. NANOSCALE 2019; 11:16377-16383. [PMID: 31436277 DOI: 10.1039/c9nr04895b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Within the past few years, atomically thin black phosphorus (BP) has been demonstrated as a fascinating new 2D material that is promising for novel nanoelectronic and nanophotonic applications, due to its many unique properties such as a direct and widely tunable bandgap, high carrier mobility and remarkable intrinsic in-plane anisotropy. However, its important extreme nonlinear behavior and the ultrafast dynamics of carriers under strong-field excitation have yet to be revealed. Herein, we report nonperturbative high harmonic generation (HHG) in monolayer BP by first-principles simulations. We show that BP exhibits extraordinary HHG properties, with clear advantages over three major types of 2D materials under intensive study, i.e., semimetallic graphene, semiconducting MoS2, and insulating hexagonal boron nitride, in terms of HHG cutoff energy and spectral intensity. This study advances the scope of current research activities on BP into a new regime, suggesting its promising future in the applications of extreme-ultraviolet and attosecond nanophotonics and also opening doors to investigate the strong-field and ultrafast carrier dynamics of this emerging material.
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Affiliation(s)
- Zi-Yu Chen
- National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China.
| | - Rui Qin
- National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China.
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66
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Lian CS, Heil C, Liu X, Si C, Giustino F, Duan W. Coexistence of Superconductivity with Enhanced Charge Density Wave Order in the Two-Dimensional Limit of TaSe 2. J Phys Chem Lett 2019; 10:4076-4081. [PMID: 31276411 DOI: 10.1021/acs.jpclett.9b01480] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Bulk 2H-TaSe2 is a model charge density wave (CDW) metal with superconductivity emerging at extremely low temperature (Tc = 0.1 K). Here, by first-principles calculations including the explicit calculation of the screened Coulomb interaction, we demonstrate enhanced superconductivity in the CDW state of monolayer 1H-TaSe2 observed in recent experiments. Its ground-state 3 × 3 CDW phase features triangular clustering of Ta atoms and possesses a large electron-phonon coupling of λ = 0.74, yielding an order of magnitude higher superconducting Tc compared to the bulk. Upon lowering the thickness from bulk to monolayer TaSe2, the CDW intensifies with slightly decreased Fermi-level density of states, while superconductivity gets boosted via a largely increased intrinsic electron-phonon coupling strength, which overcomes both the CDW effect and naturally reinforced Coulomb repulsion. These results uncover the simultaneously enhanced CDW and superconducting orders in the two-dimensional limit for the first time and have key implications for other CDW metals like 2H-TaS2.
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Affiliation(s)
- Chao-Sheng Lian
- International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering , Zhengzhou University , Zhengzhou 450001 , China
- Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics , Tsinghua University , Beijing 100084 , China
| | - Christoph Heil
- Institute of Theoretical and Computational Physics , Graz University of Technology, NAWI Graz , 8010 Graz , Austria
| | - Xiaoyu Liu
- Institute for Advanced Study , Tsinghua University , Beijing 100084 , China
| | - Chen Si
- School of Materials Science and Engineering , Beihang University , Beijing 100191 , China
| | - Feliciano Giustino
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Wenhui Duan
- Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics , Tsinghua University , Beijing 100084 , China
- Institute for Advanced Study , Tsinghua University , Beijing 100084 , China
- Collaborative Innovation Center of Quantum Matter , Beijing 100084 , China
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67
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Ugeda MM. Stable in harsh environments. NATURE MATERIALS 2019; 18:539-540. [PMID: 31114061 DOI: 10.1038/s41563-019-0351-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Affiliation(s)
- Miguel M Ugeda
- Donostia International Physics Center (DIPC), San Sebastián, Spain.
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68
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Hopkinson DG, Zólyomi V, Rooney AP, Clark N, Terry DJ, Hamer M, Lewis DJ, Allen CS, Kirkland AI, Andreev Y, Kudrynskyi Z, Kovalyuk Z, Patanè A, Fal'ko VI, Gorbachev R, Haigh SJ. Formation and Healing of Defects in Atomically Thin GaSe and InSe. ACS NANO 2019; 13:5112-5123. [PMID: 30946569 DOI: 10.1021/acsnano.8b08253] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two dimensional III-VI metal monochalcogenide materials, such as GaSe and InSe, are attracting considerable attention due to their promising electronic and optoelectronic properties. Here, an investigation of point and extended atomic defects formed in mono-, bi-, and few-layer GaSe and InSe crystals is presented. Using state-of-the-art scanning transmission electron microscopy, it is observed that these materials can form both metal and selenium vacancies under the action of the electron beam. Selenium vacancies are observed to be healable: recovering the perfect lattice structure in the presence of selenium or enabling incorporation of dopant atoms in the presence of impurities. Under prolonged imaging, multiple point defects are observed to coalesce to form extended defect structures, with GaSe generally developing trigonal defects and InSe primarily forming line defects. These insights into atomic behavior could be harnessed to synthesize and tune the properties of 2D post-transition-metal monochalcogenide materials for optoelectronic applications.
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Affiliation(s)
- David G Hopkinson
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Materials , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - Viktor Zólyomi
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - Aidan P Rooney
- School of Materials , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - Nick Clark
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Materials , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - Daniel J Terry
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - Matthew Hamer
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - David J Lewis
- School of Materials , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
| | - Christopher S Allen
- Electron Physical Sciences Imaging Centre , Diamond Light Source Ltd. , Didcot , Oxfordshire OX11 0DE , United Kingdom
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Angus I Kirkland
- Electron Physical Sciences Imaging Centre , Diamond Light Source Ltd. , Didcot , Oxfordshire OX11 0DE , United Kingdom
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Yuri Andreev
- National Tomsk State Research University , 634050 Tomsk , Russian Federation
| | - Zakhar Kudrynskyi
- School of Physics and Astronomy , University of Nottingham , Nottingham NG7 2RD , United Kingdom
| | - Zakhar Kovalyuk
- Institute for Problems of Materials Science , National Academy of Sciences of Ukraine , Chernivtsi Branch, 58001 Chernivtsi , Ukraine
| | - Amalia Patanè
- School of Physics and Astronomy , University of Nottingham , Nottingham NG7 2RD , United Kingdom
| | - Vladimir I Fal'ko
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
- Henry Royce Institute for Advanced Materials , Manchester M13 9PL , United Kingdom
| | - Roman Gorbachev
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
- Henry Royce Institute for Advanced Materials , Manchester M13 9PL , United Kingdom
| | - Sarah J Haigh
- National Graphene Institute , University of Manchester , Booth Street East , Manchester M13 9PL , United Kingdom
- School of Materials , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom
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69
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Pei M, Qian J, Jiang S, Guo J, Yang C, Pan D, Wang Q, Wang X, Shi Y, Li Y. pJ-Level Energy-Consuming, Low-Voltage Ferroelectric Organic Field-Effect Transistor Memories. J Phys Chem Lett 2019; 10:2335-2340. [PMID: 31016982 DOI: 10.1021/acs.jpclett.9b00864] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Ferroelectric organic field-effect transistors (Fe-OFETs) have attracted considerable attention because of their promising potential for memory applications, while a critical issue is the large energy consumption mainly caused by a high operating voltage and slow data switching. Here, we employ ultrathin ferroelectric polymer and semiconducting molecular crystals to create low-voltage Fe-OFET memories. Devices require only pJ-level energy consumption. The writing and erasing processes require ∼1.2 and 1.6 pJ/bit, respectively, and the reading energy is ∼1.9 pJ/bit (on state) and ∼0.2 fJ/bit (off state). Thus, our memories consume only <0.1% of the energy required for devices using bulk functional layers. Besides, our devices also exhibit low contact resistance and steep subthreshold swing. Therefore, we provide a strategy that opens up a path for Fe-OFETs toward emerging applications, such as wearable electronics.
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Affiliation(s)
- Mengjiao Pei
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Jun Qian
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Sai Jiang
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Jianhang Guo
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Chengdong Yang
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Danfeng Pan
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Qijing Wang
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Xinran Wang
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Yi Shi
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
| | - Yun Li
- National Laboratory of Solid-State Microstructures, School of Electronic Science and Engineering, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing , Jiangsu 210093 , People's Republic of China
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70
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Birowska M, Urban J, Baranowski M, Maude DK, Plochocka P, Szwacki NG. The impact of hexagonal boron nitride encapsulation on the structural and vibrational properties of few layer black phosphorus. NANOTECHNOLOGY 2019; 30:195201. [PMID: 30699401 DOI: 10.1088/1361-6528/ab0332] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The encapsulation of two-dimensional layered materials such as black phosphorus is of paramount importance for their stability in air. However, the encapsulation poses several questions, namely, how it affects, via the weak van der Waals forces, the properties of the black phosphorus and whether these properties can be tuned on demand. Prompted by these questions, we have investigated the impact of hexagonal boron nitride encapsulation on the structural and vibrational properties of few layer black phosphorus, using a first-principles method in the framework of density functional theory. We demonstrate that the encapsulation with hexagonal boron nitride imposes biaxial strain on the black phosphorus material, flattening its puckered structure, by decreasing the thickness of the layers via the increase of the puckered angle and the intra-layer P-P bonds. This work exemplifies the evolution of structural parameters in layered materials after the encapsulation process. We find that after encapsulation, phosphorene (single layer black phosphorous) contracts by 1.1% in the armchair direction and stretches by 1.3% in the zigzag direction, whereas few layer black phosphorus mainly expands by up to 3% in the armchair direction. However, these relatively small strains induced by the hexagonal BN, lead to significant changes in the vibrational properties of black phosphorus, with the redshifts of up to 10 cm-1 of the high frequency optical mode A g 1. In general, structural changes induced by the encapsulation process open the door to substrate controlled strain engineering in two-dimensional crystals.
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Affiliation(s)
- Magdalena Birowska
- University of Warsaw, Faculty of Physics, Pasteura 5, 02-093 Warsaw, Poland
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71
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Neupane GP, Zhou K, Chen S, Yildirim T, Zhang P, Lu Y. In-Plane Isotropic/Anisotropic 2D van der Waals Heterostructures for Future Devices. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2019; 15:e1804733. [PMID: 30714302 DOI: 10.1002/smll.201804733] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 12/27/2018] [Indexed: 06/09/2023]
Abstract
Mono- to few-layers of 2D semiconducting materials have uniquely inherent optical, electronic, and magnetic properties that make them ideal for probing fundamental scientific phenomena up to the 2D quantum limit and exploring their emerging technological applications. This Review focuses on the fundamental optoelectronic studies and potential applications of in-plane isotropic/anisotropic 2D semiconducting heterostructures. Strong light-matter interaction, reduced dimensionality, and dielectric screening in mono- to few-layers of 2D semiconducting materials result in strong many-body interactions, leading to the formation of robust quasiparticles such as excitons, trions, and biexcitons. An in-plane isotropic nature leads to the quasi-2D particles, whereas, an anisotropic nature leads to quasi-1D particles. Hence, in-plane isotropic/anisotropic 2D heterostructures lead to the formation of quasi-1D/2D particle systems allowing for the manipulation of high binding energy quasi-1D particle populations for use in a wide variety of applications. This Review emphasizes an exciting 1D-2D particles dynamic in such heterostructures and their potential for high-performance photoemitters and exciton-polariton lasers. Moreover, their scopes are also broadened in thermoelectricity, piezoelectricity, photostriction, energy storage, hydrogen evolution reactions, and chemical sensor fields. The unique in-plane isotropic/anisotropic 2D heterostructures may open the possibility of engineering smart devices in the nanodomain with complex opto-electromechanical functions.
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Affiliation(s)
- Guru Prakash Neupane
- College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518052, Guangdong, China
- Research School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, ACT, 2601, Australia
| | - Kai Zhou
- College of Mechatronics and Control Engineering, Shenzhen University, Nan-hai Ave 3688, Shenzhen, 518060, Guangdong, China
| | - Songsong Chen
- College of Mechatronics and Control Engineering, Shenzhen University, Nan-hai Ave 3688, Shenzhen, 518060, Guangdong, China
| | - Tanju Yildirim
- College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518052, Guangdong, China
| | - Peixin Zhang
- College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518052, Guangdong, China
| | - Yuerui Lu
- College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518052, Guangdong, China
- Research School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, ACT, 2601, Australia
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72
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Hamer MJ, Zultak J, Tyurnina AV, Zólyomi V, Terry D, Barinov A, Garner A, Donoghue J, Rooney AP, Kandyba V, Giampietri A, Graham A, Teutsch N, Xia X, Koperski M, Haigh SJ, Fal'ko VI, Gorbachev RV, Wilson NR. Indirect to Direct Gap Crossover in Two-Dimensional InSe Revealed by Angle-Resolved Photoemission Spectroscopy. ACS NANO 2019; 13:2136-2142. [PMID: 30676744 DOI: 10.1021/acsnano.8b08726] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Atomically thin films of III-VI post-transition metal chalcogenides (InSe and GaSe) form an interesting class of two-dimensional semiconductors that feature a strong variation of their band gap as a function of the number of layers in the crystal and, specifically for InSe, an expected crossover from a direct gap in the bulk to a weakly indirect band gap in monolayers and bilayers. Here, we apply angle-resolved photoemission spectroscopy with submicrometer spatial resolution (μARPES) to visualize the layer-dependent valence band structure of mechanically exfoliated crystals of InSe. We show that for one-layer and two-layer InSe the valence band maxima are away from the Γ-point, forming an indirect gap, with the conduction band edge known to be at the Γ-point. In contrast, for six or more layers the band gap becomes direct, in good agreement with theoretical predictions. The high-quality monolayer and bilayer samples enable us to resolve, in the photoluminescence spectra, the band-edge exciton (A) from the exciton (B) involving holes in a pair of deeper valence bands, degenerate at Γ, with a splitting that agrees with both μARPES data and the results of DFT modeling. Due to the difference in symmetry between these two valence bands, light emitted by the A-exciton should be predominantly polarized perpendicular to the plane of the two-dimensional crystal, which we have verified for few-layer InSe crystals.
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Affiliation(s)
- Matthew J Hamer
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Johanna Zultak
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Anastasia V Tyurnina
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Viktor Zólyomi
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Daniel Terry
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Alexei Barinov
- Elettra - Sincrotrone Trieste , S.C.p.A., Basovizza ( TS ), 34149 , Italy
| | - Alistair Garner
- School of Materials , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Jack Donoghue
- School of Materials , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Aidan P Rooney
- School of Materials , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Viktor Kandyba
- Elettra - Sincrotrone Trieste , S.C.p.A., Basovizza ( TS ), 34149 , Italy
| | - Alessio Giampietri
- Elettra - Sincrotrone Trieste , S.C.p.A., Basovizza ( TS ), 34149 , Italy
| | - Abigail Graham
- Department of Physics , University of Warwick , Coventry , CV4 7AL , U.K
| | - Natalie Teutsch
- Department of Physics , University of Warwick , Coventry , CV4 7AL , U.K
| | - Xue Xia
- Department of Physics , University of Warwick , Coventry , CV4 7AL , U.K
| | - Maciej Koperski
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Sarah J Haigh
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- School of Materials , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
| | - Vladimir I Fal'ko
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- Henry Royce Institute , Oxford Road , Manchester , M13 9PL , U.K
| | - Roman V Gorbachev
- School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- National Graphene Institute , University of Manchester , Oxford Road , Manchester , M13 9PL , U.K
- Henry Royce Institute , Oxford Road , Manchester , M13 9PL , U.K
| | - Neil R Wilson
- Department of Physics , University of Warwick , Coventry , CV4 7AL , U.K
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73
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Wu P, Ameen T, Zhang H, Bendersky L, Ilatikhameneh H, Klimeck G, Rahman R, Davydov AV, Appenzeller J. Complementary Black Phosphorus Tunneling Field-Effect Transistors. ACS NANO 2019; 13:377-385. [PMID: 30563322 PMCID: PMC7292334 DOI: 10.1021/acsnano.8b06441] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Band-to-band tunneling field-effect transistors (TFETs) have emerged as promising candidates for low-power integration circuits beyond conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) and have been demonstrated to overcome the thermionic limit, which results intrinsically in sub-threshold swings of at least 60 mV/dec at room temperature. Here, we demonstrate complementary TFETs based on few-layer black phosphorus, in which multiple top gates create electrostatic doping in the source and drain regions. By electrically tuning the doping types and levels in the source and drain regions, the device can be reconfigured to allow for TFET or MOSFET operation and can be tuned to be n-type or p-type. Owing to the proper choice of materials and careful engineering of device structures, record-high current densities have been achieved in 2D TFETs. Full-band atomistic quantum transport simulations of the fabricated devices agree quantitatively with the current-voltage measurements, which gives credibility to the promising simulation results of ultrascaled phosphorene TFETs. Using atomistic simulations, we project substantial improvements in the performance of the fabricated TFETs when channel thicknesses and oxide thicknesses are scaled down.
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Affiliation(s)
- Peng Wu
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Tarek Ameen
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- Network for Computational Nanotechnology, Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Huairuo Zhang
- Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
- Theiss Research, Inc., La Jolla, California 92037, USA
| | - Leonid Bendersky
- Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
| | - Hesameddin Ilatikhameneh
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- Network for Computational Nanotechnology, Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Gerhard Klimeck
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- Network for Computational Nanotechnology, Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Rajib Rahman
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- Network for Computational Nanotechnology, Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Albert V. Davydov
- Materials Science and Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
| | - Joerg Appenzeller
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
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74
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Wu Y, He J, Liu J, Xing H, Mao Z, Liu Y. Dimensional reduction and ionic gating induced enhancement of superconductivity in atomically thin crystals of 2H-TaSe 2. NANOTECHNOLOGY 2019; 30:035702. [PMID: 30418952 DOI: 10.1088/1361-6528/aaea3b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The effects of dimensional reduction and ion intercalation on superconductivity (SC) in the presence of charge density waves (CDWs) in two-dimensional crystals of 2H-TaSe2 were characterized. We prepared atomically thin crystals by mechanical exfoliation and performed electrical transport measurements on devices made by photolithography. The superconducting transition temperature (T c SC ) was found to increase monotonically as the thickness decreased, changing from 0.14 K in the bulk to higher than 1.4 K for a 3-nm-thick crystal. The temperature dependence of upper critical field was found to be anomalous. The CDW transition temperature (T c CDW ) was found to decrease, but to a less extent than T c SC , from 120 K in the bulk to around 113 K for the 3-nm-thick crystal. In addition, ion intercalation was found to increase T c SC and suppress T c CDW in an atomically thin crystal of 2H-TaSe2. The implications of these findings are discussed. We suggest that dimensional reduction and ion intercalation are potentially effective ways to engineer material properties for layered transition metal chalcogenides.
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Affiliation(s)
- Yueshen Wu
- Key Laboratory of Artificial Structures and Quantum Control and Shanghai Center for Complex Physics, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
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75
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Pseudodoping of a metallic two-dimensional material by the supporting substrate. Nat Commun 2019; 10:180. [PMID: 30643132 PMCID: PMC6331619 DOI: 10.1038/s41467-018-08088-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 12/07/2018] [Indexed: 11/08/2022] Open
Abstract
Charge transfers resulting from weak bondings between two-dimensional materials and the supporting substrates are often tacitly associated with their work function differences. In this context, two-dimensional materials could be normally doped at relatively low levels. Here, we demonstrate how even weak hybridization with substrates can lead to an apparent heavy doping, using the example of monolayer 1H-TaS2 grown on Au(111). Ab-initio calculations show that sizable changes in Fermi areas can arise, while the transferred charge between substrate and two-dimensional material is much smaller than the variation of Fermi areas suggests. This mechanism, which we refer to as pseudodoping, is associated with non-linear energy-dependent shifts of electronic spectra, which our scanning tunneling spectroscopy experiments reveal for clean and defective TaS2 monolayer on Au(111). The influence of pseudodoping on the formation of many-body states in two-dimensional metallic materials is analyzed, shedding light on utilizing pseudodoping to control electronic phase diagrams. Weak hybridization of two-dimensional metallic materials with their substrates plays a crucial role in charge transfer and doping characteristics. Here, the authors report heavy doping of monolayer 1H-TaS2 synthesized on Au(111) by ab-initio calculations and STM/STS experiments.
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76
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Martinez-Castro J, Mauro D, Pásztor Á, Gutiérrez-Lezama I, Scarfato A, Morpurgo AF, Renner C. Scanning Tunneling Microscopy of an Air Sensitive Dichalcogenide Through an Encapsulating Layer. NANO LETTERS 2018; 18:6696-6702. [PMID: 30354173 DOI: 10.1021/acs.nanolett.8b01978] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Many atomically thin exfoliated two-dimensional (2D) materials degrade when exposed to ambient conditions. They can be protected and investigated by means of transport and optical measurements if they are encapsulated between chemically inert single layers in the controlled atmosphere of a glovebox. Here, we demonstrate that the same encapsulation procedure is also compatible with scanning tunneling microscopy (STM) and spectroscopy (STS). To this end, we report a systematic STM/STS investigation of a model system consisting of an exfoliated 2H-NbSe2 crystal capped with a protective 2H-MoS2 monolayer. We observe different electronic coupling between MoS2 and NbSe2 from a strong coupling when their lattices are aligned within a few degrees to essentially no coupling for 30° misaligned layers. We show that STM always probes intrinsic NbSe2 properties such as the superconducting gap and charge density wave at low temperature when setting the tunneling bias inside the MoS2 band gap, irrespective of the relative angle between the NbSe2 and MoS2 lattices. This study demonstrates that encapsulation is fully compatible with STM/STS investigations of 2D materials.
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77
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Tian H, Wang XF, Mohammad MA, Gou GY, Wu F, Yang Y, Ren TL. A hardware Markov chain algorithm realized in a single device for machine learning. Nat Commun 2018; 9:4305. [PMID: 30333492 PMCID: PMC6192990 DOI: 10.1038/s41467-018-06644-w] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2017] [Accepted: 09/18/2018] [Indexed: 11/23/2022] Open
Abstract
There is a growing need for developing machine learning applications. However, implementation of the machine learning algorithm consumes a huge number of transistors or memory devices on-chip. Developing a machine learning capability in a single device has so far remained elusive. Here, we build a Markov chain algorithm in a single device based on the native oxide of two dimensional multilayer tin selenide. After probing the electrical transport in vertical tin oxide/tin selenide/tin oxide heterostructures, two sudden current jumps are observed during the set and reset processes. Furthermore, five filament states are observed. After classifying five filament states into three states of the Markov chain, the probabilities between each states show convergence values after multiple testing cycles. Based on this device, we demo a fixed-probability random number generator within 5% error rate. This work sheds light on a single device as one hardware core with Markov chain algorithm. Despite the need to develop resistive random access memory (RRAM) devices for machine learning, RRAM array-based hardware methods for algorithm require external electronics. Here, the authors realize a Markov chain algorithm in a single 2D multilayer SnSe device without external electronics.
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Affiliation(s)
- He Tian
- Institute of Microelectronics, Tsinghua University, Beijing, 100084, China. .,Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, 100084, China.
| | - Xue-Feng Wang
- Institute of Microelectronics, Tsinghua University, Beijing, 100084, China.,Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, 100084, China
| | - Mohammad Ali Mohammad
- School of Chemical and Materials Engineering (SCME), National University of Sciences and Technology (NUST), Sector H-12, Islamabad, 44000, Pakistan
| | - Guang-Yang Gou
- Institute of Microelectronics, Tsinghua University, Beijing, 100084, China.,Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, 100084, China
| | - Fan Wu
- Institute of Microelectronics, Tsinghua University, Beijing, 100084, China.,Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, 100084, China
| | - Yi Yang
- Institute of Microelectronics, Tsinghua University, Beijing, 100084, China.,Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, 100084, China
| | - Tian-Ling Ren
- Institute of Microelectronics, Tsinghua University, Beijing, 100084, China. .,Beijing National Research Center for Information Science and Technology (BNRist), Tsinghua University, Beijing, 100084, China.
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78
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Lu MY, Chang YT, Chen HJ. Efficient Self-Driven Photodetectors Featuring a Mixed-Dimensional van der Waals Heterojunction Formed from a CdS Nanowire and a MoTe 2 Flake. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1802302. [PMID: 30198180 DOI: 10.1002/smll.201802302] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 07/20/2018] [Indexed: 06/08/2023]
Abstract
Heterojunctions formed from low-dimensional materials can result in photovoltaic and photodetection devices displaying exceptional physical properties and excellent performance. Herein, a mixed-dimensional van der Waals (vdW) heterojunction comprising a 1D n-type Ga-doped CdS nanowire and a 2D p-type MoTe2 flake is demonstrated; the corresponding photovoltaic device exhibits an outstanding conversion efficiency of 15.01% under illumination with white light at 650 µW cm-2 . A potential difference of 80 meV measured, using Kelvin probe force microscopy, at the CdS-MoTe2 interface confirms the separation and accumulation of photoexcited carriers upon illumination. Moreover, the photodetection characteristics of the vdW heterojunction device at zero bias reveal a rapid response time (<50 ms) and a photoresponsivity that are linearly proportional to the power density of the light. Interestingly, the response of the vdW heterojunction device is negligible when illuminated at 580 nm; this exceptional behavior is presumably due to the rapid rate of recombination of the photoexcited carriers of MoTe2 . Such mixed-dimensional vdW heterojunctions appear to be novel design elements for efficient photovoltaic and self-driven photodetection devices.
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Affiliation(s)
- Ming-Yen Lu
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 300, Taiwan
- High Entropy Materials Center, National Tsing Hua University, Hsinchu, 300, Taiwan
| | - Yung-Ting Chang
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 300, Taiwan
| | - Hsin-Ju Chen
- Graduate Institute of Opto-Mechatronics, National Chung Cheng University, Chia-Yi, 62102, Taiwan
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79
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Clark N, Nguyen L, Hamer MJ, Schedin F, Lewis EA, Prestat E, Garner A, Cao Y, Zhu M, Kashtiban R, Sloan J, Kepaptsoglou D, Gorbachev RV, Haigh SJ. Scalable Patterning of Encapsulated Black Phosphorus. NANO LETTERS 2018; 18:5373-5381. [PMID: 30067903 PMCID: PMC6265956 DOI: 10.1021/acs.nanolett.8b00946] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 07/27/2018] [Indexed: 05/22/2023]
Abstract
Atomically thin black phosphorus (BP) has attracted considerable interest due to its unique properties, such as an infrared band gap that depends on the number of layers and excellent electronic transport characteristics. This material is known to be sensitive to light and oxygen and degrades in air unless protected with an encapsulation barrier, limiting its exploitation in electrical devices. We present a new scalable technique for nanopatterning few layered BP by direct electron beam exposure of encapsulated crystals, achieving a spatial resolution down to 6 nm. By encapsulating the BP with single layer graphene or hexagonal boron nitride (hBN), we show that a focused electron probe can be used to produce controllable local oxidation of BP through nanometre size defects created in the encapsulation layer by the electron impact. We have tested the approach in the scanning transmission electron microscope (STEM) and using industry standard electron beam lithography (EBL). Etched regions of the BP are stabilized by a thin passivation layer and demonstrate typical insulating behavior as measured at 300 and 4.3 K. This new scalable approach to nanopatterning of thin air sensitive crystals has the potential to facilitate their wider use for a variety of sensing and electronics applications.
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Affiliation(s)
- Nick Clark
- School
of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
| | - Lan Nguyen
- School
of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
| | - Matthew J. Hamer
- School
of Physics and Astronomy, University of
Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom
| | - Fredrik Schedin
- National
Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
| | - Edward A. Lewis
- School
of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
| | - Eric Prestat
- School
of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
| | - Alistair Garner
- School
of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
| | - Yang Cao
- School
of Physics and Astronomy, University of
Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom
| | - Mengjian Zhu
- School
of Physics and Astronomy, University of
Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom
| | - Reza Kashtiban
- Department
of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - Jeremy Sloan
- Department
of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - Demie Kepaptsoglou
- SuperSTEM
Laboratory, STFC Daresbury Campus, Daresbury, WA4 4AD, United Kingdom
| | - Roman V. Gorbachev
- School
of Physics and Astronomy, University of
Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom
- (R.V.G.) E-mail:
| | - Sarah J. Haigh
- School
of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United
Kingdom
- (S.J.H.) E-mail:
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80
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Bertolazzi S, Gobbi M, Zhao Y, Backes C, Samorì P. Molecular chemistry approaches for tuning the properties of two-dimensional transition metal dichalcogenides. Chem Soc Rev 2018; 47:6845-6888. [PMID: 30043037 DOI: 10.1039/c8cs00169c] [Citation(s) in RCA: 118] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Two-dimensional (2D) semiconductors, such as ultrathin layers of transition metal dichalcogenides (TMDs), offer a unique combination of electronic, optical and mechanical properties, and hold potential to enable a host of new device applications spanning from flexible/wearable (opto)electronics to energy-harvesting and sensing technologies. A critical requirement for developing practical and reliable electronic devices based on semiconducting TMDs consists in achieving a full control over their charge-carrier polarity and doping. Inconveniently, such a challenging task cannot be accomplished by means of well-established doping techniques (e.g. ion implantation and diffusion), which unavoidably damage the 2D crystals resulting in degraded device performances. Nowadays, a number of alternatives are being investigated, including various (supra)molecular chemistry approaches relying on the combination of 2D semiconductors with electroactive donor/acceptor molecules. As yet, a large variety of molecular systems have been utilized for functionalizing 2D TMDs via both covalent and non-covalent interactions. Such research endeavours enabled not only the tuning of the charge-carrier doping but also the engineering of the optical, electronic, magnetic, thermal and sensing properties of semiconducting TMDs for specific device applications. Here, we will review the most enlightening recent advancements in experimental (supra)molecular chemistry methods for tailoring the properties of atomically-thin TMDs - in the form of substrate-supported or solution-dispersed nanosheets - and we will discuss the opportunities and the challenges towards the realization of novel hybrid materials and devices based on 2D semiconductors and molecular systems.
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Affiliation(s)
- Simone Bertolazzi
- Université de Strasbourg, CNRS, ISIS, 8 alleé Gaspard Monge, 67000 Strasbourg, France.
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81
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Ponomarev E, Ubrig N, Gutiérrez-Lezama I, Berger H, Morpurgo AF. Semiconducting van der Waals Interfaces as Artificial Semiconductors. NANO LETTERS 2018; 18:5146-5152. [PMID: 30001136 DOI: 10.1021/acs.nanolett.8b02066] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Recent technical progress demonstrates the possibility of stacking together virtually any combination of atomically thin crystals of van der Waals bonded compounds to form new types of heterostructures and interfaces. As a result, there is the need to understand at a quantitative level how the interfacial properties are determined by the properties of the constituent 2D materials. We address this problem by studying the transport and optoelectronic response of two different interfaces based on transition-metal dichalcogenide monolayers, namely WSe2-MoSe2 and WSe2-MoS2. By exploiting the spectroscopic capabilities of ionic liquid gated transistors, we show how the conduction and valence bands of the individual monolayers determine the bands of the interface, and we establish quantitatively (directly from the measurements) the energetic alignment of the bands in the different materials as well as the magnitude of the interfacial band gap. Photoluminescence and photocurrent measurements allow us to conclude that the band gap of the WSe2-MoSe2 interface is direct in k space, whereas the gap of WSe2/MoS2 is indirect. For WSe2/MoSe2, we detect the light emitted from the decay of interlayer excitons and determine experimentally their binding energy using the values of the interfacial band gap extracted from transport measurements. The technique that we employed to reach this conclusion demonstrates a rather-general strategy for characterizing quantitatively the interfacial properties in terms of the properties of the constituent atomic layers. The results presented here further illustrate how van der Waals interfaces of two distinct 2D semiconducting materials are composite systems that truly behave as artificial semiconductors, the properties of which can be deterministically defined by the selection of the appropriate constituent semiconducting monolayers.
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Affiliation(s)
- Evgeniy Ponomarev
- DQMP and GAP , Université de Genéve , 24 quai Ernest Ansermet , CH-1211 Geneva , Switzerland
| | - Nicolas Ubrig
- DQMP and GAP , Université de Genéve , 24 quai Ernest Ansermet , CH-1211 Geneva , Switzerland
| | | | - Helmuth Berger
- Institut de Physique de la Matiére Complexe , EPFL , CCH-1015 Lausanne , Switzerland
| | - Alberto F Morpurgo
- DQMP and GAP , Université de Genéve , 24 quai Ernest Ansermet , CH-1211 Geneva , Switzerland
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82
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Kim HH, Yang B, Patel T, Sfigakis F, Li C, Tian S, Lei H, Tsen AW. One Million Percent Tunnel Magnetoresistance in a Magnetic van der Waals Heterostructure. NANO LETTERS 2018; 18:4885-4890. [PMID: 30001134 DOI: 10.1021/acs.nanolett.8b01552] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We report the observation of a very large negative magnetoresistance effect in a van der Waals tunnel junction incorporating a thin magnetic semiconductor, CrI3, as the active layer. At constant voltage bias, current increases by nearly one million percent upon application of a 2 T field. The effect arises from a change between antiparallel to parallel alignment of spins across the different CrI3 layers. Our results elucidate the nature of the magnetic state in ultrathin CrI3 and present new opportunities for spintronics based on two-dimensional materials.
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Affiliation(s)
- Hyun Ho Kim
- Institute for Quantum Computing , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
- Department of Chemistry , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
| | - Bowen Yang
- Institute for Quantum Computing , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
- Department of Physics and Astronomy , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
| | - Tarun Patel
- Institute for Quantum Computing , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
- Department of Physics and Astronomy , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
| | - Francois Sfigakis
- Institute for Quantum Computing , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
- Department of Chemistry , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
| | - Chenghe Li
- Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices , Renmin University of China , Beijing 100872 , China
| | - Shangjie Tian
- Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices , Renmin University of China , Beijing 100872 , China
| | - Hechang Lei
- Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices , Renmin University of China , Beijing 100872 , China
| | - Adam W Tsen
- Institute for Quantum Computing , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
- Department of Chemistry , University of Waterloo , Waterloo , Ontario N2L 3G1 , Canada
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83
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Pham T, Oh S, Stetz P, Onishi S, Kisielowski C, Cohen ML, Zettl A. Torsional instability in the single-chain limit of a transition metal trichalcogenide. Science 2018; 361:263-266. [DOI: 10.1126/science.aat4749] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Accepted: 05/16/2018] [Indexed: 12/14/2022]
Affiliation(s)
- Thang Pham
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA
- Kavli Energy NanoSciences Institute, University of California, Berkeley, CA 94720, USA
| | - Sehoon Oh
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Patrick Stetz
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Kavli Energy NanoSciences Institute, University of California, Berkeley, CA 94720, USA
| | - Seita Onishi
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Kavli Energy NanoSciences Institute, University of California, Berkeley, CA 94720, USA
| | - Christian Kisielowski
- Molecular Foundry and Joint Center for Artificial Photosynthesis, Berkeley, CA 94720, USA
| | - Marvin L. Cohen
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Alex Zettl
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Kavli Energy NanoSciences Institute, University of California, Berkeley, CA 94720, USA
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84
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Jain A, Bharadwaj P, Heeg S, Parzefall M, Taniguchi T, Watanabe K, Novotny L. Minimizing residues and strain in 2D materials transferred from PDMS. NANOTECHNOLOGY 2018; 29:265203. [PMID: 29644983 DOI: 10.1088/1361-6528/aabd90] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Integrating layered two-dimensional (2D) materials into 3D heterostructures offers opportunities for novel material functionalities and applications in electronics and photonics. In order to build the highest quality heterostructures, it is crucial to preserve the cleanliness and morphology of 2D material surfaces that come in contact with polymers such as PDMS during transfer. Here we report that substantial residues and up to ∼0.22% compressive strain can be present in monolayer MoS2 transferred using PDMS. We show that a UV-ozone pre-cleaning of the PDMS surface before exfoliation significantly reduces organic residues on transferred MoS2 flakes. An additional 200 ◦C vacuum anneal after transfer efficiently removes interfacial bubbles and wrinkles as well as accumulated strain, thereby restoring the surface morphology of transferred flakes to their native state. Our recipe is important for building clean heterostructures of 2D materials and increasing the reproducibility and reliability of devices based on them.
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Affiliation(s)
- Achint Jain
- Photonics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
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85
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Sohn E, Xi X, He WY, Jiang S, Wang Z, Kang K, Park JH, Berger H, Forró L, Law KT, Shan J, Mak KF. An unusual continuous paramagnetic-limited superconducting phase transition in 2D NbSe 2. NATURE MATERIALS 2018; 17:504-508. [PMID: 29713039 DOI: 10.1038/s41563-018-0061-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 03/16/2018] [Indexed: 06/08/2023]
Abstract
Time reversal and spatial inversion are two key symmetries for conventional Bardeen-Cooper-Schrieffer (BCS) superconductivity 1 . Breaking inversion symmetry can lead to mixed-parity Cooper pairing and unconventional superconducting properties1-5. Two-dimensional (2D) NbSe2 has emerged as a new non-centrosymmetric superconductor with the unique out-of-plane or Ising spin-orbit coupling (SOC)6-9. Here we report the observation of an unusual continuous paramagnetic-limited superconductor-normal metal transition in 2D NbSe2. Using tunelling spectroscopy under high in-plane magnetic fields, we observe a continuous closing of the superconducting gap at the upper critical field at low temperatures, in stark contrast to the abrupt first-order transition observed in BCS thin-film superconductors10-12. The paramagnetic-limited continuous transition arises from a large spin susceptibility of the superconducting phase due to the Ising SOC. The result is further supported by self-consistent mean-field calculations based on the ab initio band structure of 2D NbSe2. Our findings establish 2D NbSe2 as a promising platform to explore novel spin-dependent superconducting phenomena and device concepts 1 , such as equal-spin Andreev reflection 13 and topological superconductivity14-16.
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Affiliation(s)
- Egon Sohn
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Xiaoxiang Xi
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Wen-Yu He
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Shengwei Jiang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Zefang Wang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Kaifei Kang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Ju-Hyun Park
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - Helmuth Berger
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - László Forró
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Kam Tuen Law
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Jie Shan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
| | - Kin Fai Mak
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
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86
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Frisenda R, Molina-Mendoza AJ, Mueller T, Castellanos-Gomez A, van der Zant HSJ. Atomically thin p-n junctions based on two-dimensional materials. Chem Soc Rev 2018; 47:3339-3358. [PMID: 29683464 DOI: 10.1039/c7cs00880e] [Citation(s) in RCA: 90] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Recent research in two-dimensional (2D) materials has boosted a renovated interest in the p-n junction, one of the oldest electrical components which can be used in electronics and optoelectronics. 2D materials offer remarkable flexibility to design novel p-n junction device architectures, not possible with conventional bulk semiconductors. In this Review we thoroughly describe the different 2D p-n junction geometries studied so far, focusing on vertical (out-of-plane) and lateral (in-plane) 2D junctions and on mixed-dimensional junctions. We discuss the assembly methods developed to fabricate 2D p-n junctions making a distinction between top-down and bottom-up approaches. We also revise the literature studying the different applications of these atomically thin p-n junctions in electronic and optoelectronic devices. We discuss experiments on 2D p-n junctions used as current rectifiers, photodetectors, solar cells and light emitting devices. The important electronics and optoelectronics parameters of the discussed devices are listed in a table to facilitate their comparison. We conclude the Review with a critical discussion about the future outlook and challenges of this incipient research field.
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Affiliation(s)
- Riccardo Frisenda
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus de Cantoblanco, E-28049 Madrid, Spain.
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87
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Abate Y, Akinwande D, Gamage S, Wang H, Snure M, Poudel N, Cronin SB. Recent Progress on Stability and Passivation of Black Phosphorus. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1704749. [PMID: 29749007 DOI: 10.1002/adma.201704749] [Citation(s) in RCA: 119] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2017] [Revised: 12/29/2017] [Indexed: 05/08/2023]
Abstract
From a fundamental science perspective, black phosphorus (BP) is a canonical example of a material that possesses fascinating surface and electronic properties. It has extraordinary in-plane anisotropic electrical, optical, and vibrational states, as well as a tunable band gap. However, instability of the surface due to chemical degradation in ambient conditions remains a major impediment to its prospective applications. Early studies were limited by the degradation of black phosphorous surfaces in air. Recently, several robust strategies have been developed to mitigate these issues, and these novel developments can potentially allow researchers to exploit the extraordinary properties of this material and devices made out of it. Here, the fundamental chemistry of BP degradation and the tremendous progress made to address this issue are extensively reviewed. Device performances of encapsulated BP are also compared with nonencapsulated BP. In addition, BP possesses sensitive anisotropic photophysical surface properties such as excitons, surface plasmons/phonons, and topologically protected and Dirac semi-metallic surface states. Ambient degradation as well as any passivation method used to protect the surface could affect the intrinsic surface properties of BP. These properties and the extent of their modifications by both the degradation and passivation are reviewed.
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Affiliation(s)
- Yohannes Abate
- Department of Physics and Astronomy, University of Georgia, Athens, GA, 30602, USA
| | - Deji Akinwande
- Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, TX, 78758, USA
| | - Sampath Gamage
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA
| | - Han Wang
- Viterbi School of Engineering University of Southern California, Los Angeles, CA, 90089, USA
| | - Michael Snure
- Air Force Research Laboratory, Wright Patterson Air Force Base, OH, 45433, USA
| | - Nirakar Poudel
- Viterbi School of Engineering University of Southern California, Los Angeles, CA, 90089, USA
| | - Stephen B Cronin
- Viterbi School of Engineering University of Southern California, Los Angeles, CA, 90089, USA
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88
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Lian CS, Si C, Duan W. Unveiling Charge-Density Wave, Superconductivity, and Their Competitive Nature in Two-Dimensional NbSe 2. NANO LETTERS 2018; 18:2924-2929. [PMID: 29652158 DOI: 10.1021/acs.nanolett.8b00237] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Recently, charge-density wave (CDW) and superconductivity are observed to coexist in atomically thin metallic NbSe2. Lacking of knowledge on the structural details of CDW, however, prevents us to explore its interplay with superconductivity. Using first-principles calculations, we identify the ground state 3 × 3 CDW atomic structure of monolayer NbSe2, which is characterized by the formation of triangular Nb clusters and shows a scanning tunnelling microscopy (STM) image and Raman CDW modes in good agreement with experiments. We further demonstrate that from bulk to monolayer NbSe2, as the layer thickness decreases, the CDW order is gradually enhanced with rising energy gain and strengthened Fermi surface gapping, while superconductivity is weakened due to the increasingly reduced Fermi level density of states in the CDW state. These results well explain the observed opposite thickness dependencies of CDW and superconducting transition temperatures and uncover the nature of competitive interaction between the two collective orders in two-dimensional NbSe2.
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Affiliation(s)
- Chao-Sheng Lian
- Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics , Tsinghua University , Beijing 100084 , People's Republic of China
| | - Chen Si
- School of Materials Science and Engineering , Beihang University , Beijing 100191 , People's Republic of China
| | - Wenhui Duan
- Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics , Tsinghua University , Beijing 100084 , People's Republic of China
- Collaborative Innovation Center of Quantum Matter , Beijing 100084 , People's Republic of China
- Institute for Advanced Study , Tsinghua University , Beijing 100084 , People's Republic of China
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89
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Shen W, Hu C, Tao J, Liu J, Fan S, Wei Y, An C, Chen J, Wu S, Li Y, Liu J, Zhang D, Sun L, Hu X. Resolving the optical anisotropy of low-symmetry 2D materials. NANOSCALE 2018; 10:8329-8337. [PMID: 29687795 DOI: 10.1039/c7nr09173g] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Optical anisotropy is one of the most fundamental physical characteristics of emerging low-symmetry two-dimensional (2D) materials. It provides abundant structural information and is crucial for creating diverse nanoscale devices. Here, we have proposed an azimuth-resolved microscopic approach to directly resolve the normalized optical difference along two orthogonal directions at normal incidence. The differential principle ensures that the approach is only sensitive to anisotropic samples and immune to isotropic materials. We studied the optical anisotropy of bare and encapsulated black phosphorus (BP) and unveiled the interference effect on optical anisotropy, which is critical for practical applications in optical and optoelectronic devices. A multi-phase model based on the scattering matrix method was developed to account for the interference effect and then the crystallographic directions were unambiguously determined. Our result also suggests that the optical anisotropy is a probe to measure the thickness with monolayer resolution. Furthermore, the optical anisotropy of rhenium disulfide (ReS2), another class of anisotropic 2D materials, with a 1T distorted crystal structure, was investigated, which demonstrates that our approach is suitable for other anisotropic 2D materials. This technique is ideal for optical anisotropy characterization and will inspire future efforts in BP and related anisotropic 2D nanomaterials for engineering new conceptual nanodevices.
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Affiliation(s)
- Wanfu Shen
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, No. 92 Weijin Road, CN-300072 Tianjin, China.
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90
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Masubuchi S, Morimoto M, Morikawa S, Onodera M, Asakawa Y, Watanabe K, Taniguchi T, Machida T. Autonomous robotic searching and assembly of two-dimensional crystals to build van der Waals superlattices. Nat Commun 2018; 9:1413. [PMID: 29650955 PMCID: PMC5897399 DOI: 10.1038/s41467-018-03723-w] [Citation(s) in RCA: 76] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2017] [Accepted: 03/08/2018] [Indexed: 11/09/2022] Open
Abstract
Van der Waals heterostructures are comprised of stacked atomically thin two-dimensional crystals and serve as novel materials providing unprecedented properties. However, the random natures in positions and shapes of exfoliated two-dimensional crystals have required the repetitive manual tasks of optical microscopy-based searching and mechanical transferring, thereby severely limiting the complexity of heterostructures. To solve the problem, here we develop a robotic system that searches exfoliated two-dimensional crystals and assembles them into superlattices inside the glovebox. The system can autonomously detect 400 monolayer graphene flakes per hour with a small error rate (<7%) and stack four cycles of the designated two-dimensional crystals per hour with few minutes of human intervention for each stack cycle. The system enabled fabrication of the superlattice consisting of 29 alternating layers of the graphene and the hexagonal boron nitride. This capacity provides a scalable approach for prototyping a variety of van der Waals superlattices.
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Affiliation(s)
- Satoru Masubuchi
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan.
| | - Masataka Morimoto
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
| | - Sei Morikawa
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
| | - Momoko Onodera
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
| | - Yuta Asakawa
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan
| | - Tomoki Machida
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8505, Japan.
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91
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de la Barrera SC, Sinko MR, Gopalan DP, Sivadas N, Seyler KL, Watanabe K, Taniguchi T, Tsen AW, Xu X, Xiao D, Hunt BM. Tuning Ising superconductivity with layer and spin-orbit coupling in two-dimensional transition-metal dichalcogenides. Nat Commun 2018; 9:1427. [PMID: 29650994 PMCID: PMC5897486 DOI: 10.1038/s41467-018-03888-4] [Citation(s) in RCA: 84] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 03/20/2018] [Indexed: 12/01/2022] Open
Abstract
Systems simultaneously exhibiting superconductivity and spin–orbit coupling are predicted to provide a route toward topological superconductivity and unconventional electron pairing, driving significant contemporary interest in these materials. Monolayer transition-metal dichalcogenide (TMD) superconductors in particular lack inversion symmetry, yielding an antisymmetric form of spin–orbit coupling that admits both spin-singlet and spin-triplet components of the superconducting wavefunction. Here, we present an experimental and theoretical study of two intrinsic TMD superconductors with large spin–orbit coupling in the atomic layer limit, metallic 2H-TaS2 and 2H-NbSe2. We investigate the superconducting properties as the material is reduced to monolayer thickness and show that high-field measurements point to the largest upper critical field thus reported for an intrinsic TMD superconductor. In few-layer samples, we find the enhancement of the upper critical field is sustained by the dominance of spin–orbit coupling over weak interlayer coupling, providing additional candidate systems for supporting unconventional superconducting states in two dimensions. Monolayer transition-metal dichalcogenide (TMD) is promising to host features of topological superconductivity. Here, de la Barrera et al. study layered compounds, 2H-TaS2 and 2H-NbSe2, in their atomic layer limit and find a largest upper critical field for an intrinsic TMD superconductor.
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Affiliation(s)
| | - Michael R Sinko
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Devashish P Gopalan
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Nikhil Sivadas
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA.,School of Applied and Engineering Physics, Cornell University, Ithaca, NY, 14853, USA
| | - Kyle L Seyler
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - Adam W Tsen
- Institute for Quantum Computing and Department of Chemistry, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, 98195, USA.,Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
| | - Di Xiao
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Benjamin M Hunt
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA.
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92
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Wu S, Fatemi V, Gibson QD, Watanabe K, Taniguchi T, Cava RJ, Jarillo-Herrero P. Observation of the quantum spin Hall effect up to 100 kelvin in a monolayer crystal. Science 2018; 359:76-79. [PMID: 29302010 DOI: 10.1126/science.aan6003] [Citation(s) in RCA: 486] [Impact Index Per Article: 81.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2017] [Accepted: 11/17/2017] [Indexed: 12/14/2022]
Abstract
A variety of monolayer crystals have been proposed to be two-dimensional topological insulators exhibiting the quantum spin Hall effect (QSHE), possibly even at high temperatures. Here we report the observation of the QSHE in monolayer tungsten ditelluride (WTe2) at temperatures up to 100 kelvin. In the short-edge limit, the monolayer exhibits the hallmark transport conductance, ~e2/h per edge, where e is the electron charge and h is Planck's constant. Moreover, a magnetic field suppresses the conductance, and the observed Zeeman-type gap indicates the existence of a Kramers degenerate point and the importance of time-reversal symmetry for protection from elastic backscattering. Our results establish the QSHE at temperatures much higher than in semiconductor heterostructures and allow for exploring topological phases in atomically thin crystals.
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Affiliation(s)
- Sanfeng Wu
- Department of Physics, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA.
| | - Valla Fatemi
- Department of Physics, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA.
| | - Quinn D Gibson
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Robert J Cava
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Pablo Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
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93
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He Z, Yang Y, Liu JW, Yu SH. Emerging tellurium nanostructures: controllable synthesis and their applications. Chem Soc Rev 2018; 46:2732-2753. [PMID: 28425532 DOI: 10.1039/c7cs00013h] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Tellurium (Te) is a rare element in trace amounts of about one part per billion, comparable to that of platinum and ranked 75th in the abundance of the elements in the earth crust. Te nanostructures, as narrow bandgap semiconductors, have numerous potential applications in the fabrication of many modern devices. The past decades have witnessed an explosion in new strategies for synthesizing diverse emerging Te nanostructures with controlled compositions, sizes, shapes, and structures. Their structure-determined nature makes functional Te nanomaterials an attractive candidate for modern applications. This review focuses on the synthesis and morphology control of emerging Te nanostructures and summarizes the latest developments in the applications of Te nanostructures, such as their use as chemical transformation templates to access a huge family of nanowires/nanotubes, batteries, photodetectors, ion detection and removal, element doping, piezoelectric energy harvesting, gas sensing, thermoelectric devices and many other device applications. Various Te nanostructures with different shapes and structures will exploit the beneficial properties associated with their assembly process and nanofabrication. Finally, the prospects for future applications of Te nanomaterials are summarized and highlighted.
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Affiliation(s)
- Zhen He
- Division of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Collaborative Innovation Center of Suzhou Nano Science and Technology, Hefei Science Centre, CAS, CAS Center for Excellence in Nanoscience, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
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94
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Solís-Fernández P, Bissett M, Ago H. Synthesis, structure and applications of graphene-based 2D heterostructures. Chem Soc Rev 2018; 46:4572-4613. [PMID: 28691726 DOI: 10.1039/c7cs00160f] [Citation(s) in RCA: 100] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
With the profuse amount of two-dimensional (2D) materials discovered and the improvements in their synthesis and handling, the field of 2D heterostructures has gained increased interest in recent years. Such heterostructures not only overcome the inherent limitations of each of the materials, but also allow the realization of novel properties by their proper combination. The physical and mechanical properties of graphene mean it has a prominent place in the area of 2D heterostructures. In this review, we will discuss the evolution and current state in the synthesis and applications of graphene-based 2D heterostructures. In addition to stacked and in-plane heterostructures with other 2D materials and their potential applications, we will also cover heterostructures realized with lower dimensionality materials, along with intercalation in few-layer graphene as a special case of a heterostructure. Finally, graphene heterostructures produced using liquid phase exfoliation techniques and their applications to energy storage will be reviewed.
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95
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Lewis EA, Brent JR, Derby B, Haigh SJ, Lewis DJ. Solution processing of two-dimensional black phosphorus. Chem Commun (Camb) 2018; 53:1445-1458. [PMID: 28054045 DOI: 10.1039/c6cc09658a] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Phosphorene, or two-dimensional (2D) black phosphorus (BP) was the first synthetic 2D elemental allotrope beyond graphene to be isolated and studied. It is useful due to its high p-type carrier mobility and direct band gap that is tunable in the range ca. 0.3-2 eV thus bridging the energy gap between graphene and transition metal dichalcogenides such as molybdenum disulfide. Beyond the 'Scotch-Tape' method that was used to isolate the first samples of 2D BP for prototype studies, a range of potentially scalable solution processing techniques emerged later that can produce electronics grade material. This feature article focuses on such solution-process routes to 2D BP and highlights challenges in processing the material, mainly caused by its susceptibility to oxidation, as well as illuminating new avenues and opportunities in the area.
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Affiliation(s)
- Edward A Lewis
- School of Materials, University of Manchester, M13 9PL, UK.
| | - Jack R Brent
- School of Materials, University of Manchester, M13 9PL, UK.
| | - Brian Derby
- School of Materials, University of Manchester, M13 9PL, UK.
| | - Sarah J Haigh
- School of Materials, University of Manchester, M13 9PL, UK.
| | - David J Lewis
- School of Materials, University of Manchester, M13 9PL, UK.
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96
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Frisenda R, Navarro-Moratalla E, Gant P, Pérez De Lara D, Jarillo-Herrero P, Gorbachev RV, Castellanos-Gomez A. Recent progress in the assembly of nanodevices and van der Waals heterostructures by deterministic placement of 2D materials. Chem Soc Rev 2018; 47:53-68. [PMID: 29111548 DOI: 10.1039/c7cs00556c] [Citation(s) in RCA: 218] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Designer heterostructures can now be assembled layer-by-layer with unmatched precision thanks to the recently developed deterministic placement methods to transfer two-dimensional (2D) materials. This possibility constitutes the birth of a very active research field on the so-called van der Waals heterostructures. Moreover, these deterministic placement methods also open the door to fabricate complex devices, which would be otherwise very difficult to achieve by conventional bottom-up nanofabrication approaches, and to fabricate fully-encapsulated devices with exquisite electronic properties. The integration of 2D materials with existing technologies such as photonic and superconducting waveguides and fiber optics is another exciting possibility. Here, we review the state-of-the-art of the deterministic placement methods, describing and comparing the different alternative methods available in the literature, and we illustrate their potential to fabricate van der Waals heterostructures, to integrate 2D materials into complex devices and to fabricate artificial bilayer structures where the layers present a user-defined rotational twisting angle.
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Affiliation(s)
- Riccardo Frisenda
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia), Madrid, E-28049, Spain.
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97
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Quantum phase transitions in highly crystalline two-dimensional superconductors. Nat Commun 2018; 9:778. [PMID: 29472627 PMCID: PMC5823914 DOI: 10.1038/s41467-018-03275-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Accepted: 02/01/2018] [Indexed: 11/09/2022] Open
Abstract
Superconductor-insulator transition is one of the remarkable phenomena driven by quantum fluctuation in two-dimensional (2D) systems. Such a quantum phase transition (QPT) was investigated predominantly on highly disordered thin films with amorphous or granular structures using scaling law with constant exponents. Here, we provide a totally different view of QPT in highly crystalline 2D superconductors. According to the magneto-transport measurements in 2D superconducting ZrNCl and MoS2, we found that the quantum metallic state commonly observed at low magnetic fields is converted via the quantum Griffiths state to the weakly localized metal at high magnetic fields. The scaling behavior, characterized by the diverging dynamical critical exponent (Griffiths singularity), indicates that the quantum fluctuation manifests itself as superconducting puddles, in marked contrast to the thermal fluctuation. We suggest that an evolution from the quantum metallic to the quantum Griffiths state is generic nature in highly crystalline 2D superconductors with weak pinning potentials.
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98
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Telford EJ, Benyamini A, Rhodes D, Wang D, Jung Y, Zangiabadi A, Watanabe K, Taniguchi T, Jia S, Barmak K, Pasupathy AN, Dean CR, Hone J. Via Method for Lithography Free Contact and Preservation of 2D Materials. NANO LETTERS 2018; 18:1416-1420. [PMID: 29385346 DOI: 10.1021/acs.nanolett.7b05161] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Atomically thin 2D materials span the common components of electronic circuits as metals, semiconductors, and insulators, and can manifest correlated phases such as superconductivity, charge density waves, and magnetism. An ongoing challenge in the field is to incorporate these 2D materials into multilayer heterostructures with robust electrical contacts while preventing disorder and degradation. In particular, preserving and studying air-sensitive 2D materials has presented a significant challenge since they readily oxidize under atmospheric conditions. We report a new technique for contacting 2D materials, in which metal via contacts are integrated into flakes of insulating hexagonal boron nitride, and then placed onto the desired conducting 2D layer, avoiding direct lithographic patterning onto the 2D conductor. The metal contacts are planar with the bottom surface of the boron nitride and form robust contacts to multiple 2D materials. These structures protect air-sensitive 2D materials for months with no degradation in performance. This via contact technique will provide the capability to produce "atomic printed circuit boards" that can form the basis of more complex multilayer heterostructures.
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Affiliation(s)
- Evan J Telford
- Department of Physics, Columbia University , New York, New York 10027, United States
| | - Avishai Benyamini
- Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States
| | - Daniel Rhodes
- Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States
| | - Da Wang
- Department of Physics, Columbia University , New York, New York 10027, United States
| | - Younghun Jung
- Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States
| | - Amirali Zangiabadi
- Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States
| | - Kenji Watanabe
- National Institute for Materials Science , 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science , 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Shuang Jia
- International Center for Quantum Materials, School of Physics, Peking University , Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter , Beijing 100871, China
| | - Katayun Barmak
- Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States
| | - Abhay N Pasupathy
- Department of Physics, Columbia University , New York, New York 10027, United States
| | - Cory R Dean
- Department of Physics, Columbia University , New York, New York 10027, United States
| | - James Hone
- Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States
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99
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Tan SJR, Abdelwahab I, Chu L, Poh SM, Liu Y, Lu J, Chen W, Loh KP. Quasi-Monolayer Black Phosphorus with High Mobility and Air Stability. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:1704619. [PMID: 29314299 DOI: 10.1002/adma.201704619] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 10/13/2017] [Indexed: 05/28/2023]
Abstract
Black phosphorus (BP) exhibits thickness-dependent band gap and high electronic mobility. The chemical intercalation of BP with alkali metal has attracted attention recently due to the generation of universal superconductivity regardless of the type of alkali metals. However, both ultrathin BP, as well as alkali metal-intercalated BP, are highly unstable and corrode rapidly under ambient conditions. This study demonstrates that alkali metal hydride intercalation decouples monolayer to few layers BP from the bulk BP, allowing an optical gap of ≈1.7 eV and an electronic gap of 1.98 eV to be measured by photoluminescence and electron energy loss spectroscopy at the intercalated regions. Raman and transport measurements confirm that chemically intercalated BP exhibits enhanced stability, while maintaining a high hole mobility of up to ≈800 cm2 V-1 s-1 and on/off ratio exceeding 103 . The use of alkali metal hydrides as intercalants should be applicable to a wide range of layered 2D materials and pave the way for generating highly stable, quasi-monolayer 2D materials.
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Affiliation(s)
- Sherman Jun Rong Tan
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
| | - Ibrahim Abdelwahab
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
| | - Leiqiang Chu
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
| | - Sock Mui Poh
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
| | - Yanpeng Liu
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
| | - Jiong Lu
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
| | - Wei Chen
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
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100
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Zhang S, Guo S, Chen Z, Wang Y, Gao H, Gómez-Herrero J, Ares P, Zamora F, Zhu Z, Zeng H. Recent progress in 2D group-VA semiconductors: from theory to experiment. Chem Soc Rev 2018; 47:982-1021. [DOI: 10.1039/c7cs00125h] [Citation(s) in RCA: 595] [Impact Index Per Article: 99.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This review provides recent theoretical and experimental progress in the fundamental properties, electronic modulations, fabrications and applications of 2D group-VA materials.
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Affiliation(s)
- Shengli Zhang
- MIIT Key Laboratory of Advanced Display Materials and Devices
- Ministry of Industry and Information Technology
- Institute of Optoelectronics & Nanomaterials
- Nanjing University of Science and Technology
- Nanjing
| | - Shiying Guo
- MIIT Key Laboratory of Advanced Display Materials and Devices
- Ministry of Industry and Information Technology
- Institute of Optoelectronics & Nanomaterials
- Nanjing University of Science and Technology
- Nanjing
| | - Zhongfang Chen
- Department of Chemistry
- Institute for Functional Nanomaterials
- University of Puerto Rico
- San Juan
- USA
| | - Yeliang Wang
- Institute of Physics and University of Chinese Academy of Sciences
- Chinese Academy of Sciences
- Beijing 100190
- China
| | - Hongjun Gao
- Institute of Physics and University of Chinese Academy of Sciences
- Chinese Academy of Sciences
- Beijing 100190
- China
| | - Julio Gómez-Herrero
- Departamento de Física de la Materia Condensada
- Universidad Autónoma de Madrid
- Madrid E 28049
- Spain
| | - Pablo Ares
- Departamento de Física de la Materia Condensada
- Universidad Autónoma de Madrid
- Madrid E 28049
- Spain
| | - Félix Zamora
- Departamento de Química Inorgánica
- Universidad Autónoma de Madrid
- Madrid E 28049
- Spain
| | - Zhen Zhu
- Materials Department
- University of California
- Santa Barbara
- USA
| | - Haibo Zeng
- MIIT Key Laboratory of Advanced Display Materials and Devices
- Ministry of Industry and Information Technology
- Institute of Optoelectronics & Nanomaterials
- Nanjing University of Science and Technology
- Nanjing
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