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Fang H, Mahalingam H, Li X, Han X, Qiu Z, Han Y, Noori K, Dulal D, Chen H, Lyu P, Yang T, Li J, Su C, Chen W, Cai Y, Neto AHC, Novoselov KS, Rodin A, Lu J. Atomically precise vacancy-assembled quantum antidots. Nat Nanotechnol 2023; 18:1401-1408. [PMID: 37653051 DOI: 10.1038/s41565-023-01495-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Accepted: 08/01/2023] [Indexed: 09/02/2023]
Abstract
Patterning antidots, which are regions of potential hills that repel electrons, into well-defined antidot lattices creates fascinating artificial periodic structures, leading to anomalous transport properties and exotic quantum phenomena in two-dimensional systems. Although nanolithography has brought conventional antidots from the semiclassical regime to the quantum regime, achieving precise control over the size of each antidot and its spatial period at the atomic scale has remained challenging. However, attaining such control opens the door to a new paradigm, enabling the creation of quantum antidots with discrete quantum hole states, which, in turn, offer a fertile platform to explore novel quantum phenomena and hot electron dynamics in previously inaccessible regimes. Here we report an atomically precise bottom-up fabrication of a series of atomic-scale quantum antidots through a thermal-induced assembly of a chalcogenide single vacancy in PtTe2. Such quantum antidots consist of highly ordered single-vacancy lattices, spaced by a single Te atom, reaching the ultimate downscaling limit of antidot lattices. Increasing the number of single vacancies in quantum antidots strengthens the cumulative repulsive potential and consequently enhances the collective interference of multiple-pocket scattered quasiparticles inside quantum antidots, creating multilevel quantum hole states with a tunable gap from the telecom to far-infrared regime. Moreover, precisely engineered quantum hole states of quantum antidots are geometry protected and thus survive on oxygen substitutional doping. Therefore, single-vacancy-assembled quantum antidots exhibit unprecedented robustness and property tunability, positioning them as highly promising candidates for advancing quantum information and photocatalysis technologies.
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Affiliation(s)
- Hanyan Fang
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Harshitra Mahalingam
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
| | - Xinzhe Li
- School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, China
| | - Xu Han
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Zhizhan Qiu
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
| | - Yixuan Han
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Keian Noori
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore, Singapore
| | | | - Hongfei Chen
- Joint Key Laboratory of Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Taipa, China
| | - Pin Lyu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Tianhao Yang
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Jing Li
- Key Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing, China
| | - Chenliang Su
- International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, Institute of Microscale Optoelectronics, Shenzhen University, Shenzhen, China
| | - Wei Chen
- Department of Chemistry, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore, Singapore
| | - Yongqing Cai
- Joint Key Laboratory of Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Taipa, China
| | - A H Castro Neto
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore, Singapore
| | - Kostya S Novoselov
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore, Singapore
| | - Aleksandr Rodin
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore, Singapore.
- Yale-NUS College, Singapore, Singapore.
- Materials Science and Engineering, National University of Singapore, Singapore, Singapore.
| | - Jiong Lu
- Department of Chemistry, National University of Singapore, Singapore, Singapore.
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore.
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore, Singapore.
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2
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Whitcher TJ, Fauzi AD, Diao C, Chi X, Syahroni A, Asmara TC, Breese MBH, Castro Neto AH, Wee ATS, Majidi MA, Rusydi A. Reply to: Reassessing the existence of soft X-ray correlated plasmons. Nat Commun 2023; 14:6754. [PMID: 37875490 PMCID: PMC10597986 DOI: 10.1038/s41467-023-40652-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 08/01/2023] [Indexed: 10/26/2023] Open
Affiliation(s)
- T J Whitcher
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore.
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore.
- Centre for Advanced 2D Materials, National University of Singapore, 2 Science Drive 3, Singapore, 117546, Singapore.
| | - A D Fauzi
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - C Diao
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - X Chi
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - A Syahroni
- Department of Physics, University of Indonesia, Depok, 16424, Indonesia
| | - T C Asmara
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
| | - M B H Breese
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - A H Castro Neto
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, Singapore, 117456, Singapore
| | - A T S Wee
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, Singapore, 117456, Singapore
| | - M A Majidi
- Department of Physics, University of Indonesia, Depok, 16424, Indonesia
| | - A Rusydi
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore.
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore.
- Centre for Advanced 2D Materials, National University of Singapore, 2 Science Drive 3, Singapore, 117546, Singapore.
- NUS Graduate School for Integrative Sciences and Engineering, Singapore, 117456, Singapore.
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3
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Carrio JAG, Talluri VP, Toolahalli ST, Echeverrigaray SG, Neto AHC. Gas stripping assisted vapour permeation using graphene membrane on silicon carbide for ethanol recovery. Sci Rep 2023; 13:9781. [PMID: 37328566 DOI: 10.1038/s41598-023-37080-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 06/15/2023] [Indexed: 06/18/2023] Open
Abstract
The conventional methods for ethanol recovery in low concentrations from diluted aqueous solutions are limited by the high energy consumed. Therefore, developing a cost-effective advanced membrane process for ethanol recovery and concentration is still necessary. A gas stripping-assisted vapour permeation (GSVP) process was applied to concentrate ethanol by the selective removal of water using hydrophilic graphene oxide (GO) membranes. Silicon carbide porous tubes were internally coated with GO-based membranes with an average thickness of 1.1 μm as a selective layer. Dry N2 was bubbled into the feed solution, carrying the saturated vapours to the separation module. The modified GSVP process was implemented to recover ethanol at lower temperatures than direct distillation and close-ended GSVP processes. The performance of the membrane-coated tubes was evaluated as a function of temperature and feed concentration, ranging from 23 to 60 °C and 10 wt% to 50 wt%. Distillates with 67 wt% and 87 wt% were obtained from feeds with 10 and 50 wt% ethanol at 50 °C, respectively. The evaporation energy spent by the modified GSVP process using GO-coated SiC tubes was 22% and 31% lower than the traditional distillation and vapour stripping processes.
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Affiliation(s)
- Juan A G Carrio
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore.
| | - Vssl Prasad Talluri
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - Swamy T Toolahalli
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - Sergio G Echeverrigaray
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
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Donato KZ, Tan HL, Marangoni VS, Martins MVS, Ng PR, Costa MCF, Jain P, Lee SJ, Koon GKW, Donato RK, Castro Neto AH. Graphene oxide classification and standardization. Sci Rep 2023; 13:6064. [PMID: 37055491 PMCID: PMC10102077 DOI: 10.1038/s41598-023-33350-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 04/12/2023] [Indexed: 04/15/2023] Open
Abstract
There is a need to classify and standardize graphene-related materials giving the growing use of this materials industrially. One of the most used and more difficult to classify is graphene oxide (GO). Inconsistent definitions of GO, closely relating it to graphene, are found in the literature and industrial brochures. Hence, although they have very different physicochemical properties and industrial applications, commonly used classifications of graphene and GO definitions are not substantial. Consequently, the lack of regulation and standardization create trust issues among sellers and buyers that impede industrial development and progress. With that in mind, this study offers a critical assessment of 34 commercially available GOs, characterized using a systematic and reliable protocol for accessing their quality. We establish correlations between GO physicochemical properties and its applications leading to rationale for its classification.
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Grants
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- Medium-Sized Centre Programme - Centre for Advanced 2D Materials (CA2DM) National Research Foundation, Prime Minister's Office
- EDUNC-33-18-279-V12 Ministry of Education - Singapore
- EDUNC-33-18-279-V12 Ministry of Education - Singapore
- EDUNC-33-18-279-V12 Ministry of Education - Singapore
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Affiliation(s)
- Katarzyna Z Donato
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - Hui Li Tan
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - Valeria S Marangoni
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
- Ilum School of Science, Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, 13083-970, Brazil
| | - Marcos V S Martins
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK
| | - Pei Rou Ng
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, 117544, Singapore
| | - Mariana C F Costa
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, 117544, Singapore
| | - Purvi Jain
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
- Nanyang Technological University, Singapore, 639798, Singapore
| | - Sarah J Lee
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - Gavin K W Koon
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - Ricardo K Donato
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore.
| | - A H Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore.
- Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore.
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, 117544, Singapore.
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5
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Whitcher TJ, Fauzi AD, Caozheng D, Chi X, Syahroni A, Asmara TC, Breese MBH, Neto AHC, Wee ATS, Majidi MA, Rusydi A. Unravelling strong electronic interlayer and intralayer correlations in a transition metal dichalcogenide. Nat Commun 2021; 12:6980. [PMID: 34848717 PMCID: PMC8632915 DOI: 10.1038/s41467-021-27182-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 10/27/2021] [Indexed: 11/23/2022] Open
Abstract
Electronic correlations play important roles in driving exotic phenomena in condensed matter physics. They determine low-energy properties through high-energy bands well-beyond optics. Great effort has been made to understand low-energy excitations such as low-energy excitons in transition metal dichalcogenides (TMDCs), however their high-energy bands and interlayer correlation remain mysteries. Herewith, by measuring temperature- and polarization-dependent complex dielectric and loss functions of bulk molybdenum disulphide from near-infrared to soft X-ray, supported with theoretical calculations, we discover unconventional soft X-ray correlated-plasmons with low-loss, and electronic transitions that reduce dimensionality and increase correlations, accompanied with significantly modified low-energy excitons. At room temperature, interlayer electronic correlations, together with the intralayer correlations in the c-axis, are surprisingly strong, yielding a three-dimensional-like system. Upon cooling, wide-range spectral-weight transfer occurs across a few tens of eV and in-plane p-d hybridizations become enhanced, revealing strong Coulomb correlations and electronic anisotropy, yielding a two-dimensional-like system. Our result shows the importance of strong electronic, interlayer and intralayer correlations in determining electronic structure and opens up applications of utilizing TMDCs on plasmonic nanolithrography.
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Affiliation(s)
- T J Whitcher
- Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore.
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore.
- Centre for Advanced 2D Materials, National University of Singapore, 2 Science Drive 3, Singapore, 117546, Singapore.
| | - Angga Dito Fauzi
- Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - D Caozheng
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - X Chi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Centre for Advanced 2D Materials, National University of Singapore, 2 Science Drive 3, Singapore, 117546, Singapore
| | - A Syahroni
- Department of Physics, University of Indonesia, Depok, 16424, Indonesia
| | - T C Asmara
- Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
| | - M B H Breese
- Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - A H Castro Neto
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - A T S Wee
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - M Aziz Majidi
- Department of Physics, University of Indonesia, Depok, 16424, Indonesia
| | - A Rusydi
- Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117576, Singapore.
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore.
- Centre for Advanced 2D Materials, National University of Singapore, 2 Science Drive 3, Singapore, 117546, Singapore.
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore.
- NUS Graduate School for Integrative Sciences and Engineering, Singapore, 117456, Singapore.
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Trushin M, Castro Neto AH. Stability of a Rolled-Up Conformation State for Two-Dimensional Materials in Aqueous Solutions. Phys Rev Lett 2021; 127:156101. [PMID: 34678010 DOI: 10.1103/physrevlett.127.156101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 09/15/2021] [Indexed: 06/13/2023]
Abstract
Two-dimensional (2D) materials can roll up, forming stable scrolls under suitable conditions. However, the great diversity of materials and fabrication techniques has resulted in a huge parameter space significantly complicating the theoretical description of scrolls. In this Letter, we describe a universal binding energy of scrolls determined solely by their material parameters, the bending stiffness, and the Hamaker coefficient. Aiming to predict the stability of functionalized scrolls in water solutions, we consider the electrostatic double-layer repulsion force that may overcome the binding energy and flatten the scrolls. Our predictions are represented as comprehensive maps indicating the stable and unstable regions of a rolled-up conformation state in the space of material and external parameters. While focusing mostly on functionalized graphene in this work, our approach is applicable to the whole range of 2D materials able to form scrolls.
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Affiliation(s)
- Maxim Trushin
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546
| | - A H Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546
- Department of Material Science Engineering, National University of Singapore, Singapore 117575
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7
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Carvalho A, Trevisanutto PE, Taioli S, Castro Neto AH. Computational methods for 2D materials modelling. Rep Prog Phys 2021; 84:106501. [PMID: 34474406 DOI: 10.1088/1361-6633/ac2356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 09/02/2021] [Indexed: 06/13/2023]
Abstract
Materials with thickness ranging from a few nanometers to a single atomic layer present unprecedented opportunities to investigate new phases of matter constrained to the two-dimensional plane. Particle-particle Coulomb interaction is dramatically affected and shaped by the dimensionality reduction, driving well-established solid state theoretical approaches to their limit of applicability. Methodological developments in theoretical modelling and computational algorithms, in close interaction with experiments, led to the discovery of the extraordinary properties of two-dimensional materials, such as high carrier mobility, Dirac cone dispersion and bright exciton luminescence, and inspired new device design paradigms. This review aims to describe the computational techniques used to simulate and predict the optical, electronic and mechanical properties of two-dimensional materials, and to interpret experimental observations. In particular, we discuss in detail the particular challenges arising in the simulation of two-dimensional constrained fermions and quasiparticles, and we offer our perspective on the future directions in this field.
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Affiliation(s)
- A Carvalho
- Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, 117546, Singapore
| | - P E Trevisanutto
- European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*-FBK) and Trento Institute for Fundamental Physics and Applications (TIFPA-INFN), Via Sommarive, 14, 38123 Povo TN, Trento, Italy
| | - S Taioli
- European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*-FBK) and Trento Institute for Fundamental Physics and Applications (TIFPA-INFN), Via Sommarive, 14, 38123 Povo TN, Trento, Italy
- Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya 29, St. Petersburg 195251, Russia
| | - A H Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, 117546, Singapore
- Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore
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Rosa V, Malhotra R, Agarwalla SV, Morin JLP, Luong-Van EK, Han YM, Chew RJJ, Seneviratne CJ, Silikas N, Tan KS, Nijhuis CA, Castro Neto AH. Graphene Nanocoating: High Quality and Stability upon Several Stressors. J Dent Res 2021; 100:1169-1177. [PMID: 34253090 DOI: 10.1177/00220345211024526] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Titanium implants present 2 major drawbacks-namely, the long time needed for osseointegration and the lack of inherent antimicrobial properties. Surface modifications and coatings to improve biomaterials can lose their integrity and biological potential when exposed to stressful microenvironments. Graphene nanocoating (GN) can be deposited onto actual-size dental and orthopedic implants. It has antiadhesive properties and can enhance bone formation in vivo. However, its ability to maintain structural integrity and quality when challenged by biologically relevant stresses remains largely unknown. GN was produced by chemical vapor deposition and transferred to titanium via a polymer-assisted transfer technique. GN has high inertness and did not increase expression of inflammatory markers by macrophages, even in the presence of lipopolysaccharides. It kept high coverage at the top tercile of tapered dental implant collars after installation and removal from bone substitute and pig maxilla. It also resisted microbiologically influenced corrosion, and it maintained very high coverage area and quality after prolonged exposure to biofilms and their removal by different techniques. Our findings show that GN is unresponsive to harsh and inflammatory environments and that it maintains a promising level of structural integrity on the top tercile of dental implant collars, which is the area highly affected by biofilms during the onset of implant diseases. Our findings open the avenues for the clinical studies required for the use of GN in the development of implants that have higher osteogenic potential and are less prone to implant diseases.
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Affiliation(s)
- V Rosa
- Faculty of Dentistry, National University of Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - R Malhotra
- Faculty of Dentistry, National University of Singapore, Singapore
| | - S V Agarwalla
- Faculty of Dentistry, National University of Singapore, Singapore
| | - J L P Morin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - E K Luong-Van
- Faculty of Dentistry, National University of Singapore, Singapore
| | - Y M Han
- Department of Chemistry, National University of Singapore, Singapore
| | - R J J Chew
- Faculty of Dentistry, National University of Singapore, Singapore
| | | | - N Silikas
- Division of Dentistry, School of Medical Sciences, University of Manchester, Manchester, United Kingdom
| | - K S Tan
- Faculty of Dentistry, National University of Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - C A Nijhuis
- Department of Molecules and Materials, Faculty of Science and Technology, University of Twente, Enschede, Netherlands
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
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9
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Malhotra R, Han Y, Nijhuis CA, Silikas N, Castro Neto AH, Rosa V. Graphene nanocoating provides superb long-lasting corrosion protection to titanium alloy. Dent Mater 2021; 37:1553-1560. [PMID: 34420797 DOI: 10.1016/j.dental.2021.08.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2021] [Revised: 07/17/2021] [Accepted: 08/04/2021] [Indexed: 11/30/2022]
Abstract
OBJECTIVE The presence of metallic species around failed implants raises concerns about the stability of titanium alloy (Ti-6Al-4V). Graphene nanocoating on titanium alloy (GN) has promising anti-corrosion properties, but its long-term protective potential and structural stability remains unknown. The objective was to determine GN's anti-corrosion potential and stability over time. METHODS GN and uncoated titanium alloy (Control) were challenged with a highly acidic fluorinated corrosive medium (pH 2.0) for up to 240 days. The samples were periodically tested using potentiodynamic polarization curves, electrochemical impedance spectroscopy and inductively coupled plasma-atomic emission spectroscopy (elemental release). The integrity of samples was determined using Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. Statistical analyses were performed with one-sample t-test, paired t-test and one-way ANOVA with Tukey post-hoc test with a pre-set significance level of 5%. RESULTS There was negligible corrosion and elemental loss on GN. After 240 days of corrosion challenge, the corrosion rate and roughness increased by two and twelve times for the Control whereas remained unchanged for GN. The nanocoating presented remarkably high structural integrity and coverage area (>98%) at all time points tested. SIGNIFICANCE Graphene nanocoating protects titanium alloy from corrosion and dissolution over a long period while maintaining high structural integrity. This coating has promising potential for persistent protection of titanium and potentially other metallic alloys against corrosion.
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Affiliation(s)
- Ritika Malhotra
- Faculty of Dentistry, National University of Singapore, Singapore.
| | - Yingmei Han
- Department of Chemistry, National University of Singapore, Singapore.
| | - Christian A Nijhuis
- Department of Molecules and Materials, Faculty of Science and Technology, University of Twente, Netherlands.
| | - Nikolaos Silikas
- Dental Biomaterials, Dentistry, The University of Manchester, Manchester, United Kingdom.
| | - A H Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, Singapore.
| | - Vinicius Rosa
- Faculty of Dentistry, National University of Singapore, Singapore; Centre for Advanced 2D Materials, National University of Singapore, Singapore.
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10
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Costa MCF, Marangoni VS, Ng PR, Nguyen HTL, Carvalho A, Castro Neto AH. Accelerated Synthesis of Graphene Oxide from Graphene. Nanomaterials (Basel) 2021; 11:551. [PMID: 33671695 PMCID: PMC7926456 DOI: 10.3390/nano11020551] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 02/18/2021] [Accepted: 02/18/2021] [Indexed: 12/28/2022]
Abstract
Graphene oxide (GO) is an oxygenated functionalized form of graphene that has received considerable attention because of its unique physical and chemical properties that are suitable for a large number of industrial applications. Herein, GO is rapidly obtained directly from the oxidation of graphene using an environmentally friendly modified Hummers method. As the starting material consists of graphene flakes, intercalant agents are not needed and the oxidation reaction is enhanced, leading to orders of magnitude reduction in the reaction time compared to the conventional methods of graphite oxidation. With a superior surface area, the graphene flakes are quickly and more homogeneously oxidized since the flakes are exposed at the same extension to the chemical agents, excluding the necessity of sonication to separate the stacked layers of graphite. This strategy shows an alternative approach to quickly producing GO with different degrees of oxidation that can be potentially used in distinct areas ranging from biomedical to energy storage applications.
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Affiliation(s)
- Mariana C. F. Costa
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117456, Singapore; (M.C.F.C.); (V.S.M.); (P.R.N.); (H.T.L.N.); (A.C.)
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
| | - Valeria S. Marangoni
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117456, Singapore; (M.C.F.C.); (V.S.M.); (P.R.N.); (H.T.L.N.); (A.C.)
| | - Pei Rou Ng
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117456, Singapore; (M.C.F.C.); (V.S.M.); (P.R.N.); (H.T.L.N.); (A.C.)
| | - Hang T. L. Nguyen
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117456, Singapore; (M.C.F.C.); (V.S.M.); (P.R.N.); (H.T.L.N.); (A.C.)
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117456, Singapore; (M.C.F.C.); (V.S.M.); (P.R.N.); (H.T.L.N.); (A.C.)
| | - A. H. Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117456, Singapore; (M.C.F.C.); (V.S.M.); (P.R.N.); (H.T.L.N.); (A.C.)
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
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11
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Li J, Song P, Zhao J, Vaklinova K, Zhao X, Li Z, Qiu Z, Wang Z, Lin L, Zhao M, Herng TS, Zuo Y, Jonhson W, Yu W, Hai X, Lyu P, Xu H, Yang H, Chen C, Pennycook SJ, Ding J, Teng J, Castro Neto AH, Novoselov KS, Lu J. Printable two-dimensional superconducting monolayers. Nat Mater 2021; 20:181-187. [PMID: 33106649 DOI: 10.1038/s41563-020-00831-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2020] [Accepted: 09/15/2020] [Indexed: 06/11/2023]
Abstract
Two-dimensional superconductor (2DSC) monolayers with non-centrosymmetry exhibit unconventional Ising pair superconductivity and an enhanced upper critical field beyond the Pauli paramagnetic limit, driving intense research interest. However, they are often susceptible to structural disorder and environmental oxidation, which destroy electronic coherence and provide technical challenges in the creation of artificial van der Waals heterostructures (vdWHs) for devices. Herein, we report a general and scalable synthesis of highly crystalline 2DSC monolayers via a mild electrochemical exfoliation method using flexible organic ammonium cations solvated with neutral solvent molecules as co-intercalants. Using NbSe2 as a model system, we achieved a high yield (>75%) of large-sized single-crystal monolayers up to 300 µm. The as-fabricated, twisted NbSe2 vdWHs demonstrate high stability, good interfacial properties and a critical current that is modulated by magnetic field when one flux quantum fits to an integer number of moiré cells. Additionally, formulated 2DSC inks can be exploited to fabricate wafer-scale 2D superconducting wire arrays and three-dimensional superconducting composites with desirable morphologies.
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Affiliation(s)
- Jing Li
- Department of Chemistry, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
| | - Peng Song
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Jinpei Zhao
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Kristina Vaklinova
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
| | - Xiaoxu Zhao
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Zejun Li
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Zhizhan Qiu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Zihao Wang
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Li Lin
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Meng Zhao
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - Tun Seng Herng
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Yuxin Zuo
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Win Jonhson
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Wei Yu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Xiao Hai
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Pin Lyu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Haomin Xu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Huimin Yang
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Cheng Chen
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Stephen J Pennycook
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Jun Ding
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Jinghua Teng
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore
| | - Kostya S Novoselov
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore.
- Department of Materials Science & Engineering, National University of Singapore, Singapore, Singapore.
- National Graphene Institute, University of Manchester, Manchester, UK.
| | - Jiong Lu
- Department of Chemistry, National University of Singapore, Singapore, Singapore.
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore.
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12
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Agarwalla SV, Ellepola K, Silikas N, Castro Neto AH, Seneviratne CJ, Rosa V. Persistent inhibition of Candida albicans biofilm and hyphae growth on titanium by graphene nanocoating. Dent Mater 2020; 37:370-377. [PMID: 33358443 DOI: 10.1016/j.dental.2020.11.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 10/30/2020] [Accepted: 11/26/2020] [Indexed: 01/01/2023]
Abstract
OBJECTIVES Candida albicanscolonizes biomaterial surfaces and are highly resistant to therapeutics. Graphene nanocoating on titanium compromises initial biofilm formation. However, its sustained antibiofilm potential is unknown. The objective of this study was to investigate the potential of graphene nanocoating to decrease long-term fungal biofilm development and hyphae growth on titanium. METHODS Graphene nanocoating was deposited twice (TiGD) or five times (TiGV) on grade 4 titanium with vacuum assisted technique and characterized with Raman spectroscopy and atomic force microscope. The biofilm formation and hyphae growth of C. albicans was monitored for seven days by CFU, XTT, confocal, mean cell density and scanning electronic microscopy (SEM). Uncoated titanium was the Control. All tests had three independent biological samples and were performed in independent triplicates. Data was analyzed with one- or two-way ANOVA and Tukey's HSD (α = 0.05). RESULTS Both TiGD and TiGV presented less biofilms at all times points compared with Control. The confocal and SEM images revealed few adhered cells on graphene coated samples, absence of hyphae and no features of a mature biofilm architecture. The increase in number of layers of graphene nanocoating did not improve its antibiofilm potential. SIGNIFICANCE The graphene nanocoating exerted a long-term persistent inhibitory effect on the biofilm formation on titanium. The fewer cells that were able to attach on graphene coated titanium were scattered and unable to form a mature biofilm with hyphae elements. The findings open opportunities to prevent microbial attachment and proliferation on implantable materials without the use of antibiotics.
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Affiliation(s)
| | - Kassapa Ellepola
- Louisiana State University Health Sciences Center, School of Dentistry, USA
| | - Nikolaos Silikas
- Division of Dentistry, School of Medical Sciences, University of Manchester, Manchester, United Kingdom
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - Chaminda Jayampath Seneviratne
- National Dental Centre Singapore, SingHealth, Duke NUS Medical School, 05, Hospital Avenue, National Dental Centre Singapor, Singapore.
| | - Vinicius Rosa
- Faculty of Dentistry, National University of Singapore, 9 Lower Kent Ridge Road, Singapore; Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore; NUS Craniofacial Research and Innovation Center, National University of Singapore, Singapore.
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13
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Li Z, Zhang X, Zhao X, Li J, Herng TS, Xu H, Lin F, Lyu P, Peng X, Yu W, Hai X, Chen C, Yang H, Martin J, Lu J, Luo X, Castro Neto AH, Pennycook SJ, Ding J, Feng Y, Lu J. Imprinting Ferromagnetism and Superconductivity in Single Atomic Layers of Molecular Superlattices. Adv Mater 2020; 32:e1907645. [PMID: 32419256 DOI: 10.1002/adma.201907645] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 04/08/2020] [Accepted: 04/23/2020] [Indexed: 06/11/2023]
Abstract
Ferromagnetism and superconductivity are two antagonistic phenomena since ferromagnetic exchange fields tend to destroy singlet Cooper pairs. Reconciliation of these two competing phases has been achieved in vertically stacked heterostructures where these two orders are confined in different layers. However, controllable integration of these two phases in one atomic layer is a longstanding challenge. Here, an interlayer-space-confined chemical design (ICCD) is reported for the synthesis of dilute single-atom-doped TaS2 molecular superlattice, whereby ferromagnetism is observed in the superconducting TaS2 layers. The intercalation of 2H-TaS2 crystal with bulky organic ammonium molecule expands its van der Waals gap for single-atom doping via co-intercalated cobalt ions, resulting in the formation of quasi-monolayer Co-doped TaS2 superlattices. Isolated Co atoms are decorated in the basal plane of the TaS2 via substituting the Ta atom or anchoring at a hollow site, wherein the orbital-selected p-d hybridization between Co and neighboring Ta and S atoms induces local magnetic moments with strong ferromagnetic coupling. This ICCD approach can be applied to various metal ions, enabling the synthesis of a series of crystal-size TaS2 molecular superlattices.
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Affiliation(s)
- Zejun Li
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Xiuying Zhang
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing, 100871, P. R. China
| | - Xiaoxu Zhao
- Department of Materials Science & Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Jing Li
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Tun Seng Herng
- Department of Materials Science & Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Haomin Xu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Fanrong Lin
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117542, Singapore
| | - Pin Lyu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Xinnan Peng
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Wei Yu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Xiao Hai
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Cheng Chen
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Huimin Yang
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
| | - Jens Martin
- Institut für Kristallzüchtung, Max-Born-Str. 2, Berlin, 12489, Germany
| | - Jing Lu
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing, 100871, P. R. China
| | - Xin Luo
- School of Physics, Sun Yat-sen University, Guangzhou, 510275, P. R. China
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117542, Singapore
| | - Stephen J Pennycook
- Department of Materials Science & Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Jun Ding
- Department of Materials Science & Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Yuanping Feng
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117542, Singapore
| | - Jiong Lu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
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14
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Malhotra R, Han YM, Morin JLP, Luong-Van EK, Chew RJJ, Castro Neto AH, Nijhuis CA, Rosa V. Inhibiting Corrosion of Biomedical-Grade Ti-6Al-4V Alloys with Graphene Nanocoating. J Dent Res 2020; 99:285-292. [PMID: 31905311 DOI: 10.1177/0022034519897003] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The identification of metal ions and particles in the vicinity of failed implants has raised the concern that biomedical titanium alloys undergo corrosion in healthy and infected tissues. Various surface modifications and coatings have been investigated to prevent the deterioration and biocorrosion of titanium alloys but so far with limited success. Graphene is a cytocompatible atom-thick film made of carbon atoms. It has a very high surface area and can be deposited onto metal objects with complex shapes. As the carbon lattice has a very small pore size, graphene has promising impermeability capacity. Here, we show that graphene coating can effectively protect Ti-6Al-4V from corrosion. Graphene nanocoatings were produced on Ti-6Al-4V grade 5 and 23 discs and subjected to corrosive challenge (0.5M NaCl supplemented with 2-ppm fluoride, pH of 2.0) up to 30 d. The linear polarization resistance curves and electrochemical impedance spectroscopy analysis showed that the graphene-coated samples presented higher corrosion resistance and electrochemical stability at all time points. Moreover, the corrosion rate of the graphene-coated samples was very low and stable (~0.001 mm/y), whereas that of the uncoated controls increased up to 16 and 5 times for grade 5 and 23 (~0.091 mm/y) at the end point, respectively. The surface oxidation, degradation (e.g., crevice defects), and leaching of Ti, Al, and V ions observed in the uncoated controls were prevented by the graphene nanocoating. The Raman mappings confirmed that the graphene nanocoating presented high structural stability and resistance to mechanical stresses and chemical degradation, keeping >99% of coverage after corrosion challenge. Our findings open the avenues for the use of graphene as anticorrosion coatings for metal biomedical alloys and implantable devices.
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Affiliation(s)
- R Malhotra
- Faculty of Dentistry, National University of Singapore, Singapore
| | - Y M Han
- Department of Chemistry, National University of Singapore, Singapore
| | - J L P Morin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - E K Luong-Van
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - R J J Chew
- Faculty of Dentistry, National University of Singapore, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore.,Department of Materials Science and Engineering, National University of Singapore, Singapore
| | - C A Nijhuis
- Department of Chemistry, National University of Singapore, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore.,NUSNNI-Nanocore, National University of Singapore, Singapore.,Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore
| | - V Rosa
- Faculty of Dentistry, National University of Singapore, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore.,Department of Materials Science and Engineering, National University of Singapore, Singapore
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15
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Qiu Z, Trushin M, Fang H, Verzhbitskiy I, Gao S, Laksono E, Yang M, Lyu P, Li J, Su J, Telychko M, Watanabe K, Taniguchi T, Wu J, Neto AHC, Yang L, Eda G, Adam S, Lu J. Giant gate-tunable bandgap renormalization and excitonic effects in a 2D semiconductor. Sci Adv 2019; 5:eaaw2347. [PMID: 31334350 PMCID: PMC6641939 DOI: 10.1126/sciadv.aaw2347] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 06/14/2019] [Indexed: 05/19/2023]
Abstract
Understanding the remarkable excitonic effects and controlling the exciton binding energies in two-dimensional (2D) semiconductors are crucial in unlocking their full potential for use in future photonic and optoelectronic devices. Here, we demonstrate large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide (ReSe2) on a back-gated graphene device. We used scanning tunneling spectroscopy and differential reflectance spectroscopy to measure the quasiparticle electronic and optical bandgap of single-layer ReSe2, respectively, yielding a large exciton binding energy of 520 meV. Further, we achieved continuous tuning of the electronic bandgap and exciton binding energy of monolayer ReSe2 by hundreds of milli-electron volts through electrostatic gating, attributed to tunable Coulomb interactions arising from the gate-controlled free carriers in graphene. Our findings open a new avenue for controlling the bandgap renormalization and exciton binding energies in 2D semiconductors for a wide range of technological applications.
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Affiliation(s)
- Zhizhan Qiu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 28 Medical Drive, Singapore 117456, Singapore
| | - Maxim Trushin
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Hanyan Fang
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Ivan Verzhbitskiy
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
| | - Shiyuan Gao
- Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Evan Laksono
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
| | - Ming Yang
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Singapore 138634, Singapore
| | - Pin Lyu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Jing Li
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Jie Su
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Mykola Telychko
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Kenji Watanabe
- National Institute of Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute of Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Jishan Wu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - A. H. Castro Neto
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
| | - Li Yang
- Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Goki Eda
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
| | - Shaffique Adam
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
- Yale-NUS College, 16 College Avenue West, Singapore 138527, Singapore
| | - Jiong Lu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Corresponding author.
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16
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Agarwalla SV, Ellepola K, Costa MCFD, Fechine GJM, Morin JLP, Castro Neto AH, Seneviratne CJ, Rosa V. Hydrophobicity of graphene as a driving force for inhibiting biofilm formation of pathogenic bacteria and fungi. Dent Mater 2019; 35:403-413. [PMID: 30679015 DOI: 10.1016/j.dental.2018.09.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 09/18/2018] [Accepted: 09/26/2018] [Indexed: 10/27/2022]
Abstract
OBJECTIVE To evaluate the surface and wettability characteristics and the microbial biofilm interaction of graphene coating on titanium. METHODS Graphene was deposited on titanium (Control) via a liquid-free technique. The transfer was performed once (TiGS), repeated two (TiGD) and five times (TiGV) and characterized by AFM (n=10), Raman spectroscopy (n=10), contact angle and SFE (n=5). Biofilm formation (n=3) to Streptococcus mutans, Enterococcus faecalis, Pseudomonas aeruginosa and Candida albicans was evaluated after 24h by CV assay, CFU, XTT and confocal microscopy. Statistics were performed by one-way Anova, Tukey's tests and Pearson's correlation analysis at a pre-set significance level of 5 %. RESULTS Raman mappings revealed coverage yield of 82 % for TiGS and ≥99 % for TiGD and TiGV. Both TiGD and TiGV presented FWHM>44cm-1 and ID/IG ratio<0.12, indicating multiple graphene layers and occlusion of defects. The contact angle was significantly higher for TiGD and TiGV (110° and 117°) comparing to the Control (70°). The SFE was lower for TiGD (13.8mN/m) and TiGV (12.1mN/m) comparing to Control (38.3mN/m). TiGD was selected for biofilm assays and exhibited significant reduction in biofilm formation for all microorganisms compared to Control. There were statistical correlations between the high contact angle and low SFE of TiGD and decreased biofilm formation. SIGNIFICANCE TiGD presented high quality and coverage and decreased biofilm formation for all species. The increased hydrophobicity of graphene films was correlated with the decreased biofilm formation for various species.
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Affiliation(s)
| | - Kassapa Ellepola
- Faculty of Dentistry, National University of Singapore, Singapore
| | | | | | - Julien Luc Paul Morin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore
| | | | - Vinicius Rosa
- Faculty of Dentistry, National University of Singapore, Singapore; Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore.
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17
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Liu Y, Rodrigues JNB, Luo YZ, Li L, Carvalho A, Yang M, Laksono E, Lu J, Bao Y, Xu H, Tan SJR, Qiu Z, Sow CH, Feng YP, Neto AHC, Adam S, Lu J, Loh KP. Tailoring sample-wide pseudo-magnetic fields on a graphene-black phosphorus heterostructure. Nat Nanotechnol 2018; 13:828-834. [PMID: 29941889 DOI: 10.1038/s41565-018-0178-z] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 05/23/2018] [Indexed: 05/22/2023]
Abstract
Spatially tailored pseudo-magnetic fields (PMFs) can give rise to pseudo-Landau levels and the valley Hall effect in graphene. At an experimental level, it is highly challenging to create the specific strain texture that can generate PMFs over large areas. Here, we report that superposing graphene on multilayer black phosphorus creates shear-strained superlattices that generate a PMF over an entire graphene-black phosphorus heterostructure with edge size of tens of micrometres. The PMF is intertwined with the spatial period of the moiré pattern, and its spatial distribution and intensity can be modified by changing the relative orientation of the two materials. We show that the emerging pseudo-Landau levels influence the transport properties of graphene-black phosphorus field-effect transistor devices with Hall bar geometry. The application of an external magnetic field allows us to enhance or reduce the effective field depending on the valley polarization with the prospect of developing a valley filter.
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Affiliation(s)
- Yanpeng Liu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
| | - J N B Rodrigues
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Yong Zheng Luo
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Linjun Li
- Department of Chemistry, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Ming Yang
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore, Singapore
| | - Evan Laksono
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Junpeng Lu
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Yang Bao
- Department of Chemistry, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
| | - Hai Xu
- Department of Chemistry, National University of Singapore, Singapore, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
| | - Sherman J R Tan
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore
| | - Zhizhan Qiu
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore
| | - Chorng Haur Sow
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Yuan Ping Feng
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Shaffique Adam
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore.
- Department of Physics, National University of Singapore, Singapore, Singapore.
- Yale-NUS College, Singapore, Singapore.
| | - Jiong Lu
- Department of Chemistry, National University of Singapore, Singapore, Singapore.
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore.
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore, Singapore, Singapore.
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore.
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18
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Xiang D, Liu T, Xu J, Tan JY, Hu Z, Lei B, Zheng Y, Wu J, Neto AHC, Liu L, Chen W. Two-dimensional multibit optoelectronic memory with broadband spectrum distinction. Nat Commun 2018; 9:2966. [PMID: 30054482 PMCID: PMC6063921 DOI: 10.1038/s41467-018-05397-w] [Citation(s) in RCA: 94] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2017] [Accepted: 06/19/2018] [Indexed: 11/09/2022] Open
Abstract
Optoelectronic memory plays a vital role in modern semiconductor industry. The fast emerging requirements for device miniaturization and structural flexibility have diverted research interest to two-dimensional thin layered materials. Here, we report a multibit nonvolatile optoelectronic memory based on a heterostructure of monolayer tungsten diselenide and few-layer hexagonal boron nitride. The tungsten diselenide/boron nitride memory exhibits a memory switching ratio approximately 1.1 × 106, which ensures over 128 (7 bit) distinct storage states. The memory demonstrates robustness with retention time over 4.5 × 104 s. Moreover, the ability of broadband spectrum distinction enables its application in filter-free color image sensor. This concept is further validated through the realization of integrated tungsten diselenide/boron nitride pixel matrix which captured a specific image recording the three primary colors (red, green, and blue). The heterostructure architecture is also applicable to other two-dimensional materials, which is confirmed by the realization of black phosphorus/boron nitride optoelectronic memory.
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Affiliation(s)
- Du Xiang
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Tao Liu
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Jilian Xu
- State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun, 130033, People's Republic of China
| | - Jun Y Tan
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Zehua Hu
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Bo Lei
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Yue Zheng
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Jing Wu
- Institute of Materials Research and Engineering (IMRE), 2 Fusionopolis Way, Singapore, 138634, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Lei Liu
- State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun, 130033, People's Republic of China
| | - Wei Chen
- Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore.
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore.
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore.
- National University of Singapore (Suzhou) Research Institute, 377 Lin Quan Street, Suzhou Industrial Park, Jiang Su, 215123, China.
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19
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Ermakov A, Lim SH, Gorelik S, Kauling AP, de Oliveira RVB, Castro Neto AH, Glukhovskoy E, Gorin DA, Sukhorukov GB, Kiryukhin MV. Polyelectrolyte-Graphene Oxide Multilayer Composites for Array of Microchambers which are Mechanically Robust and Responsive to NIR Light. Macromol Rapid Commun 2018; 40:e1700868. [DOI: 10.1002/marc.201700868] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/14/2018] [Indexed: 11/11/2022]
Affiliation(s)
- Alexey Ermakov
- Institute of Materials Research and Engineering; Agency for Science,; Technology and Research (A*STAR); 2 Fusionopolis Way, Innovis, #08-03 Singapore 138634 Singapore
- Educational Research Institute of Nanostructures and Biosystems; N. G. Chernyshevsky Saratov State University; 83 Astrakhanskaya Street Saratov 410012 Russia
| | - Su Hui Lim
- Institute of Materials Research and Engineering; Agency for Science,; Technology and Research (A*STAR); 2 Fusionopolis Way, Innovis, #08-03 Singapore 138634 Singapore
| | - Sergey Gorelik
- Institute of Materials Research and Engineering; Agency for Science,; Technology and Research (A*STAR); 2 Fusionopolis Way, Innovis, #08-03 Singapore 138634 Singapore
| | - Alan P. Kauling
- Centre for Advanced 2D Materials; National University of Singapore; 6 Science Drive 2 Singapore 117546 Singapore
| | - Ricardo V. B. de Oliveira
- Centre for Advanced 2D Materials; National University of Singapore; 6 Science Drive 2 Singapore 117546 Singapore
| | - A. H. Castro Neto
- Centre for Advanced 2D Materials; National University of Singapore; 6 Science Drive 2 Singapore 117546 Singapore
| | - Evgeniy Glukhovskoy
- Educational Research Institute of Nanostructures and Biosystems; N. G. Chernyshevsky Saratov State University; 83 Astrakhanskaya Street Saratov 410012 Russia
| | - Dmitry A. Gorin
- Educational Research Institute of Nanostructures and Biosystems; N. G. Chernyshevsky Saratov State University; 83 Astrakhanskaya Street Saratov 410012 Russia
- Biophotonics Lab Center of Photonics & Quantum Materials; Skolkovo Institute of Science and Technology; Nobel Str. 3 Moscow 143026 Russia
| | - Gleb B. Sukhorukov
- School of Engineering and Materials Science; Queen Mary University of London; Mile End Road London E1 4NS UK
| | - Maxim V. Kiryukhin
- Institute of Materials Research and Engineering; Agency for Science,; Technology and Research (A*STAR); 2 Fusionopolis Way, Innovis, #08-03 Singapore 138634 Singapore
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20
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Dubey N, Ellepola K, Decroix FED, Morin JLP, Castro Neto AH, Seneviratne CJ, Rosa V. Graphene onto medical grade titanium: an atom-thick multimodal coating that promotes osteoblast maturation and inhibits biofilm formation from distinct species. Nanotoxicology 2018; 12:274-289. [PMID: 29409364 DOI: 10.1080/17435390.2018.1434911] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The time needed for the osseointegration of titanium implants is deemed too long. Moreover, the bacterial colonization of their surfaces is a major cause of failure. Graphene can overcome these issues but its wet transfer onto substrates employs hazardous chemicals limiting the clinical applications. Alternatively, dry transfer technique has been developed, but the biological properties of this technique remain unexplored. Here, a dry transfer technique based on a hot-pressing method allowed to coat titanium substrates with high-quality graphene and coverage area >90% with a single transfer. The graphene-coated titanium is cytocompatible, did not induce cell membrane damage, induced human osteoblast maturation (gene and protein level), and increased the deposition of mineralized matrix compared to titanium alone. Moreover, graphene decreased the formation of biofilms from Streptococcus mutans, Enterococcus faecalis and even from whole saliva on titanium without killing the bacteria. These findings confirm that coating of titanium with graphene via a dry transfer technique is a promising strategy to improve osseointegration and prevent biofilm formation on implants and devices.
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Affiliation(s)
- Nileshkumar Dubey
- a Faculty of Dentistry , National University of Singapore , Singapore , Singapore
| | - Kassapa Ellepola
- a Faculty of Dentistry , National University of Singapore , Singapore , Singapore
| | - Fanny E D Decroix
- b Centre for Advanced 2D Materials and Graphene Research Centre , National University of Singapore , Singapore , Singapore
| | - Julien L P Morin
- b Centre for Advanced 2D Materials and Graphene Research Centre , National University of Singapore , Singapore , Singapore
| | - A H Castro Neto
- b Centre for Advanced 2D Materials and Graphene Research Centre , National University of Singapore , Singapore , Singapore
| | | | - Vinicius Rosa
- a Faculty of Dentistry , National University of Singapore , Singapore , Singapore.,b Centre for Advanced 2D Materials and Graphene Research Centre , National University of Singapore , Singapore , Singapore
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21
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Qiu Z, Fang H, Carvalho A, Rodin AS, Liu Y, Tan SJR, Telychko M, Lv P, Su J, Wang Y, Castro Neto AH, Lu J. Resolving the Spatial Structures of Bound Hole States in Black Phosphorus. Nano Lett 2017; 17:6935-6940. [PMID: 29035538 DOI: 10.1021/acs.nanolett.7b03356] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding the local electronic properties of individual defects and dopants in black phosphorus (BP) is of great importance for both fundamental research and technological applications. Here, we employ low-temperature scanning tunnelling microscope (LT-STM) to probe the local electronic structures of single acceptors in BP. We demonstrate that the charge state of individual acceptors can be reversibly switched by controlling the tip-induced band bending. In addition, acceptor-related resonance features in the tunnelling spectra can be attributed to the formation of Rydberg-like bound hole states. The spatial mapping of the quantum bound states shows two distinct shapes evolving from an extended ellipse shape for the 1s ground state to a dumbbell shape for the 2px excited state. The wave functions of bound hole states can be well-described using the hydrogen-like model with anisotropic effective mass, corroborated by our theoretical calculations. Our findings not only provide new insight into the many-body interactions around single dopants in this anisotropic two-dimensional material but also pave the way to the design of novel quantum devices.
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Affiliation(s)
- Zhizhan Qiu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore , 28 Medical Drive, Singapore 117456
| | - Hanyan Fang
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - A S Rodin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Yanpeng Liu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Sherman J R Tan
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore , 28 Medical Drive, Singapore 117456
| | - Mykola Telychko
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Pin Lv
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
| | - Jie Su
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Yewu Wang
- Department of Physics & State Key Laboratory of Silicon Materials, Zhejiang University , Hangzhou 310027, P. R. China
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
- Department of Physics, National University of Singapore , 3 Science Drive 2, Singapore 117542
| | - Jiong Lu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
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22
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Gogoi PK, Hu Z, Wang Q, Carvalho A, Schmidt D, Yin X, Chang YH, Li LJ, Sow CH, Neto AHC, Breese MBH, Rusydi A, Wee ATS. Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS_{2}. Phys Rev Lett 2017; 119:077402. [PMID: 28949667 DOI: 10.1103/physrevlett.119.077402] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Indexed: 06/07/2023]
Abstract
Using wide spectral range in situ spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS_{2} isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92 eV) and B (2.02 eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the band structure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS_{2}.
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Affiliation(s)
- Pranjal Kumar Gogoi
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Zhenliang Hu
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
| | - Qixing Wang
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
| | - Daniel Schmidt
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Xinmao Yin
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
| | - Yung-Huang Chang
- Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan
| | - Lain-Jong Li
- Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia
| | - Chorng Haur Sow
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
| | - A H Castro Neto
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
| | - Mark B H Breese
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Andrivo Rusydi
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
- NUSNNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
| | - Andrew T S Wee
- Department of Physics, Faculty of Science, National University of Singapore, Singapore 117542, Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
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23
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Liu Y, Qiu Z, Carvalho A, Bao Y, Xu H, Tan SJR, Liu W, Castro Neto AH, Loh KP, Lu J. Gate-Tunable Giant Stark Effect in Few-Layer Black Phosphorus. Nano Lett 2017; 17:1970-1977. [PMID: 28195492 DOI: 10.1021/acs.nanolett.6b05381] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Two-dimensional black phosphorus (BP) has sparked enormous research interest due to its high carrier mobility, layer-dependent direct bandgap and outstanding in-plane anisotropic properties. BP is one of the few two-dimensional materials where it is possible to tune the bandgap over a wide energy range from the visible up to the infrared. In this article, we report the observation of a giant Stark effect in electrostatically gated few-layer BP. Using low-temperature scanning tunnelling microscopy, we observed that in few-layer BP, when electrons are injected, a monotonic reduction of the bandgap occurs. The injected electrons compensate the existing defect-induced holes and achieve up to 35.5% bandgap modulation in the light-doping regime. When probed by tunnelling spectroscopy, the local density of states in few-layer BP shows characteristic resonance features arising from layer-dependent sub-band structures due to quantum confinement effects. The demonstration of an electrical gate-controlled giant Stark effect in BP paves the way to designing electro-optic modulators and photodetector devices that can be operated in a wide electromagnetic spectral range.
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Affiliation(s)
- Yanpeng Liu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Zhizhan Qiu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore , 28 Medical Drive, Singapore 117456
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
- Department of Physics, National University of Singapore , 3 Science Drive 2, Singapore 117542
| | - Yang Bao
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Hai Xu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Sherman J R Tan
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore , 28 Medical Drive, Singapore 117456
| | - Wei Liu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
- Department of Physics, National University of Singapore , 3 Science Drive 2, Singapore 117542
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Jiong Lu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
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24
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Yu WJ, Vu QA, Oh H, Nam HG, Zhou H, Cha S, Kim JY, Carvalho A, Jeong M, Choi H, Castro Neto AH, Lee YH, Duan X. Unusually efficient photocurrent extraction in monolayer van der Waals heterostructure by tunnelling through discretized barriers. Nat Commun 2016; 7:13278. [PMID: 27827360 PMCID: PMC5105192 DOI: 10.1038/ncomms13278] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 09/16/2016] [Indexed: 12/24/2022] Open
Abstract
Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device.
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Affiliation(s)
- Woo Jong Yu
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
- Department of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea
- Samsung-SKKU Graphene Center (SSGC), Suwon 16419, Republic of Korea
| | - Quoc An Vu
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
- Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Hyemin Oh
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Hong Gi Nam
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Hailong Zhou
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
| | - Soonyoung Cha
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea
| | - Joo-Youn Kim
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Munseok Jeong
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Hyunyong Choi
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea
| | - A. H. Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Young Hee Lee
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
- Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Xiangfeng Duan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
- California Nanosystems Institute, University of California, Los Angeles, California 90095, USA
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25
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26
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Ribeiro HB, Villegas CEP, Bahamon DA, Muraca D, Castro Neto AH, de Souza EAT, Rocha AR, Pimenta MA, de Matos CJS. Edge phonons in black phosphorus. Nat Commun 2016; 7:12191. [PMID: 27412813 PMCID: PMC4947165 DOI: 10.1038/ncomms12191] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Accepted: 06/09/2016] [Indexed: 12/01/2022] Open
Abstract
Black phosphorus has recently emerged as a new layered crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and behaviour of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements. Black phosphorus is an allotrope of phosphorous that, like graphite, can be exfoliated to create two-dimensional materials. Here, the authors use Raman spectroscopy and density functional theory calculations to investigate the anomalous behaviour of phonons near different black phosphorus edges.
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Affiliation(s)
- H B Ribeiro
- MackGraphe-Graphene and Nanomaterials Research Center, Mackenzie Presbyterian University, 01302-907 São Paulo, Brazil
| | - C E P Villegas
- Instituto de Física Teórica, Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), 01140-070 São Paulo, Brazil
| | - D A Bahamon
- MackGraphe-Graphene and Nanomaterials Research Center, Mackenzie Presbyterian University, 01302-907 São Paulo, Brazil
| | - D Muraca
- Instituto de Física Gleb Wataghin (IFGW), Universidade Estadual de Campinas, 13083-970 Campinas, Brazil
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
| | - E A T de Souza
- MackGraphe-Graphene and Nanomaterials Research Center, Mackenzie Presbyterian University, 01302-907 São Paulo, Brazil
| | - A R Rocha
- Instituto de Física Teórica, Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), 01140-070 São Paulo, Brazil
| | - M A Pimenta
- Departamento de Física, Universidade Federal de Minas Gerais (UFMG), 30161-970 Belo Horizonte, Brazil
| | - C J S de Matos
- MackGraphe-Graphene and Nanomaterials Research Center, Mackenzie Presbyterian University, 01302-907 São Paulo, Brazil
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27
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Kozawa D, Carvalho A, Verzhbitskiy I, Giustiniano F, Miyauchi Y, Mouri S, Castro Neto AH, Matsuda K, Eda G. Evidence for Fast Interlayer Energy Transfer in MoSe2/WS2 Heterostructures. Nano Lett 2016; 16:4087-93. [PMID: 27324060 DOI: 10.1021/acs.nanolett.6b00801] [Citation(s) in RCA: 102] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Strongly bound excitons confined in two-dimensional (2D) semiconductors are dipoles with a perfect in-plane orientation. In a vertical stack of semiconducting 2D crystals, such in-plane excitonic dipoles are expected to efficiently couple across van der Waals gap due to strong interlayer Coulomb interaction and exchange their energy. However, previous studies on heterobilayers of group 6 transition metal dichalcogenides (TMDs) found that the exciton decay dynamics is dominated by interlayer charge transfer (CT) processes. Here, we report an experimental observation of fast interlayer energy transfer (ET) in MoSe2/WS2 heterostructures using photoluminescence excitation (PLE) spectroscopy. The temperature dependence of the transfer rates suggests that the ET is Förster-type involving excitons in the WS2 layer resonantly exciting higher-order excitons in the MoSe2 layer. The estimated ET time of the order of 1 ps is among the fastest compared to those reported for other nanostructure hybrid systems such as carbon nanotube bundles. Efficient ET in these systems offers prospects for optical amplification and energy harvesting through intelligent layer engineering.
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Affiliation(s)
- Daichi Kozawa
- Institute of Advanced Energy, Kyoto University , Gokasho, Uji, Kyoto 611-0011, Japan
- Department of Applied Physics, Waseda University , 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan
- Department of Applied Physics, Nagoya University , Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
| | - Alexandra Carvalho
- Department of Physics, National University of Singapore , 2 Science Drive 3, 117551, Singapore
- Centre for Advanced 2D Materials, National University of Singapore , 6 Science Drive 2, 117546, Singapore
| | - Ivan Verzhbitskiy
- Department of Physics, National University of Singapore , 2 Science Drive 3, 117551, Singapore
- Centre for Advanced 2D Materials, National University of Singapore , 6 Science Drive 2, 117546, Singapore
| | - Francesco Giustiniano
- Department of Physics, National University of Singapore , 2 Science Drive 3, 117551, Singapore
- Centre for Advanced 2D Materials, National University of Singapore , 6 Science Drive 2, 117546, Singapore
| | - Yuhei Miyauchi
- Institute of Advanced Energy, Kyoto University , Gokasho, Uji, Kyoto 611-0011, Japan
- PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Shinichiro Mouri
- Institute of Advanced Energy, Kyoto University , Gokasho, Uji, Kyoto 611-0011, Japan
| | - A H Castro Neto
- Department of Physics, National University of Singapore , 2 Science Drive 3, 117551, Singapore
- Centre for Advanced 2D Materials, National University of Singapore , 6 Science Drive 2, 117546, Singapore
| | - Kazunari Matsuda
- Institute of Advanced Energy, Kyoto University , Gokasho, Uji, Kyoto 611-0011, Japan
| | - Goki Eda
- Department of Physics, National University of Singapore , 2 Science Drive 3, 117551, Singapore
- Centre for Advanced 2D Materials, National University of Singapore , 6 Science Drive 2, 117546, Singapore
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, 117543, Singapore
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Abstract
The relation between unusual Mexican-hat band dispersion, ferromagnetism, and ferroelasticity is investigated using a combination of analytical, first-principles, and phenomenological methods. The class of material with Mexican-hat band edge is studied using the α-SnO monolayer as a prototype. Such a band edge causes a van Hove singularity diverging with 1/sqrt[E], and a charge doping in these bands can lead to time-reversal symmetry breaking. Herein, we show that a material with Mexican-hat band dispersion, α-SnO, can be ferroelastic or paraelastic depending on the number of layers. Also, an unexpected multiferroic phase is obtained in a range of hole density for which the material presents ferromagnetism and ferroelasticity simultaneously.
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Affiliation(s)
- L Seixas
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
- MackGraphe-Graphene and Nanomaterials Research Center, Mackenzie Presbyterian University, 01302-907 São Paulo, São Paulo, Brazil
| | - A S Rodin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
| | - A Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117542, Singapore
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29
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Schmidt H, Yudhistira I, Chu L, Castro Neto AH, Özyilmaz B, Adam S, Eda G. Quantum Transport and Observation of Dyakonov-Perel Spin-Orbit Scattering in Monolayer MoS_{2}. Phys Rev Lett 2016; 116:046803. [PMID: 26871351 DOI: 10.1103/physrevlett.116.046803] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2015] [Indexed: 06/05/2023]
Abstract
Monolayers of group 6 transition metal dichalcogenides are promising candidates for future spin-, valley-, and charge-based applications. Quantum transport in these materials reflects a complex interplay between real spin and pseudospin (valley) relaxation processes, which leads to either positive or negative quantum correction to the classical conductivity. Here we report experimental observation of a crossover from weak localization to weak antilocalization in highly n-doped monolayer MoS_{2}. We show that the crossover can be explained by a single parameter associated with electron spin lifetime of the system. At low temperatures and high carrier densities, the spin lifetime is inversely proportional to momentum relaxation time; this indicates that spin relaxation occurs via a Dyakonov-Perel mechanism.
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Affiliation(s)
- H Schmidt
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
| | - I Yudhistira
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
| | - L Chu
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
| | - B Özyilmaz
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
| | - S Adam
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
- Yale-NUS College, 16 College Ave West, 138527 Singapore
| | - G Eda
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117551 Singapore
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore
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30
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Ni GX, Wang H, Wu JS, Fei Z, Goldflam MD, Keilmann F, Özyilmaz B, Castro Neto AH, Xie XM, Fogler MM, Basov DN. Plasmons in graphene moiré superlattices. Nat Mater 2015; 14:1217-22. [PMID: 26413987 DOI: 10.1038/nmat4425] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Accepted: 08/17/2015] [Indexed: 05/23/2023]
Abstract
Moiré patterns are periodic superlattice structures that appear when two crystals with a minor lattice mismatch are superimposed. A prominent recent example is that of monolayer graphene placed on a crystal of hexagonal boron nitride. As a result of the moiré pattern superlattice created by this stacking, the electronic band structure of graphene is radically altered, acquiring satellite sub-Dirac cones at the superlattice zone boundaries. To probe the dynamical response of the moiré graphene, we use infrared (IR) nano-imaging to explore propagation of surface plasmons, collective oscillations of electrons coupled to IR light. We show that interband transitions associated with the superlattice mini-bands in concert with free electrons in the Dirac bands produce two additive contributions to composite IR plasmons in graphene moiré superstructures. This novel form of collective modes is likely to be generic to other forms of moiré-forming superlattices, including van der Waals heterostructures.
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Affiliation(s)
- G X Ni
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
| | - H Wang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road Shanghai 200050, China
| | - J S Wu
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
| | - Z Fei
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
| | - M D Goldflam
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
| | - F Keilmann
- Ludwig-Maximilians-Universität and Center for Nanoscience, 80539 München, Germany
| | - B Özyilmaz
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore
| | - X M Xie
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road Shanghai 200050, China
| | - M M Fogler
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
| | - D N Basov
- Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
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31
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Lu J, Wu J, Carvalho A, Ziletti A, Liu H, Tan J, Chen Y, Castro Neto AH, Özyilmaz B, Sow CH. Bandgap Engineering of Phosphorene by Laser Oxidation toward Functional 2D Materials. ACS Nano 2015; 9:10411-10421. [PMID: 26364647 DOI: 10.1021/acsnano.5b04623] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We demonstrate a straightforward and effective laser pruning approach to reduce multilayer black phosphorus (BP) to few-layer BP under ambient condition. Phosphorene oxides and suboxides are formed and the degree of laser-induced oxidation is controlled by the laser power. Since the band gaps of the phosphorene suboxide depend on the oxygen concentration, this simple technique is able to realize localized band gap engineering of the thin BP. Micropatterns of few-layer phosphorene suboxide flakes with unique optical and fluorescence properties are created. Remarkably, some of these suboxide flakes display long-term (up to 2 weeks) stability in ambient condition. Comparing against the optical properties predicted by first-principle calculations, we develop a "calibration" map in using focused laser power as a handle to tune the band gap of the BP suboxide flake. Moreover, the surface of the laser patterned region is altered to be sensitive to toxic gas by way of fluorescence contrast. Therefore, the multicolored display is further demonstrated as a toxic gas monitor. In addition, the BP suboxide flake is demonstrated to exhibit higher drain current modulation and mobility comparable to that of the pristine BP in the electronic application.
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Affiliation(s)
- Junpeng Lu
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore
| | - Jing Wu
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore
| | - Alexandra Carvalho
- Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore , 6 Science Drive 2, Singapore 117546, Singapore
| | - Angelo Ziletti
- Department of Chemistry, Boston University , 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States
| | - Hongwei Liu
- Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research) , 3 Research Link, Singapore 117602, Singapore
| | - Junyou Tan
- Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore , 6 Science Drive 2, Singapore 117546, Singapore
| | - Yifan Chen
- Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research) , 3 Research Link, Singapore 117602, Singapore
| | - A H Castro Neto
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore
- Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore , 6 Science Drive 2, Singapore 117546, Singapore
| | - Barbaros Özyilmaz
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore
- Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore , 6 Science Drive 2, Singapore 117546, Singapore
| | - Chorng Haur Sow
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore
- Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore , 6 Science Drive 2, Singapore 117546, Singapore
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32
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Edmonds MT, Tadich A, Carvalho A, Ziletti A, O'Donnell KM, Koenig SP, Coker DF, Özyilmaz B, Neto AHC, Fuhrer MS. Creating a Stable Oxide at the Surface of Black Phosphorus. ACS Appl Mater Interfaces 2015; 7:14557-14562. [PMID: 26126232 DOI: 10.1021/acsami.5b01297] [Citation(s) in RCA: 166] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The stability of the surface of in situ cleaved black phosphorus crystals upon exposure to atmosphere is investigated with synchrotron-based photoelectron spectroscopy. After 2 days atmosphere exposure a stable subnanometer layer of primarily P2O5 forms at the surface. The work function increases by 0.1 eV from 3.9 eV for as-cleaved black phosphorus to 4.0 eV after formation of the 0.4 nm thick oxide, with phosphorus core levels shifting by <0.1 eV. The results indicate minimal charge transfer, suggesting that the oxide layer is suitable for passivation or as an interface layer for further dielectric deposition.
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Affiliation(s)
- M T Edmonds
- ‡School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
| | - A Tadich
- §Australian Synchrotron, 700 Blackburn Road, Clayton, Victoria 3183, Australia
| | | | - A Ziletti
- #Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - K M O'Donnell
- □Department of Imaging and Applied Physics, Curtin University, Bentley, Western Australia 6102, Australia
| | | | - D F Coker
- #Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | | | - A H Castro Neto
- ○Department of Physics, Boston University, Boston, Massachusetts 02215, United States
| | - M S Fuhrer
- ‡School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
- △Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 207424111, United States
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33
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Lin AL, Rodrigues JNB, Su C, Milletari M, Loh KP, Wu T, Chen W, Neto AHC, Adam S, Wee ATS. Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite. Sci Rep 2015; 5:11430. [PMID: 26100970 PMCID: PMC4477240 DOI: 10.1038/srep11430] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 05/05/2015] [Indexed: 11/26/2022] Open
Abstract
Magnetic materials have found wide application ranging from electronics and memories to medicine. Essential to these advances is the control of the magnetic order. To date, most room-temperature applications have a fixed magnetic moment whose orientation is manipulated for functionality. Here we demonstrate an iron-oxide and graphene oxide nanocomposite based device that acts as a tunable ferromagnet at room temperature. Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m2/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process. We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.
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Affiliation(s)
- Aigu L Lin
- 1] NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore,28 Medical Drive, Singapore 117456 [2] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [3] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - J N B Rodrigues
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - Chenliang Su
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117543
| | - M Milletari
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - Kian Ping Loh
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117543
| | - Tom Wu
- Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Wei Chen
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117543
| | - A H Castro Neto
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - Shaffique Adam
- 1] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [2] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542 [3] Yale-NUS College, 16 College Ave West, Singapore 138527
| | - Andrew T S Wee
- 1] NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore,28 Medical Drive, Singapore 117456 [2] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [3] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542
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34
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Cheng CM, Xie LF, Pachoud A, Moser HO, Chen W, Wee ATS, Castro Neto AH, Tsuei KD, Özyilmaz B. Anomalous spectral features of a neutral bilayer graphene. Sci Rep 2015; 5:10025. [PMID: 25985064 PMCID: PMC4434949 DOI: 10.1038/srep10025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 02/23/2015] [Indexed: 11/11/2022] Open
Abstract
Graphene and its bilayer are two-dimensional systems predicted to show exciting many-body effects near the neutrality point. The ideal tool to investigate spectrum reconstruction effects is angle-resolved photoemission spectroscopy (ARPES) as it probes directly the band structure with information about both energy and momentum. Here we reveal, by studying undoped exfoliated bilayer graphene with ARPES, two essential aspects of its many-body physics: the electron-phonon scattering rate has an anisotropic k-dependence and the type of electronic liquid is non-Fermi liquid. The latter behavior is evident from an observed electron-electron scattering rate that scales linearly with energy from 100 meV to 600 meV and that is associated with the proximity of bilayer graphene to a two-dimensional quantum critical point of competing orders.
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Affiliation(s)
- C-M Cheng
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan
| | - L F Xie
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,NanoCore, 4 Engineering Drive 3, National University of Singapore 117576, Singapore
| | - A Pachoud
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Graduate School for Integrative Sciences and Engineering (NGS), National University of Singapore, 28 Medical Drive, 117456, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - H O Moser
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link 117603, Singapore.,Karlsruhe Institute of Technology (KIT), Network of Excellent Retired Scientists (NES) and Institute of Microstructure Technology (IMT), Postfach 3640, 76021 Karlsruhe, Germany
| | - W Chen
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - A T S Wee
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - A H Castro Neto
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - K-D Tsuei
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan.,Department of Physics, National Tsing Hua University, 101 Sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan
| | - B Özyilmaz
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,NanoCore, 4 Engineering Drive 3, National University of Singapore 117576, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
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35
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Lu J, Carvalho A, Chan XK, Liu H, Liu B, Tok ES, Loh KP, Castro Neto AH, Sow CH. Atomic healing of defects in transition metal dichalcogenides. Nano Lett 2015; 15:3524-32. [PMID: 25923457 DOI: 10.1021/acs.nanolett.5b00952] [Citation(s) in RCA: 96] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
As-grown transition metal dichalcogenides are usually chalcogen deficient and therefore contain a high density of chalcogen vacancies, deep electron traps which can act as charged scattering centers, reducing the electron mobility. However, we show that chalcogen vacancies can be effectively passivated by oxygen, healing the electronic structure of the material. We proposed that this can be achieved by means of surface laser modification and demonstrate the efficiency of this processing technique, which can enhance the conductivity of monolayer WSe2 by ∼400 times and its photoconductivity by ∼150 times.
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Affiliation(s)
- Junpeng Lu
- †Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - Alexandra Carvalho
- ‡Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore, 6 Science Drive 2, Singapore 117546
| | - Xinhui Kim Chan
- †Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - Hongwei Liu
- §Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602
| | - Bo Liu
- ‡Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore, 6 Science Drive 2, Singapore 117546
| | - Eng Soon Tok
- †Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
| | - Kian Ping Loh
- ‡Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore, 6 Science Drive 2, Singapore 117546
- ∥Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
| | - A H Castro Neto
- †Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
- ‡Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore, 6 Science Drive 2, Singapore 117546
| | - Chorng Haur Sow
- †Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
- ‡Center For Advanced 2D Materials and Graphene Research Center, National University of Singapore, 6 Science Drive 2, Singapore 117546
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36
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Abstract
Surface reactions with oxygen are a fundamental cause of the degradation of phosphorene. Using first-principles calculations, we show that for each oxygen atom adsorbed onto phosphorene there is an energy release of about 2 eV. Although the most stable oxygen adsorbed forms are electrically inactive and lead only to minor distortions of the lattice, there are low energy metastable forms which introduce deep donor and/or acceptor levels in the gap. We also propose a mechanism for phosphorene oxidation involving reactive dangling oxygen atoms and we suggest that dangling oxygen atoms increase the hydrophilicity of phosphorene.
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Affiliation(s)
- A Ziletti
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
| | - A Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore, Singapore
| | - D K Campbell
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
| | - D F Coker
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA and Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, D-79104 Freiburg, Germany
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546 Singapore, Singapore and Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
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37
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Avsar A, Tan JY, Taychatanapat T, Balakrishnan J, Koon G, Yeo Y, Lahiri J, Carvalho A, Rodin AS, O’Farrell E, Eda G, Castro Neto AH, Özyilmaz B. Spin–orbit proximity effect in graphene. Nat Commun 2014; 5:4875. [DOI: 10.1038/ncomms5875] [Citation(s) in RCA: 350] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Accepted: 07/31/2014] [Indexed: 01/13/2023] Open
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38
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Lu J, Gomes LC, Nunes RW, Castro Neto AH, Loh KP. Lattice relaxation at the interface of two-dimensional crystals: graphene and hexagonal boron-nitride. Nano Lett 2014; 14:5133-9. [PMID: 25083603 DOI: 10.1021/nl501900x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Heteroepitaxy of two-dimensional (2D) crystals, such as hexagonal boron nitride (BN) on graphene (G), can occur at the edge of an existing heterointerface. Understanding strain relaxation at such 2D laterally fused interface is useful in fabricating heterointerfaces with a high degree of atomic coherency and structural stability. We use in situ scanning tunneling microscopy to study the 2D heteroepitaxy of BN on graphene edges on a Ru(0001) surface with the aim of understanding the propagation of interfacial strain. We found that defect-free, pseudomorphic growth of BN on a graphene edge "substrate" occurs only for a short distance (<1.29 nm) perpendicular to the interface, beyond which misfit zero-dimensional dislocations occur to reduce the elastic strain energy. Boundary states originating from a coherent zigzag-linked G/BN boundary are observed to greatly enhance the local conductivity, thus affording a new avenue to construct one-dimensional transport channels in G/BN hybrid interface.
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Affiliation(s)
- Jiong Lu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, 117543, Singapore
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39
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Abstract
The band structure of single-layer black phosphorus and the effect of strain are predicted using density functional theory and tight-binding models. Having determined the localized orbital composition of the individual bands from first principles, we use the system symmetry to write down the effective low-energy Hamiltonian at the Γ point. From numerical calculations and arguments based on the crystal structure of the material, we show that the deformation in the direction normal to the plane can be used to change the gap size and induce a semiconductor-metal transition.
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Affiliation(s)
- A S Rodin
- Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
| | - A Carvalho
- Graphene Research Centre and Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - A H Castro Neto
- Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA and Graphene Research Centre and Department of Physics, National University of Singapore, Singapore 117542, Singapore
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40
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Schmidt H, Wang S, Chu L, Toh M, Kumar R, Zhao W, Neto AHC, Martin J, Adam S, Özyilmaz B, Eda G. Transport properties of monolayer MoS2 grown by chemical vapor deposition. Nano Lett 2014; 14:1909-13. [PMID: 24640984 DOI: 10.1021/nl4046922] [Citation(s) in RCA: 188] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Recent success in the growth of monolayer MoS2 via chemical vapor deposition (CVD) has opened up prospects for the implementation of these materials into thin film electronic and optoelectronic devices. Here, we investigate the electronic transport properties of individual crystallites of high quality CVD-grown monolayer MoS2. The devices show low temperature mobilities up to 500 cm(2) V(-1) s(-1) and a clear signature of metallic conduction at high doping densities. These characteristics are comparable to the electronic properties of the best mechanically exfoliated monolayers in literature, verifying the high electronic quality of the CVD-grown materials. We analyze the different scattering mechanisms and show that the short-range scattering plays a dominant role in the highly conducting regime at low temperatures. Additionally, the influence of optical phonons as a limiting factor is discussed.
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Affiliation(s)
- Hennrik Schmidt
- Graphene Research Centre, National University of Singapore , 6 Science Drive 2, Singapore 117546
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41
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Dai S, Fei Z, Ma Q, Rodin AS, Wagner M, McLeod AS, Liu MK, Gannett W, Regan W, Watanabe K, Taniguchi T, Thiemens M, Dominguez G, Castro Neto AH, Zettl A, Keilmann F, Jarillo-Herrero P, Fogler MM, Basov DN. Tunable phonon polaritons in atomically thin van der Waals crystals of boron nitride. Science 2014; 343:1125-9. [PMID: 24604197 DOI: 10.1126/science.1246833] [Citation(s) in RCA: 434] [Impact Index Per Article: 43.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
van der Waals heterostructures assembled from atomically thin crystalline layers of diverse two-dimensional solids are emerging as a new paradigm in the physics of materials. We used infrared nanoimaging to study the properties of surface phonon polaritons in a representative van der Waals crystal, hexagonal boron nitride. We launched, detected, and imaged the polaritonic waves in real space and altered their wavelength by varying the number of crystal layers in our specimens. The measured dispersion of polaritonic waves was shown to be governed by the crystal thickness according to a scaling law that persists down to a few atomic layers. Our results are likely to hold true in other polar van der Waals crystals and may lead to new functionalities.
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Affiliation(s)
- S Dai
- Department of Physics, University of California, San Diego (UCSD), La Jolla, CA 92093, USA
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42
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Ferreira A, Rappoport TG, Cazalilla MA, Castro Neto AH. Extrinsic spin Hall effect induced by resonant skew scattering in graphene. Phys Rev Lett 2014; 112:066601. [PMID: 24580699 DOI: 10.1103/physrevlett.112.066601] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Indexed: 06/03/2023]
Abstract
We show that the extrinsic spin Hall effect can be engineered in monolayer graphene by decoration with small doses of adatoms, molecules, or nanoparticles originating local spin-orbit perturbations. The analysis of the single impurity scattering problem shows that intrinsic and Rashba spin-orbit local couplings enhance the spin Hall effect via skew scattering of charge carriers in the resonant regime. The solution of the transport equations for a random ensemble of spin-orbit impurities reveals that giant spin Hall currents are within the reach of the current state of the art in device fabrication. The spin Hall effect is robust with respect to thermal fluctuations and disorder averaging.
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Affiliation(s)
- Aires Ferreira
- Graphene Research Centre and Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117546, Singapore
| | - Tatiana G Rappoport
- Instituto de Física, Universidade Federal do Rio de Janeiro, CP 68.528, 21941-972 Rio de Janeiro, RJ, Brazil
| | - Miguel A Cazalilla
- Graphene Research Centre and Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117546, Singapore and Department of Physics, National Tsing Hua University, and National Center for Theoretical Sciences (NCTS), Hsinchu City, Taiwan
| | - A H Castro Neto
- Graphene Research Centre and Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117546, Singapore and Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
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43
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Qi Z, Bahamon DA, Pereira VM, Park HS, Campbell DK, Neto AHC. Resonant tunneling in graphene pseudomagnetic quantum dots. Nano Lett 2013; 13:2692-2697. [PMID: 23659203 DOI: 10.1021/nl400872q] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction.
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Affiliation(s)
- Zenan Qi
- Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
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44
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Sushkov OP, Castro Neto AH. Topological insulating states in laterally patterned ordinary semiconductors. Phys Rev Lett 2013; 110:186601. [PMID: 23683229 DOI: 10.1103/physrevlett.110.186601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Indexed: 06/02/2023]
Abstract
We propose that ordinary semiconductors with large spin-orbit coupling, such as GaAs, can host stable, robust, and tunable topological states in the presence of quantum confinement and superimposed potentials with hexagonal symmetry. We show that the electronic gaps which support chiral spin edge states can be as large as the electronic bandwidth in the heterostructure miniband. The existing lithographic technology can produce a topological insulator operating at a temperature of 10-100 K. Improvement of lithographic techniques will open the way to a tunable room temperature topological insulator.
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Affiliation(s)
- O P Sushkov
- School of Physics, University of New South Wales, Sydney 2052, Australia
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45
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Britnell L, Ribeiro RM, Eckmann A, Jalil R, Belle BD, Mishchenko A, Kim YJ, Gorbachev RV, Georgiou T, Morozov SV, Grigorenko AN, Geim AK, Casiraghi C, Castro Neto AH, Novoselov KS. Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films. Science 2013; 340:1311-4. [PMID: 23641062 DOI: 10.1126/science.1235547] [Citation(s) in RCA: 942] [Impact Index Per Article: 85.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- L Britnell
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
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46
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Zou X, Shang J, Leaw J, Luo Z, Luo L, La-o-Vorakiat C, Cheng L, Cheong SA, Su H, Zhu JX, Liu Y, Loh KP, Castro Neto AH, Yu T, Chia EEM. Terahertz conductivity of twisted bilayer graphene. Phys Rev Lett 2013; 110:067401. [PMID: 23432306 DOI: 10.1103/physrevlett.110.067401] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Indexed: 06/01/2023]
Abstract
Using terahertz time-domain spectroscopy, the real part of optical conductivity [σ(1)(ω)] of twisted bilayer graphene was obtained at different temperatures (10-300 K) in the frequency range 0.3-3 THz. On top of a Drude-like response, we see a strong peak in σ(1)(ω) at ~2.7 THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, which is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers.
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Affiliation(s)
- Xingquan Zou
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore
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47
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Zhao W, Ribeiro RM, Toh M, Carvalho A, Kloc C, Castro Neto AH, Eda G. Origin of indirect optical transitions in few-layer MoS2, WS2, and WSe2. Nano Lett 2013; 13:5627-34. [PMID: 24168432 DOI: 10.1021/nl403270k] [Citation(s) in RCA: 194] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
It has been well-established that single layer MX2 (M = Mo, W and X = S, Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect gap multilayer counterparts. In few-layer MX2, there are two valleys along the Γ-K line with similar energy. There is little understanding on which of the two valleys forms the conduction band minimum (CBM) in this thickness regime. We investigate the conduction band valley structure in few-layer MX2 by examining the temperature-dependent shift of indirect exciton photoluminescence peak. Highly anisotropic thermal expansion of the lattice and the corresponding evolution of the band structure result in a distinct peak shift for indirect transitions involving the K and Λ (midpoint along Γ-K) valleys. We identify the origin of the indirect emission and concurrently determine the relative energy of these valleys.
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Affiliation(s)
- Weijie Zhao
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore
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48
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Huang H, Wei D, Sun J, Wong SL, Feng YP, Neto AHC, Wee ATS. Spatially resolved electronic structures of atomically precise armchair graphene nanoribbons. Sci Rep 2012; 2:983. [PMID: 23248746 PMCID: PMC3523290 DOI: 10.1038/srep00983] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 12/04/2012] [Indexed: 01/23/2023] Open
Abstract
Graphene has attracted much interest in both academia and industry. The challenge of making it semiconducting is crucial for applications in electronic devices. A promising approach is to reduce its physical size down to the nanometer scale. Here, we present the surface-assisted bottom-up fabrication of atomically precise armchair graphene nanoribbons (AGNRs) with predefined widths, namely 7-, 14- and 21-AGNRs, on Ag(111) as well as their spatially resolved width-dependent electronic structures. STM/STS measurements reveal their associated electron scattering patterns and the energy gaps over 1 eV. The mechanism to form such AGNRs is addressed based on the observed intermediate products. Our results provide new insights into the local properties of AGNRs, and have implications for the understanding of their electrical properties and potential applications.
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Affiliation(s)
- Han Huang
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117542.
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Alexandre SS, Lúcio AD, Neto AHC, Nunes RW. Correlated magnetic states in extended one-dimensional defects in graphene. Nano Lett 2012; 12:5097-5102. [PMID: 22950362 DOI: 10.1021/nl3017434] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Ab initio calculations indicate that while the electronic states introduced by tilt grain boundaries in graphene are only partially confined to the defect core, a translational grain boundary introduces states near the Fermi level that are very strongly confined to the core of the defect, and display a ferromagnetic instability. The translational boundary lies along a graphene zigzag direction and its magnetic state is akin to that which has been theoretically predicted to occur on zigzag edges of graphene ribbons. Unlike ribbon edges, the translational grain boundary is fully immersed within the bulk of graphene, hence its magnetic state is protected from the contamination and reconstruction effects that have hampered experimental detection of the magnetic ribbon states. Moreover, our calculations suggest that charge transfer between grain boundaries and the bulk in graphene is short ranged, with charge redistribution confined to ~5 Å from the geometric center of the 1D defects.
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Affiliation(s)
- Simone S Alexandre
- Departamento de Física, ICEx, Universidade Federal de Minas Gerais, 31270-901, Belo Horizonte, MG, Brazil
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50
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Abstract
The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times, acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction.
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Affiliation(s)
- H Ochoa
- Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain
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