1
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Whelan PR, De Fazio D, Pasternak I, Thomsen JD, Zelzer S, Mikkelsen MO, Booth TJ, Diekhöner L, Sassi U, Johnstone D, Midgley PA, Strupinski W, Jepsen PU, Ferrari AC, Bøggild P. Mapping nanoscale carrier confinement in polycrystalline graphene by terahertz spectroscopy. Sci Rep 2024; 14:3163. [PMID: 38326379 PMCID: PMC10850153 DOI: 10.1038/s41598-024-51548-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] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Accepted: 01/06/2024] [Indexed: 02/09/2024] Open
Abstract
Terahertz time-domain spectroscopy (THz-TDS) can be used to map spatial variations in electrical properties such as sheet conductivity, carrier density, and carrier mobility in graphene. Here, we consider wafer-scale graphene grown on germanium by chemical vapor deposition with non-uniformities and small domains due to reconstructions of the substrate during growth. The THz conductivity spectrum matches the predictions of the phenomenological Drude-Smith model for conductors with non-isotropic scattering caused by backscattering from boundaries and line defects. We compare the charge carrier mean free path determined by THz-TDS with the average defect distance assessed by Raman spectroscopy, and the grain boundary dimensions as determined by transmission electron microscopy. The results indicate that even small angle orientation variations below 5° within graphene grains influence the scattering behavior, consistent with significant backscattering contributions from grain boundaries.
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Affiliation(s)
- Patrick R Whelan
- DTU Physics, Technical University of Denmark, Fysikvej, Bld. 309, 2800, Kongens Lyngby, Denmark
- Department of Materials and Production, Aalborg University, Skjernvej 4A, 9220, Aalborg, Denmark
| | - Domenico De Fazio
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge, CB3 0FA, UK
- Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, 30172, Venice, Italy
| | - Iwona Pasternak
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662, Warsaw, Poland
- Vigo System S.A., 129/133 Poznanska Str, 05-850, Ozarow Mazowiecki, Poland
| | - Joachim D Thomsen
- DTU Physics, Technical University of Denmark, Fysikvej, Bld. 309, 2800, Kongens Lyngby, Denmark
| | - Steffen Zelzer
- Department of Materials and Production, Aalborg University, Skjernvej 4A, 9220, Aalborg, Denmark
| | - Martin O Mikkelsen
- Department of Materials and Production, Aalborg University, Skjernvej 4A, 9220, Aalborg, Denmark
| | - Timothy J Booth
- DTU Physics, Technical University of Denmark, Fysikvej, Bld. 309, 2800, Kongens Lyngby, Denmark
- Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
| | - Lars Diekhöner
- Department of Materials and Production, Aalborg University, Skjernvej 4A, 9220, Aalborg, Denmark
| | - Ugo Sassi
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge, CB3 0FA, UK
| | - Duncan Johnstone
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK
| | - Paul A Midgley
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK
| | - Wlodek Strupinski
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662, Warsaw, Poland
- Vigo System S.A., 129/133 Poznanska Str, 05-850, Ozarow Mazowiecki, Poland
| | - Peter U Jepsen
- Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
- DTU Fotonik, Technical University of Denmark, Ørsteds Plads 343, 2800, Kongens Lyngby, Denmark
| | - Andrea C Ferrari
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge, CB3 0FA, UK
| | - Peter Bøggild
- DTU Physics, Technical University of Denmark, Fysikvej, Bld. 309, 2800, Kongens Lyngby, Denmark.
- Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark.
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2
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Ji J, Zhou Y, Zhou B, Desgué E, Legagneux P, Jepsen PU, Bøggild P. Probing Carrier Dynamics in Large-Scale MBE-Grown PtSe 2 Films by Terahertz Spectroscopy. ACS Appl Mater Interfaces 2023. [PMID: 37883033 DOI: 10.1021/acsami.3c09792] [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] [Indexed: 10/27/2023]
Abstract
Atomically thin platinum diselenide (PtSe2) films are promising for applications in the fields of electronics, spintronics, and photodetectors owing to their tunable electronic structure and high carrier mobility. Using terahertz (THz) spectroscopy techniques, we investigated the layer-dependent semiconducting-to-metallic phase transition and associated intrinsic carrier dynamics in large-scale PtSe2 films grown by molecular beam epitaxy. The uniformity of large-scale PtSe2 films was characterized by spatially and frequency-resolved THz-based sheet conductivity mapping. Furthermore, we use an optical-pump-THz-probe technique to study the transport dynamics of photoexcited carriers and explore light-induced intergrain carrier transport in PtSe2 films. We demonstrate large-scale THz-based mapping of the electrical properties of transition metal dichalcogenide films and show that the two noncontact THz-based approaches provide insight in the spatial and temporal properties of PtSe2 films.
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Affiliation(s)
- Jie Ji
- Department of Physics, Technical University of Denmark, Kgs. Lyngby 2800, Denmark
| | - Yingqiu Zhou
- Department of Physics, Technical University of Denmark, Kgs. Lyngby 2800, Denmark
| | - Binbin Zhou
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Kgs. Lyngby 2800, Denmark
| | - Eva Desgué
- Thales Research and Technology, Palaiseau 91767, France
| | | | - Peter Uhd Jepsen
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Kgs. Lyngby 2800, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark, Kgs. Lyngby 2800, Denmark
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3
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Kapfer M, Jessen BS, Eisele ME, Fu M, Danielsen DR, Darlington TP, Moore SL, Finney NR, Marchese A, Hsieh V, Majchrzak P, Jiang Z, Biswas D, Dudin P, Avila J, Watanabe K, Taniguchi T, Ulstrup S, Bøggild P, Schuck PJ, Basov DN, Hone J, Dean CR. Programming twist angle and strain profiles in 2D materials. Science 2023; 381:677-681. [PMID: 37561852 DOI: 10.1126/science.ade9995] [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: 09/21/2022] [Accepted: 06/21/2023] [Indexed: 08/12/2023]
Abstract
Moiré superlattices in twisted two-dimensional materials have generated tremendous excitement as a platform for achieving quantum properties on demand. However, the moiré pattern is highly sensitive to the interlayer atomic registry, and current assembly techniques suffer from imprecise control of the average twist angle, spatial inhomogeneity in the local twist angle, and distortions caused by random strain. We manipulated the moiré patterns in hetero- and homobilayers through in-plane bending of monolayer ribbons, using the tip of an atomic force microscope. This technique achieves continuous variation of twist angles with improved twist-angle homogeneity and reduced random strain, resulting in moiré patterns with tunable wavelength and ultralow disorder. Our results may enable detailed studies of ultralow-disorder moiré systems and the realization of precise strain-engineered devices.
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Affiliation(s)
- Maëlle Kapfer
- Department of Physics, Columbia University, New York, NY, USA
| | - Bjarke S Jessen
- Department of Physics, Columbia University, New York, NY, USA
| | - Megan E Eisele
- Department of Physics, Columbia University, New York, NY, USA
| | - Matthew Fu
- Department of Physics, Columbia University, New York, NY, USA
| | - Dorte R Danielsen
- Center for Nanostructured Graphene, Technical University of Denmark, DK-2800, Denmark
- DTU Physics, Technical University of Denmark, DK-2800, Denmark
| | - Thomas P Darlington
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Samuel L Moore
- Department of Physics, Columbia University, New York, NY, USA
| | - Nathan R Finney
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Ariane Marchese
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Valerie Hsieh
- Department of Physics, Columbia University, New York, NY, USA
| | - Paulina Majchrzak
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Zhihao Jiang
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Deepnarayan Biswas
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Pavel Dudin
- Synchrotron SOLEIL, Université Paris-Saclay, F-91192 Gif sur Yvette, France
| | - José Avila
- Synchrotron SOLEIL, Université Paris-Saclay, F-91192 Gif sur Yvette, France
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Søren Ulstrup
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene, Technical University of Denmark, DK-2800, Denmark
- DTU Physics, Technical University of Denmark, DK-2800, Denmark
| | - P J Schuck
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Dmitri N Basov
- Department of Physics, Columbia University, New York, NY, USA
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Cory R Dean
- Department of Physics, Columbia University, New York, NY, USA
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4
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Ghimire G, Ulaganathan RK, Tempez A, Ilchenko O, Unocic RR, Heske J, Miakota DI, Xiang C, Chaigneau M, Booth T, Bøggild P, Thygesen KS, Geohegan DB, Canulescu S. Molybdenum Disulfide Nanoribbons with Enhanced Edge Nonlinear Response and Photoresponsivity. Adv Mater 2023:e2302469. [PMID: 37246801 DOI: 10.1002/adma.202302469] [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] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 05/04/2023] [Indexed: 05/30/2023]
Abstract
MoS2 nanoribbons have attracted an increased interest due to their properties, which can be tailored by tuning their dimensions. Herein, we demonstrate the growth of MoS2 nanoribbons and 3D triangular crystals formed by the reaction between ultra-thin films of MoO3 grown by Pulsed Laser Deposition and NaF in a sulfur-rich environment. The multilayer nanoribbons can reach up to 10 μm in length, and feature single-layer edges, forming a monolayer-multilayer MoS2 junction enabled by the lateral modulation in thickness. The single-layer edges of the nanoribbons show a pronounced second harmonic generation due to the symmetry breaking, in contrast to the centrosymmetric multilayer structure, which is unsusceptible to the second-order nonlinear process. A pronounced splitting of the Raman spectra was observed in MoS2 nanoribbons arising from distinct contributions from the monolayer edges and multilayer core. Nanoscale imaging reveals a blue-shifted exciton emission of the monolayer edge compared to the triangular MoS2 monolayers due to built-in local strain and disorder. We further report on an ultrasensitive photodetector made of a single MoS2 nanoribbon with a responsivity of 8.72×102 A/W at 532 nm, among the highest reported up-to-date for single-nanoribbon photodetectors. Our findings can inspire the design of MoS2 semiconductors with tunable geometries for efficient optoelectronic devices. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Ganesh Ghimire
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Roskilde, 4000, Denmark
| | - Rajesh Kumar Ulaganathan
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Roskilde, 4000, Denmark
| | | | - Oleksii Ilchenko
- Department of Health Technology Nanoprobes, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark
| | - Raymond R Unocic
- Center for Nanophase Materials Sciences and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37830, United States
| | - Julian Heske
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark
| | - Denys I Miakota
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Roskilde, 4000, Denmark
| | - Cheng Xiang
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark
| | | | - Tim Booth
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark
| | - Kristian S Thygesen
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark
| | - David B Geohegan
- Center for Nanophase Materials Sciences and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37830, United States
| | - Stela Canulescu
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Roskilde, 4000, Denmark
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5
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Zhou B, Rasmussen M, Whelan PR, Ji J, Shivayogimath A, Bøggild P, Jepsen PU. Non-Linear Conductivity Response of Graphene on Thin-Film PET Characterized by Transmission and Reflection Air-Plasma THz-TDS. Sensors (Basel) 2023; 23:3669. [PMID: 37050729 PMCID: PMC10099266 DOI: 10.3390/s23073669] [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] [Figures] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Revised: 03/28/2023] [Accepted: 03/29/2023] [Indexed: 06/19/2023]
Abstract
We demonstrate that the conductivity of graphene on thin-film polymer substrates can be accurately determined by reflection-mode air-plasma-based THz time-domain spectroscopy (THz-TDS). The phase uncertainty issue associated with reflection measurements is discussed, and our implementation is validated by convincing agreement with graphene electrical properties extracted from more conventional transmission-mode measurements. Both the reflection and transmission THz-TDS measurements reveal strong non-linear and instantaneous conductivity depletion across an ultra-broad bandwidth (1-9 THz) under relatively high incident THz electrical field strengths (up to 1050 kV/cm).
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Affiliation(s)
- Binbin Zhou
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Mattias Rasmussen
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | | | - Jie Ji
- Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Abhay Shivayogimath
- Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Peter Uhd Jepsen
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
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6
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Mølvig BH, Bæk T, Ji J, Bøggild P, Lange SJ, Jepsen PU. Terahertz Cross-Correlation Spectroscopy and Imaging of Large-Area Graphene. Sensors (Basel) 2023; 23:3297. [PMID: 36992008 PMCID: PMC10059862 DOI: 10.3390/s23063297] [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] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 03/08/2023] [Accepted: 03/16/2023] [Indexed: 06/19/2023]
Abstract
We demonstrate the use of a novel, integrated THz system to obtain time-domain signals for spectroscopy in the 0.1-1.4 THz range. The system employs THz generation in a photomixing antenna excited by a broadband amplified spontaneous emission (ASE) light source and THz detection with a photoconductive antenna by coherent cross-correlation sampling. We benchmark the performance of our system against a state-of-the-art femtosecond-based THz time-domain spectroscopy system in terms of mapping and imaging of the sheet conductivity of large-area graphene grown by chemical vapor deposition (CVD) and transferred to a PET polymer substrate. We propose to integrate the algorithm for the extraction of the sheet conductivity with the data acquisition, thereby enabling true in-line monitoring capability of the system for integration in graphene production facilities.
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Affiliation(s)
- Bjørn Hübschmann Mølvig
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Thorsten Bæk
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
- GLAZE Technologies Aps, 2950 Vedbæk, Denmark
| | - Jie Ji
- Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Simon Jappe Lange
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
- GLAZE Technologies Aps, 2950 Vedbæk, Denmark
| | - Peter Uhd Jepsen
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
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7
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Abstract
More than a decade after the first demonstration of large-scale graphene synthesis by chemical vapor deposition, the commercialization of graphene products is limited not only by price, but also by consistency, reproducibility, and predictability. Here, the author discusses the reproducibility issues in the field and proposes possible solutions to improve the reliability of published results.
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Affiliation(s)
- Peter Bøggild
- Department of Physics, Technical University of Denmark, 2800 Kgs, Lyngby, Denmark.
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8
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Jones AJH, Gammelgaard L, Sauer MO, Biswas D, Koch RJ, Jozwiak C, Rotenberg E, Bostwick A, Watanabe K, Taniguchi T, Dean CR, Jauho AP, Bøggild P, Pedersen TG, Jessen BS, Ulstrup S. Nanoscale View of Engineered Massive Dirac Quasiparticles in Lithographic Superstructures. ACS Nano 2022; 16:19354-19362. [PMID: 36321616 DOI: 10.1021/acsnano.2c08929] [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] [Indexed: 06/16/2023]
Abstract
Massive Dirac fermions are low-energy electronic excitations characterized by a hyperbolic band dispersion. They play a central role in several emerging physical phenomena such as topological phase transitions, anomalous Hall effects, and superconductivity. This work demonstrates that massive Dirac fermions can be controllably induced by lithographically patterning superstructures of nanoscale holes in a graphene device. Their band dispersion is systematically visualized using angle-resolved photoemission spectroscopy with nanoscale spatial resolution. A linear scaling of effective mass with feature sizes is reported, underlining the Dirac nature of the superstructures. In situ electrostatic doping dramatically enhances the effective hole mass and leads to the direct observation of an electronic band gap that results in a peak-to-peak band separation of 0.64 ± 0.03 eV, which is shown via first-principles calculations to be strongly renormalized by carrier-induced screening. The methodology demonstrates band structure engineering guided by directly viewing structurally and electrically tunable massive Dirac quasiparticles in lithographic superstructures at the nanoscale.
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Affiliation(s)
- Alfred J H Jones
- Department of Physics and Astronomy, Aarhus University, 8000Aarhus C, Denmark
| | - Lene Gammelgaard
- DTU Physics, Technical University of Denmark, 2800Kgs. Lyngby, Denmark
- Center for Nanostructured Graphene, Technical University of Denmark, 2800Kgs. Lyngby, Denmark
| | - Mikkel O Sauer
- Department of Materials and Production, Aalborg University, 9220Aalborg Øst, Denmark
- Department of Mathematical Science, Aalborg University, 9220Aalborg Øst, Denmark
- Center for Nanostructured Graphene (CNG), 9220Aalborg Øst, Denmark
| | - Deepnarayan Biswas
- Department of Physics and Astronomy, Aarhus University, 8000Aarhus C, Denmark
| | - Roland J Koch
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | - Chris Jozwiak
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | - Eli Rotenberg
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | - Aaron Bostwick
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
| | - Cory R Dean
- Department of Physics, Columbia University, New York, New York10027, United States
| | - Antti-Pekka Jauho
- DTU Physics, Technical University of Denmark, 2800Kgs. Lyngby, Denmark
- Center for Nanostructured Graphene, Technical University of Denmark, 2800Kgs. Lyngby, Denmark
| | - Peter Bøggild
- DTU Physics, Technical University of Denmark, 2800Kgs. Lyngby, Denmark
- Center for Nanostructured Graphene, Technical University of Denmark, 2800Kgs. Lyngby, Denmark
| | - Thomas G Pedersen
- Department of Materials and Production, Aalborg University, 9220Aalborg Øst, Denmark
- Center for Nanostructured Graphene (CNG), 9220Aalborg Øst, Denmark
| | - Bjarke S Jessen
- Department of Physics, Columbia University, New York, New York10027, United States
| | - Søren Ulstrup
- Department of Physics and Astronomy, Aarhus University, 8000Aarhus C, Denmark
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9
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Pizzocchero F, Jessen BS, Gammelgaard L, Andryieuski A, Whelan PR, Shivayogimath A, Caridad JM, Kling J, Petrone N, Tang PT, Malureanu R, Hone J, Booth TJ, Lavrinenko A, Bøggild P. Chemical Vapor-Deposited Graphene on Ultraflat Copper Foils for van der Waals Hetero-Assembly. ACS Omega 2022; 7:22626-22632. [PMID: 35811885 PMCID: PMC9260747 DOI: 10.1021/acsomega.2c01946] [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] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Accepted: 06/09/2022] [Indexed: 06/15/2023]
Abstract
The purity and morphology of the copper surface is important for the synthesis of high-quality, large-grained graphene by chemical vapor deposition. We find that atomically smooth copper foils-fabricated by physical vapor deposition and subsequent electroplating of copper on silicon wafer templates-exhibit strongly reduced surface roughness after the annealing of the copper catalyst, and correspondingly lower nucleation and defect density of the graphene film, when compared to commercial cold-rolled copper foils. The "ultrafoils"-ultraflat foils-facilitate easier dry pickup and encapsulation of graphene by hexagonal boron nitride, which we believe is due to the lower roughness of the catalyst surface promoting a conformal interface and subsequent stronger van der Waals adhesion between graphene and hexagonal boron nitride.
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Affiliation(s)
- Filippo Pizzocchero
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
| | - Bjarke S. Jessen
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
- Department
of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Lene Gammelgaard
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
| | - Andrei Andryieuski
- DTU
Electro, Technical University of Denmark, Ørsteds pl. 343, Kongens Lyngby 2800 Denmark
| | - Patrick R. Whelan
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
- Department
of Materials and Production, Aalborg University, Skjernvej 4A, Aalborg 9220, Denmark
| | - Abhay Shivayogimath
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
| | - José M. Caridad
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
- Department
of Applied Physics and USAL NanoLab, University
of Salamanca, 37008 Salamanca, Spain
| | - Jens Kling
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Nanolab, Technical University of Denmark, Fysikvej 307, Kongens Lyngby 2800, Denmark
| | - Nicholas Petrone
- Department
of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Peter T. Tang
- IPU,
Danmarks Tekniske Universitet, Produktionstorvet 425, Kongens Lyngby 2800 Denmark
| | - Radu Malureanu
- DTU
Electro, Technical University of Denmark, Ørsteds pl. 343, Kongens Lyngby 2800 Denmark
| | - James Hone
- Department
of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Timothy J. Booth
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
| | - Andrei Lavrinenko
- DTU
Electro, Technical University of Denmark, Ørsteds pl. 343, Kongens Lyngby 2800 Denmark
| | - Peter Bøggild
- CNG—Center
of Nanostructured Graphene, Kongens
Lyngby 2800 Denmark
- DTU
Physics, Technical University of Denmark, Building 309, Kongens Lyngb 2800 Denmark
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10
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Yao W, Zhang J, Ji J, Yang H, Zhou B, Chen X, Bøggild P, Jepsen PU, Tang J, Wang F, Zhang L, Liu J, Wu B, Dong J, Liu Y. Bottom-Up-Etching-Mediated Synthesis of Large-Scale Pure Monolayer Graphene on Cyclic-Polishing-Annealed Cu(111). Adv Mater 2022; 34:e2108608. [PMID: 34820918 DOI: 10.1002/adma.202108608] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Revised: 11/22/2021] [Indexed: 06/13/2023]
Abstract
Synthesis of large-scale single-crystalline graphene monolayers without multilayers involves the fabrication of proper single-crystalline substrates and the ubiquitous formation of multilayered graphene islands during chemical vapor deposition. Here, a method of cyclic electrochemical polishing combined with thermal annealing, which allows the conversion of commercial polycrystalline Cu foils to single-crystal Cu(111) with an almost 100% yield, is presented. A global "bottom-up-etching" method that is capable of fabricating large-area pure single-crystalline graphene monolayers without multilayers through selectively etching bottom multilayered graphene underneath large area as-grown graphene monolayer on Cu(111) surface is demonstrated. Terahertz time-domain spectroscopy (THz-TDS) measurement of the pure monolayer graphene film shows a high average sheet conductivity of 2.8 mS and mean carrier mobility of 6903 cm2 V-1 s-1 over a large area. Density functional theory (DFT) calculations show that the selective etching is induced by the much easier diffusion of hydrogen atoms than hydrocarbon radicals across the edges of the top graphene layer, and the simulated selective etching processes based on phase field modeling are well consistent with experimental observations. This work provides new ways toward the production of single-crystal Cu(111) and the synthesis of pure monolayer graphene with high electronic quality.
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Affiliation(s)
- Wenqian Yao
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Beijing, 100190, P. R. China
- Sino-Danish Center for Education and Research, Sino-Danish College, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jianing Zhang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Beijing, 100190, P. R. China
- Sino-Danish Center for Education and Research, Sino-Danish College, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jie Ji
- Department of Physics, Technical University of Denmark, Kongens Lyngby, DK-2800, Denmark
| | - He Yang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Beijing, 100190, P. R. China
| | - Binbin Zhou
- Department of Photonics, Technical University of Denmark, Kongens Lyngby, DK-2800, Denmark
| | - Xin Chen
- Department of Physics, Technical University of Denmark, Kongens Lyngby, DK-2800, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark, Kongens Lyngby, DK-2800, Denmark
| | - Peter U Jepsen
- Department of Photonics, Technical University of Denmark, Kongens Lyngby, DK-2800, Denmark
| | - Jilin Tang
- Beijing National Laboratory for Molecular Sciences, National Centre for Mass Spectrometry in Beijing, CAS Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Fuyi Wang
- Beijing National Laboratory for Molecular Sciences, National Centre for Mass Spectrometry in Beijing, CAS Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Li Zhang
- Analytical Instrumentation Center, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P. R. China
| | - Jiahui Liu
- Analytical Instrumentation Center, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P. R. China
| | - Bin Wu
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Beijing, 100190, P. R. China
| | - Jichen Dong
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Beijing, 100190, P. R. China
| | - Yunqi Liu
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Beijing, 100190, P. R. China
- Sino-Danish Center for Education and Research, Sino-Danish College, University of Chinese Academy of Sciences, Beijing, 100049, China
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11
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Gammelgaard L, Whelan PR, Booth TJ, Bøggild P. Long-term stability and tree-ring oxidation of WSe 2 using phase-contrast AFM. Nanoscale 2021; 13:19238-19246. [PMID: 34787157 DOI: 10.1039/d1nr05413a] [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] [Indexed: 06/13/2023]
Abstract
In this work, we use atomic force microscopy (AFM) to investigate the long-term evolution of oxidative defects of tungsten diselenide (WSe2) in ambient conditions over a period of 75 months, which is the longest such study performed on any layered material. In particular, we find that phase-imaging AFM of mechanically exfoliated WSe2 crystals provides convenient, direct identification of exposed and covered step-edges, and together with topographic thickness measurements allows complete determination of the layer arrangement in a multilayer flake. Step-edges with low or no phase-contrast consistently exhibit long-term stability in ambient conditions, indicating that they are covered and effectively protected by above-lying WSe2 layers. On the contrary, step-edges with initial high phase-contrast are clearly degraded after medium- to long-term exposure to ambient conditions (up to six months), indicating that these are not covered by other layers. Similar behaviour was observed for MoTe2 and MoS2. The correlation between phase-contrast and step order was confirmed by cross-sectional transmission electron microscopy. By comparing the phase-contrast line-traces in different locations and at different times, we find that long-term storage in ambient conditions led to evolution of a distinct ring-like pattern resembling the tree-lines arising from seasonal changes. Indeed the phase-contrast showed correlation with the average amount of sun-hours registered at the storage location. Storage in darkness slowed down the evolution of the tree-ring lines, in accordance with this explanation. Our work provides a unique dataset on long-term degradation of one of the most stable transition metal dichalcogenides, as well as insights into the conditions causing acceleration or inhibition of the degradation process.
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Affiliation(s)
- Lene Gammelgaard
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby, Denmark.
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
| | - Patrick R Whelan
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby, Denmark.
- Department of Materials and Production, Aalborg University, Skjernvej 4A, 9220 Aalborg, Denmark
| | - Timothy J Booth
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby, Denmark.
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby, Denmark.
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
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12
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Danielsen DR, Lyksborg-Andersen A, Nielsen KES, Jessen BS, Booth TJ, Doan MH, Zhou Y, Bøggild P, Gammelgaard L. Super-Resolution Nanolithography of Two-Dimensional Materials by Anisotropic Etching. ACS Appl Mater Interfaces 2021; 13:41886-41894. [PMID: 34431654 DOI: 10.1021/acsami.1c09923] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Nanostructuring allows altering of the electronic and photonic properties of two-dimensional (2D) materials. The efficiency, flexibility, and convenience of top-down lithography processes are, however, compromised by nanometer-scale edge roughness and resolution variability issues, which especially affect the performance of 2D materials. Here, we study how dry anisotropic etching of multilayer 2D materials with sulfur hexafluoride (SF6) may overcome some of these issues, showing results for hexagonal boron nitride (hBN), tungsten disulfide (WS2), tungsten diselenide (WSe2), molybdenum disulfide (MoS2), and molybdenum ditelluride (MoTe2). Scanning electron microscopy and transmission electron microscopy reveal that etching leads to anisotropic hexagonal features in the studied transition metal dichalcogenides, with the relative degree of anisotropy ranked as: WS2 > WSe2 > MoTe2 ∼ MoS2. Etched holes are terminated by zigzag edges while etched dots (protrusions) are terminated by armchair edges. This can be explained by Wulff constructions, taking the relative stabilities of the edges and the AA' stacking order into account. Patterns in WS2 are transferred to an underlying graphite layer, demonstrating a possible use for creating sub-10 nm features. In contrast, multilayer hBN exhibits no lateral anisotropy but shows consistent vertical etch angles, independent of crystal orientation. Using an hBN crystal as the base, ultrasharp corners can be created in lithographic patterns, which are then transferred to a graphite crystal underneath. We find that the anisotropic SF6 reactive ion etching process makes it possible to downsize nanostructures and obtain smooth edges, sharp corners, and feature sizes significantly below the resolution limit of electron beam lithography. The nanostructured 2D materials can be used themselves or as etch masks to pattern other nanomaterials.
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Affiliation(s)
- Dorte R Danielsen
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
| | - Anton Lyksborg-Andersen
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
- DTU Nanolab - National Centre for Nano Fabrication and Characterization, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
| | - Kirstine E S Nielsen
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
| | - Bjarke S Jessen
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Timothy J Booth
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
| | - Manh-Ha Doan
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
| | - Yingqiu Zhou
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
| | - Peter Bøggild
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
| | - Lene Gammelgaard
- Department of Physics, Technical University of Denmark (DTU), Kgs. Lyngby 2800, Denmark
- Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby DK-2800, Denmark
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13
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Fischer M, Caridad JM, Sajid A, Ghaderzadeh S, Ghorbani-Asl M, Gammelgaard L, Bøggild P, Thygesen KS, Krasheninnikov AV, Xiao S, Wubs M, Stenger N. Controlled generation of luminescent centers in hexagonal boron nitride by irradiation engineering. Sci Adv 2021; 7:7/8/eabe7138. [PMID: 33597249 PMCID: PMC7888958 DOI: 10.1126/sciadv.abe7138] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 01/06/2021] [Indexed: 05/22/2023]
Abstract
Luminescent centers in the two-dimensional material hexagonal boron nitride have the potential to enable quantum applications at room temperature. To be used for applications, it is crucial to generate these centers in a controlled manner and to identify their microscopic nature. Here, we present a method inspired by irradiation engineering with oxygen atoms. We systematically explore the influence of the kinetic energy and the irradiation fluence on the generation of luminescent centers. We find modifications of their density for both parameters, while a fivefold enhancement is observed with increasing fluence. Molecular dynamics simulations clarify the generation mechanism of these centers and their microscopic nature. We infer that VNCB and [Formula: see text] are the most likely centers formed. Ab initio calculations of their optical properties show excellent agreement with our experiments. Our methodology generates quantum emitters in a controlled manner and provides insights into their microscopic nature.
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Affiliation(s)
- M Fischer
- Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- NanoPhoton - Center for Nanophotonics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - J M Caridad
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Department of Physics and NanoLund, Lund University, box 118, 22100 Lund, Sweden
| | - A Sajid
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - S Ghaderzadeh
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
| | - M Ghorbani-Asl
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
| | - L Gammelgaard
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - P Bøggild
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - K S Thygesen
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - A V Krasheninnikov
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
- Department of Applied Physics, Aalto University, 00076 Espoo, Finland
| | - S Xiao
- Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- NanoPhoton - Center for Nanophotonics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - M Wubs
- Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- NanoPhoton - Center for Nanophotonics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - N Stenger
- Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
- Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- NanoPhoton - Center for Nanophotonics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
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14
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Luo B, Yang S, Yuan A, Zhang B, Li D, Bøggild P, Booth TJ. Selective area oxidation of copper derived from chemical vapor deposited graphene microstructure. Nanotechnology 2020; 31:485603. [PMID: 32936786 DOI: 10.1088/1361-6528/abb26d] [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] [Indexed: 06/11/2023]
Abstract
The barrier properties of graphene coating are highly correlated with its microstructure which is then determined by the chemical vapor deposition (CVD) growth history on metals. We demonstrate here an unrevealed selective area oxidation of copper under graphene, which is derived from the implicit-etching-controlled CVD growth mode of graphene. By charactering and analyzing the selective area patterns of Cu oxidation, an etched pattern trace with nano/microvoids during graphene growth has been proposed to account for this. Based on such selective oxidation of Cu, distributed galvanic corrosion will be triggered and proceed locally at the interface of graphene-Cu system to coalescence together under a continuous corrosion environment, eventually presenting a homogeneous oxidation of Cu and gradual decoupling of graphene-Cu system. This discovery will assist our understanding of the barrier properties of two-dimensional materials and can be extended to other applications related to quality monitoring of grown materials and defects-based chemical modifications.
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Affiliation(s)
- Birong Luo
- Department of Physics and Materials Science, Tianjin Normal University, Tianjin, People's Republic of China
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15
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Whelan PR, Shen Q, Luo D, Wang M, Ruoff RS, Jepsen PU, Bøggild P, Zhou B. Reference-free THz-TDS conductivity analysis of thin conducting films. Opt Express 2020; 28:28819-28830. [PMID: 33114792 DOI: 10.1364/oe.402447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Accepted: 09/01/2020] [Indexed: 06/11/2023]
Abstract
We present a reference-free method to determine electrical parameters of thin conducting films by steady state transmission-mode terahertz time-domain spectroscopy (THz-TDS). We demonstrate that the frequency-dependent AC conductivity of graphene can be acquired by comparing the directly transmitted THz pulse with a transient internal reflection within the substrate which avoids the need for a standard reference scan. The DC sheet conductivity, scattering time, carrier density, mobility, and Fermi velocity of graphene are retrieved subsequently by fitting the AC conductivity with the Drude model. This reference-free method was investigated with two complementary THz setups: one commercial fibre-coupled THz spectrometer with fast scanning rate (0.2-1.5 THz) and one air-plasma based ultra-broadband THz spectrometer for greatly extended frequency range (2-10 THz). Certain propagation correction terms for more accurate retrieval of electrical parameters are discussed.
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16
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Mackenzie DMA, Kalhauge KG, Whelan PR, Østergaard FW, Pasternak I, Strupinski W, Bøggild P, Jepsen PU, Petersen DH. Wafer-scale graphene quality assessment using micro four-point probe mapping. Nanotechnology 2020; 31:225709. [PMID: 32167935 DOI: 10.1088/1361-6528/ab7677] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Micro four-point probes (M4PP) provide rapid and automated lithography-free transport properties of planar surfaces including two-dimensional materials. We perform sheet conductance wafer maps of graphene directly grown on a 100 mm diameter SiC wafer using a multiplexed seven-point probe with minor additional measurement time compared to a four-point probe. Comparing the results of three subprobes we find that compared to a single-probe result, our measurement yield increases from 72%-84% to 97%. The additional data allows for correlation analysis between adjacent subprobes, that must measure the same values in case the sample is uniform on the scale of the electrode pitch. We observe that the relative difference in measured sheet conductance between two adjacent subprobes increase in the transition between large and low conductance regions. We mapped sheet conductance of graphene as it changed over several weeks. Terahertz time-domain spectroscopy conductivity maps both before and after M4PP mapping showed no significant change due to M4PP measurement, with both methods showing the same qualitative changes over time.
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Affiliation(s)
- David M A Mackenzie
- Center for Nanostructured Graphene (CNG), Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark. Department of Electronics and Nanoengineering, Aalto University, PO Box 13500, FI-00076 Aalto, Finland
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17
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Luo B, Koleini M, Whelan PR, Shivayogimath A, Brandbyge M, Bøggild P, Booth TJ. Graphene-Subgrain-Defined Oxidation of Copper. ACS Appl Mater Interfaces 2019; 11:48518-48524. [PMID: 31797664 DOI: 10.1021/acsami.9b15931] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The correlation between the crystal structure of chemical vapor deposition (CVD)-grown graphene and the crystal structure of the Cu growth substrate and their mutual effect on the oxidation of the underlying Cu are systematically explored. We report that natural oxygen or water intercalation along the graphene-Cu interface results in an orientation-dependent oxidation rate of the Cu surface, particularly noticeable for bicrystal graphene domains on the same copper grain, suggesting that the relative crystal orientation of subgrains determines the degree of Cu oxidation. Atomistic force field calculations support these observations, showing that graphene domains have preferential alignment with the Cu(111) with a smaller average height above the global Cu surface as compared to intermediate orientations, and that this is the origin of the heterogeneous oxidation rate of Cu. This work demonstrates that the natural oxidation resistance of Cu coated by graphene is highly dependent on the crystal orientation and lattice alignment of Cu and graphene, which is key information for engineering the interface configuration of the graphene-Cu system for specific functionalities in mechanical, anticorrosion, and electrical applications of CVD-grown graphene.
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Affiliation(s)
- Birong Luo
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
- College of Physics and Materials Science, Tianjin International Joint Research Centre of Surface Technology for Energy Storage Materials , Tianjin Normal University , 300387 Tianjin , P. R. China
| | - Mohammad Koleini
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
| | - Patrick R Whelan
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
- Center for Nanostructured Graphene (CNG) , Technical University of Denmark , 2800 Kgs. Lyngby , Denmark
| | - Abhay Shivayogimath
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
- Center for Nanostructured Graphene (CNG) , Technical University of Denmark , 2800 Kgs. Lyngby , Denmark
| | - Mads Brandbyge
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
| | - Peter Bøggild
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
- Center for Nanostructured Graphene (CNG) , Technical University of Denmark , 2800 Kgs. Lyngby , Denmark
| | - Timothy J Booth
- DTU Physics , Technical University of Denmark , Ørsteds Plads, 345C , 2800 Kgs. Lyngby , Denmark
- Center for Nanostructured Graphene (CNG) , Technical University of Denmark , 2800 Kgs. Lyngby , Denmark
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18
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Mishra N, Forti S, Fabbri F, Martini L, McAleese C, Conran BR, Whelan PR, Shivayogimath A, Jessen BS, Buß L, Falta J, Aliaj I, Roddaro S, Flege JI, Bøggild P, Teo KBK, Coletti C. Wafer-Scale Synthesis of Graphene on Sapphire: Toward Fab-Compatible Graphene. Small 2019; 15:e1904906. [PMID: 31668009 DOI: 10.1002/smll.201904906] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Indexed: 05/26/2023]
Abstract
The adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high-quality material on technologically relevant substrates, over wafer-scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al-rich reconstruction 31 × 31 R ± 9 ° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm2 V-1 s-1 . The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back-end-of-line integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.
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Affiliation(s)
- Neeraj Mishra
- Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127, Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genova, Italy
| | - Stiven Forti
- Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127, Pisa, Italy
| | - Filippo Fabbri
- Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127, Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genova, Italy
| | - Leonardo Martini
- Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127, Pisa, Italy
| | - Clifford McAleese
- AIXTRON Ltd., Buckingway Business Park, Anderson Rd, Swavesey, Cambridge, CB24 4FQ, UK
| | - Ben R Conran
- AIXTRON Ltd., Buckingway Business Park, Anderson Rd, Swavesey, Cambridge, CB24 4FQ, UK
| | - Patrick R Whelan
- DTU Physics, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
- Center for Nanostructured Graphene (CNG), Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
| | - Abhay Shivayogimath
- DTU Physics, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
- Center for Nanostructured Graphene (CNG), Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
| | - Bjarke S Jessen
- DTU Physics, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
- Center for Nanostructured Graphene (CNG), Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
| | - Lars Buß
- Institute of Solid State Physics, University of Bremen, Bremen, 28334, Germany
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, Bremen, 28334, Germany
| | - Ilirjan Aliaj
- NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127, Pisa, Italy
| | - Stefano Roddaro
- NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127, Pisa, Italy
- Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, 56127, Pisa, Italy
| | - Jan I Flege
- Institute of Solid State Physics, University of Bremen, Bremen, 28334, Germany
- Brandenburg University of Technology Cottbus-Senftenberg, Chair of Applied Physics and Semiconductor Spectroscopy, Konrad-Zuse-Str. 1, 03046, Cottbus, Germany
| | - Peter Bøggild
- DTU Physics, Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
- Center for Nanostructured Graphene (CNG), Ørsteds Plads 345C, 2800, Kongens Lyngby, Denmark
| | - Kenneth B K Teo
- AIXTRON Ltd., Buckingway Business Park, Anderson Rd, Swavesey, Cambridge, CB24 4FQ, UK
| | - Camilla Coletti
- Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127, Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genova, Italy
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Chaves FA, Jiménez D, Santos JE, Bøggild P, Caridad JM. Electrostatics of metal-graphene interfaces: sharp p-n junctions for electron-optical applications. Nanoscale 2019; 11:10273-10281. [PMID: 31086868 DOI: 10.1039/c9nr02029b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Creation of sharp lateral p-n junctions in graphene devices, with transition widths w well below the Fermi wavelength λF of graphene's charge carriers, is vital to study and exploit these electronic systems for electron-optical applications. The achievement of such junctions is, however, not trivial due to the presence of a considerable out-of-plane electric field in lateral p-n junctions, resulting in large widths. Metal-graphene interfaces represent a novel, promising and easy to implement technique to engineer such sharp lateral p-n junctions in graphene field-effect devices, in clear contrast to the much wider (i.e. smooth) junctions achieved via conventional local gating. In this work, we present a systematic and robust investigation of the electrostatic problem of metal-induced lateral p-n junctions in gated graphene devices for electron-optics applications, systems where the width w of the created junctions is not only determined by the metal used but also depends on external factors such as device geometries, dielectric environment and different operational parameters such as carrier density and temperature. Our calculations demonstrate that sharp junctions (w ≪ λF) can be achieved via metal-graphene interfaces at room temperature in devices surrounded by dielectric media with low relative permittivity (<10). In addition, we show how specific details such as the separation distance between metal and graphene and the permittivity of the gap in-between plays a critical role when defining the p-n junction, not only defining its width w but also the energy shift of graphene underneath the metal. These results can be extended to any two-dimensional (2D) electronic system doped by the presence of metal clusters and thus are relevant for understanding interfaces between metals and other 2D materials.
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Affiliation(s)
- Ferney A Chaves
- Department d'Enginyeria Electrònica, Escola d'Enginyeria, Campus UAB, Bellaterra, 08193 Barcelona, Spain
| | - David Jiménez
- Department d'Enginyeria Electrònica, Escola d'Enginyeria, Campus UAB, Bellaterra, 08193 Barcelona, Spain
| | - Jaime E Santos
- Centro de Física, Universidade do Minho, P-4710-057 Braga, Portugal
| | - Peter Bøggild
- Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.
| | - José M Caridad
- Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.
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20
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Jessen BS, Gammelgaard L, Thomsen MR, Mackenzie DMA, Thomsen JD, Caridad JM, Duegaard E, Watanabe K, Taniguchi T, Booth TJ, Pedersen TG, Jauho AP, Bøggild P. Lithographic band structure engineering of graphene. Nat Nanotechnol 2019; 14:340-346. [PMID: 30778216 DOI: 10.1038/s41565-019-0376-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 01/15/2019] [Indexed: 06/09/2023]
Abstract
Two-dimensional materials such as graphene allow direct access to the entirety of atoms constituting the crystal. While this makes shaping by lithography particularly attractive as a tool for band structure engineering through quantum confinement effects, edge disorder and contamination have so far limited progress towards experimental realization. Here, we define a superlattice in graphene encapsulated in hexagonal boron nitride, by etching an array of holes through the heterostructure with minimum feature sizes of 12-15 nm. We observe a magnetotransport regime that is distinctly different from the characteristic Landau fan of graphene, with a sizeable bandgap that can be tuned by a magnetic field. The measurements are accurately described by transport simulations and analytical calculations. Finally, we observe strong indications that the lithographically engineered band structure at the main Dirac point is cloned to a satellite peak that appears due to moiré interactions between the graphene and the encapsulating material.
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Affiliation(s)
- Bjarke S Jessen
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Lene Gammelgaard
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Morten R Thomsen
- Center for Nanostructured Graphene, Aalborg University, Aalborg, Denmark
- Department of Physics and Nanotechnology, Aalborg University, Aalborg, Denmark
| | - David M A Mackenzie
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- Department of Electronics and Nanoengineering, Aalto University, Aalto, Finland
| | - Joachim D Thomsen
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - José M Caridad
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Emil Duegaard
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - Timothy J Booth
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Thomas G Pedersen
- Center for Nanostructured Graphene, Aalborg University, Aalborg, Denmark
- Department of Physics and Nanotechnology, Aalborg University, Aalborg, Denmark
| | - Antti-Pekka Jauho
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark.
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark.
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark.
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21
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Thomsen JD, Kling J, Mackenzie DMA, Bøggild P, Booth TJ. Oxidation of Suspended Graphene: Etch Dynamics and Stability Beyond 1000 °C. ACS Nano 2019; 13:2281-2288. [PMID: 30625274 DOI: 10.1021/acsnano.8b08979] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We study the oxidation of clean suspended mono- and few-layer graphene in real time by in situ environmental transmission electron microscopy. At an oxygen pressure below 0.1 mbar, we observe anisotropic oxidation in which armchair-oriented hexagonal holes are formed with a sharp edge roughness below 1 nm. At a higher pressure, we observe an increasingly isotropic oxidation, eventually leading to irregular holes at a pressure of 6 mbar. In addition, we find that few-layer flakes are stable against oxidation at temperatures up to at least 1000 °C in the absence of impurities and electron-beam-induced defects. These findings show, first, that the oxidation behavior of mono- and few-layer graphene depends critically on the intrinsic roughness, cleanliness and any imposed roughness or additional reactivity from a supporting substrate and, second, that the activation energy for oxidation of pristine suspended few-layer graphene is up to 43% higher than previously reported for graphite. In addition, we have developed a cleaning scheme that results in the near-complete removal of hydrocarbon residues over the entire visible sample area. These results have implications for applications of graphene where edge roughness can critically affect the performance of devices and more generally highlight the surprising (meta)stability of the basal plane of suspended bilayer and thicker graphene toward oxidative environments at high temperature.
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Affiliation(s)
- Joachim Dahl Thomsen
- Center for Nanostructured Graphene, Department of Micro and Nanotechnology , Technical University of Denmark , DK-2800 Kongens Lyngby , Denmark
| | - Jens Kling
- Center for Electron Nanoscopy , Technical University of Denmark , DK-2800 Kongens Lyngby , Denmark
| | - David M A Mackenzie
- Center for Nanostructured Graphene, Department of Micro and Nanotechnology , Technical University of Denmark , DK-2800 Kongens Lyngby , Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene, Department of Micro and Nanotechnology , Technical University of Denmark , DK-2800 Kongens Lyngby , Denmark
| | - Timothy J Booth
- Center for Nanostructured Graphene, Department of Micro and Nanotechnology , Technical University of Denmark , DK-2800 Kongens Lyngby , Denmark
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22
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Abstract
Graphene field-effect transistors (GFETs) offer a possibility of exploiting unique physical properties of graphene in realizing novel electronic circuits. However, graphene circuits often lack the voltage swing and switchability of Si complementary metal-oxide-semiconductor (CMOS) circuits, which are the main building block of modern electronics. Here we introduce graphene in Si CMOS circuits to exploit favorable electronic properties of both technologies and realize a new class of simple oscillators using only a GFET, Si CMOS D latch, and timing RC circuit. The operation of the two types of realized oscillators is based on the ambipolarity of graphene, i.e., the symmetry of the transfer curve of GFETs around the Dirac point. The ambipolarity of graphene also allowed to turn the oscillators into pulse-width modulators (with a duty cycle ratio ∼1 : 4) and voltage-controlled oscillators (with a frequency ratio ∼1 : 8) without any circuit modifications. The oscillation frequency was in the range from 4 kHz to 4 MHz and limited only by the external circuit connections, rather than components themselves. The demonstrated graphene-Si CMOS hybrid circuits pave the way to the more widespread adoption of graphene in electronics.
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Affiliation(s)
- Carlo Gilardi
- L-NESS, Department of Physics, Politecnico di Milano, Via Anzani 42, 22100 Como, Italy.
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23
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Whelan PR, Panchal V, Petersen DH, Mackenzie DMA, Melios C, Pasternak I, Gallop J, Østerberg FW, U Jepsen P, Strupinski W, Kazakova O, Bøggild P. Electrical Homogeneity Mapping of Epitaxial Graphene on Silicon Carbide. ACS Appl Mater Interfaces 2018; 10:31641-31647. [PMID: 30130090 DOI: 10.1021/acsami.8b11428] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Epitaxial graphene is a promising route to wafer-scale production of electronic graphene devices. Chemical vapor deposition of graphene on silicon carbide offers epitaxial growth with layer control but is subject to significant spatial and wafer-to-wafer variability. We use terahertz time-domain spectroscopy and micro four-point probes to analyze the spatial variations of quasi-freestanding bilayer graphene grown on 4 in. silicon carbide (SiC) wafers and find significant variations in electrical properties across large regions, which are even reproduced across graphene on different SiC wafers cut from the same ingot. The dc sheet conductivity of epitaxial graphene was found to vary more than 1 order of magnitude across a 4 in. SiC wafer. To determine the origin of the variations, we compare different optical and scanning probe microscopies with the electrical measurements from nano- to millimeter scale and identify three distinct qualities of graphene, which can be attributed to the microstructure of the SiC surface.
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Affiliation(s)
- Patrick R Whelan
- DTU Fotonik , Technical University of Denmark , Ørsteds Plads 343 , DK-2800 Kongens Lyngby , Denmark
| | - Vishal Panchal
- National Physical Laboratory , Hampton Road , Teddington TW11 0LW , U.K
| | | | | | - Christos Melios
- National Physical Laboratory , Hampton Road , Teddington TW11 0LW , U.K
| | - Iwona Pasternak
- Faculty of Physics , Warsaw University of Technology , Koszykowa 75 , 00-662 Warsaw , Poland
| | - John Gallop
- National Physical Laboratory , Hampton Road , Teddington TW11 0LW , U.K
| | | | - Peter U Jepsen
- DTU Fotonik , Technical University of Denmark , Ørsteds Plads 343 , DK-2800 Kongens Lyngby , Denmark
| | - Wlodek Strupinski
- Faculty of Physics , Warsaw University of Technology , Koszykowa 75 , 00-662 Warsaw , Poland
| | - Olga Kazakova
- National Physical Laboratory , Hampton Road , Teddington TW11 0LW , U.K
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24
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Calogero G, Papior NR, Bøggild P, Brandbyge M. Large-scale tight-binding simulations of quantum transport in ballistic graphene. J Phys Condens Matter 2018; 30:364001. [PMID: 30061475 DOI: 10.1088/1361-648x/aad6f1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Graphene has proven to host outstanding mesoscopic effects involving massless Dirac quasiparticles travelling ballistically resulting in the current flow exhibiting light-like behaviour. A new branch of 2D electronics inspired by the standard principles of optics is rapidly evolving, calling for a deeper understanding of transport in large-scale devices at a quantum level. Here we perform large-scale quantum transport calculations based on a tight-binding model of graphene and the non-equilibrium Green's function method and include the effects of p-n junctions of different shape, magnetic field, and absorptive regions acting as drains for current. We stress the importance of choosing absorbing boundary conditions in the calculations to correctly capture how current flows in the limit of infinite devices. As a specific application we present a fully quantum-mechanical framework for the '2D Dirac fermion microscope' recently proposed by Bøggild et al (2017 Nat. Commun. 8 10.1038), tackling several key electron-optical effects therein predicted via semiclassical trajectory simulations, such as electron beam collimation, deflection and scattering off Veselago dots. Our results confirm that a semiclassical approach to a large extend is sufficient to capture the main transport features in the mesoscopic limit and the optical regime, but also that a richer electron-optical landscape is to be expected when coherence or other purely quantum effects are accounted for in the simulations.
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Affiliation(s)
- Gaetano Calogero
- Department of Micro- and Nanotechnology, Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Bldg. 345E, DK-2800 Kongens Lyngby, Denmark
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25
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Caridad JM, Calogero G, Pedrinazzi P, Santos JE, Impellizzeri A, Gunst T, Booth TJ, Sordan R, Bøggild P, Brandbyge M. A Graphene-Edge Ferroelectric Molecular Switch. Nano Lett 2018; 18:4675-4683. [PMID: 30029573 DOI: 10.1021/acs.nanolett.8b00797] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We show that polar molecules (water, ammonia, and nitrogen dioxide) adsorbed solely at the exposed edges of an encapsulated graphene sheet exhibit ferroelectricity, collectively orienting and switching reproducibly between two available states in response to an external electric field. This ferroelectric molecular switching introduces drastic modifications to the graphene bulk conductivity and produces a large and ambipolar charge bistability in micrometer-size graphene devices. This system comprises an experimental realization of envisioned memory capacitive ("memcapacitive") devices whose capacitance is a function of their charging history, here conceived via confined and correlated polar molecules at the one-dimensional edge of a two-dimensional crystal.
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Affiliation(s)
- José M Caridad
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
| | - Gaetano Calogero
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
| | - Paolo Pedrinazzi
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
- L-NESS Laboratory, Department of Physics , Politecnico di Milano , Via Anzani 42 , 22100 Como , Italy
| | - Jaime E Santos
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
- Centro de Física and Departamento de Física , Universidade do Minho , P-4710-057 Braga , Portugal
| | - Anthony Impellizzeri
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
- Dipartimento di Fisica e Astronomia , Università di Catania , 64 Via Santa Sofia , 95123 Catania , Italy
| | - Tue Gunst
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
| | - Timothy J Booth
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
| | - Roman Sordan
- L-NESS Laboratory, Department of Physics , Politecnico di Milano , Via Anzani 42 , 22100 Como , Italy
| | - Peter Bøggild
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
| | - Mads Brandbyge
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology , Technical University of Denmark , 2800 Kongens Lyngby , Denmark
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26
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Whelan PR, Huang D, Mackenzie D, Messina SA, Li Z, Li X, Li Y, Booth TJ, Jepsen PU, Shi H, Bøggild P. Conductivity mapping of graphene on polymeric films by terahertz time-domain spectroscopy. Opt Express 2018; 26:17748-17754. [PMID: 30114060 DOI: 10.1364/oe.26.017748] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Accepted: 06/21/2018] [Indexed: 06/08/2023]
Abstract
Fast inline characterization of the electrical properties of graphene on polymeric substrates is an essential requirement for quality control in industrial graphene production. Here we show that it is possible to measure the sheet conductivity of graphene on polymer films by terahertz time-domain spectroscopy (THz-TDS) when all internally reflected echoes in the substrate are taken into consideration. The conductivity measured by THz-TDS is comparable to values obtained from four point probe measurements. THz-TDS maps of 25x30 cm2 area graphene films were recorded and the DC conductivity and carrier scattering time were extracted from the measurements. Additionally, the THz-TDS conductivity maps highlight tears and holes in the graphene film, which are not easily visible by optical inspection.
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27
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Mackenzie DMA, Whelan PR, Bøggild P, Jepsen PU, Redo-Sanchez A, Etayo D, Fabricius N, Petersen DH. Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping. Opt Express 2018; 26:9220-9229. [PMID: 29715876 DOI: 10.1364/oe.26.009220] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 03/19/2018] [Indexed: 06/08/2023]
Abstract
We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.
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28
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Caridad JM, Power SR, Lotz MR, Shylau AA, Thomsen JD, Gammelgaard L, Booth TJ, Jauho AP, Bøggild P. Conductance quantization suppression in the quantum Hall regime. Nat Commun 2018; 9:659. [PMID: 29440635 PMCID: PMC5811439 DOI: 10.1038/s41467-018-03064-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [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: 09/04/2017] [Accepted: 01/17/2018] [Indexed: 11/14/2022] Open
Abstract
Conductance quantization is the quintessential feature of electronic transport in non-interacting mesoscopic systems. This phenomenon is observed in quasi one-dimensional conductors at zero magnetic field B, and the formation of edge states at finite magnetic fields results in wider conductance plateaus within the quantum Hall regime. Electrostatic interactions can change this picture qualitatively. At finite B, screening mechanisms in narrow, gated ballistic conductors are predicted to give rise to an increase in conductance and a suppression of quantization due to the appearance of additional conduction channels. Despite being a universal effect, this regime has proven experimentally elusive because of difficulties in realizing one-dimensional systems with sufficiently hard-walled, disorder-free confinement. Here, we experimentally demonstrate the suppression of conductance quantization within the quantum Hall regime for graphene nanoconstrictions with low edge roughness. Our findings may have profound impact on fundamental studies of quantum transport in finite-size, two-dimensional crystals with low disorder. Conductance quantization is the hallmark of non-interacting confined systems. The authors show that the quantization in graphene nanoconstrictions with low edge disorder is suppressed in the quantum Hall regime. This is explained by the addition of new conductance channels due to electrostatic screening.
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Affiliation(s)
- José M Caridad
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark.
| | - Stephen R Power
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark.,Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, Barcelona, 08193, Spain.,Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), 08193, Spain
| | - Mikkel R Lotz
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - Artsem A Shylau
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - Joachim D Thomsen
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - Lene Gammelgaard
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - Timothy J Booth
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - Antti-Pekka Jauho
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, 2800, Kongens Lyngby, Denmark.
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29
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Shivayogimath A, Mackenzie D, Luo B, Hansen O, Bøggild P, Booth TJ. Probing the Gas-Phase Dynamics of Graphene Chemical Vapour Deposition using in-situ UV Absorption Spectroscopy. Sci Rep 2017; 7:6183. [PMID: 28733662 PMCID: PMC5522467 DOI: 10.1038/s41598-017-06276-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [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: 02/02/2017] [Accepted: 05/11/2017] [Indexed: 11/09/2022] Open
Abstract
The processes governing multilayer nucleation in the chemical vapour deposition (CVD) of graphene are important for obtaining high-quality monolayer sheets, but remain poorly understood. Here we show that higher-order carbon species in the gas-phase play a major role in multilayer nucleation, through the use of in-situ ultraviolet (UV) absorption spectroscopy. These species are the volatilized products of reactions between hydrogen and carbon contaminants that have backstreamed into the reaction chamber from downstream system components. Consequently, we observe a dramatic suppression of multilayer nucleation when backstreaming is suppressed. These results point to an important and previously undescribed mechanism for multilayer nucleation, wherein higher-order gas-phase carbon species play an integral role. Our work highlights the importance of gas-phase dynamics in understanding the overall mechanism of graphene growth.
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Affiliation(s)
- Abhay Shivayogimath
- DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kongens Lyngby, 2800, Denmark
| | - David Mackenzie
- DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kongens Lyngby, 2800, Denmark
| | - Birong Luo
- DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kongens Lyngby, 2800, Denmark
| | - Ole Hansen
- DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kongens Lyngby, 2800, Denmark
| | - Peter Bøggild
- DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kongens Lyngby, 2800, Denmark.,Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, 345C, Kongens Lyngby, 2800, Denmark
| | - Timothy J Booth
- DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kongens Lyngby, 2800, Denmark. .,Centre for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, 345C, Kongens Lyngby, 2800, Denmark.
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30
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Kretschmer S, Komsa HP, Bøggild P, Krasheninnikov AV. Structural Transformations in Two-Dimensional Transition-Metal Dichalcogenide MoS 2 under an Electron Beam: Insights from First-Principles Calculations. J Phys Chem Lett 2017; 8:3061-3067. [PMID: 28617607 DOI: 10.1021/acs.jpclett.7b01177] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The polymorphism of two-dimensional (2D) transition-metal dichalcogenides (TMDs) and different electronic properties of the polymorphs make TMDs particularly promising materials in the context of applications in electronics. Recently, local transformations from the semiconducting trigonal prismatic H phase to the metallic octahedral T phase in 2D MoS2 have been induced by electron irradiation [ Nat. Nanotech. 2014 , 9 , 391 ], but the mechanism of the transformations remains elusive. Using density functional theory calculations, we study the energetics of the stable and metastable phases of 2D MoS2 when additional charge, mechanical strain, and vacancies are present. We also investigate the role of finite temperatures, which appear to be critical for the transformations. On the basis of the results of our calculations, we propose an explanation for the beam-induced transformations, which are likely promoted by charge redistribution in the monolayer due to electronic excitations combined with formation of vacancies under electron beam and buildup of the associated mechanical strain in the sample. As this mechanism should be relevant to other 2D TMDs, our results provide hints for further development and optimization of electron-beam-mediated engineering of the atomic structure and electronic properties of 2D TMDs with subnanometer resolution.
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Affiliation(s)
- Silvan Kretschmer
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf , 01314 Dresden, Germany
| | - Hannu-Pekka Komsa
- Department of Applied Physics, Aalto University School of Science , PO Box 11100, 00076 Aalto, Finland
| | - Peter Bøggild
- CNG - Center of Nanostructured Graphene, DTU Nanotech, Technical University of Denmark , Lyngby DK-2800, Denmark
| | - Arkady V Krasheninnikov
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf , 01314 Dresden, Germany
- Department of Applied Physics, Aalto University School of Science , PO Box 11100, 00076 Aalto, Finland
- CNG - Center of Nanostructured Graphene, DTU Nanotech, Technical University of Denmark , Lyngby DK-2800, Denmark
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31
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Galbiati M, Stoot AC, Mackenzie DMA, Bøggild P, Camilli L. Real-time oxide evolution of copper protected by graphene and boron nitride barriers. Sci Rep 2017; 7:39770. [PMID: 28067249 PMCID: PMC5220376 DOI: 10.1038/srep39770] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [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: 08/25/2016] [Accepted: 11/28/2016] [Indexed: 11/09/2022] Open
Abstract
Applying protective or barrier layers to isolate a target item from the environment is a common approach to prevent or delay its degradation. The impermeability of two-dimensional materials such as graphene and hexagonal boron nitride (hBN) has generated a great deal of interest in corrosion and material science. Owing to their different electronic properties (graphene is a semimetal, whereas hBN is a wide-bandgap insulator), their protection behaviour is distinctly different. Here we investigate the performance of graphene and hBN as barrier coatings applied on copper substrates through a real-time study in two different oxidative conditions. Our findings show that the evolution of the copper oxidation is remarkably different for the two coating materials.
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Affiliation(s)
- M Galbiati
- Department of Micro- and Nanotechnology, DK-2800 Kgs. Lyngby, Denmark
| | - A C Stoot
- Department of Micro- and Nanotechnology, DK-2800 Kgs. Lyngby, Denmark
| | - D M A Mackenzie
- Department of Micro- and Nanotechnology, DK-2800 Kgs. Lyngby, Denmark
| | - P Bøggild
- Department of Micro- and Nanotechnology, DK-2800 Kgs. Lyngby, Denmark
| | - L Camilli
- Department of Micro- and Nanotechnology, DK-2800 Kgs. Lyngby, Denmark
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32
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Wang R, Whelan PR, Braeuninger-Weimer P, Tappertzhofen S, Alexander-Webber JA, Van Veldhoven ZA, Kidambi PR, Jessen BS, Booth T, Bøggild P, Hofmann S. Catalyst Interface Engineering for Improved 2D Film Lift-Off and Transfer. ACS Appl Mater Interfaces 2016; 8:33072-33082. [PMID: 27934130 PMCID: PMC5249221 DOI: 10.1021/acsami.6b11685] [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] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Accepted: 11/10/2016] [Indexed: 05/26/2023]
Abstract
The mechanisms by which chemical vapor deposited (CVD) graphene and hexagonal boron nitride (h-BN) films can be released from a growth catalyst, such as widely used copper (Cu) foil, are systematically explored as a basis for an improved lift-off transfer. We show how intercalation processes allow the local Cu oxidation at the interface followed by selective oxide dissolution, which gently releases the 2D material (2DM) film. Interfacial composition change and selective dissolution can thereby be achieved in a single step or split into two individual process steps. We demonstrate that this method is not only highly versatile but also yields graphene and h-BN films of high quality regarding surface contamination, layer coherence, defects, and electronic properties, without requiring additional post-transfer annealing. We highlight how such transfers rely on targeted corrosion at the catalyst interface and discuss this in context of the wider CVD growth and 2DM transfer literature, thereby fostering an improved general understanding of widely used transfer processes, which is essential to numerous other applications.
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Affiliation(s)
- Ruizhi Wang
- Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
| | - Patrick R. Whelan
- Center for Nanostructured Graphene (CNG),
DTU Nanotech, Technical University of Denmark, DK-2800, Kongens
Lyngby, Denmark
| | | | - Stefan Tappertzhofen
- Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
| | | | - Zenas A. Van Veldhoven
- Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, United Kingdom
| | - Piran R. Kidambi
- Department of Mechanical Engineering, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Bjarke S. Jessen
- Center for Nanostructured Graphene (CNG),
DTU Nanotech, Technical University of Denmark, DK-2800, Kongens
Lyngby, Denmark
| | - Timothy Booth
- Center for Nanostructured Graphene (CNG),
DTU Nanotech, Technical University of Denmark, DK-2800, Kongens
Lyngby, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene (CNG),
DTU Nanotech, Technical University of Denmark, DK-2800, Kongens
Lyngby, Denmark
| | - Stephan Hofmann
- Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
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33
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Abstract
A new failure mechanism for high-quality multilayer graphene coatings in acidic media is described.
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Affiliation(s)
- F. Yu
- Technical University of Denmark
- Department of Micro- and Nanotechnology
- Kgs. Lyngby
- Denmark
| | - A. C. Stoot
- Technical University of Denmark
- Department of Micro- and Nanotechnology
- Kgs. Lyngby
- Denmark
| | - P. Bøggild
- Technical University of Denmark
- Department of Micro- and Nanotechnology
- Kgs. Lyngby
- Denmark
| | - L. Camilli
- Technical University of Denmark
- Department of Micro- and Nanotechnology
- Kgs. Lyngby
- Denmark
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34
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Buron JD, Mackenzie DMA, Petersen DH, Pesquera A, Centeno A, Bøggild P, Zurutuza A, Jepsen PU. Terahertz wafer-scale mobility mapping of graphene on insulating substrates without a gate. Opt Express 2015; 23:30721-30729. [PMID: 26698704 DOI: 10.1364/oe.23.030721] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We demonstrate wafer-scale, non-contact mapping of essential carrier transport parameters, carrier mobility (µdrift), carrier density (Ns), DC sheet conductance (σdc), and carrier scattering time (τsc) in CVD graphene, using spatially resolved terahertz time-domain conductance spectroscopy. σdc and τsc are directly extracted from Drude model fits to terahertz conductance spectra obtained in each pixel of 10 × 10 cm2 maps with a 400 µm step size. σdc- and τsc-maps are translated into µdrift and Ns maps through Boltzmann transport theory for graphene charge carriers and these parameters are directly compared to van der Pauw device measurements on the same wafer. The technique is compatible with all substrate materials that exhibit a reasonably low absorption coefficient for terahertz radiation. This includes many materials used for transferring CVD graphene in production facilities as well as in envisioned products, such as polymer films, glass substrates, cloth, or paper substrates.
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Abstract
Carrier mobility and chemical doping level are essential figures of merit for graphene, and large-scale characterization of these properties and their uniformity is a prerequisite for commercialization of graphene for electronics and electrodes. However, existing mapping techniques cannot directly assess these vital parameters in a non-destructive way. By deconvoluting carrier mobility and density from non-contact terahertz spectroscopic measurements of conductance in graphene samples with terahertz-transparent backgates, we are able to present maps of the spatial variation of both quantities over large areas. The demonstrated non-contact approach provides a drastically more efficient alternative to measurements in contacted devices, with potential for aggressive scaling towards wafers/minute. The observed linear relation between conductance and carrier density in chemical vapour deposition graphene indicates dominance by charged scatterers. Unexpectedly, significant variations in mobility rather than doping are the cause of large conductance inhomogeneities, highlighting the importance of statistical approaches when assessing large-area graphene transport properties.
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Affiliation(s)
- Jonas D Buron
- DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - Filippo Pizzocchero
- DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - Peter U Jepsen
- DTU Fotonik - Department of Photonics Engineering, Technical University of Denmark, Building 343 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - Dirch H Petersen
- DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - José M Caridad
- DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - Bjarke S Jessen
- DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - Timothy J Booth
- 1] DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark [2] DTU Center for Nanostructured Graphene (CNG), DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
| | - Peter Bøggild
- 1] DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark [2] DTU Center for Nanostructured Graphene (CNG), DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark
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36
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Shvets V, Hentschel T, Schulte L, Tschammer LK, Cagliani A, Bøggild P, Almdal K, Ndoni S. Transfer of Direct and Moiré Patterns by Reactive Ion Etching Through Ex Situ Fabricated Nanoporous Polymer Masks. Langmuir 2015; 31:6245-6252. [PMID: 25984754 DOI: 10.1021/acs.langmuir.5b00482] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present a conceptually simple approach to nanolithographic patterning utilizing ex situ fabricated nanoporous masks from block copolymers. The fabricated block copolymer (BC) masks show predictable morphology based on the correlation between BC composition and bulk properties, independent of substrates' surface properties. The masks are prepared by microtoming of prealigned nanoporous polymer monoliths of hexagonal morphology at controlled angles; they appear as 30-60 nm thick films of typical dimensions 100 μm × 200 μm. Masks cut perpendicular to the cylindrical axis show monocrystalline hexagonal packing of 10 nm pores with a principal period of 20 nm. We demonstrate the transfer of the hexagonal pattern onto silicon by means of reactive ion etching through the masks. In addition, patterns of elliptic and slit-like holes on silicon are obtained by utilizing masks cut at 45° relative to the cylinder axis. Finally, we demonstrate the first transfer of moiré patterns from block copolymer masks to substrate. The nanoporous masks prepared ex situ show outstanding long-range order and can be applied directly onto any flat substrate, eliminating the need for topographic and chemical surface modification, which are essential prerequisites for the conventional procedure of block copolymer directed self-assembly. The demonstrated elliptic and moiré pattern transfers prove that the proposed ex situ procedure allows us to realize nanolithographic patterns that are difficult to realize by the conventional approach alone.
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Affiliation(s)
- Violetta Shvets
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
| | - Thomas Hentschel
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- §Dow Olefinverbund GmbH, D-06201 Merseburg, Germany
| | - Lars Schulte
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
| | - Lisa K Tschammer
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
| | - Alberto Cagliani
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
| | - Peter Bøggild
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
| | - Kristoffer Almdal
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
| | - Sokol Ndoni
- †Technical University of Denmark, Dept. of Micro and Nanotechnology, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
- ‡Center for Nanostructured Graphene (CNG), Technical University of Denmark, Ørsteds Plads, Building 345 East, DK-2800 Kgs. Lyngby, Denmark
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37
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Cagliani A, Lindvall N, Larsen MBBS, Mackenzie DMA, Jessen BS, Booth TJ, Bøggild P. Defect/oxygen assisted direct write technique for nanopatterning graphene. Nanoscale 2015; 7:6271-6277. [PMID: 25779889 DOI: 10.1039/c4nr07585d] [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] [Indexed: 06/04/2023]
Abstract
High resolution nanopatterning of graphene enables manipulation of electronic, optical and sensing properties of graphene. In this work we present a straightforward technique that does not require any lithographic mask to etch nanopatterns into graphene. The technique relies on the damaged graphene to be etched selectively in an oxygen rich environment with respect to non-damaged graphene. Sub-40 nm features were etched into graphene by selectively exposing it to a 100 keV electron beam and then etching the damaged areas away in a conventional oven. Raman spectroscopy was used to evaluate the extent of damage induced by the electron beam as well as the effects of the selective oxidative etching on the remaining graphene.
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Affiliation(s)
- Alberto Cagliani
- DTU Nanotech-Center for Nanostructured Graphene, Technical University of Denmark, Building 345 East, DK-2800 Kgs. Lyngby, Denmark.
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38
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Ferrari AC, Bonaccorso F, Fal'ko V, Novoselov KS, Roche S, Bøggild P, Borini S, Koppens FHL, Palermo V, Pugno N, Garrido JA, Sordan R, Bianco A, Ballerini L, Prato M, Lidorikis E, Kivioja J, Marinelli C, Ryhänen T, Morpurgo A, Coleman JN, Nicolosi V, Colombo L, Fert A, Garcia-Hernandez M, Bachtold A, Schneider GF, Guinea F, Dekker C, Barbone M, Sun Z, Galiotis C, Grigorenko AN, Konstantatos G, Kis A, Katsnelson M, Vandersypen L, Loiseau A, Morandi V, Neumaier D, Treossi E, Pellegrini V, Polini M, Tredicucci A, Williams GM, Hong BH, Ahn JH, Kim JM, Zirath H, van Wees BJ, van der Zant H, Occhipinti L, Di Matteo A, Kinloch IA, Seyller T, Quesnel E, Feng X, Teo K, Rupesinghe N, Hakonen P, Neil SRT, Tannock Q, Löfwander T, Kinaret J. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems. Nanoscale 2015; 7:4598-810. [PMID: 25707682 DOI: 10.1039/c4nr01600a] [Citation(s) in RCA: 976] [Impact Index Per Article: 108.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.
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Affiliation(s)
- Andrea C Ferrari
- Cambridge Graphene Centre, University of Cambridge, Cambridge, CB3 0FA, UK.
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39
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Buron JD, Petersen DH, Bøggild P, Cooke DG, Hilke M, Sun J, Whiteway E, Jessen BS, Nielsen PF, Hansen O, Yurgens A, Jepsen PU. Correction to graphene uniformity conductance mapping. Nano Lett 2015; 15:803. [PMID: 25470179 DOI: 10.1021/nl504550p] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
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40
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Rasappa S, Caridad JM, Schulte L, Cagliani A, Borah D, Morris MA, Bøggild P, Ndoni S. High quality sub-10 nm graphene nanoribbons by on-chip PS-b-PDMS block copolymer lithography. RSC Adv 2015. [DOI: 10.1039/c5ra11735f] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
“High quality sub-10 nm graphene nanoribbons by on-chip PS-b-PDMS block copolymer lithography”, SEM image of sub-10 nm graphene nanoribbons fabricated using a brushless lamellar PS-b-PDMS (5k–5.5k) block copolymer and its Raman spectra.
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Affiliation(s)
- Sozaraj Rasappa
- Department of Micro and Nanotechnology
- Technical University of Denmark
- DK-2800 Kgs. Lyngby
- Denmark
- Center for Nanostructured Graphene
| | - José M. Caridad
- Department of Micro and Nanotechnology
- Technical University of Denmark
- DK-2800 Kgs. Lyngby
- Denmark
- Center for Nanostructured Graphene
| | - Lars Schulte
- Department of Micro and Nanotechnology
- Technical University of Denmark
- DK-2800 Kgs. Lyngby
- Denmark
- Center for Nanostructured Graphene
| | - Alberto Cagliani
- Department of Micro and Nanotechnology
- Technical University of Denmark
- DK-2800 Kgs. Lyngby
- Denmark
- Center for Nanostructured Graphene
| | - Dipu Borah
- Materials Section
- Department of Chemistry
- University College Cork
- Cork
- Ireland
| | - Michael A. Morris
- Materials Section
- Department of Chemistry
- University College Cork
- Cork
- Ireland
| | - Peter Bøggild
- Department of Micro and Nanotechnology
- Technical University of Denmark
- DK-2800 Kgs. Lyngby
- Denmark
- Center for Nanostructured Graphene
| | - Sokol Ndoni
- Department of Micro and Nanotechnology
- Technical University of Denmark
- DK-2800 Kgs. Lyngby
- Denmark
- Center for Nanostructured Graphene
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41
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Buron JD, Pizzocchero F, Jessen BS, Booth TJ, Nielsen PF, Hansen O, Hilke M, Whiteway E, Jepsen PU, Bøggild P, Petersen DH. Electrically continuous graphene from single crystal copper verified by terahertz conductance spectroscopy and micro four-point probe. Nano Lett 2014; 14:6348-6355. [PMID: 25317778 DOI: 10.1021/nl5028167] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [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 electrical performance of graphene synthesized by chemical vapor deposition and transferred to insulating surfaces may be compromised by extended defects, including for instance grain boundaries, cracks, wrinkles, and tears. In this study, we experimentally investigate and compare the nano- and microscale electrical continuity of single layer graphene grown on centimeter-sized single crystal copper with that of previously studied graphene films, grown on commercially available copper foil, after transfer to SiO2 surfaces. The electrical continuity of the graphene films is analyzed using two noninvasive conductance characterization methods: ultrabroadband terahertz time-domain spectroscopy and micro four-point probe, which probe the electrical properties of the graphene film on different length scales, 100 nm and 10 μm, respectively. Ultrabroadband terahertz time-domain spectroscopy allows for measurement of the complex conductance response in the frequency range 1-15 terahertz, covering the entire intraband conductance spectrum, and reveals that the conductance response for the graphene grown on single crystalline copper intimately follows the Drude model for a barrier-free conductor. In contrast, the graphene grown on commercial copper foil shows a distinctly non-Drude conductance spectrum that is better described by the Drude-Smith model, which incorporates the effect of preferential carrier backscattering associated with extended, electronic barriers with a typical separation on the order of 100 nm. Micro four-point probe resistance values measured on graphene grown on single crystalline copper in two different voltage-current configurations show close agreement with the expected distributions for a continuous 2D conductor, in contrast with previous observations on graphene grown on commercial copper foil. The terahertz and micro four-point probe conductance values of the graphene grown on single crystalline copper shows a close to unity correlation, in contrast with those of the graphene grown on commercial copper foil, which we explain by the absence of extended defects on the microscale in CVD graphene grown on single crystalline copper. The presented results demonstrate that the graphene grown on single crystal copper is electrically continuous on the nanoscopic, microscopic, as well as intermediate length scales.
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Affiliation(s)
- Jonas D Buron
- DTU Nanotech, Technical University of Denmark , Ørsteds Plads 345E, Kongens Lyngby 2800, Denmark
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42
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Zhu X, Wang W, Yan W, Larsen MB, Bøggild P, Pedersen TG, Xiao S, Zi J, Mortensen NA. Plasmon-phonon coupling in large-area graphene dot and antidot arrays fabricated by nanosphere lithography. Nano Lett 2014; 14:2907-2913. [PMID: 24707792 DOI: 10.1021/nl500948p] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Nanostructured graphene on SiO2 substrates paves the way for enhanced light-matter interactions and explorations of strong plasmon-phonon hybridization in the mid-infrared regime. Unprecedented large-area graphene nanodot and antidot optical arrays are fabricated by nanosphere lithography, with structural control down to the sub-100 nm regime. The interaction between graphene plasmon modes and the substrate phonons is experimentally demonstrated, and structural control is used to map out the hybridization of plasmons and phonons, showing coupling energies of the order 20 meV. Our findings are further supported by theoretical calculations and numerical simulations.
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Affiliation(s)
- Xiaolong Zhu
- Department of Photonics Engineering, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark
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43
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Balzer F, Henrichsen HH, Klarskov MB, Booth TJ, Sun R, Parisi J, Schiek M, Bøggild P. Directed self-assembled crystalline oligomer domains on graphene and graphite. Nanotechnology 2014; 25:035602. [PMID: 24356510 DOI: 10.1088/0957-4484/25/3/035602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We observe the formation of thin films of fibre-like aggregates from the prototypical organic semiconductor molecule para-hexaphenylene (p-6P) on graphite thin flakes and on monolayer graphene. Using atomic force microscopy, scanning electron microscopy, x-ray diffraction, polarized fluorescence microscopy, and bireflectance microscopy, the molecular orientations on the surface are deduced and correlated to both the morphology as well as to the high-symmetry directions of the graphitic surface: the molecules align with their long axis at ±11° with respect to a high-symmetry direction. The results show that the graphene surface can be used as a growth substrate to direct the self-assembly of organic molecular thin films and nanofibres, both with and without lithographical processing.
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44
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Savenko A, Yildiz I, Petersen DH, Bøggild P, Bartenwerfer M, Krohs F, Oliva M, Harzendorf T. Ultra-high aspect ratio replaceable AFM tips using deformation-suppressed focused ion beam milling. Nanotechnology 2013; 24:465701. [PMID: 24149369 DOI: 10.1088/0957-4484/24/46/465701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Fabrication of ultra-high aspect ratio exchangeable and customizable tips for atomic force microscopy (AFM) using lateral focused ion beam (FIB) milling is presented. While on-axis FIB milling does allow high aspect ratio (HAR) AFM tips to be defined, lateral milling gives far better flexibility in terms of defining the shape and size of the tip. Due to beam-induced deformation, it has so far not been possible to define HAR structures using lateral FIB milling. In this work we obtain aspect ratios of up to 45, with tip diameters down to 9 nm, by a deformation-suppressing writing strategy. Several FIB milling strategies for obtaining sharper tips are discussed. Finally, assembly of the HAR tips on a custom-designed probe as well as the first AFM scanning is shown.
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Affiliation(s)
- Alexey Savenko
- DTU Nanotech-Department of Micro- and Nanotechnology, Technical University of Denmark, Ørsteds Plads 345Ø, DK-2800 Kongens Lyngby, Denmark. DTU CEN-Center for Electron Nanoscopy, Technical University of Denmark, Fysikvej 307, DK-2800 Kongens Lyngby, Denmark
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45
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Rasmussen JT, Gunst T, Bøggild P, Jauho AP, Brandbyge M. Electronic and transport properties of kinked graphene. Beilstein J Nanotechnol 2013; 4:103-10. [PMID: 23503656 PMCID: PMC3596121 DOI: 10.3762/bjnano.4.12] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Accepted: 01/31/2013] [Indexed: 05/28/2023]
Abstract
Local curvature, or bending, of a graphene sheet is known to increase the chemical reactivity presenting an opportunity for templated chemical functionalisation. Using first-principles calculations based on density functional theory (DFT), we investigate the reaction barrier reduction for the adsorption of atomic hydrogen at linear bends in graphene. We find a significant barrier lowering (≈15%) for realistic radii of curvature (≈20 Å) and that adsorption along the linear bend leads to a stable linear kink. We compute the electronic transport properties of individual and multiple kink lines, and demonstrate how these act as efficient barriers for electron transport. In particular, two parallel kink lines form a graphene pseudo-nanoribbon structure with a semimetallic/semiconducting electronic structure closely related to the corresponding isolated ribbons; the ribbon band gap translates into a transport gap for electronic transport across the kink lines. We finally consider pseudo-ribbon-based heterostructures and propose that such structures present a novel approach for band gap engineering in nanostructured graphene.
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Affiliation(s)
- Jesper Toft Rasmussen
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Tue Gunst
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Antti-Pekka Jauho
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Mads Brandbyge
- Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
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Abstract
In this paper, we introduce a comprehensive and versatile approach to the parametric shape optimization of oleophobic surfaces. We evaluate the performance of inverse trapezoid microstructures in terms of three objective parameters: apparent contact angle, maximum sustainable hydrostatic pressure, and mechanical robustness (Im, M.; Im, H:; Lee, J.H.; Yoon, J.B.; Choi, Y.K. A robust superhydrophobic and superoleophobic surface with inverse-trapezoidal microstructures on a large transparent flexible substrate. Soft Matter 2010, 6, 1401-1404; Im, M.; Im, H:; Lee, J.H.; Yoon, J.B.; Choi, Y.K. Analytical Modeling and Thermodynamic Analysis of Robust Superhydrophobic Surfaces with Inverse-Trapezoidal Microstructures. Langmuir 2010, 26, 17389-17397). We find that each of these parameters, if considered alone, would give trivial optima, while their interplay provides a well-defined optimal shape and aspect ratio. The inclusion of mechanical robustness in combination with conventional performance characteristics favors solutions relevant for practical applications, as mechanical stability is a critical issue not often addressed in idealized models.
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Affiliation(s)
- Andrea Cavalli
- Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, DK-2800 Kongens Lyngby, Denmark.
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47
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Buron JD, Petersen DH, Bøggild P, Cooke DG, Hilke M, Sun J, Whiteway E, Nielsen PF, Hansen O, Yurgens A, Jepsen PU. Graphene conductance uniformity mapping. Nano Lett 2012; 12:5074-5081. [PMID: 22947167 DOI: 10.1021/nl301551a] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We demonstrate a combination of micro four-point probe (M4PP) and non-contact terahertz time-domain spectroscopy (THz-TDS) measurements for centimeter scale quantitative mapping of the sheet conductance of large area chemical vapor deposited graphene films. Dual configuration M4PP measurements, demonstrated on graphene for the first time, provide valuable statistical insight into the influence of microscale defects on the conductance, while THz-TDS has potential as a fast, non-contact metrology method for mapping of the spatially averaged nanoscopic conductance on wafer-scale graphene with scan times of less than a minute for a 4-in. wafer. The combination of M4PP and THz-TDS conductance measurements, supported by micro Raman spectroscopy and optical imaging, reveals that the film is electrically continuous on the nanoscopic scale with microscopic defects likely originating from the transfer process, dominating the microscale conductance of the investigated graphene film.
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Affiliation(s)
- Jonas D Buron
- Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
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48
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Abstract
Monolayer graphene oxide (mGO) is shown to effectively protect molecular thin films from reorganization and function as an atomically thin barrier for vapor-deposited Ti/Al metal top electrodes. Fragile organic Langmuir-Blodgett (LB) films of C(22) fatty acid cadmium salts (cadmium(II) behenate) were covered by a compressed mosaic LB film of mGO flakes. These hybrid LB films were examined with atomic force microscopy (AFM) and X-ray reflectivity, both with and without the metal top electrodes. While the AFM enabled surface and morphology analysis, the X-ray reflectivity allowed for a detailed structural depth profiling of the organic film and mGO layer below the metal top layers. The structure of the mGO-protected LB films was found to be perfectly preserved; in contrast, it has previously been shown that metal deposition completely destroys the first two LB layers of unprotected films. This study provides clear evidence of the efficient protection offered by a single atomic layer of GO.
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Affiliation(s)
- Søren Petersen
- Nano-Science Center & Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
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49
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Kallesøe C, Wen CY, Booth TJ, Hansen O, Bøggild P, Ross FM, Mølhave K. In situ TEM creation and electrical characterization of nanowire devices. Nano Lett 2012; 12:2965-2970. [PMID: 22545629 DOI: 10.1021/nl300704u] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor-liquid-solid method, to form bridges between Si cantilevers. We characterize the formation of the contact between the nanowire and the cantilever, showing that the nature of the connection depends on the flow of heat and electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis.
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Affiliation(s)
- Christian Kallesøe
- Department of Micro- and Nanotechnology, Technical University of Denmark, Kgs. Lyngby, Denmark
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Kallesøe C, Larsen MB, Bøggild P, Mølhave K. 3D mechanical measurements with an atomic force microscope on 1D structures. Rev Sci Instrum 2012; 83:023704. [PMID: 22380096 DOI: 10.1063/1.3681784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have developed a simple method to characterize the mechanical properties of three dimensional nanostructures, such as nanorods standing up from a substrate. With an atomic force microscope the cantilever probe is used to deflect a horizontally aligned nanorod at different positions along the nanorod, using the apex of the cantilever itself rather than the tip normally used for probing surfaces. This enables accurate determination of nanostructures' spring constant. From these measurements, Young's modulus is found on many individual nanorods with different geometrical and material structures in a short time. Based on this method Young's modulus of carbon nanofibers and epitaxial grown III-V nanowires has been determined.
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Affiliation(s)
- Christian Kallesøe
- Department of Micro- and Nanotechnology, Technical University of Denmark, Kgs. Lyngby, DK-2800, Denmark.
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