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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] [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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Nosan M, Pavko L, Finšgar M, Kolar M, Genorio B. Improving Electroactivity of N-Doped Graphene Derivatives with Electrical Induction Heating. ACS APPLIED ENERGY MATERIALS 2022; 5:9571-9580. [PMID: 36034758 PMCID: PMC9400296 DOI: 10.1021/acsaem.2c01184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 07/14/2022] [Indexed: 06/15/2023]
Abstract
Graphene derivatives doped with nitrogen have already been identified as active non-noble metal materials for oxygen reduction reaction (ORR) in PEM and alkaline fuel cells. However, an efficient and scalable method to prepare active, stable, and high-surface-area non-noble metal catalysts remains a challenge. Therefore, an efficient, potentially scalable strategy to improve the specific surface area of N-doped graphene derivatives needs to be developed. Here, we report a novel, rapid, and scalable electrical induction heating method for the preparation of N-doped heat-treated graphene oxide derivatives (N-htGOD) with a high specific surface area. The application of the induction heating method has been shown to shorten the reaction time and improve the energy efficiency of the process. The materials synthesized by induction heating exhibited very high specific surface area and showed improved ORR activity compared to the conventional synthesis method. Moreover, we demonstrated that the temperature program of induction heating could fine-tune the concentration of nitrogen functionalities. In particular, the graphitic-N configuration increases with increasing final temperature, in parallel with the increasing ORR activity. The presented results will contribute to the understanding and development of nonmetal N-htGOD for energy storage and conversion applications.
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Affiliation(s)
- Miha Nosan
- Faculty
of Chemistry and Chemical Technology, University
of Ljubljana, Večna pot 113, Ljubljana SI-1000, Slovenia
| | - Luka Pavko
- Faculty
of Chemistry and Chemical Technology, University
of Ljubljana, Večna pot 113, Ljubljana SI-1000, Slovenia
- National
Institute of Chemistry, Hajdrihova 19, Ljubljana SI-1000, Slovenia
| | - Matjaž Finšgar
- Faculty
of Chemistry and Chemical Engineering, University
of Maribor, Smetanova ulica 17, Maribor SI-2000, Slovenia
| | - Mitja Kolar
- Faculty
of Chemistry and Chemical Technology, University
of Ljubljana, Večna pot 113, Ljubljana SI-1000, Slovenia
| | - Boštjan Genorio
- Faculty
of Chemistry and Chemical Technology, University
of Ljubljana, Večna pot 113, Ljubljana SI-1000, Slovenia
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3
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Garnica B. SA, Knaust M, Fatikow S. Automatic Micro-Robotic Identification and Electrical Characterization of Graphene. MICROMACHINES 2019; 10:mi10120870. [PMID: 31835719 PMCID: PMC6952813 DOI: 10.3390/mi10120870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 11/27/2019] [Accepted: 12/06/2019] [Indexed: 06/10/2023]
Abstract
Micromechanically exfoliating graphene on S i / S i O 2 substrates is commonplace for graphene researchers, but locating actual graphene flakes on these substrates is a high-effort and tiresome task. The main purpose of this work was to establish a completely automated procedure to identify those graphene flakes with as little human interaction as possible, improving on the limitations of current methods. Furthermore, automatic electrical characterization of the identified flakes was performed. The proposed micro-robotic automation sequence consists of three main steps. To start, a sample surface plane is calculated, based on multiple foci points across the substrate. Secondly, flakes on the substrate are identified in the hue, saturation, and value (HSV) color space, with an implementation to fit the measurement probe, used to avoid undersized samples and adjust the flake orientation. Finally, electrical characterization is performed based on four point probe measurements with the Van der Pauw method. Results of the successfully implemented automation sequence are presented together with flake electrical properties and validation.
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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 APPLIED MATERIALS & 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] [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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Wang X, Chen Y, Wu G, Wang J, Tian B, Sun S, Shen H, Lin T, Hu W, Kang T, Tang M, Xiao Y, Sun J, Meng X, Chu J. Graphene Dirac point tuned by ferroelectric polarization field. NANOTECHNOLOGY 2018; 29:134002. [PMID: 29339566 DOI: 10.1088/1361-6528/aaa852] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Graphene has received numerous attention for future nanoelectronics and optoelectronics. The Dirac point is a key parameter of graphene that provides information about its carrier properties. There are lots of methods to tune the Dirac point of graphene, such as chemical doping, impurities, defects, and disorder. In this study, we report a different approach to tune the Dirac point of graphene using a ferroelectric polarization field. The Dirac point can be adjusted to near the ferroelectric coercive voltage regardless its original position. We have ensured this phenomenon by temperature-dependent experiments, and analyzed its mechanism with the theory of impurity correlation in graphene. Additionally, with the modulation of ferroelectric polymer, the current on/off ratio and mobility of graphene transistor both have been improved. This work provides an effective method to tune the Dirac point of graphene, which can be readily used to configure functional devices such as p-n junctions and inverters.
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Affiliation(s)
- Xudong Wang
- Hunan Provincial Key Laboratory of Key Film Materials & Application for Equipments, School of Material Sciences and Engineering, Xiangtan University, Xiangtan, 411105, Hunan, People's Republic of China. State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500Yu Tian Road, Shanghai 200083, People's Republic of China. Hunan Provincial Key Laboratory of Thin Film Materials and Devices, School of Material Sciences and Engineering, Xiangtan University, Xiangtan 411105, Hunan, People's Republic of China
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Sul O, Kim K, Jung Y, Choi E, Lee SB. Selective Dirac voltage engineering of individual graphene field-effect transistors for digital inverter and frequency multiplier integrations. NANOTECHNOLOGY 2017; 28:37LT01. [PMID: 28762338 DOI: 10.1088/1361-6528/aa8335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The ambipolar band structure of graphene presents unique opportunities for novel electronic device applications. A cycle of gate voltage sweep in a conventional graphene transistor produces a frequency-doubled output current. To increase the frequency further, we used various graphene doping control techniques to produce Dirac voltage engineered graphene channels. The various surface treatments and substrate conditions produced differently doped graphene channels that were integrated on a single substrate and multiple Dirac voltages were observed by applying a single gate voltage sweep. We applied the Dirac voltage engineering techniques to graphene field-effect transistors on a single chip for the fabrication of a frequency multiplier and a logic inverter demonstrating analog and digital circuit application possibilities.
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Affiliation(s)
- Onejae Sul
- Institute of Nano Science and Technology, Hanyang University, Wangshimni-ro 222, Seongdong-gu, 04763, Seoul, Republic of Korea
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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 LETTERS 2014; 14:6348-6355. [PMID: 25317778 DOI: 10.1021/nl5028167] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [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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Zimmermann S, Garnica Barragan SA, Fatikow S. Nanorobotic Processing of Graphene: A platform tailored for rapid prototyping of graphene-based devices. IEEE NANOTECHNOLOGY MAGAZINE 2014. [DOI: 10.1109/mnano.2014.2326969] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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9
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Abstract
Graphene is a single layer of covalently bonded carbon atoms, which was discovered only 8 years ago and yet has already attracted intense research and commercial interest. Initial research focused on its remarkable electronic properties, such as the observation of massless Dirac fermions and the half-integer quantum Hall effect. Now graphene is finding application in touch-screen displays, as channels in high-frequency transistors and in graphene-based integrated circuits. The potential for using the unique properties of graphene in terahertz-frequency electronics is particularly exciting; however, initial experiments probing the terahertz-frequency response of graphene are only just emerging. Here we show that the photoconductivity of graphene at terahertz frequencies is dramatically altered by the adsorption of atmospheric gases, such as nitrogen and oxygen. Furthermore, we observe the signature of terahertz stimulated emission from gas-adsorbed graphene. Our findings highlight the importance of environmental conditions on the design and fabrication of high-speed, graphene-based devices. Graphene is a single layer of carbon atoms whose high electron mobility offers potential for cheap, high-speed opto-electronic devices. Docherty et al. show that the terahertz frequency photoconductivity in graphene depends crucially on the type and density of environmental gas adsorbed.
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Perkins E, Barreto L, Wells J, Hofmann P. Surface-sensitive conductivity measurement using a micro multi-point probe approach. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:033901. [PMID: 23556824 DOI: 10.1063/1.4793376] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
An instrument for microscale electrical transport measurements in ultra-high vacuum is presented. The setup is constructed around collinear lithographically-created multi-point probes with a contact spacing down to 500 nm. Most commonly, twelve-point probes are used. These probes are approached to the surface via piezoelectric positioners. Standard four-point resistance measurements can be performed using any combination of contacts out of the twelve available. Current/voltage measurements are taken semi-automatically for a variety of the possible contact configurations, effectively emulating measurements with an equidistant four-point probe for a wide range of contact spacings. In this way, it is possible to distinguish between bulk-like and surface-like conduction. The paper describes the design of the instrument and the approach to data and error analysis. Application examples are given for epitaxial graphene on SiC and degenerately doped Bi₂Se₃.
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Affiliation(s)
- Edward Perkins
- Department of Physics and Astronomy, Interdisciplinary Nanoscience Center, Aarhus University, 8000 Aarhus C, Denmark
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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 LETTERS 2012; 12:5074-5081. [PMID: 22947167 DOI: 10.1021/nl301551a] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [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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Tselev A, Lavrik NV, Vlassiouk I, Briggs DP, Rutgers M, Proksch R, Kalinin SV. Near-field microwave scanning probe imaging of conductivity inhomogeneities in CVD graphene. NANOTECHNOLOGY 2012; 23:385706. [PMID: 22948033 DOI: 10.1088/0957-4484/23/38/385706] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We have performed near-field scanning microwave microscopy (SMM) of graphene grown by chemical vapor deposition. Due to the use of probe-sample capacitive coupling and a relatively high ac frequency of a few GHz, this scanning probe method allows mapping of local conductivity without a dedicated counter electrode, with a spatial resolution of about 50 nm. Here, the coupling was enabled by atomic layer deposition of alumina on top of graphene, which in turn enabled imaging both large-area films, as well as micron-sized islands, with a dynamic range covering a low sheet resistance of a metal film and a high resistance of highly disordered graphene. The structures of graphene grown on Ni films and Cu foils are explored, and the effects of growth conditions are elucidated. We present a simple general scheme for interpretation of the contrast in the SMM images of our graphene samples and other two-dimensional conductors, which is supported by extensive numerical finite-element modeling. We further demonstrate that combination of the SMM and numerical modeling allows quantitative information about the sheet resistance of graphene to be obtained, paving the pathway for characterization of graphene conductivity with a sub-100 nm special resolution.
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Affiliation(s)
- Alexander Tselev
- The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
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Lizzit S, Larciprete R, Lacovig P, Dalmiglio M, Orlando F, Baraldi A, Gammelgaard L, Barreto L, Bianchi M, Perkins E, Hofmann P. Transfer-free electrical insulation of epitaxial graphene from its metal substrate. NANO LETTERS 2012; 12:4503-4507. [PMID: 22871144 DOI: 10.1021/nl301614j] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
High-quality, large-area epitaxial graphene can be grown on metal surfaces, but its transport properties cannot be exploited because the electrical conduction is dominated by the substrate. Here we insulate epitaxial graphene on Ru(0001) by a stepwise intercalation of silicon and oxygen, and the eventual formation of a SiO(2) layer between the graphene and the metal. We follow the reaction steps by X-ray photoemission spectroscopy and demonstrate the electrical insulation using a nanoscale multipoint probe technique.
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Affiliation(s)
- Silvano Lizzit
- Sincrotrone Trieste, S.S. 14 Km 163.5, 34149 Trieste, Italy
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