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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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2
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Chen S, Yang R, Zhou Y, Qin B, Li Y, Zheng J, Liang Y, Li T, Liu J. Terahertz wave modulation properties of graphene with different excitation laser power. RSC Adv 2022; 12:27275-27280. [PMID: 36276014 PMCID: PMC9512082 DOI: 10.1039/d2ra04133b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 09/13/2022] [Indexed: 11/28/2022] Open
Abstract
The terahertz wave modulation properties of graphene were investigated using an external 975 nm continuous wave laser with different power. Upon excitation laser, the transmission and modulation depth was measured using terahertz time-domain spectroscopy. The experimental results showed that the modulation depth of monolayer graphene and 3-layer graphene was 16% and 32% under the 1495 mW excitation power. Further, we analyzed the graphene modulation mechanism based on the Drude model and the thin-film approximation. Both theoretical analysis and calculation results showed that the terahertz wave could be modulated using graphene with different excitation laser power. Terahertz wave modulation properties of graphene are investigated using an external 975 nm continuous wave laser. The modulation depth of monolayer graphene and 3-layer graphene was 16% and 32% under 1495 mW excitation power.![]()
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Affiliation(s)
- Shaohang Chen
- School of Electronic and Automation, Guilin University of Electronic Technology, Guilin 541004, China
- School of Electronic and Automation, Guilin University of Aerospace Technology, Guilin 541004, China
| | - Ruizhao Yang
- Optoelectronic Information Research Center, School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin 537000, China
| | - Yanni Zhou
- Optoelectronic Information Research Center, School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin 537000, China
| | - Binyi Qin
- Key Laboratory of Complex System Optimization and Big Data Processing, Guangxi Colleges and Universities, Yulin Normal University, Yulin 537000, China
- Research Center of Intelligent Information and Communication Technology, School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin, China
| | - Yun Li
- School of Chemistry and Food Science, Yulin Normal University, Yulin 537000, China
| | - Jincun Zheng
- Key Laboratory of Complex System Optimization and Big Data Processing, Guangxi Colleges and Universities, Yulin Normal University, Yulin 537000, China
- Research Center of Intelligent Information and Communication Technology, School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin, China
| | - Yizhi Liang
- Optoelectronic Information Research Center, School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin 537000, China
| | - Tinghui Li
- Optoelectronic Information Research Center, School of Physics and Telecommunication Engineering, Yulin Normal University, Yulin 537000, China
- Clooege of Electronic Engineering, Guangxi Normal University, Yulin 537000, China
| | - Jianming Liu
- School of Electronic and Automation, Guilin University of Electronic Technology, Guilin 541004, China
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3
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Systematic THz study of the substrate effect in limiting the mobility of graphene. Sci Rep 2021; 11:8729. [PMID: 33888755 PMCID: PMC8062515 DOI: 10.1038/s41598-021-87894-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2021] [Accepted: 04/05/2021] [Indexed: 12/15/2022] Open
Abstract
We explore the substrate-dependent charge carrier dynamics of large area graphene films using contact-free non-invasive terahertz spectroscopy. The graphene samples are deposited on seven distinct substrates relevant to semiconductor technologies and flexible/photodetection devices. Using a Drude model for Dirac fermions in graphene and a fitting method based on statistical signal analysis, we extract transport properties such as the charge carrier density and carrier mobility. We find that graphene films supported by substrates with minimal charged impurities exhibit an enhanced carrier mobility, while substrates with a high surface roughness generally lead to a lower transport performance. The smallest amount of doping is observed for graphene placed on the polymer Zeonor, which also has the highest carrier mobility. This work provides valuable guidance in choosing an optimal substrate for graphene to enable applications where high mobility is required.
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Abstract
Conductive thin films are an essential component of many electronic devices. Measuring their conductivity accurately is necessary for quality control and process monitoring. We compare conductivity measurements on films for flexible electronics using three different techniques: four-point probe, microwave resonator and terahertz time-domain spectroscopy. Multiple samples were examined, facilitating the comparison of the three techniques. Sheet resistance values at DC, microwave and terahertz frequencies were obtained and were found to be in close agreement.
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5
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Toqeer I, Yaqoob MZ, Ghaffar A, Alkanhal MAS, Khan Y, Aladadi YT. Reflectance and transmittance of terahertz waves from graphene embedded into metamaterial structures. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2021; 38:465-475. [PMID: 33798175 DOI: 10.1364/josaa.412649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 02/04/2021] [Indexed: 06/12/2023]
Abstract
In this work, the theoretical study of the interaction of terahertz (THz) waves with graphene embedded into two different semi-infinite metamaterials was carried out. To model the graphene, the effective surface conductivity approach based on the Kubo formalism was used. In addition, two types of metamaterials, i.e., double-positive (DPS) and double-negative (DNG), were studied in the THz regime. The numerical modeling of metamaterials was performed in the framework of causality-principle-based Kramers-Kronig relations. The reflectance and transmittance from the graphene-embedded metamaterial structures are studied for the following four different configurations: DPS-Graphene-DPS, DPS-Graphene-DNG, DNG-Graphene-DPS, and DNG-Graphene-DNG. The influence of the chemical potential and scattering rate on the reflectance and transmittance for each configuration is analyzed. It is concluded that the DPS-Graphene-DPS and DNG-Graphene-DNG configurations behave as anti-reflectors for the THz waves, while the DPS-Graphene-DNG and DNG-Graphene-DPS configurations are suitable for THz reflector applications. Moreover, a parametric study revealed that the relative permittivity of the partnering metamaterial can be used as an additional degree of freedom to control the reflectance and transmittance of THz waves. In conclusion, the transmissive and reflective characteristics of THz waves can be controlled effectively with the appropriate choice of graphene parameters, as well as the configuration of metamaterial structures. The convergence of the analytical and numerical results is found with the published results under special conditions. The present work may have potential applications in the design of THz wave controllers, reflectors, absorbers, and anti-reflectors.
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Khambampati AK, Rahman SA, Sharma SK, Kim WY, Kim KY. Imaging Conductivity Changes in Monolayer Graphene Using Electrical Impedance Tomography. MICROMACHINES 2020; 11:mi11121074. [PMID: 33271930 PMCID: PMC7761263 DOI: 10.3390/mi11121074] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 11/26/2020] [Accepted: 11/28/2020] [Indexed: 11/24/2022]
Abstract
Recently, graphene has gained a lot of attention in the electronic industry due to its unique properties and has paved the way for realizing novel devices in the field of electronics. For the development of new device applications, it is necessary to grow large wafer-sized monolayer graphene samples. Among the methods to synthesize large graphene films, chemical vapor deposition (CVD) is one of the promising and common techniques. However, during the growth and transfer of the CVD graphene monolayer, defects such as wrinkles, cracks, and holes appear on the graphene surface. These defects can influence the electrical properties and it is of interest to know the quality of graphene samples non-destructively. Electrical impedance tomography (EIT) can be applied as an alternate method to determine conductivity distribution non-destructively. The EIT inverse problem of reconstructing conductivity is highly non-linear and is heavily dependent on measurement accuracy and modeling errors related to an accurate knowledge of electrode location, contact resistances, the exact outer boundary of the graphene wafer, etc. In practical situations, it is difficult to eliminate these modeling errors as complete knowledge of the electrode contact impedance and outer domain boundary is not fully available, and this leads to an undesirable solution. In this paper, a difference imaging approach is proposed to estimate the conductivity change of graphene with respect to the reference distribution from the data sets collected before and after the change. The estimated conductivity change can be used to locate the defects on the graphene surface caused due to the CVD transfer process or environment interaction. Numerical and experimental results with graphene sample of size 2.5 × 2.5 cm are performed to determine the change in conductivity distribution and the results show that the proposed difference imaging approach handles the modeling errors and estimates the conductivity distribution with good accuracy.
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7
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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. OPTICS 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] [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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8
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D'Arco A, Mussi V, Petrov S, Tofani S, Petrarca M, Beccherelli R, Dimitrov D, Marinova V, Lupi S, Zografopoulos DC. Fabrication and spectroscopic characterization of graphene transparent electrodes on flexible cyclo-olefin substrates for terahertz electro-optic applications. NANOTECHNOLOGY 2020; 31:364006. [PMID: 32460247 DOI: 10.1088/1361-6528/ab96e6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We demonstrate graphene on flexible, low-loss, cyclo-olefin polymer films as transparent electrodes for terahertz electro-optic devices and applications. Graphene was grown by chemical vapor deposition and transferred to cyclo-olefin polymer substrates by the thermal release tape method as layers on an approximate area of 4 cm2. The structural and electromagnetic properties of the graphene samples as well as their spatial variation were systematically mapped by means of µRaman, terahertz time-domain and mid-infrared spectroscopy. Thanks to the small thickness and very low intrinsic absorption of the employed substrates, both high transmittance and conductivity were recorded, demonstrating the suitability of the technique for the fabrication of a new class of transparent and flexible electrodes working in the terahertz spectrum.
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Affiliation(s)
- Annalisa D'Arco
- Department of Physics,'Sapienza' University of Rome, Piazzale Aldo Moro 2, I-00185, Rome, Italy. Roma1-INFN, Piazzale Aldo Moro, 2, I-00185, Rome, Italy
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9
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Nakajima H, Morimoto T, Okigawa Y, Yamada T, Ikuta Y, Kawahara K, Ago H, Okazaki T. Imaging of local structures affecting electrical transport properties of large graphene sheets by lock-in thermography. SCIENCE ADVANCES 2019; 5:eaau3407. [PMID: 30746485 PMCID: PMC6358317 DOI: 10.1126/sciadv.aau3407] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 12/13/2018] [Indexed: 05/30/2023]
Abstract
The distribution of defects and dislocations in graphene layers has become a very important concern with regard to the electrical and electronic transport properties of device applications. Although several experiments have shown the influence of defects on the electrical properties of graphene, these studies were limited to measuring microscopic areas because of their long measurement times. Here, we successfully imaged various local defects in a large area of chemical vapor deposition graphene within a reasonable amount of time by using lock-in thermography (LIT). The differences in electrical resistance caused by the micrometer-scale defects, such as cracks and wrinkles, and atomic-scale domain boundaries were apparent as nonuniform Joule heating on polycrystalline and epitaxially grown graphene. The present results indicate that LIT can serve as a fast and effective method of evaluating the quality and uniformity of large graphene films for device applications.
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Affiliation(s)
- H. Nakajima
- CNT-Application Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
| | - T. Morimoto
- CNT-Application Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
| | - Y. Okigawa
- Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
| | - T. Yamada
- Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
| | - Y. Ikuta
- CNT-Application Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
| | - K. Kawahara
- Global Innovation Center, Kyushu University, Fukuoka 816-8580, Japan
| | - H. Ago
- Global Innovation Center, Kyushu University, Fukuoka 816-8580, Japan
| | - T. Okazaki
- CNT-Application Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
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10
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Skalsky S, Molloy J, Naftaly M, Sainsbury T, Paton KR. Terahertz time-domain spectroscopy as a novel metrology tool for liquid-phase exfoliated few-layer graphene. NANOTECHNOLOGY 2019; 30:025709. [PMID: 30398164 DOI: 10.1088/1361-6528/aae8ce] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Few-layer graphene (FLG) platelets exfoliated directly from graphite are finding a wide range of potential applications, including composites and printed electronics. However, characterisation of the FLG material following incorporation into polymers, including the quality of the dispersion, remains a challenge. Here, we present the use of terahertz time-domain spectroscopy as a potential solution to this challenge which could form the basis of a rapid characterisation tool. The THz refractive index was found to be highly sensitive to the loading of FLG, opening the route to mapping local FLG concentration within a polymer composite sample. By fitting the measured permittivity of the flakes to the Drude-Smith model of conductivity, we also show that the carrier concentrations of these materials are comparable to un-doped chemical vapour deposition produced materials. The ability to measure electronic properties of FLG following processing is important to ensure that defects have not been introduced or chemical functionalisation removed during processing.
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11
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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. OPTICS 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] [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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12
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Lin H, Braeuninger-Weimer P, Kamboj VS, Jessop DS, Degl'Innocenti R, Beere HE, Ritchie DA, Zeitler JA, Hofmann S. Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy. Sci Rep 2017; 7:10625. [PMID: 28878213 PMCID: PMC5587735 DOI: 10.1038/s41598-017-09809-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 08/07/2017] [Indexed: 11/09/2022] Open
Abstract
We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films on sapphire, silicon dioxide/silicon and germanium. We validate the technique against measurements performed with previously established conventional transmission based THz-TDS and are able to resolve conductivity changes in response to induced back-gate voltages. Compared to the transmission geometry, measurement in reflection mode requires careful alignment and complex analysis, but circumvents the need of a terahertz transparent substrate, potentially enabling fast, contactless, in-line characterisation of graphene films on non-insulating substrates such as germanium.
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Affiliation(s)
- Hungyen Lin
- Department of Engineering, Lancaster University, Lancaster, LA1 4YW, United Kingdom.
| | - Philipp Braeuninger-Weimer
- Department of Engineering, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0FA, United Kingdom.
| | - Varun S Kamboj
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - David S Jessop
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - Riccardo Degl'Innocenti
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - Harvey E Beere
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - David A Ritchie
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - J Axel Zeitler
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, CB2 3RA, United Kingdom
| | - Stephan Hofmann
- Department of Engineering, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0FA, United Kingdom
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Chatzakis I, Li Z, Benderskii AV, Cronin SB. Broadband terahertz modulation in electrostatically-doped artificial trilayer graphene. NANOSCALE 2017; 9:1721-1726. [PMID: 28091664 DOI: 10.1039/c6nr07054j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report a terahertz optical modulator consisting of randomly stacked trilayer graphene (TLG) deposited on an oxidized silicon substrate by means of THz-Time Domain Spectroscopy (THz-TDS). Here, the gate tuning of the Fermi level of the TLG provides the fundamental basis for the modulation of THz transmission. We measured a 15% change in the THz transmission of this device over a broad frequency range (0.6-1.6 THz). We also observed a strong absorption >80% in the time-domain signals and a frequency independence of the conductivity. Furthermore, unlike previous studies, we find that the underlying silicon substrate, which serves as a gate electrode for the graphene, also exhibits substantial modulation of the transmitted THz radiation under applied voltage biases.
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Affiliation(s)
- Ioannis Chatzakis
- Department of Electrical Engineering, University of Southern California, Los Angeles, California, CA 90089, USA.
| | - Zhen Li
- Department of Electrical Engineering, University of Southern California, Los Angeles, California, CA 90089, USA.
| | - Alexander V Benderskii
- Department of Chemistry, University of Southern California, Los Angeles, California, CA 90089, USA
| | - Stephen B Cronin
- Department of Electrical Engineering, University of Southern California, Los Angeles, California, CA 90089, USA. and Department of Chemistry, University of Southern California, Los Angeles, California, CA 90089, USA and Department of Physics, University of Southern California, Los Angeles, California, CA 90089, USA
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14
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Clericò V, Notario JAD, Campos N, Gómez D, Diez E, Velazquez JE, Meziani YM. Terahertz spectroscopy of a multilayers flake of graphene. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/1742-6596/647/1/012040] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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15
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Qiao Z, Qin C, Gao Y, Zhang G, Chen R, Xiao L, Jia S. Modulation of the optical transmittance in monolayer graphene oxide by using external electric field. Sci Rep 2015; 5:14441. [PMID: 26404872 PMCID: PMC5155675 DOI: 10.1038/srep14441] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 08/28/2015] [Indexed: 11/23/2022] Open
Abstract
Graphene oxide (GO) emerges as a functional material in optoelectronic devices due to its broad spectrum response and abundant optical properties. In this article, it is demonstrated that the change of optical transmittance amplitude for monolayer GO (mGO) could be up to 24.8% by an external electric field. The frequency harmonics for transmittance spectra are analyzed by use of Fast Fourier Transforms to give an insight into the modulation mechanism. Two physical models, the electrical permittivity and the sheet conductivity which linearly vary as the electric field, are proposed to response for the transmittance modulation. The model-based simulations agree reasonable well with the experimental results.
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Affiliation(s)
- Zhixing Qiao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Chengbing Qin
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Yan Gao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Guofeng Zhang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Ruiyun Chen
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Liantuan Xiao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Suotang Jia
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
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Jnawali G, Rao Y, Beck JH, Petrone N, Kymissis I, Hone J, Heinz TF. Observation of Ground- and Excited-State Charge Transfer at the C60/Graphene Interface. ACS NANO 2015; 9:7175-7185. [PMID: 26072947 DOI: 10.1021/acsnano.5b01896] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We examine charge transfer interactions in the hybrid system of a film of C60 molecules deposited on single-layer graphene using Raman spectroscopy and Terahertz (THz) time-domain spectroscopy. In the absence of photoexcitation, we find that the C60 molecules in the deposited film act as electron acceptors for graphene, yielding increased hole doping in the graphene layer. Hole doping of the graphene film by a uniform C60 film at a level of 5.6 × 10(12)/cm(2) or 0.04 holes per interfacial C60 molecule was determined by the use of both Raman and THz spectroscopy. We also investigate transient charge transfer occurring upon photoexcitation by femtosecond laser pulses with a photon energy of 3.1 eV. The C60/graphene hybrid exhibits a short-lived (ps) decrease in THz conductivity, followed by a long-lived increase in conductivity. The initial negative photoconductivity transient, which decays within 2 ps, reflects the intrinsic photoresponse of graphene. The longer-lived positive conductivity transient, with a lifetime on the order of 100 ps, is attributed to photoinduced hole doping of graphene by interfacial charge transfer. We discuss possible microscopic pathways for hot carrier processes in the hybrid system.
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Affiliation(s)
- Giriraj Jnawali
- †Department of Physics, Columbia University, New York, New York 10027, United States
| | - Yi Rao
- †Department of Physics, Columbia University, New York, New York 10027, United States
| | - Jonathan H Beck
- §Department of Electrical Engineering, Columbia University, New York, New York 10027, United States
| | - Nicholas Petrone
- ∥Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Ioannis Kymissis
- §Department of Electrical Engineering, Columbia University, New York, New York 10027, United States
| | - James Hone
- ∥Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Tony F Heinz
- †Department of Physics, Columbia University, New York, New York 10027, United States
- §Department of Electrical Engineering, Columbia University, New York, New York 10027, United States
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17
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Buron JD, Pizzocchero F, Jepsen PU, Petersen DH, Caridad JM, Jessen BS, Booth TJ, Bøggild P. Graphene mobility mapping. Sci Rep 2015. [PMID: 26204815 PMCID: PMC4513276 DOI: 10.1038/srep12305] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
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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18
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Cervetti C, Heintze E, Gorshunov B, Zhukova E, Lobanov S, Hoyer A, Burghard M, Kern K, Dressel M, Bogani L. Sub-terahertz frequency-domain spectroscopy reveals single-grain mobility and scatter influence of large-area graphene. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2015; 27:2635-2641. [PMID: 25787669 DOI: 10.1002/adma.201500599] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Indexed: 06/04/2023]
Abstract
The response of individual domains in wafer-sized chemical vapor deposition graphene is measured by contactless sub-terahertz interferometry, observing the intrinsic optical conductance and reaching very high mobility values. It is shown that charged scatterers limit the mobility, validating previous theoretical predictions, and sub-terahertz quality assessment is demonstrated, as necessary for large-scale applications in touchscreens, as well as wearable and optoelectronic devices.
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Affiliation(s)
- Christian Cervetti
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550, Stuttgart, Germany
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19
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Zhang W, Pham PHQ, Brown ER, Burke PJ. AC conductivity parameters of graphene derived from THz etalon transmittance. NANOSCALE 2014; 6:13895-13899. [PMID: 25307168 DOI: 10.1039/c4nr03222e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
THz frequency-domain transmittance measurements were carried out on chemical-vapor-deposited (CVD) graphene films transferred to high-resistivity silicon substrates, and packaged as back-gated graphene field effect transistors (G-FETs). The graphene AC conductivity σ(ω), both real and imaginary parts, is determined between 0.2 and 1.2 THz from the transmittance using the transmission matrix method and curve-fitting techniques. Critical parameters such as the charge-impurity scattering width and chemical potential are calculated. It is found that not only the sheet charge density but also the scattering parameter can be modified by the back-gate voltage.
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Affiliation(s)
- Weidong Zhang
- Terahertz Sensors Laboratory, Departments of Physics and Electrical Engineering, Wright State University, Dayton, OH 45435, USA.
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20
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Wu Y, Ruan X, Chen CH, Shin YJ, Lee Y, Niu J, Liu J, Chen Y, Yang KL, Zhang X, Ahn JH, Yang H. Graphene/liquid crystal based terahertz phase shifters. OPTICS EXPRESS 2013; 21:21395-21402. [PMID: 24104014 DOI: 10.1364/oe.21.021395] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Due to its high electrical conductivity and excellent transmittance at terahertz frequencies, graphene is a promising candidate as transparent electrodes for terahertz devices. We demonstrate a liquid crystal based terahertz phase shifter with the graphene films as transparent electrodes. The maximum phase shift is 10.8 degree and the saturation voltage is 5 V with a 50 µm liquid crystal cell. The transmittance at terahertz frequencies and electrical conductivity depending on the number of graphene layer are also investigated. The proposed phase shifter provides a continuous tunability, fully electrical controllability, and low DC voltage operation.
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21
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Hong JT, Lee KM, Son BH, Park SJ, Park DJ, Park JY, Lee S, Ahn YH. Terahertz conductivity of reduced graphene oxide films. OPTICS EXPRESS 2013; 21:7633-7640. [PMID: 23546146 DOI: 10.1364/oe.21.007633] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We performed time-domain terahertz (THz) spectroscopy on reduced graphene oxide (rGO) network films coated on quartz substrates from dispersion solutions by spraying method. The rGO network films demonstrate high conductivity of about 900 S/cm in the THz frequency range after a high temperature reduction process. The frequency-dependent conductivities and the refractive indexes of the rGO films have been obtained and analyzed with respect to the Drude free-electron model, which is characterized by large scattering rate. Finally, we demonstrate that the THz conductivities can be manipulated by controlling the reduction process, which correlates well with the DC conductivity above the percolation limit.
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Affiliation(s)
- J T Hong
- Department of Physics and Division of Energy Systems Research, Ajou University, Suwon 443-749, South Korea
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22
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Jnawali G, Rao Y, Yan H, Heinz TF. Observation of a transient decrease in terahertz conductivity of single-layer graphene induced by ultrafast optical excitation. NANO LETTERS 2013; 13:524-30. [PMID: 23330567 DOI: 10.1021/nl303988q] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We have measured the terahertz frequency-dependent sheet conductivity and its transient response following femtosecond optical excitation for single-layer graphene samples grown by chemical vapor deposition. The conductivity of the unexcited graphene sheet, which was spontaneously doped, showed a strong free-carrier response. The THz conductivity matched a Drude model over the available THz spectral range and yielded an average carrier scattering time of 70 fs. Upon photoexcitation, we observed a transient decrease in graphene conductivity. The THz frequency-dependence of the graphene photoresponse differs from that of the unexcited material but remains compatible with a Drude form. We show that the negative photoconductive response arises from an increase in the carrier scattering rate, with a minor offsetting increase in the Drude weight. This behavior, which differs in sign from that reported previously for epitaxial graphene, is expected for samples with relatively high mobilities and doping levels. The photoinduced conductivity transient has a picosecond lifetime and is associated with nonequilibrium excitation conditions in the graphene.
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Affiliation(s)
- Giriraj Jnawali
- Department of Physics, Columbia University, New York, New York 10027, USA
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23
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Sensale-Rodriguez B, Rafique S, Yan R, Zhu M, Protasenko V, Jena D, Liu L, Xing HG. Terahertz imaging employing graphene modulator arrays. OPTICS EXPRESS 2013; 21:2324-30. [PMID: 23389211 DOI: 10.1364/oe.21.002324] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
In this paper we propose and experimentally demonstrate arrays of graphene electro-absorption modulators as electrically reconfigurable patterns for terahertz cameras. The active element of these modulators consists of only single-atom-thick graphene, achieving a modulation of the THz wave reflectance > 50% with a potential modulation depth approaching 100%. Although the prototype presented here only contains 4x4 pixels, it reveals the possibility of developing reliable low-cost video-rate THz imaging systems employing single detector.
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24
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Zhou Y, Xu X, Fan H, Ren Z, Bai J, Wang L. Tunable magnetoplasmons for efficient terahertz modulator and isolator by gated monolayer graphene. Phys Chem Chem Phys 2013; 15:5084-90. [DOI: 10.1039/c3cp43994a] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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25
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Weis P, Garcia-Pomar JL, Höh M, Reinhard B, Brodyanski A, Rahm M. Spectrally wide-band terahertz wave modulator based on optically tuned graphene. ACS NANO 2012; 6:9118-9124. [PMID: 22992128 DOI: 10.1021/nn303392s] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
New applications in the realms of terahertz (THz) technology require versatile adaptive optics and powerful modulation techniques. Semiconductors have proven to provide fast all-optical terahertz wave modulation over a wide frequency band. We show that the attenuation and modulation depth in optically driven silicon modulators can be significantly enhanced by deposition of graphene on silicon (GOS). We observed a wide-band tunability of the THz transmission in a frequency range from 0.2 to 2 THz and a maximum modulation depth of 99%. The maximum difference between the transmission through silicon and GOS is Δt = 0.18 at a low photodoping power of 40 mW. At higher modulation power, the enhancement decreased due to charge carrier saturation. We developed a semianalytical band structure model of the graphene-silicon interface to describe the observed attenuation and modulation depth in GOS.
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Affiliation(s)
- Peter Weis
- Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Erwin-Schroedinger-Strasse, 67663 Kaiserslautern, Germany
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26
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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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27
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Sensale-Rodriguez B, Yan R, Rafique S, Zhu M, Li W, Liang X, Gundlach D, Protasenko V, Kelly MM, Jena D, Liu L, Xing HG. Extraordinary control of terahertz beam reflectance in graphene electro-absorption modulators. NANO LETTERS 2012; 12:4518-4522. [PMID: 22862777 DOI: 10.1021/nl3016329] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We demonstrate a graphene-based electro-absorption modulator achieving extraordinary control of terahertz reflectance. By concentrating the electric field intensity in an active layer of graphene, an extraordinary modulation depth of 64% is achieved while simultaneously exhibiting low insertion loss (∼2 dB), which is remarkable since the active region of the device is atomically thin. This modulator performance, among the best reported to date, indicates the enormous potential of graphene for terahertz reconfigurable optoelectronic devices.
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Affiliation(s)
- Berardi Sensale-Rodriguez
- Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States.
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28
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Cooke DG, Krebs FC, Jepsen PU. Direct observation of sub-100 fs mobile charge generation in a polymer-fullerene film. PHYSICAL REVIEW LETTERS 2012; 108:056603. [PMID: 22400948 DOI: 10.1103/physrevlett.108.056603] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Indexed: 05/31/2023]
Abstract
The formation of mobile charges in a roll-to-roll processed poly-3-hexylthiophene-fullerene bulk heterojunction film is observed directly by using transient terahertz spectroscopy with sub-100 fs temporal resolution. The transient terahertz ac conductivity reveals that 20% of the incident pump photons are converted into highly delocalized charges within the 40 fs, 3.1 eV pump pulse duration, which then rapidly becomes localized within 120 fs. Approximately 2/3 of these carriers subsequently decay, possibly into an exciton, on a 1 ps time scale.
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Affiliation(s)
- D G Cooke
- Department of Physics, McGill University, Montreal, Canada H3A 2T8
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29
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Affiliation(s)
- Jason B. Baxter
- Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania, 19104, United States
| | - Glenn W. Guglietta
- Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania, 19104, United States
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