1
|
Huang Z, Bai Y, Zhao Y, Liu L, Zhao X, Wu J, Watanabe K, Taniguchi T, Yang W, Shi D, Xu Y, Zhang T, Zhang Q, Tan PH, Sun Z, Meng S, Wang Y, Du L, Zhang G. Observation of phonon Stark effect. Nat Commun 2024; 15:4586. [PMID: 38811589 DOI: 10.1038/s41467-024-48992-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Accepted: 05/15/2024] [Indexed: 05/31/2024] Open
Abstract
Stark effect, the electric-field analogue of magnetic Zeeman effect, is one of the celebrated phenomena in modern physics and appealing for emergent applications in electronics, optoelectronics, as well as quantum technologies. While in condensed matter it has prospered only for excitons, whether other collective excitations can display Stark effect remains elusive. Here, we report the observation of phonon Stark effect in a two-dimensional quantum system of bilayer 2H-MoS2. The longitudinal acoustic phonon red-shifts linearly with applied electric fields and can be tuned over ~1 THz, evidencing giant Stark effect of phonons. Together with many-body ab initio calculations, we uncover that the observed phonon Stark effect originates fundamentally from the strong coupling between phonons and interlayer excitons (IXs). In addition, IX-mediated electro-phonon intensity modulation up to ~1200% is discovered for infrared-active phonon A2u. Our results unveil the exotic phonon Stark effect and effective phonon engineering by IX-mediated mechanism, promising for a plethora of exciting many-body physics and potential technological innovations.
Collapse
Affiliation(s)
- Zhiheng Huang
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Yunfei Bai
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Yanchong Zhao
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Le Liu
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Xuan Zhao
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Jiangbin Wu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, China
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Wei Yang
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Dongxia Shi
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Yang Xu
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Tiantian Zhang
- CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Qingming Zhang
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Science and Technology, Lanzhou University, Lanzhou, 730000, China
| | - Ping-Heng Tan
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, China
| | - Zhipei Sun
- QTF Centre of Excellence, Department of Electronics and Nanoengineering, Aalto University, Tietotie 3, FI-02150, Espoo, Finland
| | - Sheng Meng
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong Province, 523808, China
| | - Yaxian Wang
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
| | - Luojun Du
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China.
| | - Guangyu Zhang
- Beijing National Laboratory for Condensed Matter Physics; Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China.
- Songshan Lake Materials Laboratory, Dongguan, Guangdong Province, 523808, China.
| |
Collapse
|
2
|
Gadelha AC, Nguyen VH, Neto EGS, Santana F, Raschke MB, Lamparski M, Meunier V, Charlier JC, Jorio A. Electron-Phonon Coupling in a Magic-Angle Twisted-Bilayer Graphene Device from Gate-Dependent Raman Spectroscopy and Atomistic Modeling. NANO LETTERS 2022; 22:6069-6074. [PMID: 35878122 DOI: 10.1021/acs.nanolett.2c00905] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The importance of phonons in the strong correlation phenomena observed in twisted-bilayer graphene (TBG) at the so-called magic-angle is under debate. Here we apply gate-dependent micro-Raman spectroscopy to monitor the G band line width in TBG devices of twist angles θ = 0° (Bernal), ∼1.1° (magic-angle), and ∼7° (large-angle). The results show a broad and p-/n-asymmetric doping behavior at the magic angle, in clear contrast to the behavior observed in twist angles above and below this point. Atomistic modeling reproduces the experimental observations in close connection with the joint density of electronic states in the electron-phonon scattering process, revealing how the unique electronic structure of magic-angle TBGs influences the electron-phonon coupling and, consequently, the G band line width. Overall, the value of the G band line width in magic-angle TBG is larger when compared to that of the other samples, in qualitative agreement with our calculations.
Collapse
Affiliation(s)
- Andreij C Gadelha
- Physics Department, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil
- Department of Physics, and JILA, University of Colorado at Boulder, Boulder, Colorado 80309, United States
| | - Viet-Hung Nguyen
- Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain (UCLouvain), Louvain-la-Neuve 1348, Belgium
| | - Eliel G S Neto
- Physics Institute, Universidade Federal da Bahia, Salvador, Bahia 40170-115 Brazil
| | - Fabiano Santana
- Physics Department, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil
| | - Markus B Raschke
- Department of Physics, and JILA, University of Colorado at Boulder, Boulder, Colorado 80309, United States
| | - Michael Lamparski
- Department of Physics, Applied Physics, and Astronomy, Jonsson Rowland Science Center, Troy, New York 12180-3590, United States
| | - Vincent Meunier
- Department of Physics, Applied Physics, and Astronomy, Jonsson Rowland Science Center, Troy, New York 12180-3590, United States
| | - Jean-Christophe Charlier
- Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain (UCLouvain), Louvain-la-Neuve 1348, Belgium
| | - Ado Jorio
- Physics Department, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil
| |
Collapse
|
3
|
Madito MJ. Correlation of the Graphene Fermi-Level Shift and the Enhanced Electrochemical Performance of Graphene-Manganese Phosphate for Hybrid Supercapacitors: Raman Spectroscopy Analysis. ACS APPLIED MATERIALS & INTERFACES 2021; 13:37014-37026. [PMID: 34318656 DOI: 10.1021/acsami.1c07104] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
A high structurally stable graphene-manganese phosphate (graphene-Mn3P2O8) composite with excellent cycling stability was prepared by the facile hydrothermal method. The correlation between the high electrochemical performance of graphene-Mn3P2O8 composite and the graphene Fermi-level shift was investigated using Raman spectroscopy by monitoring the disorder in the sp2 network of the composite graphene arising from the heterogeneous atoms doping during hydrothermal synthesis. The response of the Raman signatures of graphene to the chemical doping effect correlated to the electronic band structure in the vicinity of the Dirac point showed an upshift in the graphene Fermi level with an average value of about 190 meV, indicating that the composite graphene is n-type-doped. This was confirmed by X-ray photoelectron spectroscopy data, which showed a relatively high concentration of electron-donating heterogeneous atoms in the composite graphene. The electrochemical analysis confirmed that the n-type-doped composite graphene has enhanced the electrical conductivity of the Mn3P2O8 electrode and decreased the potential barriers between the electrode surface and electrolyte highest occupied molecular orbital (HOMO) for enhanced interfacial charge transfer between the electrode surface and the electrolyte; hence, the graphene-Mn3P2O8 composite electrode exhibited a high specific capacity of 38.4 mA h g-1 compared to the pristine Mn3P2O8 electrode (7.2 mA h g-1). Due to its excellent cycling stability (∼100% capacity retention over 5000 charge-discharge cycles at 5 A g-1), graphene-Mn3P2O8 composite is a promising electrode material for hybrid supercapacitors.
Collapse
Affiliation(s)
- Moshawe J Madito
- Institute for Nanotechnology and Water Sustainability (iNanoWS), College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710, South Africa
| |
Collapse
|
4
|
Almodóvar P, Santos F, González J, Ramírez-Castellanos J, González-Calbet JM, Díaz-Guerra C, Fernández Romero AJ. Study of Cr2O3 nanoparticles supported on carbonaceous materials as catalysts for O2 reduction reaction. J Electroanal Chem (Lausanne) 2021. [DOI: 10.1016/j.jelechem.2021.115441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
|
5
|
Bae G, Song DS, Lim YR, Jeon IS, Jang M, Yoon Y, Jeon C, Song W, Myung S, Lee SS, Park CY, An KS. Chemical Patterning of Graphene via Metal-Assisted Highly Energetic Electron Irradiation for Graphene Homojunction-Based Gas Sensors. ACS APPLIED MATERIALS & INTERFACES 2020; 12:47802-47810. [PMID: 32985173 DOI: 10.1021/acsami.0c12063] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
To gain the target functionality of graphene for gas detection, nonfocused and large-scale compatible MeV electron beam irradiation on graphene with Ag patterns is innovatively adopted in air for chemical patterning of graphene. This strategy allows the metal-assisted site-specific oxidation of graphene to realize monolithically integrated graphene-chemically patterned graphene (CPG)-graphene homojunction-based gas sensors. The size-tunable CPG patterns can be mediated by regulating the size of Ag prepatterns. The impacts of highly energetic electron irradiation (HEEI) on graphene are summarized as follows: (i) the selective p-type doping and the defect generation of graphene by the HEEI-induced oxidation, (ii) the resistance of the homojunction devices manipulated by the HEEI dose, (iii) the band gap opening of graphene as well as the lowering of the Fermi level, (iv) the work function values for pristine graphene and CPG corresponding to 4.14 and 4.88 eV, respectively, and (v) graphene-CPG-graphene homojunction for NO2 gas, revealing an 839% enhanced gas response compared with that of the pristine graphene-based gas sensor.
Collapse
Affiliation(s)
- Garam Bae
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
- Department of Physics, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 16419, Republic of Korea
| | - Da Som Song
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Yi Rang Lim
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - In Su Jeon
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Moonjeong Jang
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Yeoheung Yoon
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Cheolho Jeon
- Advanced Nano Surface Research Group, Korea Basic Science Institute, Daejeon 34133, Republic of Korea
| | - Wooseok Song
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Sung Myung
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Sun Sook Lee
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| | - Chong-Yun Park
- Department of Physics, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 16419, Republic of Korea
| | - Ki-Seok An
- Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea
| |
Collapse
|
6
|
Gao Z, Li M, Wang JS. Insight into Two-Dimensional Borophene: Five-Center Bond and Phonon-Mediated Superconductivity. ACS APPLIED MATERIALS & INTERFACES 2019; 11:47279-47288. [PMID: 31736292 DOI: 10.1021/acsami.9b17896] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We report a previously unknown monolayer borophene allotrope and we call it super-B with a flat structure based on ab initio calculations. It has good thermal, dynamical, and mechanical stability compared with many other typical borophenes. We find that super-B has a fascinating chemical bond environment consisting of standard sp, sp2 hybridizations, and delocalized five-center three-electron π bond, called π(5c-3e). This particular electronic structure plays a pivotal role in stabilizing the super-B chemically. By extra doping, super-B can be transformed into a Dirac material from pristine metal. Like graphene, it can also sustain tensile strain smaller than 24%, indicating superior flexibility. Moreover, due to the small atomic mass and large density of states at the Fermi level, super-B has the highest critical temperature Tc of 25.3 K in single-element superconductors at ambient conditions. We attribute this high Tc of super-B to the giant anharmonicity of two linear acoustic phonon branches and an unusually low optic phonon mode. These predictions provide new insight into the chemical nature of low dimensional boron nanostructures and highlight the potential applications of designing flexible devices and high Tc superconductor.
Collapse
Affiliation(s)
- Zhibin Gao
- Department of Physics , National University of Singapore , Singapore 117551 , Republic of Singapore
| | - Mengyang Li
- Institute for Chemical Physics & Department of Chemistry, Graduate School of Science , Xi'an Jiaotong University , Xi'an 710049 , China
| | - Jian-Sheng Wang
- Department of Physics , National University of Singapore , Singapore 117551 , Republic of Singapore
| |
Collapse
|
7
|
Electron-Phonon Coupling as the Source of 1/f Noise in Carbon Soot. Sci Rep 2019; 9:947. [PMID: 30700741 PMCID: PMC6353950 DOI: 10.1038/s41598-018-36544-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 11/22/2018] [Indexed: 11/25/2022] Open
Abstract
Two 1/f noise peaks were found in a carbon soot resistor at voltages characteristic of Kohn anomalies in graphite. The ratio of the electron-phonon coupling matrix elements at the anomalies calculated from the noise peak intensities is the same as the one obtained from the Raman frequencies. This demonstrates that the electron-phonon coupling is the microscopic source of 1/f noise in carbon soot. A new, very general formula was deduced for the frequency exponent, wherein nonlinearity and dispersion are the only ingredients. The interplay between nonlinearity and dispersion in this formula describes the sublinear-supralinear transitions experimentally observed at both anomalies in the voltage dependence of the frequency exponent. A quadratic dependence of the 1/f noise parameter on the matrix element is proposed and applied to explain the M-shape of the 1/f noise in graphene. We found that the frequency exponent mimics the dependence of the noise intensity in the whole voltage range, while both are the image of the graphite phonon spectrum. This implies that the source of nonlinearity is in the electron-phonon coupling which modulates the slope of the spectrum. It requires the presence of 1/f noise in the thermal noise background of the resistor till phonon frequencies.
Collapse
|
8
|
Wu J, Xie L. Structural Quantification for Graphene and Related Two-Dimensional Materials by Raman Spectroscopy. Anal Chem 2018; 91:468-481. [DOI: 10.1021/acs.analchem.8b04991] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Juanxia Wu
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, P. R. China
| | - Liming Xie
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, P. R. China
- School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
- International College, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| |
Collapse
|
9
|
Wu JB, Lin ML, Cong X, Liu HN, Tan PH. Raman spectroscopy of graphene-based materials and its applications in related devices. Chem Soc Rev 2018; 47:1822-1873. [PMID: 29368764 DOI: 10.1039/c6cs00915h] [Citation(s) in RCA: 512] [Impact Index Per Article: 85.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Graphene-based materials exhibit remarkable electronic, optical, and mechanical properties, which has resulted in both high scientific interest and huge potential for a variety of applications. Furthermore, the family of graphene-based materials is growing because of developments in preparation methods. Raman spectroscopy is a versatile tool to identify and characterize the chemical and physical properties of these materials, both at the laboratory and mass-production scale. This technique is so important that most of the papers published concerning these materials contain at least one Raman spectrum. Thus, here, we systematically review the developments in Raman spectroscopy of graphene-based materials from both fundamental research and practical (i.e., device applications) perspectives. We describe the essential Raman scattering processes of the entire first- and second-order modes in intrinsic graphene. Furthermore, the shear, layer-breathing, G and 2D modes of multilayer graphene with different stacking orders are discussed. Techniques to determine the number of graphene layers, to probe resonance Raman spectra of monolayer and multilayer graphenes and to obtain Raman images of graphene-based materials are also presented. The extensive capabilities of Raman spectroscopy for the investigation of the fundamental properties of graphene under external perturbations are described, which have also been extended to other graphene-based materials, such as graphene quantum dots, carbon dots, graphene oxide, nanoribbons, chemical vapor deposition-grown and SiC epitaxially grown graphene flakes, composites, and graphene-based van der Waals heterostructures. These fundamental properties have been used to probe the states, effects, and mechanisms of graphene materials present in the related heterostructures and devices. We hope that this review will be beneficial in all the aspects of graphene investigations, from basic research to material synthesis and device applications.
Collapse
Affiliation(s)
- Jiang-Bin Wu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | | | | | | | | |
Collapse
|
10
|
Abstract
By combining optical imaging, Raman spectroscopy, kelvin probe force microscopy (KFPM), and photoemission electron microscopy (PEEM), we show that graphene’s layer orientation, as well as layer thickness, measurably changes the surface potential (Φ). Detailed mapping of variable-thickness, rotationally-faulted graphene films allows us to correlate Φ with specific morphological features. Using KPFM and PEEM we measure ΔΦ up to 39 mV for layers with different twist angles, while ΔΦ ranges from 36–129 mV for different layer thicknesses. The surface potential between different twist angles or layer thicknesses is measured at the KPFM instrument resolution of ≤ 200 nm. The PEEM measured work function of 4.4 eV for graphene is consistent with doping levels on the order of 1012cm−2. We find that Φ scales linearly with Raman G-peak wavenumber shift (slope = 22.2 mV/cm−1) for all layers and twist angles, which is consistent with doping-dependent changes to graphene’s Fermi energy in the ‘high’ doping limit. Our results here emphasize that layer orientation is equally important as layer thickness when designing multilayer two-dimensional systems where surface potential is considered.
Collapse
|
11
|
Kang GS, Lee CH, Lee YK, Chai GS, Lee DC, Lee S, Joh HI. Highly durable platinum nanoparticles on carbon derived from pitch-based carbon fibers for oxygen reduction reaction. Macromol Res 2017. [DOI: 10.1007/s13233-017-5159-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
12
|
Banerjee S, Park J, Hwang CS, Choi JH, Lee SC, Pati SK. Regulation of transport properties by polytypism: a computational study on bilayer MoS 2. Phys Chem Chem Phys 2017; 19:21282-21286. [PMID: 28776619 DOI: 10.1039/c7cp02973j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Being a member of the van der Waals class of solids, bilayer MoS2 exhibits polytypism due to different possible stacking arrangements, namely, 2Hc, 2Ha and 3R-polytypes. Unlike monolayer MoS2, these bilayers exhibit indirect band gaps. Band extrema states originate from a linear combination of Mo-(d) and S-(p) orbitals which are sensitive to the interlayer interactions. We have studied the impact of stacking pattern on the electronic structure and electron/hole transport properties of these polytypes. Based on first-principles computations coupled with the Boltzmann transport formalism, we found that a strong electron-hole anisotropy can be realised in the 2Ha-MoS2 polytype unlike in a monolayer which is isotropic in nature. A staggered arrangement between two layers results in a higher relaxation time for electrons compared to holes leading to anisotropy which is of importance in device engineering.
Collapse
Affiliation(s)
- Swastika Banerjee
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore-560064, India.
| | | | | | | | | | | |
Collapse
|
13
|
Liu J, Xu Y, Cai H, Zuo C, Huang Z, Lin L, Guo X, Chen Z, Lai F. Double hexagonal graphene ring synthesized using a growth-etching method. NANOSCALE 2016; 8:14178-14183. [PMID: 27387556 DOI: 10.1039/c6nr02515c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Precisely controlling the layer number, stacking order, edge configuration, shape and structure of graphene is extremely challenging but highly desirable in scientific research. In this report, a new concept named the growth-etching method has been explored to synthesize a graphene ring using the chemical vapor deposition process. The graphene ring is a hexagonal structure, which contains a hexagonal exterior edge and a hexagonal hole in the centre region. The most important concept introduced here is that the oxide nanoparticle derived from annealing is found to play a dual role. Firstly, it acts as a nucleation site to grow the hexagonal graphene domain and then it works as a defect for etching to form a hole. The evolution process of the graphene ring with the etching time was carefully studied. In addition, a double hexagonal graphene ring was successfully synthesized for the first time by repeating the growth-etching process, which not only confirms the validity and repeatability of the method developed here but may also be further extended to grow unique graphene nanostructures with three, four, or even tens of graphene rings. Finally, a schematic model was drawn to illustrate how the double hexagonal graphene ring is generated and propagated. The results shown here may provide valuable guidance for the design and growth of unique nanostructures of graphene and other two-dimensional materials.
Collapse
Affiliation(s)
- Jinyang Liu
- College of Physics and Energy, Fujian Normal University, Fuzhou, 350117, P. R. China.
| | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Binder J, Urban JM, Stepniewski R, Strupinski W, Wysmolek A. In situ Raman spectroscopy of the graphene/water interface of a solution-gated field-effect transistor: electron-phonon coupling and spectroelectrochemistry. NANOTECHNOLOGY 2016; 27:045704. [PMID: 26655462 DOI: 10.1088/0957-4484/27/4/045704] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present a novel measurement approach which combines the electrical characterization of solution-gated field-effect transistors based on epitaxial bilayer graphene on 4H-SiC (0001) with simultaneous Raman spectroscopy. By changing the gate voltage, we observed Raman signatures related to the resonant electron-phonon coupling. An analysis of these Raman bands enabled the extraction of the geometrical capacitance of the system and an accurate calculation of the Fermi levels for bilayer graphene. An intentional application of higher gate voltages allowed us to trigger electrochemical reactions, which we followed in situ by Raman spectroscopy. The reactions showed a partially reversible character, as indicated by an emergence/disappearance of peaks assigned to C-H and Si-H vibration modes as well as an increase/decrease of the defect-related Raman D band intensity. Our setup provides a highly interesting platform for future spectroelectrochemical research on electrically-induced sorption processes of graphene on the micrometer scale.
Collapse
Affiliation(s)
- J Binder
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | | | | | | | | |
Collapse
|
15
|
Shu H, Li Y, Niu X, Wang J. The stacking dependent electronic structure and optical properties of bilayer black phosphorus. Phys Chem Chem Phys 2016; 18:6085-91. [DOI: 10.1039/c5cp07995k] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The optical excitations of bilayer black phosphorus with four different stacking patterns.
Collapse
Affiliation(s)
- Huabing Shu
- Department of Physics
- Southeast University
- Nanjing 211189
- China
| | - Yunhai Li
- Department of Physics
- Southeast University
- Nanjing 211189
- China
| | - Xianghong Niu
- Department of Physics
- Southeast University
- Nanjing 211189
- China
| | - Jinlan Wang
- Department of Physics
- Southeast University
- Nanjing 211189
- China
- Synergetic Innovation Center for Quantum Effects and Applications (SICQEA)
| |
Collapse
|
16
|
Coherent Generation of Photo-Thermo-Acoustic Wave from Graphene Sheets. Sci Rep 2015; 5:10582. [PMID: 26053560 PMCID: PMC4650607 DOI: 10.1038/srep10582] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 04/17/2015] [Indexed: 11/08/2022] Open
Abstract
Many remarkable properties of graphene are derived from its large energy window for Dirac-like electronic states and have been explored for applications in electronics and photonics. In addition, strong electron-phonon interaction in graphene has led to efficient photo-thermo energy conversions, which has been harnessed for energy applications. By combining the wavelength independent absorption property and the efficient photo-thermo energy conversion, here we report a new type of applications in sound wave generation underlined by a photo-thermo-acoustic energy conversion mechanism. Most significantly, by utilizing ultrafast optical pulses, we demonstrate the ability to control the phase of sound waves generated by the photo-thermal-acoustic process. Our finding paves the way for new types of applications for graphene, such as remote non-contact speakers, optical-switching acoustic devices, etc.
Collapse
|
17
|
Hall and field-effect mobilities in few layered p-WSe₂ field-effect transistors. Sci Rep 2015; 5:8979. [PMID: 25759288 PMCID: PMC4355631 DOI: 10.1038/srep08979] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 02/12/2015] [Indexed: 12/11/2022] Open
Abstract
Here, we present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2. Without dielectric engineering and beyond a T-dependent threshold gate-voltage, we observe maximum hole mobilities approaching 350 cm2/Vs at T = 300 K. The hole Hall mobility reaches a maximum value of 650 cm2/Vs as T is lowered below ~150 K, indicating that insofar WSe2-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. The gate capacitance, as extracted from the Hall-effect, reveals the presence of spurious charges in the channel, while the two-terminal sheet resistivity displays two-dimensional variable-range hopping behavior, indicating carrier localization induced by disorder at the interface between WSe2 and SiO2. We argue that improvements in the fabrication protocols as, for example, the use of a substrate free of dangling bonds are likely to produce WSe2-based FETs displaying higher room temperature mobilities, i.e. approaching those of p-doped Si, which would make it a suitable candidate for high performance opto-electronics.
Collapse
|
18
|
Beams R, Gustavo Cançado L, Novotny L. Raman characterization of defects and dopants in graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:083002. [PMID: 25634863 DOI: 10.1088/0953-8984/27/8/083002] [Citation(s) in RCA: 141] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
In this article we review Raman studies of defects and dopants in graphene as well as the importance of both for device applications. First a brief overview of Raman spectroscopy of graphene is presented. In the following section we discuss the Raman characterization of three defect types: point defects, edges, and grain boundaries. The next section reviews the dependence of the Raman spectrum on dopants and highlights several common doping techniques. In the final section, several device applications are discussed which exploit doping and defects in graphene. Generally defects degrade the figures of merit for devices, such as carrier mobility and conductivity, whereas doping provides a means to tune the carrier concentration in graphene thereby enabling the engineering of novel material systems. Accurately measuring both the defect density and doping is critical and Raman spectroscopy provides a powerful tool to accomplish this task.
Collapse
Affiliation(s)
- Ryan Beams
- Institute of Optics, University of Rochester, Rochester, NY 14627, USA
| | | | | |
Collapse
|
19
|
Margapoti E, Strobel P, Asmar MM, Seifert M, Li J, Sachsenhauser M, Ceylan O, Palma CA, Barth JV, Garrido JA, Cattani-Scholz A, Ulloa SE, Finley JJ. Emergence of photoswitchable states in a graphene-azobenzene-Au platform. NANO LETTERS 2014; 14:6823-6827. [PMID: 25414977 DOI: 10.1021/nl503681z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The perfect transmission of charge carriers through potential barriers in graphene (Klein tunneling) is a direct consequence of the Dirac equation that governs the low-energy carrier dynamics. As a result, localized states do not exist in unpatterned graphene, but quasibound states can occur for potentials with closed integrable dynamics. Here, we report the observation of resonance states in photoswitchable self-assembled molecular(SAM)-graphene hybrid. Conductive AFM measurements performed at room temperature reveal strong current resonances, the strength of which can be reversibly gated on- and off- by optically switching the molecular conformation of the mSAM. Comparisons of the voltage separation between current resonances (∼ 70-120 mV) with solutions of the Dirac equation indicate that the radius of the gating potential is ∼ 7 ± 2 nm with a strength ≥ 0.5 eV. Our results and methods might provide a route toward optically programmable carrier dynamics and transport in graphene nanomaterials.
Collapse
Affiliation(s)
- Emanuela Margapoti
- Walter Schottky Institute - ZNN, Physik Department and NIM, Technische Universität München , Am Coulombwall 4, 80333 Garching, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
20
|
Banerjee S, Pati SK. Criticality of surface topology for charge-carrier transport characteristics in two-dimensional borocarbonitrides: design principles for an efficient electronic material. NANOSCALE 2014; 6:13430-13434. [PMID: 25283315 DOI: 10.1039/c4nr04198d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We have studied the effect of the spatial distribution of B, N and C domains in 2-dimensional borocarbonitrides and its influence on carrier mobility, based on density functional theory coupled with the Boltzmann transport equation. Two extreme features of C-domains in BN-rich B2.5CN2.5, namely, BCN-I (random) and BCN-II (localized), have been found to exhibit an electron (hole) mobility of ∼10(6) cm(2) V(-1) s(-1) (∼10(4) cm(2) V(-1) s(-1)) and ∼10(3) cm(2) V(-1) s(-1) (∼10(6) cm(2) V(-1) s(-1)), respectively. We have ascertained the underlying microscopic mechanisms behind such an extraordinarily large carrier mobility and the reversal of conduction polarity. Finally, we have derived the principle underlying the maximization of mobility and for obtaining a particular (electron/hole) conduction polarity of this nanohybrid in any stoichiometric proportion.
Collapse
Affiliation(s)
- Swastika Banerjee
- New Chemistry Unit, Jawaharlal Nehru Center for Advanced Scientific Research, Bangalore 560064, India
| | | |
Collapse
|
21
|
Fan M, Zhu C, Feng ZQ, Yang J, Liu L, Sun D. Preparation of N-doped graphene by reduction of graphene oxide with mixed microbial system and its haemocompatibility. NANOSCALE 2014; 6:4882-4888. [PMID: 24667844 DOI: 10.1039/c3nr06657f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A steady, effective and environment friendly method of introducing nitrogen into graphene is by microbial reduction of graphene oxide with mixed microorganisms from the anode chamber of microbial fuel cells (MFC). Using this method, N-doped graphene is easily obtained under mild conditions and by simple treatment processes, with the N/C ratio reaching 8.14%. Various characterizations demonstrate that the as-prepared N-doped graphene has excellent properties and is comparable with, and in some aspects, even better than, pristine graphene (containing only elemental C) prepared by chemical methods. The N-doped graphene (mainly substitution of C in the plane of the graphene sheet) with uniform distribution of N was haemocompatible, nontoxic, and water-dispersible, all of which are desirable properties for biomaterials and attributable to a synergetic metabolic effect of mixed microorganisms.
Collapse
Affiliation(s)
- Mengmeng Fan
- Chemicobiology and Functional Materials Institute of Nanjing University of Science and Technology, Xiao Ling Wei 200, Nanjing, 210094, China.
| | | | | | | | | | | |
Collapse
|
22
|
Nayak AP, Bhattacharyya S, Zhu J, Liu J, Wu X, Pandey T, Jin C, Singh AK, Akinwande D, Lin JF. Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide. Nat Commun 2014; 5:3731. [DOI: 10.1038/ncomms4731] [Citation(s) in RCA: 413] [Impact Index Per Article: 41.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Accepted: 03/27/2014] [Indexed: 12/22/2022] Open
|
23
|
Intra- and Interlayer Electron-Phonon Interactions in 12/12C and 12/13C BiLayer Graphene. APPLIED SCIENCES-BASEL 2014. [DOI: 10.3390/app4020207] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
24
|
Cava CE, Persson C, Zarbin AJG, Roman LS. Resistive switching in iron-oxide-filled carbon nanotubes. NANOSCALE 2014; 6:378-384. [PMID: 24201829 DOI: 10.1039/c3nr04320g] [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
Iron-oxide-filled carbon nanotubes exhibit an intriguing charge bipolarization behavior which allows the material to be applied in resistive memory devices. Raman analysis conducted with an electric field applied in situ shows the Kohn anomalies and a strong modification of the electronic properties related to the applied voltage intensity. In addition, the I(D)/I(G) ratio indicated the reversibility of this process. The electrical characterization indicated an electronic transport governed by two main kinds of charge hopping, one between the filling and the nanotube and the other between the nanotube shells.
Collapse
Affiliation(s)
- Carlos E Cava
- Department of Materials Engineering, Universidade Tecnológica Federal do Paraná, CEP 86036-370, Londrina, PR, Brazil.
| | | | | | | |
Collapse
|
25
|
Insights into Vibrational and Electronic Properties of MoS2 Using Raman, Photoluminescence, and Transport Studies. ACTA ACUST UNITED AC 2013. [DOI: 10.1007/978-3-319-02850-7_7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
|
26
|
Kim CJ, Brown L, Graham MW, Hovden R, Havener RW, McEuen PL, Muller DA, Park J. Stacking order dependent second harmonic generation and topological defects in h-BN bilayers. NANO LETTERS 2013; 13:5660-5665. [PMID: 24125021 DOI: 10.1021/nl403328s] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The ability to control the stacking structure in layered materials could provide an exciting approach to tuning their optical and electronic properties. Because of the lower symmetry of each constituent monolayer, hexagonal boron nitride (h-BN) allows more structural variations in multiple layers than graphene; however, the structure-property relationships in this system remain largely unexplored. Here, we report a strong correlation between the interlayer stacking structures and optical and topological properties in chemically grown h-BN bilayers, measured mainly by using dark-field transmission electron microscopy (DF-TEM) and optical second harmonic generation (SHG) mapping. Our data show that there exist two distinct h-BN bilayer structures with different interlayer symmetries that give rise to a distinct difference in their SHG intensities. In particular, the SHG signal in h-BN bilayers is observed only for structures with broken inversion symmetry, with an intensity much larger than that of single layer h-BN. In addition, our DF-TEM data identify the formation of interlayer topological defects in h-BN bilayers, likely induced by local strain, whose properties are determined by the interlayer symmetry and the different interlayer potential landscapes.
Collapse
Affiliation(s)
- Cheol-Joo Kim
- Department of Chemistry and Chemical Biology, ‡Laboratory for Atomic and Solid State Physics, §Kavli Institute at Cornell for Nanoscale Science, and ∥School of Applied and Engineering Physics, Cornell University , Ithaca, NY 14853, United States
| | | | | | | | | | | | | | | |
Collapse
|
27
|
He R, Chung TF, Delaney C, Keiser C, Jauregui LA, Shand PM, Chancey CC, Wang Y, Bao J, Chen YP. Observation of low energy Raman modes in twisted bilayer graphene. NANO LETTERS 2013; 13:3594-601. [PMID: 23859121 DOI: 10.1021/nl4013387] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Two new Raman modes below 100 cm(-1) are observed in twisted bilayer graphene grown by chemical vapor deposition. The two modes are observed in a small range of twisting angle at which the intensity of the G Raman peak is strongly enhanced, indicating that these low energy modes and the G Raman mode share the same resonance enhancement mechanism, as a function of twisting angle. The ~94 cm(-1) mode (measured with a 532 nm laser excitation) is assigned to the fundamental layer breathing vibration (ZO' mode) mediated by the twisted bilayer graphene lattice, which lacks long-range translational symmetry. The dependence of this mode's frequency and line width on the rotational angle can be explained by the double resonance Raman process that is different from the previously identified Raman processes activated by twisted bilayer graphene superlattice. The dependence also reveals the strong impact of electronic-band overlaps of the two graphene layers. Another new mode at ~52 cm(-1), not observed previously in the bilayer graphene system, is tentatively attributed to a torsion mode in which the bottom and top graphene layers rotate out-of-phase in the plane.
Collapse
Affiliation(s)
- Rui He
- Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614, United States.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Kim MH, Yan J, Suess RJ, Murphy TE, Fuhrer MS, Drew HD. Photothermal response in dual-gated bilayer graphene. PHYSICAL REVIEW LETTERS 2013; 110:247402. [PMID: 25165960 DOI: 10.1103/physrevlett.110.247402] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Indexed: 06/03/2023]
Abstract
The photovoltaic and bolometric photoresponse in gapped bilayer graphene was investigated by optical and transport measurements. A pulse coincidence technique at 1.5 μm was used to measure the response times as a function of temperature. The bolometric and photovoltaic response times were found to be identical implying that the photovoltaic response is also governed by hot electron thermal relaxation. Response times of τ ∼ 100-20 ps were found for temperatures from 3-100 K. Above 10 K, the relaxation time was observed to be τ = 25 ± 5 ps, independent of temperature within noise.
Collapse
Affiliation(s)
- M-H Kim
- Department of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA
| | - J Yan
- Department of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA and Physics Department, University of Massachusetts, Amherst, Massachusetts 01002, USA
| | - R J Suess
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA
| | - T E Murphy
- Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA
| | - M S Fuhrer
- Department of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA and School of Physics, Monash University, 3800 Victoria, Australia
| | - H D Drew
- Department of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA
| |
Collapse
|
29
|
McCann E, Koshino M. The electronic properties of bilayer graphene. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:056503. [PMID: 23604050 DOI: 10.1088/0034-4885/76/5/056503] [Citation(s) in RCA: 192] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
We review the electronic properties of bilayer graphene, beginning with a description of the tight-binding model of bilayer graphene and the derivation of the effective Hamiltonian describing massive chiral quasiparticles in two parabolic bands at low energies. We take into account five tight-binding parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra- and interlayer asymmetry between atomic sites which induce band gaps in the low-energy spectrum. The Hartree model of screening and band-gap opening due to interlayer asymmetry in the presence of external gates is presented. The tight-binding model is used to describe optical and transport properties including the integer quantum Hall effect, and we also discuss orbital magnetism, phonons and the influence of strain on electronic properties. We conclude with an overview of electronic interaction effects.
Collapse
Affiliation(s)
- Edward McCann
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
| | | |
Collapse
|
30
|
Ferrari AC, Basko DM. Raman spectroscopy as a versatile tool for studying the properties of graphene. NATURE NANOTECHNOLOGY 2013; 8:235-46. [PMID: 23552117 DOI: 10.1038/nnano.2013.46] [Citation(s) in RCA: 2205] [Impact Index Per Article: 200.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Accepted: 03/01/2013] [Indexed: 05/19/2023]
Abstract
Raman spectroscopy is an integral part of graphene research. It is used to determine the number and orientation of layers, the quality and types of edge, and the effects of perturbations, such as electric and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp(2)-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential physical processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminology that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene.
Collapse
Affiliation(s)
- Andrea C Ferrari
- Cambridge Graphene Centre, Cambridge University, 9 JJ Thomson Avenue, Cambridge CB3 OFA, UK.
| | | |
Collapse
|
31
|
Visualization of arrangements of carbon atoms in graphene layers by Raman mapping and atomic-resolution TEM. Sci Rep 2013; 3:1195. [PMID: 23378926 PMCID: PMC3561624 DOI: 10.1038/srep01195] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 01/16/2013] [Indexed: 11/16/2022] Open
Abstract
In-plane and out-of-plane arrangements of carbon atoms in graphene layers play critical roles in the fundamental physics and practical applications of these novel two-dimensional materials. Here, we report initial results on the edge/crystal orientations and stacking orders of bi- and tri-layer graphene (BLG and TLG) from Raman spectroscopy and transmission electron microscopy (TEM) experiments performed on the same sample. We introduce a new method of transferring graphene flakes onto a normal TEM grid. Using this novel method, we probed the BLG and TLG flakes that had been previously investigated by Raman scattering with high-resolution (atomic) TEM.
Collapse
|
32
|
M. Baranowski J, Mozdzonek M, Dabrowski P, Grodecki K, Osewski P, Kozlowski W, Kopciuszynski M, Strupinski W. Observation of Electron-Phonon Couplings and Fano Re-sonances in Epitaxial Bilayer Graphene. ACTA ACUST UNITED AC 2013. [DOI: 10.4236/graphene.2013.24017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
33
|
Lee JE, Ahn G, Shim J, Lee YS, Ryu S. Optical separation of mechanical strain from charge doping in graphene. Nat Commun 2012; 3:1024. [DOI: 10.1038/ncomms2022] [Citation(s) in RCA: 679] [Impact Index Per Article: 56.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Accepted: 07/25/2012] [Indexed: 12/22/2022] Open
|
34
|
Araujo PT, Mafra DL, Sato K, Saito R, Kong J, Dresselhaus MS. Phonon self-energy corrections to nonzero wave-vector phonon modes in single-layer graphene. PHYSICAL REVIEW LETTERS 2012; 109:046801. [PMID: 23006101 DOI: 10.1103/physrevlett.109.046801] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Indexed: 06/01/2023]
Abstract
Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q=0) wave vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene originating from a double-resonant Raman process with q≠0. The observed phonon renormalization effects are different from what is observed for the zone-center q=0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with nonzero wave vectors (q≠0) in single-layer graphene in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q=0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G(⋆) Raman feature at 2450 cm(-1) to include the iTO+LA combination modes with q≠0 and also the 2iTO overtone modes with q=0, showing both to be associated with wave vectors near the high symmetry point K in the Brillouin zone.
Collapse
Affiliation(s)
- P T Araujo
- Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA.
| | | | | | | | | | | |
Collapse
|
35
|
Yan J, Kim MH, Elle JA, Sushkov AB, Jenkins GS, Milchberg HM, Fuhrer MS, Drew HD. Dual-gated bilayer graphene hot-electron bolometer. NATURE NANOTECHNOLOGY 2012; 7:472-8. [PMID: 22659611 DOI: 10.1038/nnano.2012.88] [Citation(s) in RCA: 158] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Accepted: 05/01/2012] [Indexed: 05/06/2023]
Abstract
Graphene is an attractive material for use in optical detectors because it absorbs light from mid-infrared to ultraviolet wavelengths with nearly equal strength. Graphene is particularly well suited for bolometers-devices that detect temperature-induced changes in electrical conductivity caused by the absorption of light-because its small electron heat capacity and weak electron-phonon coupling lead to large light-induced changes in electron temperature. Here, we demonstrate a hot-electron bolometer made of bilayer graphene that is dual-gated to create a tunable bandgap and electron-temperature-dependent conductivity. The bolometer exhibits a noise-equivalent power (33 fW Hz(-1/2) at 5 K) that is several times lower, and intrinsic speed (>1 GHz at 10 K) three to five orders of magnitude higher than commercial silicon bolometers and superconducting transition-edge sensors at similar temperatures.
Collapse
Affiliation(s)
- Jun Yan
- Center for Nanophysics and Advanced Materials and Materials Research Science and Engineering Center, University of Maryland, College Park, MD 20742, USA
| | | | | | | | | | | | | | | |
Collapse
|
36
|
Kwon OS, Park SJ, Hong JY, Han AR, Lee JS, Lee JS, Oh JH, Jang J. Flexible FET-type VEGF aptasensor based on nitrogen-doped graphene converted from conducting polymer. ACS NANO 2012; 6:1486-93. [PMID: 22224587 DOI: 10.1021/nn204395n] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Graphene-based field-effect transistors (FETs) have been developed rapidly and are currently considered as an alternative for postsilicon electronics. In this study, polypyrrole-converted nitrogen-doped few-layer graphene (PPy-NDFLG) was grown on Cu substrate by chemical vapor deposition combined with vapor deposition polymerization and then transferred onto a flexible substrate. Furthermore, antivascular endothelial growth factor (VEGF) RNA aptamer conjugated PPy-NDFLG was integrated into a liquid-ion gated FET geometry to fabricate a high-performance VEGF aptamer-based sensor. Field-induced high sensitivity was observed for the analyte-binding events, eventually leading to the recognition of the target molecules at an unprecedentedly low concentration (100 fM). Additionally, the aptasensor had excellent reusability, mechanical bendability, and durability in the flexible process. The developed methodology describes, for the first time, the fabrication of N-doped graphene using conducting polymers including heteroatoms in their structures as the carbonization precursor and demonstrates its use in a high-performance, flexible FET-type aptasensor to detect vascular endothelial growth factor as a cancer biomarker.
Collapse
Affiliation(s)
- Oh Seok Kwon
- World Class University Program of Chemical Convergence for Energy & Environment, School of Chemical and Biological Engineering, Seoul National University, Seoul 151-742, Korea
| | | | | | | | | | | | | | | |
Collapse
|
37
|
Nandkishore R, Levitov L. Polar Kerr effect and time reversal symmetry breaking in bilayer graphene. PHYSICAL REVIEW LETTERS 2011; 107:097402. [PMID: 21929269 DOI: 10.1103/physrevlett.107.097402] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Indexed: 05/31/2023]
Abstract
The unique sensitivity of optical response to different types of symmetry breaking can be used to detect and identify spontaneously ordered many-body states in bilayer graphene. We predict a strong response at optical frequencies, sensitive to electronic phenomena at low energies, which arises because of nonzero interband matrix elements of the electric current operator. In particular, the polar Kerr rotation and reflection anisotropy provide fingerprints of the quantum anomalous Hall state and the nematic state, characterized by spontaneously broken time-reversal symmetry and lattice rotation symmetry, respectively. These optical signatures, which undergo a resonant enhancement in the near-infrared regime, lie well within reach of existing experimental techniques.
Collapse
Affiliation(s)
- Rahul Nandkishore
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | |
Collapse
|
38
|
Zhao W, Tan PH, Liu J, Ferrari AC. Intercalation of few-layer graphite flakes with FeCl3: Raman determination of Fermi level, layer by layer decoupling, and stability. J Am Chem Soc 2011; 133:5941-6. [PMID: 21434632 DOI: 10.1021/ja110939a] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We use anhydrous ferric chloride (FeCl(3)) to intercalate graphite flakes consisting of 2-4 graphene layers and to dope graphene monolayers. The intercalant, staging, stability, and doping of the resulting intercalation compounds (ICs) are characterized by Raman scattering. The G peak of heavily doped monolayer graphene upshifts to ∼1627 cm(-1). The 2-4 layer ICs have similar upshifts, and a Lorentzian line shape for the 2D band, indicating that each layer behaves as a decoupled heavily doped monolayer. By performing Raman measurements at different excitation energies, we show that, for a given doping level, the 2D peak can be suppressed by Pauli blocking for laser energy below the doping level. Thus, multiwavelength Raman spectroscopy allows a direct measurement of the Fermi level, complementary to that derived by performing measurements at fixed excitation energy significantly higher than the doping level. This allows us to estimate a Fermi level shift of up to ∼0.9 eV. These ICs are thus ideal test-beds for the physical and chemical properties of heavily doped graphenes.
Collapse
Affiliation(s)
- Weijie Zhao
- State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | | | | | | |
Collapse
|
39
|
Dresselhaus MS, Jorio A, Cançado LG, Dresselhaus G, Saito R. Raman Spectroscopy: Characterization of Edges, Defects, and the Fermi Energy of Graphene and sp 2 Carbons. GRAPHENE NANOELECTRONICS 2011. [DOI: 10.1007/978-3-642-22984-8_2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
|
40
|
Wang H, Wu Y, Cong C, Shang J, Yu T. Hysteresis of electronic transport in graphene transistors. ACS NANO 2010; 4:7221-8. [PMID: 21047068 DOI: 10.1021/nn101950n] [Citation(s) in RCA: 187] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Graphene field effect transistors commonly comprise graphene flakes lying on SiO(2) surfaces. The gate-voltage dependent conductance shows hysteresis depending on the gate sweeping rate/range. It is shown here that the transistors exhibit two different kinds of hysteresis in their electrical characteristics. Charge transfer causes a positive shift in the gate voltage of the minimum conductance, while capacitive gating can cause the negative shift of conductance with respect to gate voltage. The positive hysteretic phenomena decay with an increase of the number of layers in graphene flakes. Self-heating in a helium atmosphere significantly removes adsorbates and reduces positive hysteresis. We also observed negative hysteresis in graphene devices at low temperature. It is also found that an ice layer on/under graphene has a much stronger dipole moment than a water layer does. Mobile ions in the electrolyte gate and a polarity switch in the ferroelectric gate could also cause negative hysteresis in graphene transistors. These findings improved our understanding of the electrical response of graphene to its surroundings. The unique sensitivity to environment and related phenomena in graphene deserve further studies on nonvolatile memory, electrostatic detection, and chemically driven applications.
Collapse
Affiliation(s)
- Haomin Wang
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576
| | | | | | | | | |
Collapse
|
41
|
Cheng SG. Transport properties of monolayer and bilayer graphene p-n junctions with charge puddles in the quantum Hall regime. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:465301. [PMID: 21403362 DOI: 10.1088/0953-8984/22/46/465301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Recent experiments have confirmed that the electron-hole inhomogeneity in graphene is a new type of charge disorder. Motivated by such confirmation, we theoretically study the transport properties of a monolayer graphene (MLG) based p-n junction and a bilayer graphene (BLG) p-n junction in the quantum Hall regime where electron-hole puddles are considered. By using the non-equilibrium Green function method, both the current and conductance are obtained. We find that, in the presence of the electron-hole inhomogeneity, the lowest quantized conductance plateau at e(2)/h emerges in the MLG p-n junction under very small charge puddle disorder strength. For a BLG p-n junction, however, the conductance in the p-n region is enhanced with charge puddles, and the lowest quantized conductance plateau emerges at 2e(2)/h. Besides, when an ideal quantized conductance plateau is formed for a MLG p-n junction, the universal conductance fluctuation is found to be 2e(2)/3h. Furthermore, we also investigate the influence of Anderson disorder on such p-n junctions and the comparison and discussion are given accordingly. To compare the two models with different types of disorder, we investigate the conductance distribution specially. Finally the influence of disorder strength on the conductance of a MLG p-n junction is investigated.
Collapse
Affiliation(s)
- Shu-guang Cheng
- Department of Physics, Northwest University, Xi'an, People's Republic of China.
| |
Collapse
|
42
|
Xu G, Torres CM, Song EB, Tang J, Bai J, Duan X, Zhang Y, Wang KL. Enhanced conductance fluctuation by quantum confinement effect in graphene nanoribbons. NANO LETTERS 2010; 10:4590-4594. [PMID: 20939609 DOI: 10.1021/nl1025979] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Conductance fluctuation is usually unavoidable in graphene nanoribbons (GNR) due to the presence of disorder along its edges. By measuring the low-frequency noise in GNR devices, we find that the conductance fluctuation is strongly correlated with the density-of-states of GNR. In single-layer GNR, the gate-dependence of noise shows peaks whose positions quantitatively match the subband positions in the band structures of GNR. This correlation provides a robust mechanism to electrically probe the band structure of GNR, especially when the subband structures are smeared out in conductance measurement.
Collapse
Affiliation(s)
- Guangyu Xu
- Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095, United States.
| | | | | | | | | | | | | | | |
Collapse
|
43
|
Malard LM, Moreira RL, Elias DC, Plentz F, Alves ES, Pimenta MA. Thermal enhancement of chemical doping in graphene: a Raman spectroscopy study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:334202. [PMID: 21386492 DOI: 10.1088/0953-8984/22/33/334202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The Raman spectrum of monolayer graphene deposited on the top of a silicon oxide/silicon substrate was investigated as a function of temperature up to 515 K. An anomalous temperature dependence of the Raman features was observed, including an important frequency upshift for the Raman G band at room temperature, after the heating process. On the other hand, the frequency of the Raman G(') band is only slightly affected by the thermal treatment. We discuss our experimental results in terms of doping and strain effects associated with the interaction of graphene with the substrate and with the presence of water in the sample. We conclude that the doping effect gives the most important contribution to the spectral changes observed after the thermal cycle.
Collapse
Affiliation(s)
- L M Malard
- Departamento de Física, Universidade Federal de Minas Gerais, 30123-970, Belo Horizonte, Brazil
| | | | | | | | | | | |
Collapse
|
44
|
Xu Y, Li X, Dong J. Infrared and Raman spectra of AA-stacking bilayer graphene. NANOTECHNOLOGY 2010; 21:065711. [PMID: 20061600 DOI: 10.1088/0957-4484/21/6/065711] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The infrared (IR) absorption and resonant Raman spectra of the undoped AA-stacking bilayer graphene have been calculated using density-functional theory in the local density approximation. It is found that the undoped AA-stacking bilayer graphene exhibits a different characteristic jump and peak structure in its IR spectra, and a different G-band peak structure in its resonant Raman spectra, compared with those of the AB-stacking one, which are caused by the different interlayer coupling effects, due to different stacking types in both of them. Based upon the different IR and Raman spectra, a powerful experimental method can be proposed to identify accurately the stacking type and the layer number in future experiments.
Collapse
Affiliation(s)
- Yuehua Xu
- Group of Computational Condensed Matter Physics, National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing, People's Republic of China
| | | | | |
Collapse
|
45
|
Tang TT, Zhang Y, Park CH, Geng B, Girit C, Hao Z, Martin MC, Zettl A, Crommie MF, Louie SG, Shen YR, Wang F. A tunable phonon-exciton Fano system in bilayer graphene. NATURE NANOTECHNOLOGY 2010; 5:32-6. [PMID: 19915569 DOI: 10.1038/nnano.2009.334] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Accepted: 10/01/2009] [Indexed: 05/17/2023]
Abstract
Fano resonances are features in absorption, scattering or transport spectra resulting from the interaction of discrete and continuum states. They have been observed in a variety of systems. Here, we report a many-body Fano resonance in bilayer graphene that is continuously tunable by means of electrical gating. Discrete phonons and continuous exciton (electron-hole pair) transitions are coupled by electron-phonon interactions, yielding a new hybrid phonon-exciton excited state. It may also be possible to control the phonon-exciton coupling with an optical field. This tunable phonon-exciton system could allow novel applications such as phonon lasers.
Collapse
Affiliation(s)
- Tsung-Ta Tang
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
46
|
Rao C, Sood A, Subrahmanyam K, Govindaraj A. Graphen, das neue zweidimensionale Nanomaterial. Angew Chem Int Ed Engl 2009. [DOI: 10.1002/ange.200901678] [Citation(s) in RCA: 196] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
47
|
Yu YJ, Zhao Y, Ryu S, Brus LE, Kim KS, Kim P. Tuning the graphene work function by electric field effect. NANO LETTERS 2009; 9:3430-3434. [PMID: 19719145 DOI: 10.1021/nl901572a] [Citation(s) in RCA: 498] [Impact Index Per Article: 33.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report variation of the work function for single and bilayer graphene devices measured by scanning Kelvin probe microscopy (SKPM). By use of the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.
Collapse
Affiliation(s)
- Young-Jun Yu
- Department of Physics, Columbia University, New York, New York 10027, USA
| | | | | | | | | | | |
Collapse
|
48
|
Rao CNR, Sood AK, Subrahmanyam KS, Govindaraj A. Graphene: the new two-dimensional nanomaterial. Angew Chem Int Ed Engl 2009; 48:7752-77. [PMID: 19784976 DOI: 10.1002/anie.200901678] [Citation(s) in RCA: 1926] [Impact Index Per Article: 128.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.
Collapse
Affiliation(s)
- C N R Rao
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P. O., Bangalore 560 064, India.
| | | | | | | |
Collapse
|
49
|
Kuzmenko AB, Benfatto L, Cappelluti E, Crassee I, van der Marel D, Blake P, Novoselov KS, Geim AK. Gate tunable infrared phonon anomalies in bilayer graphene. PHYSICAL REVIEW LETTERS 2009; 103:116804. [PMID: 19792392 DOI: 10.1103/physrevlett.103.116804] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Indexed: 05/28/2023]
Abstract
We observe a giant increase of the infrared intensity and a softening of the in-plane antisymmetric phonon mode E(u) ( approximately 0.2 eV) in bilayer graphene as a function of the gate-induced doping. The phonon peak has a pronounced Fano-like asymmetry. We suggest that the intensity growth and the softening originate from the coupling of the phonon mode to the narrow electronic transition between parallel bands of the same character, while the asymmetry is due to the interaction with the continuum of transitions between the lowest hole and electron bands. The growth of the peak can be interpreted as a "charged-phonon" effect observed previously in organic chain conductors and doped fullerenes, which can be tuned in graphene with the gate voltage.
Collapse
Affiliation(s)
- A B Kuzmenko
- Département de Physique de la Matière Condensée, Université de Genève, CH-1211 Genève 4, Switzerland
| | | | | | | | | | | | | | | |
Collapse
|
50
|
Affiliation(s)
- Matthew J. Allen
- Department of Chemistry and Biochemistry and California NanoSystems Institute, and Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095
| | - Vincent C. Tung
- Department of Chemistry and Biochemistry and California NanoSystems Institute, and Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095
| | - Richard B. Kaner
- Department of Chemistry and Biochemistry and California NanoSystems Institute, and Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095
| |
Collapse
|