1
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Kuo DMT. Effects of metallic electrodes on the thermoelectric properties of zigzag graphene nanoribbons with periodic vacancies. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:305301. [PMID: 37068484 DOI: 10.1088/1361-648x/accdac] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Accepted: 04/17/2023] [Indexed: 06/19/2023]
Abstract
We theoretically analyze the thermoelectric properties of graphene quantum dot arrays (GQDAs) with line- or surface-contacted metal electrodes. Such GQDAs are realized as zigzag graphene nanoribbons (ZGNRs) with periodic vacancies. Gaps and minibands are formed in these GQDAs, which can have metallic and semiconducting phases. The electronic states of the first conduction (valence) miniband with nonlinear dispersion may have long coherent lengths along the zigzag edge direction. With line-contacted metal electrodes, the GQDAs have the characteristics of serially coupled quantum dots (SCQDs) if the armchair edge atoms of the ZGNRs are coupled to the electrodes. By contrast, the GQDAs have the characteristics of parallel quantum dots if the zigzag edge atoms are coupled to the electrodes. The maximum thermoelectric power factors of SCQDs with line-contacted electrodes of Cu, Au, Pt, Pd, or Ti at room temperature were similar or greater than 0.186 nW K-1; their figures of merit were greater than three. GQDAs with line-contacted metal electrodes have much better thermoelectric performance than surface contacted metal electrodes.
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Affiliation(s)
- David M T Kuo
- Department of Electrical Engineering and Department of Physics, National Central University, Chungli 320, Taiwan
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2
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Pasadas F, Feijoo PC, Mavredakis N, Pacheco-Sanchez A, Chaves FA, Jiménez D. Compact Modeling Technology for the Simulation of Integrated Circuits Based on Graphene Field-Effect Transistors. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2201691. [PMID: 35593428 DOI: 10.1002/adma.202201691] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 04/26/2022] [Indexed: 06/15/2023]
Abstract
The progress made toward the definition of a modular compact modeling technology for graphene field-effect transistors (GFETs) that enables the electrical analysis of arbitrary GFET-based integrated circuits is reported. A set of primary models embracing the main physical principles defines the ideal GFET response under DC, transient (time domain), AC (frequency domain), and noise (frequency domain) analysis. Another set of secondary models accounts for the GFET non-idealities, such as extrinsic-, short-channel-, trapping/detrapping-, self-heating-, and non-quasi static-effects, which can have a significant impact under static and/or dynamic operation. At both device and circuit levels, significant consistency is demonstrated between the simulation output and experimental data for relevant operating conditions. Additionally, a perspective of the challenges during the scale up of the GFET modeling technology toward higher technology readiness levels while drawing a collaborative scenario among fabrication technology groups, modeling groups, and circuit designers, is provided.
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Affiliation(s)
- Francisco Pasadas
- Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
- Departamento de Electrónica y Tecnología de Computadores, Universidad de Granada, Granada, 18071, Spain
| | - Pedro C Feijoo
- Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
| | - Nikolaos Mavredakis
- Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
| | - Aníbal Pacheco-Sanchez
- Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
| | - Ferney A Chaves
- Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
| | - David Jiménez
- Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
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3
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Zhao W, Zou D, Sun Z, Xu Y, Ji G, Li X, Yang C. A Single‐Molecule and Logic Gate via Optical and Acid–Base Control. ADVANCED THEORY AND SIMULATIONS 2020. [DOI: 10.1002/adts.202000163] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Wenkai Zhao
- School of Physics and Optoelectronics Engineering Ludong University Yantai Shandong 264025 P. R. China
| | - Dongqing Zou
- School of Physics and Optoelectronics Engineering Ludong University Yantai Shandong 264025 P. R. China
| | - Zhaopeng Sun
- School of Physics and Optoelectronics Engineering Ludong University Yantai Shandong 264025 P. R. China
| | - Yuqing Xu
- School of Physics and Optoelectronics Engineering Ludong University Yantai Shandong 264025 P. R. China
| | - Guomin Ji
- Department of Electrical and Computer Engineering University of Oklahoma Norman OK 73019‐0390 USA
| | - Xiaoteng Li
- School of Physics and Optoelectronics Engineering Ludong University Yantai Shandong 264025 P. R. China
| | - Chuanlu Yang
- School of Physics and Optoelectronics Engineering Ludong University Yantai Shandong 264025 P. R. China
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4
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Ban DK, Liu Y, Wang Z, Ramachandran S, Sarkar N, Shi Z, Liu W, Karkisaval AG, Martinez-Loran E, Zhang F, Glinsky G, Bandaru PR, Fan C, Lal R. Direct DNA Methylation Profiling with an Electric Biosensor. ACS NANO 2020; 14:6743-6751. [PMID: 32407064 DOI: 10.1021/acsnano.9b10085] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
DNA methylation is one of the principal epigenetic mechanisms that control gene expression in humans, and its profiling provides critical information about health and disease. Current profiling methods require chemical modification of bases followed by sequencing, which is expensive and time-consuming. Here, we report a direct and rapid determination of DNA methylation using an electric biosensor. The device consists of a DNA-tweezer probe integrated on a graphene field-effect transistor for label-free, highly sensitive, and specific methylation profiling. The device performance was evaluated with a target DNA that harbors a sequence of the methylguanine-DNA methyltransferase, a promoter of glioblastoma multiforme, a lethal brain tumor. The results show that we successfully profiled the methylated and nonmethylated forms at picomolar concentrations. Further, fluorescence kinetics and molecular dynamics simulations revealed that the position of the methylation site(s), their proximity, and accessibility to the toe-hold region of the tweezer probe are the primary determinants of the device performance.
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Affiliation(s)
- Deependra Kumar Ban
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Yushuang Liu
- School of Life Science, Inner Mongolia Agricultural University, 306 Zhaowuda Road, Hohhot 010018, China
| | - Zejun Wang
- CAS Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
| | - Srinivasan Ramachandran
- Department of Bioengineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Nirjhar Sarkar
- Materials Science and Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Ze Shi
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Wenhan Liu
- CAS Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
| | - Abhijith G Karkisaval
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Erick Martinez-Loran
- Department of Nanoengineering, University of California, San Diego, La Jolla, California 92093, United States
| | - Feng Zhang
- School of Life Science, Inner Mongolia Agricultural University, 306 Zhaowuda Road, Hohhot 010018, China
- State Key Laboratory of Respiratory Disease, Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Stomatology Hospital, Department of Biomedical Engineering, School of Basic Medical Sciences, Guangzhou Medical University, Guangzhou 511436, China
| | - Gennadi Glinsky
- Institute of Engineering in Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Prabhakar R Bandaru
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
- Materials Science and Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
- Department of Nanoengineering, University of California, San Diego, La Jolla, California 92093, United States
| | - Chunhai Fan
- CAS Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
- School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, and Institute of Molecular Medicine, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Ratnesh Lal
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
- Department of Bioengineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
- Materials Science and Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
- Institute of Engineering in Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
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5
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Urban F, Lupina G, Grillo A, Martucciello N, Di Bartolomeo A. Contact resistance and mobility in back-gate graphene transistors. NANO EXPRESS 2020. [DOI: 10.1088/2632-959x/ab7055] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
The metal-graphene contact resistance is one of the major limiting factors toward the technological exploitation of graphene in electronic devices and sensors. High contact resistance can be detrimental to device performance and spoil the intrinsic great properties of graphene. In this paper, we fabricate back-gate graphene field-effect transistors with different geometries to study the contact and channel resistance as well as the carrier mobility as a function of gate voltage and temperature. We apply the transfer length method and the y-function method showing that the two approaches can complement each other to evaluate the contact resistance and prevent artifacts in the estimation of carrier mobility dependence on the gate-voltage. We find that the gate voltage modulates both the contact and the channel resistance in a similar way but does not change the carrier mobility. We also show that raising the temperature lowers the carrier mobility, has a negligible effect on the contact resistance, and can induce a transition from a semiconducting to a metallic behavior of the graphene sheet resistance, depending on the applied gate voltage. Finally, we show that eliminating the detrimental effects of the contact resistance on the transistor channel current almost doubles the carrier field-effect mobility and that a competitive contact resistance as low as 700 Ω·μm can be achieved by the zig-zag shaping of the Ni contact.
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6
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Mach J, Procházka P, Bartošík M, Nezval D, Piastek J, Hulva J, Švarc V, Konečný M, Kormoš L, Šikola T. Electronic transport properties of graphene doped by gallium. NANOTECHNOLOGY 2017; 28:415203. [PMID: 28813368 DOI: 10.1088/1361-6528/aa86a4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In this work we present the effect of low dose gallium (Ga) deposition (<4 ML) performed in UHV (10-7 Pa) on the electronic doping and charge carrier scattering in graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.
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Affiliation(s)
- J Mach
- Central European Institute of Technology-Brno University of Technology (CEITEC BUT) Purkyňova 123, 612 00 Brno, Czechia. Institute of Physical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czechia
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7
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8
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Cusati T, Fiori G, Gahoi A, Passi V, Lemme MC, Fortunelli A, Iannaccone G. Electrical properties of graphene-metal contacts. Sci Rep 2017; 7:5109. [PMID: 28698652 PMCID: PMC5506027 DOI: 10.1038/s41598-017-05069-7] [Citation(s) in RCA: 92] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Accepted: 05/05/2017] [Indexed: 11/24/2022] Open
Abstract
The performance of devices and systems based on two-dimensional material systems depends critically on the quality of the contacts between 2D material and metal. A low contact resistance is an imperative requirement to consider graphene as a candidate material for electronic and optoelectronic devices. Unfortunately, measurements of contact resistance in the literature do not provide a consistent picture, due to limitations of current graphene technology, and to incomplete understanding of influencing factors. Here we show that the contact resistance is intrinsically dependent on graphene sheet resistance and on the chemistry of the graphene-metal interface. We present a physical model of the contacts based on ab-initio simulations and extensive experiments carried out on a large variety of samples with different graphene-metal contacts. Our model explains the spread in experimental results as due to uncontrolled graphene doping and suggests ways to engineer contact resistance. We also predict an achievable contact resistance of 30 Ω·μm for nickel electrodes, extremely promising for applications.
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Affiliation(s)
- Teresa Cusati
- Dipartimento di Ingegneria dell'Informazione, Università di Pisa Via G. Caruso 16, 56122, Pisa, Italy
| | - Gianluca Fiori
- Dipartimento di Ingegneria dell'Informazione, Università di Pisa Via G. Caruso 16, 56122, Pisa, Italy
| | - Amit Gahoi
- University of Siegen, Hölderlinstrasse 3, 57076, Siegen, Germany.,RWTH Aachen University, Chair for Electronic Devices, Aachen, Germany
| | - Vikram Passi
- University of Siegen, Hölderlinstrasse 3, 57076, Siegen, Germany.,RWTH Aachen University, Chair for Electronic Devices, Aachen, Germany
| | - Max C Lemme
- University of Siegen, Hölderlinstrasse 3, 57076, Siegen, Germany.,RWTH Aachen University, Chair for Electronic Devices, Aachen, Germany
| | - Alessandro Fortunelli
- CNR-ICCOM, Istituto di Chimica dei Composti Organometallici, Via G. Moruzzi 1, 56124, Pisa, Italy
| | - Giuseppe Iannaccone
- Dipartimento di Ingegneria dell'Informazione, Università di Pisa Via G. Caruso 16, 56122, Pisa, Italy.
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9
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Khoo KH, Leong WS, Thong JTL, Quek SY. Origin of Contact Resistance at Ferromagnetic Metal-Graphene Interfaces. ACS NANO 2016; 10:11219-11227. [PMID: 28024386 DOI: 10.1021/acsnano.6b06286] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Edge contact geometries are thought to yield ultralow contact resistances in most nonferromagnetic metal-graphene interfaces, owing to their large metal-graphene coupling strengths. Here, we examine the contact resistance of edge- versus surface-contacted ferromagnetic metal-graphene interfaces (i.e., nickel- and cobalt-graphene interfaces) using both single-layer and few-layer graphene. Good qualitative agreement is obtained between theory and experiment. In particular, in both theory and experiment, we observe that the contact resistance of edge-contacted ferromagnetic metal-graphene interfaces is much lower than that of surface-contacted ones, for all devices studied and especially for the single-layer graphene systems. We show that this difference in resistance is not due to differences in the metal-graphene coupling strength, which we quantify using Hamiltonian matrix elements. Instead, the larger contact resistance in surface contacts results from spin filtering at the interface, in contrast to the edge-contacted case where both spins are transmitted. Temperature-dependent resistance measurements beyond the Curie temperature TC show that the spin degree of freedom is indeed important for the experimentally measured contact resistance. These results show that it is possible to induce a large change in contact resistance by changing the temperature in the vicinity of TC.
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Affiliation(s)
- Khoong Hong Khoo
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 6 Science Drive 2, Singapore 117542
- Institute of High Performance Computing , 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632
| | - Wei Sun Leong
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 6 Science Drive 2, Singapore 117542
- Department of Electrical and Computer Engineering, National University of Singapore , 4 Engineering Drive 3, Singapore 117583
| | - John T L Thong
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 6 Science Drive 2, Singapore 117542
- Department of Electrical and Computer Engineering, National University of Singapore , 4 Engineering Drive 3, Singapore 117583
| | - Su Ying Quek
- Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 6 Science Drive 2, Singapore 117542
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10
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Zhang H, Chi L. Gold-Organic Hybrids: On-Surface Synthesis and Perspectives. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:10492-10498. [PMID: 27628247 DOI: 10.1002/adma.201602131] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 07/04/2016] [Indexed: 06/06/2023]
Abstract
Gold-organic hybrids can be prepared on gold substrates by on-surface dehalogenation of molecular precursors with multiple halogen substituents. Various contact geometries of covalent arylAu bonds are achieved by changing the halogen substituents in the bay or peri regions. Scanning tunneling microscopy/spectroscopy (STM/STS) investigations allow a better understanding of the structure/property relationships in various gold-aryl contacts. Recent progress on the synthesis, large-scale alignment, and STS measurement of gold-organic hybrids is described, ending with an emphasis on potential future applications, e.g., as precursors (intermediates) for the synthesis of graphene nanoribbons (GNRs) on insulating surfaces, and as a model system to investigate the role of covalent arylAu bonds in electron transport through gold-GNR contacts.
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Affiliation(s)
- Haiming Zhang
- Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, 199 Ren'ai Road, Suzhou, 215123, Jiangsu, P. R. China
| | - Lifeng Chi
- Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, 199 Ren'ai Road, Suzhou, 215123, Jiangsu, P. R. China
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11
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Fediai A, Ryndyk DA, Cuniberti G. The modular approach enables a fully ab initio simulation of the contacts between 3D and 2D materials. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:395303. [PMID: 27502169 DOI: 10.1088/0953-8984/28/39/395303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Up to now, the electrical properties of the contacts between 3D metals and 2D materials have never been computed at a fully ab initio level due to the huge number of atomic orbitals involved in a current path from an electrode to a pristine 2D material. As a result, there are still numerous open questions and controversial theories on the electrical properties of systems with 3D/2D interfaces-for example, the current path and the contact length scalability. Our work provides a first-principles solution to this long-standing problem with the use of the modular approach, a method which rigorously combines a Green function formalism with the density functional theory (DFT) for this particular contact type. The modular approach is a general approach valid for any 3D/2D contact. As an example, we apply it to the most investigated among 3D/2D contacts-metal/graphene contacts-and show its abilities and consistency by comparison with existing experimental data. As it is applicable to any 3D/2D interface, the modular approach allows the engineering of 3D/2D contacts with the pre-defined electrical properties.
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Affiliation(s)
- Artem Fediai
- Institute for Materials Science and Max Bergmann Center of Biomaterials, 01062 Dresden, Germany. Center for Advancing Electronics Dresden, TU Dresden, 01062 Dresden, Germany
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12
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Boland MJ, Sundararajan A, Farrokhi MJ, Strachan DR. Nonlinear Ballistic Transport in an Atomically Thin Material. ACS NANO 2016; 10:1231-1239. [PMID: 26630250 DOI: 10.1021/acsnano.5b06546] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Ultrashort devices that incorporate atomically thin components have the potential to be the smallest electronics. Such extremely scaled atomically thin devices are expected to show ballistic nonlinear behavior that could make them tremendously useful for ultrafast applications. While nonlinear diffusive electron transport has been widely reported, clear evidence for intrinsic nonlinear ballistic transport in the growing array of atomically thin conductors has so far been elusive. Here we report nonlinear electron transport of an ultrashort single-layer graphene channel that shows quantitative agreement with intrinsic ballistic transport. This behavior is shown to be distinctly different than that observed in similarly prepared ultrashort devices consisting, instead, of bilayer graphene channels. These results suggest that the addition of only one extra layer of an atomically thin material can make a significant impact on the nonlinear ballistic behavior of ultrashort devices, which is possibly due to the very different chiral tunneling of their charge carriers. The fact that we observe the nonlinear ballistic response at room temperature, with zero applied magnetic field, in non-ultrahigh vacuum conditions and directly on a readily accessible oxide substrate makes the nanogap technology we utilize of great potential for achieving extremely scaled high-speed atomically thin devices.
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Affiliation(s)
- Mathias J Boland
- Department of Physics & Astronomy, University of Kentucky , Lexington, Kentucky 40506, United States
| | - Abhishek Sundararajan
- Department of Physics & Astronomy, University of Kentucky , Lexington, Kentucky 40506, United States
| | - M Javad Farrokhi
- Department of Physics & Astronomy, University of Kentucky , Lexington, Kentucky 40506, United States
| | - Douglas R Strachan
- Department of Physics & Astronomy, University of Kentucky , Lexington, Kentucky 40506, United States
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Rathi S, Lee I, Lim D, Wang J, Ochiai Y, Aoki N, Watanabe K, Taniguchi T, Lee GH, Yu YJ, Kim P, Kim GH. Tunable Electrical and Optical Characteristics in Monolayer Graphene and Few-Layer MoS2 Heterostructure Devices. NANO LETTERS 2015; 15:5017-24. [PMID: 26091357 DOI: 10.1021/acs.nanolett.5b01030] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Lateral and vertical two-dimensional heterostructure devices, in particular graphene-MoS2, have attracted profound interest as they offer additional functionalities over normal two-dimensional devices. Here, we have carried out electrical and optical characterization of graphene-MoS2 heterostructure. The few-layer MoS2 devices with metal electrode at one end and monolayer graphene electrode at the other end show nonlinearity in drain current with drain voltage sweep due to asymmetrical Schottky barrier height at the contacts and can be modulated with an external gate field. The doping effect of MoS2 on graphene was observed as double Dirac points in the transfer characteristics of the graphene field-effect transistor (FET) with a few-layer MoS2 overlapping the middle part of the channel, whereas the underlapping of graphene have negligible effect on MoS2 FET characteristics, which showed typical n-type behavior. The heterostructure also exhibits a strongest optical response for 520 nm wavelength, which decreases with higher wavelengths. Another distinct feature observed in the heterostructure is the peak in the photocurrent around zero gate voltage. This peak is distinguished from conventional MoS2 FETs, which show a continuous increase in photocurrent with back-gate voltage. These results offer significant insight and further enhance the understanding of the graphene-MoS2 heterostructure.
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Affiliation(s)
| | | | | | | | - Yuichi Ochiai
- §Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
| | - Nobuyuki Aoki
- §Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
| | - Kenji Watanabe
- ∥Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- ∥Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Gwan-Hyoung Lee
- ⊥Department of Material Science and Engineering, Yonsei University, Seoul 120-749, Korea
| | - Young-Jun Yu
- #Creative Research Center for Graphene Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea
| | - Philip Kim
- ∇Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
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14
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Polukhin VA, Vatolin NA. Stability and thermal evolution of transition metal and silicon clusters. RUSSIAN CHEMICAL REVIEWS 2015. [DOI: 10.1070/rcr4411] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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15
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Development of graphene–nanometre-sized cerium oxide-incorporated aluminium and its electrochemical evaluation. APPLIED NANOSCIENCE 2015. [DOI: 10.1007/s13204-015-0438-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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16
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Ni Z, Zhong H, Jiang X, Quhe R, Luo G, Wang Y, Ye M, Yang J, Shi J, Lu J. Tunable band gap and doping type in silicene by surface adsorption: towards tunneling transistors. NANOSCALE 2014; 6:7609-7618. [PMID: 24896227 DOI: 10.1039/c4nr00028e] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
By using first-principles calculations, we predict that a sizable band gap can be opened at the Dirac point of silicene without degrading silicene's electronic properties with n-type doping by Cu, Ag, and Au adsorption, p-type doping by Ir adsorption, and neutral doping by Pt adsorption. A silicene p-i-n tunneling field effect transistor (TFET) model is designed by the adsorption of different transition metal atoms on different regions of silicene. Quantum transport simulations demonstrate that silicene TFETs have an on-off ratio of 10(3), a small sub-threshold swing of 77 mV dec(-1), and a large on-state current of over 1 mA μm(-1) under a supply voltage of about 1.7 V.
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Affiliation(s)
- Zeyuan Ni
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, China.
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17
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Ji X, Wang Y, Yu Z. A first-principle investigation of double-side CVD catalyst metal/graphene contacts. Phys Chem Chem Phys 2014; 16:12327-31. [PMID: 24824605 DOI: 10.1039/c4cp00960f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this paper, the double-side contact (DSC) properties of CVD catalyst metals and graphene (Gr) are studied by first-principle methods. Our calculation shows that two special catalyst metals Pt and Ir would have extremely small contact resistances in DSC and the physical origination of such phenomenon is explicitly analyzed. Different from the common physisorption metal which would keep Gr's intrinsic conical dispersion, the simulation results of Pt and Ir in DSC show chemisorption characters due to the charge redistribution triggered exchange-transfer mechanism. The symmetry Pauli-exclusion and charge transfer effects in DSC complexes are found to play an important role in the intriguing transition. These results may bring new information to seek a suitable lead structure for 2D materials.
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Affiliation(s)
- Xiang Ji
- Institute of Microelectronics, Tsinghua University, Beijing, China 100084.
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18
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Gong C, McDonnell S, Qin X, Azcatl A, Dong H, Chabal YJ, Cho K, Wallace RM. Realistic metal-graphene contact structures. ACS NANO 2014; 8:642-649. [PMID: 24261695 DOI: 10.1021/nn405249n] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The contact resistance of metal-graphene junctions has been actively explored and exhibited inconsistencies in reported values. The interpretation of these electrical data has been based exclusively on a side-contact model, that is, metal slabs sitting on a pristine graphene sheet. Using in situ X-ray photoelectron spectroscopy to study the wetting of metals on as-synthesized graphene on copper foil, we show that side-contact is sometimes a misleading picture. For instance, metals like Pd and Ti readily react with graphitic carbons, resulting in Pd- and Ti-carbides. Carbide formation is associated with C-C bond breaking in graphene, leading to an end-contact geometry between the metals and the periphery of the remaining graphene patches. This work validates the spontaneous formation of the metal-graphene end-contact during the metal deposition process as a result of the metal-graphene reaction instead of a simple carbon diffusion process.
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Affiliation(s)
- Cheng Gong
- Department of Materials Science and Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
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19
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Politano A, Chiarello G. Unravelling suitable graphene-metal contacts for graphene-based plasmonic devices. NANOSCALE 2013; 5:8215-8220. [PMID: 23852367 DOI: 10.1039/c3nr02027d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Plasmonic excitations in pristine and air-exposed graphene-Ru and graphene-Pt contacts have been investigated by using high-resolution electron energy loss spectroscopy. Loss measurements show that the effects of air exposure are very different in these two systems. While in graphene-Ru contacts, plasmons are completely quenched, plasmons in the graphene-Pt interface show only a frequency shift together with an overall intensity attenuation. These results pose significant questions as regards the stability in an ambient air atmosphere of graphene-based plasmonic devices and indicate a suitable choice of graphene-metal contacts.
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Affiliation(s)
- Antonio Politano
- Università degli Studi della Calabria, Dipartimento di Fisica, Italy
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20
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Liu H, Kondo H, Ohno T. Effect of contact area on electron transport through graphene-metal interface. J Chem Phys 2013; 139:074703. [DOI: 10.1063/1.4818519] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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21
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Zheng J, Wang L, Quhe R, Liu Q, Li H, Yu D, Mei WN, Shi J, Gao Z, Lu J. Sub-10 nm gate length graphene transistors: operating at terahertz frequencies with current saturation. Sci Rep 2013; 3:1314. [PMID: 23419782 PMCID: PMC3575621 DOI: 10.1038/srep01314] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Accepted: 01/10/2013] [Indexed: 11/09/2022] Open
Abstract
Radio-frequency application of graphene transistors is attracting much recent attention due to the high carrier mobility of graphene. The measured intrinsic cut-off frequency (fT) of graphene transistor generally increases with the reduced gate length (Lgate) till Lgate = 40 nm, and the maximum measured fT has reached 300 GHz. Using ab initio quantum transport simulation, we reveal for the first time that fT of a graphene transistor still increases with the reduced Lgate when Lgate scales down to a few nm and reaches astonishing a few tens of THz. We observe a clear drain current saturation when a band gap is opened in graphene, with the maximum intrinsic voltage gain increased by a factor of 20. Our simulation strongly suggests it is possible to design a graphene transistor with an extraordinary high fT and drain current saturation by continuously shortening Lgate and opening a band gap.
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Affiliation(s)
- Jiaxin Zheng
- State Key Laboratory of Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
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22
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Archambault C, Rochefort A. States modulation in graphene nanoribbons through metal contacts. ACS NANO 2013; 7:5414-5420. [PMID: 23676006 DOI: 10.1021/nn401357p] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We are reporting the results of density functional calculations of the electronic structure of finite graphene nanoribbons adsorbed on Au, Pd, and Ti electrodes. While the interaction of nanoribbons with the Au contact is more characteristic of a physisorbed state, the adsorption of Pd and Ti involves much stronger state mixing as in chemisorption. Metal-induced gap states, which can potentially short-circuit the device, are clearly revealed for the first time, allowing us to evaluate their penetration length. The evanescence of MIGS is primarily governed by the band gap of the nanoribbon, and we can estimate an acceptable minimal length for an effective transport channel to a few nanometers. Different impacts of the presence of metal-induced gap states on the properties of graphene nanoribbons are discussed in terms of charge transfer and electrostatics.
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Affiliation(s)
- Chloé Archambault
- Engineering Physics Department and Regroupement Québécois sur les Matériaux de Pointe (RQMP), École Polytechnique de Montréal, Montréal, Québec H3C 3A7, Canada
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23
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SONG Q, CAI J, ZHANG J, YU W, WANG F, XU J. Hydrogenation and cleavage of the C-O bonds in the lignin model compound phenethyl phenyl ether over a nickel-based catalyst. CHINESE JOURNAL OF CATALYSIS 2013. [DOI: 10.1016/s1872-2067(12)60535-x] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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24
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Zhang GP, Liu X, Wang CZ, Yao YX, Zhang J, Ho KM. Electronic and spin transport properties of graphene nanoribbon mediated by metal adatoms: a study by the QUAMBO-NEGF approach. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:105302. [PMID: 23399804 DOI: 10.1088/0953-8984/25/10/105302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Structural and electronic properties, including deformation, magnetic moment, Mulliken population, bond order, as well as electronic transport properties, of zigzag graphene nanoribbon (ZGNR) with Co adatoms on hollow sites are investigated by quasi-atomic minimal basis orbits (QUAMBOs), a first-principles tight binding (TB) scheme based on density functional theory (DFT), combined with a non-equilibrium Green's function. For electronic transport, below the Fermi level the transmission is strongly suppressed and spin dependent as a result of magnetism by Co adatom adsorption, while above the Fermi level the transmission is slightly distorted and spin independent. Due to the local environment dependence of QUAMBOs-TB parameters, we construct QUAMBOs-TB parameters of ZGNR leads and ZGNR with Co adatoms on hollow center sites by a divide-and-conquer approach, and accurately reproduce the electronic transmission behavior. Our QUAMBO-NEGF method is a new and promising way of examining electronic transport in large-scale systems.
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Affiliation(s)
- G P Zhang
- Ames Laboratory, US Department of Energy, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
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25
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Huang L, Yang R, Lai YC, Ferry DK. Lead-position dependent regular oscillations and random fluctuations of conductance in graphene quantum dots. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:085502. [PMID: 23343960 DOI: 10.1088/0953-8984/25/8/085502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Quantum interference causes a wavefunction to have sensitive spatial dependence, and this has a significant effect on quantum transport. For example, in a quantum-dot system, the conductance can depend on the lead positions. We investigate, for graphene quantum dots, the conductance variations with the lead positions. Since for graphene the types of boundaries, e.g., zigzag and armchair, can fundamentally affect the quantum transport characteristics, we focus on rectangular graphene quantum dots, for which the effects of boundaries can be systematically studied. For both zigzag and armchair horizontal boundaries, we find that changing the positions of the leads can induce significant conductance variations. Depending on the Fermi energy, the variations can be either regular oscillations or random conductance fluctuations. We develop a physical theory to elucidate the origin of the conductance oscillation/fluctuation patterns. In particular, quantum interference leads to standing-wave-like-patterns in the quantum dot which, in the absence of leads, are regulated by the energy-band structure of the corresponding vertical graphene ribbon. The observed 'coexistence' of regular oscillations and random fluctuations in the conductance can be exploited for the development of graphene-based nanodevices.
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Affiliation(s)
- Liang Huang
- Institute of Computational Physics and Complex Systems and Key Laboratory for Magnetism and Magnetic Materials of MOE, Lanzhou University, Lanzhou, Gansu 730000, People's Republic of China.
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26
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Ji X, Zhang J, Wang Y, Qian H, Yu Z. A theoretical model for metal–graphene contact resistance using a DFT–NEGF method. Phys Chem Chem Phys 2013; 15:17883-6. [DOI: 10.1039/c3cp52589a] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Schultz BJ, Jaye C, Lysaght PS, Fischer DA, Prendergast D, Banerjee S. On chemical bonding and electronic structure of graphene–metal contacts. Chem Sci 2013. [DOI: 10.1039/c2sc21018e] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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28
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Zheng J, Wang Y, Wang L, Quhe R, Ni Z, Mei WN, Gao Z, Yu D, Shi J, Lu J. Interfacial properties of bilayer and trilayer graphene on metal substrates. Sci Rep 2013; 3:2081. [PMID: 23803738 PMCID: PMC3694290 DOI: 10.1038/srep02081] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 06/11/2013] [Indexed: 11/09/2022] Open
Abstract
One popular approach to prepare graphene is to grow them on transition metal substrates via chemical vapor deposition. By using the density functional theory with dispersion correction, we systematically investigate for the first time the interfacial properties of bilayer (BLG) and trilayer graphene (TLG) on metal substrates. Three categories of interfacial structures are revealed. The adsorption of B(T)LG on Al, Ag, Cu, Au, and Pt substrates is a weak physisorption, but a band gap can be opened. The adsorption of B(T)LG on Ti, Ni, and Co substrates is a strong chemisorption, and a stacking-insensitive band gap is opened for the two uncontacted layers of TLG. The adsorption of B(T)LG on Pd substrate is a weaker chemisorption, with a band gap opened for the uncontacted layers. This fundamental study also helps for B(T)LG device study due to inevitable graphene/metal contact.
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Affiliation(s)
- Jiaxin Zheng
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, P. R. China
- These authors contributed equally to this work
| | - Yangyang Wang
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
- These authors contributed equally to this work
| | - Lu Wang
- Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska 68182-0266
| | - Ruge Quhe
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, P. R. China
| | - Zeyuan Ni
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
| | - Wai-Ning Mei
- Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska 68182-0266
| | - Zhengxiang Gao
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
| | - Dapeng Yu
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
| | - Junjie Shi
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
| | - Jing Lu
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, P. R. China
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29
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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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30
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Binz SM, Hupalo M, Liu X, Wang CZ, Lu WC, Thiel PA, Ho KM, Conrad EH, Tringides MC. High island densities and long range repulsive interactions: Fe on epitaxial graphene. PHYSICAL REVIEW LETTERS 2012; 109:026103. [PMID: 23030184 DOI: 10.1103/physrevlett.109.026103] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Indexed: 06/01/2023]
Abstract
The understanding of metal nucleation on graphene is essential for promising future applications, especially of magnetic metals which can be used in spintronics or computer storage media. A common method to study the grown morphology is to measure the nucleated island density n as a function of growth parameters. Surprisingly, the growth of Fe on graphene is found to be unusual because it does not follow classical nucleation: n is unexpectedtly high, it increases continuously with the deposited amount θ and shows no temperature dependence. These unusual results indicate the presence of long range repulsive interactions. Kinetic Monte Carlo simulations and density functional theory calculations support this conclusion. In addition to answering an outstanding question in epitaxial growth, i.e., to find systems where long range interactions are present, the high density of magnetic islands, tunable with θ, is of interest for nanomagnetism applications.
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Affiliation(s)
- S M Binz
- Ames Laboratory-U.S. Department of Energy, and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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31
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Barraza-Lopez S, Kindermann M, Chou MY. Charge transport through graphene junctions with wetting metal leads. NANO LETTERS 2012; 12:3424-3430. [PMID: 22676724 DOI: 10.1021/nl3004122] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Graphene is believed to be an excellent candidate material for next-generation electronic devices. However, one needs to take into account the nontrivial effect of metal contacts in order to precisely control the charge injection and extraction processes. We have performed transport calculations for graphene junctions with wetting metal leads (metal leads that bind covalently to graphene) using nonequilibrium Green's functions and density functional theory. Quantitative information is provided on the increased resistance with respect to ideal contacts and on the statistics of current fluctuations. We find that charge transport through the studied two-terminal graphene junction with Ti contacts is pseudo-diffusive up to surprisingly high energies.
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Affiliation(s)
- Salvador Barraza-Lopez
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
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32
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Gong C, Hinojos D, Wang W, Nijem N, Shan B, Wallace RM, Cho K, Chabal YJ. Metal-graphene-metal sandwich contacts for enhanced interface bonding and work function control. ACS NANO 2012; 6:5381-5387. [PMID: 22540140 DOI: 10.1021/nn301241p] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Only a small fraction of all available metals has been used as electrode materials for carbon-based devices due to metal-graphene interface debonding problems. We report an enhancement of the bonding energy of weakly interacting metals by using a metal-graphene-metal sandwich geometry, without sacrificing the intrinsic π-electron dispersions of graphene that is usually undermined by strong metal-graphene interface hybridization. This sandwich structure further makes it possible to effectively tune the doping of graphene with an appropriate selection of metals. Density functional theory calculations reveal that the strengthening of the interface interaction is ascribed to an enhancement of interface dipole-dipole interactions. Raman scattering studies of metal-graphene-copper sandwiches are used to validate the theoretically predicted tuning of graphene doping through sandwich structures.
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Affiliation(s)
- Cheng Gong
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA
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33
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Krompiewski S. Effect of the attachment of ferromagnetic contacts on the conductivity and giant magnetoresistance of graphene nanoribbons. NANOTECHNOLOGY 2012; 23:135203. [PMID: 22418824 DOI: 10.1088/0957-4484/23/13/135203] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Carbon-based nanostructures and graphene, in particular, evoke a lot of interest as new promising materials for nanoelectronics and spintronics. One of the most important issues in this context is the impact of external electrodes on the electronic properties of graphene nanoribbons (GNRs). The present theoretical method is based on the tight-binding model and a modified recursive procedure for Green's functions. The results show that within the ballistic transport regime, the so-called end-contacted geometry (of minimal GNR/electrode interface area), is usually more advantageous for practical applications than its side-contacted counterpart (with a larger coverage area), as far as the electrical conductivity is concerned. As regards the giant magnetoresistance coefficient, however, the situation is exactly the opposite, since spin-splitting effects are more pronounced in the lower conductive side-contacted setups.
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Affiliation(s)
- S Krompiewski
- Institute of Molecular Physics, Polish Academy of Sciences, ulica M Smoluchowskiego 17, 60179 Poznań, Poland.
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34
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Wu Y, Perebeinos V, Lin YM, Low T, Xia F, Avouris P. Quantum behavior of graphene transistors near the scaling limit. NANO LETTERS 2012; 12:1417-1423. [PMID: 22316333 DOI: 10.1021/nl204088b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The superior intrinsic properties of graphene have been a key research focus for the past few years. However, external components, such as metallic contacts, serve not only as essential probing elements, but also give rise to an effective electron cavity, which can form the basis for new quantum devices. In previous studies, quantum interference effects were demonstrated in graphene heterojunctions formed by a top gate. Here phase coherent transport behavior is demonstrated in a simple two terminal graphene structure with clearly resolved Fabry-Perot oscillations in sub-100 nm devices. By aggressively scaling the channel length down to 50 nm, we study the evolution of the graphene transistor from the channel-dominated diffusive regime to the contact-dominated ballistic regime. Key issues such as the current asymmetry, the question of Fermi level pinning by the contacts, the graphene screening determining the heterojunction barrier width, the scaling of minimum conductivity, and of the on/off current ratio are investigated.
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Affiliation(s)
- Yanqing Wu
- IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA.
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35
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Ni Z, Liu Q, Tang K, Zheng J, Zhou J, Qin R, Gao Z, Yu D, Lu J. Tunable bandgap in silicene and germanene. NANO LETTERS 2012; 12:113-8. [PMID: 22050667 DOI: 10.1021/nl203065e] [Citation(s) in RCA: 418] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
By using ab initio calculations, we predict that a vertical electric field is able to open a band gap in semimetallic single-layer buckled silicene and germanene. The sizes of the band gap in both silicene and germanene increase linearly with the electric field strength. Ab initio quantum transport simulation of a dual-gated silicene field effect transistor confirms that the vertical electric field opens a transport gap, and a significant switching effect by an applied gate voltage is also observed. Therefore, biased single-layer silicene and germanene can work effectively at room temperature as field effect transistors.
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Affiliation(s)
- Zeyuan Ni
- State Key Laboratory of Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, PR China
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36
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Kuroda MA, Tersoff J, Newns DM, Martyna GJ. Conductance through multilayer graphene films. NANO LETTERS 2011; 11:3629-3633. [PMID: 21834553 DOI: 10.1021/nl201436b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The ballistic conductance through junctions between multilayer graphene films and several different metals is studied using ab initio calculations within the local density approximation. The system consists of films of up to four graphene layers (Bernal stacking) between metallic electrodes, assuming reasonable metal-graphene epitaxial relationships. For some metals, the conductance decays exponentially with increasing number of layers, while for others the conductance saturates with film thickness. This difference in asymptotic behavior stems from the crystal momentum (mis)match between the bulk Fermi-level states in the electrode and those in the film. In contrast, for sufficiently thin films the bonding between the metal and the adjacent graphene layer dominates, giving a metal dependence for graphene similar to that seen experimentally for single-wall carbon nanotubes. Among the metals considered here, we find Pd to be the best for electrodes to films with up to 4 graphene layers.
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Affiliation(s)
- Marcelo A Kuroda
- IBM T. J. Watson Research Center, Yorktown Heights, NY, United States.
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37
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Di Bartolomeo A, Giubileo F, Santandrea S, Romeo F, Citro R, Schroeder T, Lupina G. Charge transfer and partial pinning at the contacts as the origin of a double dip in the transfer characteristics of graphene-based field-effect transistors. NANOTECHNOLOGY 2011; 22:275702. [PMID: 21597135 DOI: 10.1088/0957-4484/22/27/275702] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We discuss the origin of an additional dip other than the charge neutrality point observed in the transfer characteristics of graphene-based field-effect transistors with a Si/SiO2 substrate used as the back-gate. The double dip is proved to arise from charge transfer between the graphene and the metal electrodes, while charge storage at the graphene/SiO2 interface can make it more evident. Considering a different Fermi energy from the neutrality point along the channel and partial charge pinning at the contacts, we propose a model which explains all the features observed in the gate voltage loops. We finally show that the double dip enhanced hysteresis in the transfer characteristics can be exploited to realize graphene-based memory devices.
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Affiliation(s)
- Antonio Di Bartolomeo
- Dipartimento di Fisica E R Caianiello and Centro Interdipartimentale NANO_MATES, Università degli Studi di Salerno, via Ponte don Melillo, 84084 Fisciano (SA), Italy.
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38
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Wang R, Wang S, Zhang D, Li Z, Fang Y, Qiu X. Control of carrier type and density in exfoliated graphene by interface engineering. ACS NANO 2011; 5:408-412. [PMID: 21133417 DOI: 10.1021/nn102236x] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Air-stable, n-doped or p-doped graphene sheets on a chip were achieved by modifying the substrates with self-assembled layers of silane and polymer. The interfacial effects on the electronic properties of graphene were investigated using micro-Raman and Kelvin probe force microscopy (KPFM). Raman studies demonstrated that the phonon vibrations were sensitive to the doping level of graphene on the various substrates. Complementary information on the charge transfer between the graphene and substrate was extracted by measuring the surface potential of graphene flakes using KPFM, which illustrated the distribution of carriers in different graphene layers as well as the formation of dipoles at the interface. The Fermi level of single layer graphene on the modified substrates could be tuned in a range from -130 to 90 mV with respect to the Dirac point, corresponding to the doped carrier concentrations up to 10(12) cm(-2).
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Affiliation(s)
- Rui Wang
- National Center for Nanoscience and Technology, Zhongguancun, Beijing 100190, China
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39
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Xu Z, Buehler MJ. Interface structure and mechanics between graphene and metal substrates: a first-principles study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:485301. [PMID: 21406741 DOI: 10.1088/0953-8984/22/48/485301] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Graphene is a fascinating material not only for technological applications, but also as a test bed for fundamental insights into condensed matter physics due to its unique two-dimensional structure. One of the most intriguing issues is the understanding of the properties of graphene and various substrate materials. In particular, the interfaces between graphene and metal substrates are of critical importance in applications of graphene in integrated electronics, as thermal materials, and in electromechanical devices. Here we investigate the structure and mechanical interactions at a graphene-metal interface through density functional theory (DFT)-based calculations. We focus on copper (111) and nickel (111) surfaces adhered to a monolayer of graphene, and find that their cohesive energy, strength and electronic structure correlate directly with their atomic geometry. Due to the strong coupling between open d-orbitals, the nickel-graphene interface has a much stronger cohesive energy with graphene than copper. We also find that the interface cohesive energy profile features a well-and-shoulder shape that cannot be captured by simple pair-wise models such as the Lennard-Jones potential. Our results provide a detailed understanding of the interfacial properties of graphene-metal systems, and help to predict the performance of graphene-based nanoelectronics and nanocomposites. The availability of structural and energetic data of graphene-metal interfaces could also be useful for the development of empirical force fields for molecular dynamics simulations.
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Affiliation(s)
- Zhiping Xu
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Do VN, Dollfus P. Modeling of metal-graphene coupling and its influence on transport properties in graphene at the charge neutrality point. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:425301. [PMID: 21403308 DOI: 10.1088/0953-8984/22/42/425301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this work, the effect of coupling between metallic electrodes and graphene is discussed. We demonstrate that the transport properties of graphene at the charge neutrality point are very sensitive to this coupling. By introducing a model based on two real parameters, namely the real and the imaginary parts of the self-energy which describes the metal-graphene coupling, the obtained results of charge conductivity versus the Fermi energy reproduce well the essential features of experimental data such as the asymmetry between electrons and holes. Additionally, the possible role of scattering processes in the enhancement of the density of states, and thus of the minimum of conductivity, at the charge neutrality point is also discussed. This work is believed to be helpful for further studies of graphene-based devices wherein metallic electrodes may have a major impact on electrical characteristics.
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Affiliation(s)
- V Nam Do
- Hanoi Advanced School of Science and Technology, Hanoi University of Technology, 40 Ta Quang Buu, Hanoi, Vietnam
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