The Experts below are selected from a list of 7986 Experts worldwide ranked by ideXlab platform
Nongjian Tao - One of the best experts on this subject based on the ideXlab platform.
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Graphene field-effect transistors: Electrochemical gating, interfacial Capacitance, and biosensing applications
Chemistry - An Asian Journal, 2010Co-Authors: Fang Chen, Jilin Xia, Quan Qing, Nongjian TaoAbstract:Single-layer graphene has received much attention because of its unique two-dimensional crystal structure and properties. In this review, we focus on the graphene devices in solution, and their properties that are relevant to chemical and biological applications. We will discuss their charge transport, controlled by electrochemical gates, interfacial and Quantum Capacitance, charged impurities, and surface potential distribution. The sensitive dependence of graphene charge transport on the surrounding environment points to their potential applications as ultrasensitive chemical sensors and biosensors. The interfacial and Quantum Capacitance studies are directly relevant to the on-going effort of creating graphene-based ultracapacitors for energy storage.
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measurement of the Quantum Capacitance of graphene
Nature Nanotechnology, 2009Co-Authors: Jilin Xia, Fang Chen, Nongjian TaoAbstract:Graphene has received widespread attention due to its unique electronic properties1,2,3,4,5. Much of the research conducted so far has focused on electron mobility, which is determined by scattering from charged impurities and other inhomogeneities6,7. However, another important quantity, the Quantum Capacitance, has been largely overlooked. Here, we report a direct measurement of the Quantum Capacitance of graphene as a function of gate potential using a three-electrode electrochemical configuration. The Quantum Capacitance has a non-zero minimum at the Dirac point and a linear increase on both sides of the minimum with relatively small slopes. Our findings—which are not predicted by theory for ideal graphene—suggest that charged impurities also influences the Quantum Capacitance. We also measured the Capacitance in aqueous solutions at different ionic concentrations, and our results strongly indicate that the long-standing puzzle about the interfacial Capacitance in carbon-based electrodes has a Quantum origin. Electrochemical measurements show that the Quantum Capacitance of graphene is influenced by scattering from charged impurities, and also suggest that a longstanding puzzle about the interfacial Capacitance in carbon-based electrodes has a Quantum origin.
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Measurement of the Quantum Capacitance of graphene
Nature Nanotechnology, 2009Co-Authors: Jilin Xia, Jinghong Li, Fang Chen, Nongjian TaoAbstract:Graphene has received widespread attention due to its unique electronic properties. Much of the research conducted so far has focused on electron mobility, which is determined by scattering from charged impurities and other inhomogeneities. However, another important quantity, the Quantum Capacitance, has been largely overlooked. Here, we report a direct measurement of the Quantum Capacitance of graphene as a function of gate potential using a three-electrode electrochemical configuration. The Quantum Capacitance has a non-zero minimum at the Dirac point and a linear increase on both sides of the minimum with relatively small slopes. Our findings -- which are not predicted by theory for ideal graphene -- suggest that charged impurities also influences the Quantum Capacitance. We also measured the Capacitance in aqueous solutions at different ionic concentrations, and our results strongly indicate that the long-standing puzzle about the interfacial Capacitance in carbon-based electrodes has a Quantum origin.
Kosuke Nagashio - One of the best experts on this subject based on the ideXlab platform.
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graphene field effect transistor application electric band structure of graphene in transistor structure extracted from Quantum Capacitance
Journal of Materials Research, 2017Co-Authors: Kosuke NagashioAbstract:Recently, various two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides and so on, have attracted much attention in electron device research. The most important characteristic of graphene is its highest mobility of all semiconductor channels at room temperature. However, it is obvious that more than a good mobility characteristic is required to realize the field effect transistor (FET), and intense arguments from various points of view are necessary. In this paper, the issues with Si-metal oxide semiconductor FETs (Si-MOSFET) and the advantage of 2D materials are discussed. The present state of graphene FETs with respect to gate stack formation and band gap engineering is reported. Moreover, based on the density of states (DOS) of graphene extracted using the Quantum Capacitance ( C Q ) measurement, it is shown that the electric band structure of graphene in contact with gate insulators or metal electrode deviates from its intrinsic band structure.
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large fermi energy modulation in graphene transistors with high pressure o2 annealed y2o3 topgate insulators
arXiv: Materials Science, 2014Co-Authors: KOUICHI KANAYAMA, Tomonori Nishimura, Kosuke Nagashio, Akira ToriumiAbstract:We demonstrate a considerable suppression of the low-field leakage through a Y2O3 topgate insulator on graphene by applying high-pressure O2 at 100 atm during post-deposition annealing (HP-PDA). Consequently, the Quantum Capacitance measurement for the monolayer graphene reveals the largest Fermi energy modulation (EF = ~0.52 eV, i.e., the carrier density of ~2*10^13 cm^-2) in the solid-state topgate insulators reported so far. HP-PDA is the robust method to improve the electrical quality of high-k insulators on graphene.
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estimation of residual carrier density near the dirac point in graphene through Quantum Capacitance measurement
Applied Physics Letters, 2013Co-Authors: Kosuke Nagashio, Tomonori Nishimura, Akira ToriumiAbstract:We discuss the residual carrier density (n*) near the Dirac point (DP) in graphene estimated by Quantum Capacitance (CQ) and conductivity (σ) measurements. The CQ at the DP has a finite value and is independent of the temperature. A similar behavior is also observed for the conductivity at the DP, because their origin is residual carriers induced externally by charged impurities. The n* extracted from CQ, however, is often smaller than that from σ, suggesting that the mobility in the puddle region is lower than that in the linear region. The CQ measurement should be employed for estimating n* quantitatively.
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estimation of residual carrier density near the dirac point in graphene through Quantum Capacitance measurement
arXiv: Materials Science, 2013Co-Authors: Kosuke Nagashio, Tomonori Nishimura, Akira ToriumiAbstract:We discuss the residual carrier density (n*) near the Dirac point (DP) in graphene estimated by Quantum Capacitance (CQ) and conductivity measurements. The CQ at the DP has a finite value and is independent of the temperature. A similar behavior is also observed for the conductivity at the DP, because their origin is residual carriers induced externally by charged impurities. The n* extracted from CQ, however, is often smaller than that from the conductivity, suggesting that the mobility in the puddle region is lower than that in the linear region. The CQ measurement should be employed for estimating n* quantitatively.
J Guo - One of the best experts on this subject based on the ideXlab platform.
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gate electrostatics and Quantum Capacitance of graphene nanoribbons
arXiv: Mesoscale and Nanoscale Physics, 2007Co-Authors: J Guo, Youngki Yoon, Yijian OuyangAbstract:Capacitance-voltage (C-V) characteristics are important for understanding fundamental electronic structures and device applications of nanomaterials. The C-V characteristics of graphene nanoribbons (GNRs) are examined using self-consistent atomistic simulations. The results indicate strong dependence of the GNR C-V characteristics on the edge shape. For zigzag edge GNRs, highly non-uniform charge distribution in the transverse direction due to edge states lowers the gate Capacitance considerably, and the self-consistent electrostatic potential significantly alters the band structure and carrier velocity. For an armchair edge GNR, the Quantum Capacitance is a factor of 2 smaller than its corresponding zigzag carbon nanotube, and a multiple gate geometry is less beneficial for transistor applications. Magnetic field results in pronounced oscillations on C-V characteristics.
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comparison of performance limits for carbon nanoribbon and carbon nanotube transistors
Applied Physics Letters, 2006Co-Authors: Yijian Ouyang, Youngki Yoon, James K Fodor, J GuoAbstract:Carbon-based nanostructures promise near ballistic transport and are being intensively explored for device applications. In this letter, the performance limits of carbon nanoribbon (CNR) field-effect transistors (FETs) and carbon nanotube (CNT) FETs are compared. The ballistic channel conductance and the Quantum Capacitance of the CNRFET are about a factor of 2 smaller than those of the CNTFET because of the different valley degeneracy factors for CNRs and CNTs. The intrinsic speed of the CNRFET is faster due to a larger average carrier injection velocity. The gate Capacitance plays an important role in determining which transistor delivers a larger on current.
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assessment of silicon mos and carbon nanotube fet performance limits using a general theory of ballistic transistors
International Electron Devices Meeting, 2002Co-Authors: J Guo, Supriyo Datta, Mark Lundstrom, Markus Brink, Paul L Mceuen, Ali Javey, Hongjie Dai, Hyoungsub Kim, Paul C McintyreAbstract:A simple model for ballistic nanotransistors, which extends previous work by treating both the charge control and the Quantum Capacitance limits of MOSFET-like transistors, is presented. We apply this new model to MOSFET-like carbon nanotube FETs (CNTFETs) and to MOSFETs at the scaling limit. The device physics for operation at ballistic and Quantum Capacitance limits are explored. Based on the analysis of recently reported CNTFETs, we compare CNTFETs to MOSFETs. The potential performance advantages over Si that might be achieved at the scaling limit are established by using the new model.
H S P Wong - One of the best experts on this subject based on the ideXlab platform.
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a compact virtual source model for carbon nanotube fets in the sub 10 nm regime part i intrinsic elements
IEEE Transactions on Electron Devices, 2015Co-Authors: Aaron D Franklin, Wilfried Haensch, H S P WongAbstract:We present a data-calibrated compact model of carbon nanotube (CNT) FETs (CNTFETs) based on the virtual-source (VS) approach, describing the intrinsic current–voltage and charge–voltage characteristics. The features of the model include: 1) carrier VS velocity extracted from experimental devices with gate lengths down to 15 nm; 2) carrier effective mobility and velocity depending on the CNT diameter; 3) short channel effect such as inverse subthreshold slope degradation and drain-induced barrier lowering depending on the device dimensions; and 4) small-signal Capacitances including the CNT Quantum Capacitance effect to account for the decreasing gate Capacitance at high gate bias. The CNTFET model captures the dimensional scaling effects and is suitable for technology benchmarking and performance projection at the sub-10-nm technology nodes.
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a compact virtual source model for carbon nanotube fets in the sub 10 nm regime part i intrinsic elements
IEEE Transactions on Electron Devices, 2015Co-Authors: Chishuen Lee, Wilfried Haensch, Aaron D Franklin, Eric Pop, H S P WongAbstract:We present a data-calibrated compact model of carbon nanotube (CNT) FETs (CNTFETs) based on the virtual-source (VS) approach, describing the intrinsic current–voltage and charge–voltage characteristics. The features of the model include: 1) carrier VS velocity extracted from experimental devices with gate lengths down to 15 nm; 2) carrier effective mobility and velocity depending on the CNT diameter; 3) short channel effect such as inverse subthreshold slope degradation and drain-induced barrier lowering depending on the device dimensions; and 4) small-signal Capacitances including the CNT Quantum Capacitance effect to account for the decreasing gate Capacitance at high gate bias. The CNTFET model captures the dimensional scaling effects and is suitable for technology benchmarking and performance projection at the sub-10-nm technology nodes.
F J Schupp - One of the best experts on this subject based on the ideXlab platform.
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sensitive radiofrequency readout of Quantum dots using an ultra low noise squid amplifier
Journal of Applied Physics, 2020Co-Authors: F J Schupp, A. Mavalankar, I. Farrer, J P Griffiths, G A C Jones, D A Ritchie, C G Smith, F Vigneau, Yutian Wen, Leon C CamenzindAbstract:Fault-tolerant spin-based Quantum computers will require fast and accurate qubit read out. This can be achieved using radiofrequency reflectometry given sufficient sensitivity to the change in Quantum Capacitance associated with the qubit states. Here, we demonstrate a 23-fold improvement in Capacitance sensitivity by supplementing a cryogenic semiconductor amplifier with a SQUID preamplifier. The SQUID amplifier operates at a frequency near 200 MHz and achieves a noise temperature below 600 mK when integrated into a reflectometry circuit, which is within a factor 120 of the Quantum limit. It enables a record sensitivity to Capacitance of 0.07 aF / Hz. The setup is used to acquire charge stability diagrams of a gate-defined double Quantum dot in a short time with a signal-to-noise ration of about 38 in 1 μ s of integration time.
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sensitive radio frequency measurements of a Quantum dot by tuning to perfect impedance matching
arXiv: Mesoscale and Nanoscale Physics, 2015Co-Authors: N. Ares, A. Mavalankar, G. Rogers, I. Farrer, F J Schupp, J P Griffiths, G A C Jones, D A Ritchie, C G Smith, A. CottetAbstract:Electrical readout of spin qubits requires fast and sensitive measurements, but these are hindered by poor impedance matching to the device. We demonstrate perfect impedance matching in a radio-frequency readout circuit, realized by incorporating voltage-tunable varactors to cancel out parasitic Capacitances. In the optimized setup, a Capacitance sensitivity of $1.6~\mathrm{aF}/\sqrt{\mathrm{Hz}}$ is achieved at a maximum source-drain bias of $170~\mu$V root-mean-square and with bandwidth above $15~$MHz. Coulomb blockade is measured via both conductance and Capacitance in a Quantum dot, and the two contributions are found to be proportional, as expected from a quasistatic tunneling model. We benchmark our results against the requirements for single-shot qubit readout using Quantum Capacitance, a goal that has so far been elusive.
