Showing papers on "Quantum capacitance published in 2011"
TL;DR: Systematic trends not only show how the intrinsic high-density transport properties of graphene can be accessed by field effect, but also demonstrate the robustness of ion-gated graphene, which is crucial for possible future applications.
Abstract: We present a comparative study of high carrier density transport in mono-, bi-, and trilayer graphene using electric double-layer transistors to continuously tune the carrier density up to values exceeding 10(14) cm(-2). Whereas in monolayer the conductivity saturates, in bi- and trilayer filling of the higher-energy bands is observed to cause a nonmonotonic behavior of the conductivity and a large increase in the quantum capacitance. These systematic trends not only show how the intrinsic high-density transport properties of graphene can be accessed by field effect, but also demonstrate the robustness of ion-gated graphene, which is crucial for possible future applications.
322 citations
TL;DR: In this article, the interfacial capacitance of large area, single layer graphene was directly measured with electrolyte accessing both sides of the graphene sheet, consistent with charge storage having a quantum capacitance component.
Abstract: The interfacial capacitance of large area, single layer graphene was directly measured with electrolyte accessing both sides of the graphene sheet. PMMA and photoresist patterns were used as supports to suspend the CVD grown graphene in electrolyte during electrochemical testing. Both one and two sides of single layer graphene films were measured and compared. The results show that the area normalized charge that can be stored simultaneously on both sides is significantly lower than could be stored on just one side of single layer graphene, consistent with charge storage having a quantum capacitance component. These measurements are also consistent with the specific capacitance of graphene materials as previously measured in supercapacitor cells and provide a basis for the further understanding and development of graphene based materials for electrical energy storage.
205 citations
TL;DR: The results show that not much further improvement can be gained via further vertical scaling down of the gate oxide, suggesting that Y2O3 may be the ultimate dielectric material for graphene.
Abstract: A high-quality Y2O3 dielectric layer has been grown directly on graphene and used to fabricated top-gate graphene field-effect transistors (FETs), and the thickness of the dielectric layer has been reduced continuously down to 3.9 nm with an equivalent oxide thickness (EOT) of 1.5 nm and excellent insulativity. By measuring CV characteristics of two graphene FETs with different gate oxide thicknesses, the oxide capacitance and quantum capacitance are retrieved directly from the experimental CV data without introducing any additional fitting process and parameters, yielding a relative dielectric constant of κ = 10 for Y2O3 on graphene and an oxide capacitance of about 2.28 μF/cm2. It is found that for a rather large gate voltage range, this oxide capacitance is comparable and sometimes even larger than the quantum capacitance of graphene. Since the total gate capacitance is determined by the smaller of the oxide and quantum capacitance, our results show that not much further improvement can be gained via f...
141 citations
TL;DR: In this article, a model of the currentvoltage characteristics of graphene field-effect transistors is presented for analog and RF applications where band-gap engineering of graphene could be not needed.
Abstract: We present a compact physics-based model of the current-voltage characteristics of graphene field-effect transistors, of especial interest for analog and RF applications where band-gap engineering of graphene could be not needed. The physical framework is a field-effect model and drift-diffusion carrier transport. Explicit closed-form expressions have been derived for the drain current continuously covering all operation regions. The model has been benchmarked with measured prototype devices, demonstrating accuracy and predictive behavior. Finally, we show an example of projection of the intrinsic gain as a figure of merit commonly used in RF/analog applications.
121 citations
TL;DR: In this paper, the robust quantization of the Hall resistance in epitaxial graphene grown on Si-terminated SiC was explored, and it was shown that the dominance of quantum over classical capacitance in charge transfer between the substrate and graphene is such that Landau levels remain completely filled over an extraordinarily broad range of magnetic fields.
Abstract: We explore the robust quantization of the Hall resistance in epitaxial graphene grown on Si-terminated SiC. Uniquely to this system, the dominance of quantum over classical capacitance in the charge transfer between the substrate and graphene is such that Landau levels (in particular, the one at exactly zero energy) remain completely filled over an extraordinarily broad range of magnetic fields. One important implication of this pinning of the filling factor is that the system can sustain a very high nondissipative current. This makes epitaxial graphene ideally suited for quantum resistance metrology, and we have achieved a precision of 3 parts in 1010 in the Hall resistance-quantization measurements.
114 citations
TL;DR: In this article, a general microscopic capacitance model is developed and used to describe the quantum capacitance anomaly near the Dirac point of a metal-oxide-semiconductor (MOS) structure.
Abstract: Metal-oxide-semiconductor (MOS) structures based on graphene were fabricated with ultrathin Y2O3 films as the top gate oxide. While the quantum capacitance of graphene was measured using the MOS structure and shown to agree well with theory for ideal graphene at large channel potential, it deviates significantly from theory near the Dirac point. A general microscopic capacitance model is developed and used to describe the quantum capacitance anomaly near the Dirac point. Excellent agreement with experiment results was achieved using this model and key parameters including potential fluctuation and local carrier density fluctuation were retrieved.
97 citations
TL;DR: In this paper, the presence of an effective thin interfacial dielectric layer between the metal contact and the underlying graphene is explained by postulating that the metal-graphene interface is a crucial step toward reducing the contact resistance for high-performance graphene transistors.
Abstract: Metal contacts have been identified to be a key technological bottleneck for the realization of viable graphene electronics. Recently, it has been observed that for structures that possess both a top and a bottom gate, the electron-hole conductance asymmetry can be modulated by the bottom gate. In this paper, we explain this observation by postulating the presence of an effective thin interfacial dielectric layer between the metal contact and the underlying graphene. Electrical results from quantum transport calculations accounting for this modified electrostatics corroborate well with the experimentally measured contact resistances. This paper indicates that the engineering of a metal-graphene interface is a crucial step toward reducing the contact resistance for high-performance graphene transistors.
61 citations
TL;DR: In this article, the authors examined the high frequency performance limits of graphene field-effect transistors (FETs) down to a channel length of 20 nm by using self-consistent quantum simulations.
Abstract: High frequency performance limits of graphene field-effect transistors (FETs) down to a channel length of 20 nm have been examined by using self-consistent quantum simulations. The results indicate that although Klein band-to-band tunneling is significant for sub-100 nm graphene FETs, it is possible to achieve a good transconductance and ballistic on-off ratio larger than 3 even at a channel length of 20 nm. At a channel length of 20 nm, the intrinsic cut-off frequency remains at a few THz for various gate insulator thickness values, but a thin gate insulator is necessary for a good transconductance and smaller degradation of cut-off frequency in the presence of parasitic capacitance. The intrinsic cut-off frequency is close to the LC characteristic frequency set by graphene kinetic inductance (L) and quantum capacitance (C), which is about 100 GHz·μm divided by the gate length.
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58 citations
TL;DR: In this article, a model for the signal propagation along single wall CNTs (SWCNTs) of arbitrary chirality, at microwave through terahertz frequencies, taking into account both these characteristics in a self-consistent way, is proposed.
Abstract: In carbon nanotubes (CNTs) with large radii, either metallic or semiconducting, several subbands contribute to the electrical conduction, while in metallic nonarmchair nanotubes with small radii the wall curvature induces a large energy gap. In this paper, we propose a model for the signal propagation along single wall CNTs (SWCNTs) of arbitrary chirality, at microwave through terahertz frequencies, which takes into account both these characteristics in a self-consistent way. We first study an SWCNT, disregarding the wall curvature, in the frame of a semiclassical treatment based on the Boltzmann equation in the momentum-independent relaxation time approximation. It allows expressing the longitudinal dynamic conductivity in terms of the number of effective conducting channels. Next, we study the behavior of this number as the nanotube radius varies and its relation with the kinetic inductance and quantum capacitance. Furthermore, we show that the effects of the spatial dispersion are negligible in the collision dominated regimes, whereas they may be important in the collisionless regimes, giving rise to sound waves propagating with the Fermi velocity. Then, we study the effects on the electron transport of the terahertz quantum transition induced by the wall curvature by using a quantum kinetic approach. The nanotube curvature modifies the kinetic inductance and gives arise to an additional RLC branch in the equivalent circuit, related to the terahertz quantum transition. The proposed model can be used effectively for analyzing the signal propagation in complex structures composed of SWCNTs with different chirality, such as bundles of SWCNTs and multiwall CNTs, providing that the tunneling between adjacent shells may be disregarded.
56 citations
TL;DR: In this article, a model to calculate the DC characteristics of large area graphene field effect transistors is presented, which applies the carrier-density-dependent quantum capacitance and uses a steady-state velocity-field characteristics with soft saturation to describe carrier transport, and takes the carrier density dependence of the saturation velocity into account.
Abstract: A model to calculate the DC characteristics of large-area graphene field-effect transistors is presented. It applies the carrier-density-dependent quantum capacitance to calculate the carrier density, uses a steady-state velocity-field characteristics with soft saturation to describe carrier transport, and takes the carrier density dependence of the saturation velocity into account. Different from previous approaches to model graphene transistors, here the DC characteristics are obtained by feeding a drain current into the device and calculating the drain voltage for a given gate bias. The modeling results are compared with experimental data and very good agreement is obtained.
50 citations
TL;DR: In this article, the capacitance of undoped high-mobility low-density-of-states materials in double-gate device architecture is calculated in a compact model, taking the effect of wavefunction penetration into the gate oxide and the effective mass discontinuity.
Abstract: We present a compact model to calculate the capacitance of undoped high-mobility low-density-of-states materials in double-gate device architecture. Analytical equations for estimating the subband energies, while taking the effect of wavefunction penetration into the gate oxide and the effective mass discontinuity, are presented for the first time in a compact modeling framework. The surface potential equation for a two subband system is solved, assuming Fermi-Dirac statistics, and compared to numerical Schrodinger-Poisson simulations. The importance of accurately treating the charge profile distribution is illustrated, and an analytical expression for the effective oxide thickness to model the charge centroid is developed.
TL;DR: In this paper, a graphene wireless sensor concept is described, where the capacitance in a metal-insulator-graphene structure varies with charge concentration through the quantum capacitance effect.
Abstract: A graphene wireless sensor concept is described. By utilizing thin gate dielectrics, the capacitance in a metal-insulator-graphene structure varies with charge concentration through the quantum capacitance effect. Simulations using realistic structural and transport parameters predict quality factors, Q, >60 at 1 GHz. When placed in series with an ideal inductor, a resonant frequency tuning ratio of 25% (54%) is predicted for sense charge densities ranging from 0.32 to 1.6 μC/cm2 at an equivalent oxide thickness of 2.0 nm (0.5 nm). The resonant frequency has a temperature sensitivity, df/dT, less than 0.025%/K for sense charge densities >0.32 μC/cm2.
TL;DR: A direct comparison of the ballistic conductances, quantum capacitances, and kinetic inductances indicates that Ag and Cu nanowires show very similar performances.
Abstract: The electronic structure and transport properties of silver (Ag) and copper (Cu) nanowires of diameters up to 1.7 nm are investigated using first principles density functional theory and the Landauer formalism in conjunction with a supercell approach. A direct comparison of the ballistic conductances, quantum capacitances, and kinetic inductances indicates that Ag and Cu nanowires show very similar performances. Compared to the electrostatic capacitance, the quantum capacitance is found to have a negligible effect on the total capacitance of the nanowire interconnect. In contrast, the overall inductance has a dominant contribution from the kinetic inductance over the magnetic inductance.
TL;DR: The utility of the integrated capacitance bridge for measuring the quantum capacitance of nanostructures by measuring the capacitors of top-gated graphene devices and cleanly resolving the density of states is demonstrated.
Abstract: We have developed a highly sensitive integrated capacitance bridge for quantum capacitance measurements. Our bridge, based on a GaAs HEMT amplifier, delivers attofarad (aF) resolution using a small AC excitation at or below kBT over a broad temperature range (4–300 K). We have achieved a resolution at room temperature of 60 aF / Hz for a 10 mV ac excitation at 17.5 kHz, with an improved resolution at cryogenic temperatures, for the same excitation amplitude. We demonstrate the utility of our bridge for measuring the quantum capacitance of nanostructures by measuring the capacitance of top-gated graphene devices and cleanly resolving the density of states.
TL;DR: The quantum capacitance of graphene deduced from SCM results is found to increase with the layer number at the sample bias of 0 V but decreases with n at -3 V, while the magnitude of the EFM phase shift is significant between SLG and BLG but becomes much weaker between MLGs with a different n.
Abstract: The nanoscale electrical properties of single-layer graphene (SLG), bilayer graphene (BLG) and multilayer graphene (MLG) are studied by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM). The quantum capacitance of graphene deduced from SCM results is found to increase with the layer number (n) at the sample bias of 0 V but decreases with n at -3 V. Furthermore, the quantum capacitance increases very rapidly with the gate voltage for SLG, but this increase is much slowed down when n becomes greater. On the other hand, the magnitude of the EFM phase shift with respect to the SiO2 substrate increases with n at the sample bias of +2 V but decreases with n at -2 V. The difference in both quantum capacitance and EFM phase shift is significant between SLG and BLG but becomes much weaker between MLGs with a different n. The layer-dependent quantum capacitance behaviors of graphene could be attributed to their layer-dependent electronic structure as well as the layer-varied dependence on gate voltage, while the layer-dependent EFM phase shift is caused by not only the layer-dependent surface potential but also the layer-dependent capacitance derivation.
19 Jun 2011
TL;DR: In this paper, a new rectifier, referred to as a geometric diode, was proposed, which consists of a conducting thin-film, such as graphene, patterned in a geometry that leads to diode behavior.
Abstract: A solar cell using micro-antennas to convert radiation to alternating current and ultrahigh-speed diodes to rectify the AC can in principle provide extremely high conversion efficiencies. Currently investigated rectennas using metal/insulator/metal (MIM) diodes are limited in their RC response time and have poor impedance matching to the antenna. We have investigated a new rectifier, referred to as a geometric diode, which can overcome these limitations. The geometric diode consists of a conducting thin-film, such as graphene, patterned in a geometry that leads to diode behavior. We have experimentally demonstrated geometric diodes made from graphene and simulated their characteristics using the Drude model for charge transport. Here we compare the characteristics of rectennas using MIM diodes with those based on geometric diodes and show the improved performance of the latter.
TL;DR: In this article, a model for the gate capacitance was proposed to better understand the nature of the oscillations and showed that the oscillation are mostly due to the particular shape of the 1-D density of states.
Abstract: 3-D nonequilibrium Green's function simulations reveal the presence of oscillations of gate capacitance in multigate silicon nanowire FETs as the gate voltage is increased. These oscillations are due to the filling of successive energy subbands by electrons. The effect is due to both the 1-D distribution of the density of states and a change of position of the charge centroid location with gate voltage in the confined structure. This paper also proposes a model for the gate capacitance that allows one to better understand the nature of the oscillations and shows that the oscillations are mostly due to the particular shape of the 1-D density of states. The change of position of the charge centroid location contributes to a few percents in the total variation of the gate capacitance. The gate-capacitance to oxide-capacitance ratio remains low even at high gate voltages and worsens when the gate oxide thickness is decreased.
TL;DR: In this paper, the experimental gate capacitance (Cg) versus gate voltage data for InAs0.8Sb0.2 quantum-well MOSFETs was analyzed using a physics-based analytical model to obtain the quantum capacitance.
Abstract: Experimental gate capacitance (Cg) versus gate voltage data for InAs0.8Sb0.2 quantum-well MOSFET (QW-MOSFET) is analyzed using a physics-based analytical model to obtain the quantum capacitance (CQ) and centroid capacitance (Ccent). The nonparabolic electronic band structure of the InAs0.8Sb0.2 QW is incorporated in the model. The effective mass extracted from Shubnikov-de Haas magnetotransport measurements is in excellent agreement with that extracted from capacitance measurements. Our analysis confirms that in the operational range of InAs0.8Sb0.2 QW-MOSFETs, quantization and nonparabolicity in the QW enhance CQ and Ccent. Our quantitative model also provides an accurate estimate of the various contributing factors toward Cg scaling in future arsenide-antimonide MOSFETs.
TL;DR: In this paper, the conversion efficiency of field effect transistors with even-odd symmetry is elucidated, and it is shown that even symmetry, due to electronhole symmetry in graphene, affords efficient even-harmonic multiplication.
Abstract: The conversion efficiency of field-effect transistors with even-odd symmetry is elucidated in this work. From symmetry considerations, this work reveals that even symmetry, due to electron-hole symmetry in graphene, affords efficient even-harmonic multiplication. Odd symmetry, associated with linear charge transport, affords suppression of odd-harmonic signals. For the ideal symmetric transistor multiplier, conversion efficiency with relatively large power gain is achievable, while for practical graphene transistors, the efficiency can be substantially less than unity due to non-idealities such as contact resistance, high impurity densities, and low gate capacitance. In the quantum capacitance limit of graphene transistor, near-lossless conversion efficiency is available.
TL;DR: In this article, an analytical model of intrinsic carbon-nanotube field effect transistors is presented, where the origins of the channel carriers are analyzed in the ballistic limit and a noniterative surface-potential model is developed based on an analytical electrostatic model and a piecewise constant quantum-capacitance model.
Abstract: In this paper, an analytical model of intrinsic carbon-nanotube field-effect transistors is presented. The origins of the channel carriers are analyzed in the ballistic limit. A noniterative surface-potential model is developed based on an analytical electrostatic model and a piecewise constant quantum-capacitance model. The model is computationally efficient with no iteration or numerical integration involved, thus facilitating fast circuit simulation and system optimization. Essential physics such as drain-induced barrier lowering and quantum capacitance are captured with reasonable accuracy.
TL;DR: In this article, the intrinsic effects of the band-gap opening on ballistic electron transport in graphene nanoribbons and bilayer graphenes were studied based on a computational approach, and the ultimate device performances of FETs with those semiconducting graphene channels were discussed.
Abstract: Although a graphene is a zero-gap semiconductor, band-gap energy values up to several hundred millielectronvolts have been introduced by utilizing quantum-mechanical confinement in nanoribbon structures or symmetry breaking between two carbon layers in bilayer graphenes (BLGs). However, the opening of a band gap causes a significant reduction in carrier velocity due to the modulation of band structures in their low-energy spectra. In this paper, we study intrinsic effects of the band-gap opening on ballistic electron transport in graphene nanoribbons (GNRs) and BLGs based on a computational approach, and discuss the ultimate device performances of FETs with those semiconducting graphene channels. We have shown that an increase in the external electric field in BLG-FETs to obtain a larger band-gap energy degrades substantially its electrical characteristics because of deacceleration of electrons due to a Mexican hat structure; therefore, GNR-FETs outperform in principle BLG-FETs.
TL;DR: Graphene nanoribbons can serve as all-electronic ultra-high frequency oscillators and filters, thereby extending the reach of high frequency electronics into new domains.
Abstract: Here we investigate high frequency AC transport through narrow graphene nanoribbons with top-gate potentials that form a localized quantum dot. We show that as a consequence of the finite dwell time of an electron inside the quantum dot (QD), the QD behaves like a classical inductor at sufficiently high frequencies ω ≥ GHz. When the geometric capacitance of the top-gate and the quantum capacitance of the nanoribbon are accounted for, the admittance of the device behaves like a classical serial RLC circuit with resonant frequencies ω ∼ 100-900 GHz and Q-factors greater than 10(6). These results indicate that graphene nanoribbons can serve as all-electronic ultra-high frequency oscillators and filters, thereby extending the reach of high frequency electronics into new domains.
TL;DR: In this paper, the authors developed a theory for the compressibility and quantum capacitance of disordered monolayer and bilayer graphene, including the full hyperbolic band structure and band gap in the latter case.
Abstract: We develop a theory for the compressibility and quantum capacitance of disordered monolayer and bilayer graphene, including the full hyperbolic band structure and band gap in the latter case. We include the effects of disorder in our theory, which are of particular importance at the carrier densities near the Dirac point. We account for this disorder statistically using two different averaging procedures: first via averaging over the density of carriers directly, and then via averaging in the density of states to produce an effective density of carriers. We also compare the results of these two models with experimental data, and to do this we introduce a model for interlayer screening which predicts the size of the band gap between the low-energy conduction and valence bands for arbitrary gate potentials applied to both layers of bilayer graphene. We find that both models for disorder give qualitatively correct results for gapless systems, but when there is a band gap in the low-energy band structure, the density of states averaging is incorrect and disagrees with the experimental data.
Posted Content•
TL;DR: In this paper, the authors developed a simple model that captures the Fermi energy and temperature dependence of the quantum capacitance for monolayer and bilayer graphene devices, which is calculated from the broadened density of states taking into account electron-hole puddles and possible finite lifetime of electronic states through a Gaussian broadening distribution.
Abstract: Graphene nanostructures exhibit an intrinsic advantage in relation to the gate delay in three-terminal devices and provide additional benefits when operate in the quantum capacitance limit. In this paper, we developed a simple model that captures the Fermi energy and temperature dependence of the quantum capacitance for monolayer and bilayer graphene devices. Quantum capacitance is calculated from the broadened density of states taking into account electron-hole puddles and possible finite lifetime of electronic states through a Gaussian broadening distribution. The obtained results are in agreement with many features recently observed in quantum capacitance measurements on both gated monolayer and bilayer graphene devices. The temperature dependence of the minimum quantum capacitance around the charge neutrality point is also investigated.
TL;DR: This research promotes the measured precision limit of graphene-based nano-transducers by reducing quantum noises through squeezed states by proposing a scheme to obtain squeezed states through graphene nanoelectromechanical system (NEMS) taking advantage of their thin thickness in principle.
Abstract: Quantum squeezing can improve the ultimate measurement precision by squeezing one desired fluctuation of the two physical quantities in Heisenberg relation. We propose a scheme to obtain squeezed states through graphene nanoelectromechanical system (NEMS) taking advantage of their thin thickness in principle. Two key criteria of achieving squeezing states, zero-point displacement uncertainty and squeezing factor of strained multilayer graphene NEMS, are studied. Our research promotes the measured precision limit of graphene-based nano-transducers by reducing quantum noises through squeezed states.
Patent•
IBM1
TL;DR: In this article, a plate varactor includes a dielectric substrate and a first electrode embedded in a surface of the substrate, and a layer of graphene is formed over the sheet to contribute a quantum capacitance component.
Abstract: A plate varactor includes a dielectric substrate and a first electrode embedded in a surface of the substrate. A capacitor dielectric layer is disposed over the first electrode, and a layer of graphene is formed over the dielectric layer to contribute a quantum capacitance component to the dielectric layer. An upper electrode is formed on the layer of graphene. Other embodiments and methods for fabrication are also included.
01 Jan 2011
TL;DR: In this article, the relationship between various views (behavioral, structural, and physical) of a system, at different levels of abstraction, from high-level, architecture and circuits, to low-level devices and materials is explored.
Abstract: The Y-chart is a powerful tool for understanding the relationship between various views (behavioral, structural, and physical) of a system, at different levels of abstraction, from high-level, architecture and circuits, to low-level, devices and materials. We thus use the Y-chart adapted for graphene to guide the chapter and explore the relationship among the various views and levels of abstraction. We start with the innermost level, namely, the structural and chemical view. The edge chemistry of patterned graphene nanoribbons (GNRs) lies intermediate between graphene and benzene, and the corresponding strain lifts the degeneracy that otherwise promotes metallicity in bulk graphene. At the same time, roughness at the edges washes out chiral signatures, making the nanoribbon width the principal arbiter of metallicity. The width-dependent conductivity allows the design of a monolithically patterned Wide–Narrow–Wide (WNW) all graphene interconnect-channel heterostructure. In a three-terminal incarnation, this geometry exhibits superior electrostatics, a correspondingly benign short-channel effect and a reduction in the contact Schottky barrier through covalent bonding. However, the small bandgaps make the devices transparent to band-to-band tunneling. Increasing the gap with width confinement (or other ways to break the sublattice symmetry) is projected to reduce the mobility even for very pure samples, through a fundamental asymptotic constraint on the bandstructure. An analogous trade-off, ultimately between error rate (reliability) and delay (switching speed) can be projected to persist for all graphitic derivatives. Proceeding thus to a higher level, a compact model is presented to capture the complex nanoribbon circuits, culminating in inverter characteristics, design metrics, and layout diagrams.
01 Oct 2011
TL;DR: In this paper, a wireless sensor concept based upon the quantum capacitance effect in graphene is described by utilizing thin gate dielectrics (EOT < 2 nm).
Abstract: A wireless sensor concept based upon the quantum capacitance effect in graphene is described By utilizing thin gate dielectrics (EOT < 2 nm), the capacitance in a metal-insulator-graphene structure varies with charge concentration through the quantum capacitance effect The high capacitance per unit area allows orders of magnitude improvement in scalability compared to MEMS-based sensors, while the high mobility in graphene allows high quality factors, Q, to be obtained When operated away from the Dirac point, simulations using realistic structural and transport parameters predict capacitance tuning ratios of > 4 and Q values > 30 at 1 GHz When operated at the Dirac point, the capacitance shows a strong temperature sensitivity, suggesting potential applications as a wireless temperature sensor
TL;DR: In this paper, the authors focus on the properties of single-layer graphene and their properties that are relevant to chemical and biological applications, and discuss their charge transport, controlled by electrochemical gates, interfacial and quantum capacitance, charged impurities, and surface potential distribution.
Abstract: 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.
27 Dec 2011
TL;DR: In this paper, a realistic inter-CNT electrostatic coupling capacitance and tunneling conductance model for a unit bundle containing one SWCNT and one MWCNT is presented.
Abstract: The change of potential across a CNT in a bundle necessitates the need to consider the inter-CNT coupling capacitance in the equivalent circuit of CNT interconnects for VLSI circuits. This paper presents a realistic inter-CNT electrostatic coupling capacitance and tunneling conductance model for this bundle and studied its effects in detail. The equivalent transmission line circuit model of a unit bundle containing one SWCNT and one MWCNT has been shown. This new model is then used to calculate the delay induced by the inter-CNT capacitance and tunneling conductance, which predicts the relative positioning of MW/SWCNTs in mixed CNT bundle.