Showing papers on "Quantum capacitance published in 2020"
01 Aug 2020
TL;DR: In this article, a ferroelectric tunnel junction that uses layered copper indium thiophosphate (CuInP2S6) as the barrier, and graphene and chromium as asymmetric contacts is reported.
Abstract: Ferroelectric tunnel junctions use a thin ferroelectric layer as a tunnelling barrier, the height of which can be modified by switching its ferroelectric polarization. The junctions can offer low power consumption, non-volatile switching and non-destructive readout, and thus are promising for the development of memory and computing applications. However, achieving a high tunnelling electroresistance (TER) in these devices remains challenging. Typical junctions, such as those based on barium titanate or hafnium dioxide, are limited by their small barrier height modulation of around 0.1 eV. Here, we report a ferroelectric tunnel junction that uses layered copper indium thiophosphate (CuInP2S6) as the ferroelectric barrier, and graphene and chromium as asymmetric contacts. The ferroelectric field effect in CuInP2S6 can induce a barrier height modulation of 1 eV in the junction, which results in a TER of above 107. This modulation, which is shown using Kelvin probe force microscopy and Raman spectroscopy, is due to the low density of states and small quantum capacitance near the Dirac point of the semi-metallic graphene. A ferroelectric tunnel junction that uses copper indium thiophosphate as the ferroelectric barrier, and graphene and chromium as asymmetric contacts, can offer a high resistance ratio between on and off states.
117 citations
TL;DR: In this paper, a comparative supercapacitor performance of the transition metal (Co, Ni and Mn) diselenides nanostructures assembled in a symmetric electrode configuration was investigated.
47 citations
TL;DR: The lesser diffusion energy barrier for K+ ions of the K2SO4 electrolyte in the NiCo2O4 layer contributes toward higher energy storage capacity, and can serve as a high-performance electrode material for supercapacitor applications.
Abstract: In this work, we demonstrated the supercapacitor performance of pristine and composites of spinel NiCo2O4 with a multi-walled carbon nanotube (MWCNT) assembled in a two-electrode cell configuration. Spinel NiCo2O4 and NiCo2O4@MWCNT composites were synthesized via a facile hydrothermal method. The supercapacitive performance of as-synthesized NiCo2O4 and NiCo2O4@MWCNT fabricated on Ni-foam was studied in a 0.5M K2SO4 electrolyte using electrochemical measurement techniques. The symmetric cell configuration of NiCo2O4@MWCNT delivers high specific capacitance (374 F/g at 2 A/g) with high energy density and power density (95 Wh/kg and 3 964 W/kg, respectively) compared to that of pristine NiCo2O4 electrodes (137 F/g at 0.6 A/g). Furthermore, the energy storage performance of the asymmetric cells of NiCo2O4//MWCNT and NiCo2O4@MWCNT//MWCNT was studied to enhance cycling stability (retention of 74.85% over 3000 cycles). We have also theoretically studied the supercapacitance performance of pristine NiCo2O4 and NiCo2O4@SWCNT hybrid structures through its structural and electronic properties using density functional theory predictions. The higher specific capacitance of the NiCo2O4@SWCNT hybrid system with high power density and energy density is supported by the enhanced density of states near the Fermi level and increased quantum capacitance of the hybrid structure. We have theoretically computed the diffusion energy barrier of K+ ions of the K2SO4 electrolyte in the NiCo2O4 layer and compared it with the diffusion barrier for Na+ ions. The lesser diffusion energy barrier for K+ ions in the NiCo2O4 layer contributes toward higher energy storage capacity. Thus, owing to superior electrochemical performance of NiCo2O4 composites with MWCNTs, it can serve as a high-performance electrode material for supercapacitor applications.
45 citations
TL;DR: In this paper, the effect of co-dopants (N, P, and S) and transition metals (TMs) presence in mono-and multilayer graphene was systematically investigated using density functional theory (DFT) calculations.
44 citations
TL;DR: In this article, an outer-sphere nonadiabatic electron transfer reaction at the defective graphene was theoretically investigated, where the band structure from DFT, in combination with the Gerischer model, was used for the predictions.
38 citations
TL;DR: In this paper, the authors demonstrate the rational design and synthesis of ion/electron dual-conductive carbon nanoflowers assembled by N,S co-doped two-dimensional mesoporous nanosheets.
38 citations
TL;DR: In this paper, the authors proposed a compact model for nanosheet FETs that takes the effects of quantum confinement into account, and implemented it using Verilog-A in the BSIM-CMG framework for all simulations.
Abstract: We propose a compact model for nanosheet FETs that take the effects of quantum confinement into account. The model captures the nanosheet width and thickness dependence of the electrostatic dimension, density of states, effective mass, subband energies, and threshold voltages and includes them in the charge calculation, resulting in an accurate terminal charge and current characteristics. The model has been implemented using Verilog-A in the BSIM-CMG framework for all simulations. It has been validated with band-structure calculation-based TCAD simulations as well as measured data. We have also highlighted the significance of quantum mechanical effects on analog and RF performance of the device.
36 citations
TL;DR: There are enhanced density of states near the Fermi level and higher quantum capacitance for the hybrid ternary structure compared to VSe2 /SWCNTs, leading to higher energy and power density for VSe 2 /SW CNTs/rGO, supporting the experimental observation.
Abstract: In this work, the ternary hybrid structure VSe2 /SWCNTs/rGO is reported for supercapacitor applications. The ternary composite exhibits a high specific capacitance of 450 F g-1 in a symmetric cell configuration, with maximum energy density of 131.4 Wh kg-1 and power density of 27.49 kW kg-1 . The ternary hybrid also shows a cyclic stability of 91 % after 5000 cycles. Extensive density functional theory (DFT) simulations on the structure as well as on the electronic properties of the binary hybrid structure VSe2 /SWCNTs and the ternary hybrid structure VSe2 /SWCNTs/rGO have been carried out. Due to a synergic effect, there are enhanced density of states near the Fermi level and higher quantum capacitance for the hybrid ternary structure compared to VSe2 /SWCNTs, leading to higher energy and power density for VSe2 /SWCNTs/rGO, supporting our experimental observation. Computed diffusion energy barrier of electrolyte ions (K+ ) predicts that ions move faster in the ternary structure, providing higher charge storage performance.
35 citations
TL;DR: In this article, the structural, energetic, electronic and capacitance properties of B/N-doped graphdiyne were investigated by first-principles calculations, and the quantum capacitance of 2D carbon electrodes with different doping concentrations was shown to reach a record high value of 4317F/g (6150 F/g).
34 citations
TL;DR: The electrostatics of two graphene layers are investigated, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K′ points of the two layers, and the large observed value of Cm is explained by considering the finite dielectric thickness dg of each graphene layer.
Abstract: When two dimensional crystals are atomically close, their finite thickness becomes relevant. Using transport measurements, we investigate the electrostatics of two graphene layers, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K′ points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance Cm and is therefore suited to extract Cm. We explain the large observed value of Cm by considering the finite dielectric thickness dg of each graphene layer and determine dg ≈ 2.6 A. In a second experiment, we map out the entire density range with a Fabry-Perot resonator. We can precisely measure the Fermi wavelength λ in each layer, showing that the layers are decoupled. Our findings are reproduced using tight-binding calculations.
33 citations
TL;DR: In this article, the authors demonstrate the synthesis, characterization and electrochemical application of hollow-like Mn3O4 nanostructures well-dispersed on graphene matrix (MnH/G) for energy conversion application towards oxygen reduction reaction (ORR) and energy storage towards supercapacitor.
TL;DR: In this paper, a flexible symmetric supercapacitor (SSC) based on exfoliated Molybdenum disulfide (MoS2) was proposed for energy storage.
Abstract: Molybdenum disulfide (MoS2) is one of the promising electrochemical energy storage materials among the recently explored 2D materials beyond the extensively studied graphene sheets. However, MoS2 in the form of quantum sheets (QSs) has not yet been examined for use in energy storage devices (batteries and supercapacitors). Here, we demonstrate the superior electrochemical charge-storage properties of exfoliated MoS2 QSs (with lateral size in the range of 5 to 10 nm) for the first time. A salt-assisted ball milling process was used to prepare MoS2 QSs in gram scale that leads to size confinement in both lateral and vertical orientations. The electrochemical analysis of MoS2 QSs indicated their superior capacitive properties compared to the bulk MoS2, which originates from the combination of quantum capacitance and electrochemical capacitance. The device specific properties of MoS2 QSs were studied by constructing a flexible symmetric supercapacitor (SSC) that demonstrated a high device capacitance (162 F g−1), energy density (14.4 Wh kg−1), good rate capability, and long cycle life. The energy storage performance metrics of MoS2 QSs based SSC device were superior compared to the state-of-art MoS2 based supercapacitors. Furthermore, a solar-driven wireless charging power system comprising the fabricated MoS2 QSs-based SSC as an energy storage device is illustrated in the view of expanding its utility towards practical applications.
TL;DR: It is found that an asymmetric supercapacitor assembled with different doped electrodes, i.e. an F doped negative electrode and an N doped positive electrode, is the best choice for a super capacitor since this combination results in better capacitance over the entire potential window.
Abstract: We report here density functional theory calculations and molecular dynamics atomistic simulations to determine the total capacitance of graphene-modified supercapacitors. The contributions of quantum capacitance to the total capacitance for boron-, sulfur-, and fluorine-doped graphene electrodes, as well as vacancy-modified electrodes, were examined. All the doped electrodes presented significant variations in quantum capacitance (ranging from 0 to ∼200 μF cm−2) due to changes in the electronic structure of pristine graphene. The graphene-modified supercapacitors show any appreciable effect on double-layer capacitance being virtually the same for all the devices investigated. The total differential capacitance was found to be limited by the quantum capacitance, and for all the systems, it is lower than the quantum capacitance over the entire voltage window. We found that the total capacitance can be optimized by considering an adequate modification to each electrode in the supercapacitor. In addition, we found that an asymmetric supercapacitor assembled with different doped electrodes, i.e. an F doped negative electrode and an N doped positive electrode, is the best choice for a supercapacitor since this combination results in better capacitance over the entire potential window.
25 Mar 2020
TL;DR: In this article, the authors employed a facile approach to synthesize a two-dimensional/three-dimensional (2D/3D) heterostructure of hexagonal boron nitride and reduced graphite oxide (h-BN/rGO).
TL;DR: In this paper, the hybrid structure of metallic VSe2 and multi-walled carbon nanotube (MWCNT) based hybrid materials for high performance energy storage and high power operation applications is reported.
Abstract: Herein, we report the hybrid structure of metallic VSe2 and multi-walled carbon nanotube (MWCNT) based hybrid materials for high performance energy storage and high power operation applications. The dominance of capacitive energy storage performance behaviour of VSe2/MWCNT hybrids is observed. A symmetric supercapacitor cell device fabricated using VSe2/80 mg MWCNT delivered a high energy density of 46.66 W h kg−1 and a maximum power density of 14.4 kW kg−1 with a stable cyclic operation of 87% after 5000 cycles in an aqueous electrolyte. Using density functional theory calculations we have presented structural and electronic properties of the hybrid VSe2/MWCNT structure. Enhanced states near the Fermi level and higher quantum capacitance for the hybrid structure contribute towards higher energy and power density for the nanotube/VSe2.
TL;DR: In this paper, the stability, electrical properties and quantum capacitance of Ti, Au, Ag, Cu, Al, B, N, and P doping pristine and single-vacancy VS MoS2 monolayer have been studied by using the first-principles methods.
Abstract: The stability, electrical properties and quantum capacitance of Ti, Au, Ag, Cu, Al, B, N, and P doping pristine and single-vacancy VS MoS2 monolayer have been studied by using the first-principles methods. These doped atoms form strong bonds with MoS2, and the optimized structures exhibit metallicity. MoS2 monolayer has a high double layer capacitance due to its high specific surface area. However, it has low quantum capacitance hindering its application in supercapacitors. This is attributed to the confinement of the electron density of states near Fermi level of pristine MoS2 monolayer. Our calculation of quantum capacitance confirms the advantage of Al substituting S atom in single-vacancy VS MoS2 systems, and it is suitable for symmetric supercapacitors. We also find that B substituting S atom in pristine MoS2 monolayer has a high quantum capacitance, and it is available as potential electrode materials for asymmetric supercapacitors. We demonstrate that the increase of quantum capacitance is due to the formation of local states near Fermi level and/or the shift of Fermi level caused by defects and doping.
TL;DR: In this article, the influence of doping (B, N, Al, Si, P, S), vacancy, and Stone-Wales defect on stability, electronic structures, quantum capacitance, and surface charge storage of graphene is explored by density functional theory calculations.
TL;DR: Graphene technology is paves the way towards the exploitation of graphene technology to become the core of active analogue phase shifters for high-frequency operation.
Abstract: We present a graphene-based phase shifter for radio-frequency (RF) phase-array applications. The core of the designed phase-shifting system consists of a graphene field-effect transistor (GFET) used in a common source amplifier configuration. The phase of the RF signal is controlled by exploiting the quantum capacitance of graphene and its dependence on the terminal transistor biases. In particular, by independently tuning the applied gate-to-source and drain-to-source biases, we observe that the phase of the signal, in the super-high frequency band, can be varied nearly 200° with a constant gain of 2.5 dB. Additionally, if only the gate bias is used as control signal, and the drain is biased linearly dependent on the former (i.e., in a completely analogue operation), a phase shift of 85° can be achieved making use of just one transistor and keeping a gain of 0 dB with a maximum variation of 1.3 dB. The latter design can be improved by applying a balanced branch-line configuration showing to be competitive against other state-of-the-art phase shifters. This work paves the way towards the exploitation of graphene technology to become the core of active analogue phase shifters for high-frequency operation.
TL;DR: In this paper, the authors demonstrate a 23-fold improvement in capacitance sensitivity by supplementing a cryogenic semiconductor amplifier with a SQUID preamplifier, which enables a record sensitivity to capacitance of 0.07 aF / Hz.
Abstract: 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.
TL;DR: In this article, the effect of iodine on graphene frameworks is explored towards supercapacitance properties and the influence of iodide on graphene via p-p hybridization towards enhancement of specific capacitance is presented with insights from quantum simulations.
Abstract: Herein, the effect of iodine on graphene frameworks is explored towards supercapacitance properties and the influence of iodine on graphene via p–p hybridization towards the enhancement of specific capacitance is presented with insights from quantum simulations. Here, we synthesized a reduced graphene oxide flexible film (RGO/FF) and reduced graphene oxide powder (RGO/P) by HI acid treatment and studied their electrochemical energy storage (supercapacitance) performance. The main feature of this study is that iodine remains in the graphene framework during the HI treatment and enhances the supercapacitance performance. The experimental characterizations and electro-chemical measurements reveal that the iodine remaining in the graphene framework contributes towards the pseudo-capacitance properties of reduced graphene oxide and enhances the supercapacitance performance. The specific capacitance increases from 73 F g−1 in graphene to 122 F g−1 in iodine-doped graphene films. RGO/P shows a higher capacitance value compared to RGO/FF due to the easy ion intercalation and the exposure of more surface area towards the access of charged species. We have performed state-of-the-art density functional theory (DFT) simulations to study the interactions and bonding mechanism of iodine on RGO surfaces and provide theoretical insights into the electronic properties for enhanced capacitance in iodine-doped RGO. Iodine is bonded to graphene with a favourable binding energy of −0.42 eV due to the interaction of the C 2p orbitals and I 5p orbitals. The enhancement in quantum capacitance due to iodine attachment justifies the enhancement in the specific capacitance of graphene.
TL;DR: Large optomechanical coupling of a suspended carbon nanotube quantum dot and a microwave cavity is demonstrated, amplified by several orders of magnitude via the nonlinearity of Coulomb blockade.
Abstract: Cavity optomechanics allows the characterization of a vibration mode, its cooling and quantum manipulation using electromagnetic fields. Regarding nanomechanical as well as electronic properties, single wall carbon nanotubes are a prototypical experimental system. At cryogenic temperatures, as high quality factor vibrational resonators, they display strong interaction between motion and single-electron tunneling. Here, we demonstrate large optomechanical coupling of a suspended carbon nanotube quantum dot and a microwave cavity, amplified by several orders of magnitude via the nonlinearity of Coulomb blockade. From an optomechanically induced transparency (OMIT) experiment, we obtain a single photon coupling of up to g0 = 2π ⋅ 95 Hz. This indicates that normal mode splitting and full optomechanical control of the carbon nanotube vibration in the quantum limit is reachable in the near future. Mechanical manipulation and characterization via the microwave field can be complemented by the manifold physics of quantum-confined single electron devices.
TL;DR: The bandgaps and sub-band structures of various channel materials could be demonstrated by the new conceptual spectroscopy at the device scale without debatable quasiparticle effects, and the band splits by the giant Stark effect in the channel Materials could be probed, overcoming the limitations of conventional optical, photoemission, and tunneling spectroscopic.
Abstract: Each atomic layer in van der Waals heterostructures possesses a distinct electronic band structure that can be manipulated for unique device operations. In the precise device architecture, the subtle but critical band splits by the giant Stark effect between atomic layers, varied by the momentum of electrons and external electric fields in device operation, has not yet been demonstrated or applied to design original devices with the full potential of atomically thin materials. Here, resonant tunneling spectroscopy based on the negligible quantum capacitance of 2D semiconductors in resonant tunneling transistors is reported. The bandgaps and sub-band structures of various channel materials could be demonstrated by the new conceptual spectroscopy at the device scale without debatable quasiparticle effects. Moreover, the band splits by the giant Stark effect in the channel materials could be probed, overcoming the limitations of conventional optical, photoemission, and tunneling spectroscopy. The resonant tunneling spectroscopy reveals essential and practical information for novel device applications.
TL;DR: In this paper, the quantum capacitance of pristine and defective XSi3 silicene-like structures calculated using first-principles computations was analyzed and it was shown that pristine xSi3 sheets have larger quantum capacitation values (cQ = 1500-2000 F/g) in comparison with pristine XSiene and graphene.
Abstract: Silicene and silicene-like structures have attracted scientists’ attention because of their novel physical and electronic properties. Recently, they have been studied theoretically as supercapacitor and Li-ion battery electrodes. In this research, the quantum capacitance of pristine and defective silicene and XSi3 silicene-like (X = Al, B, C, N, P) structures calculated using first-principles computations. Our results show that pristine XSi3 sheets have larger quantum capacitance values (cQ = 1500–2000 F/g) in comparison with pristine silicene (cQ = 1200 F/g) and graphene (cQ = 500 F/g). Our partial density of states (PDOS) analysis showed that the origin of large quantum capacitance of XSi3 silicene-like sheets are from 2p and/or 3p orbitals of X and Si atoms. Our data indicated that defects like single vacancy, double vacancy, and Stone−Wales (SW) have not a pronounced effect on quantum capacitance of XSi3 structures.
TL;DR: In this paper, the effect of in-plane uniaxial strain on the quantum capacitance of GNR-based devices is investigated utilizing a compact analytical model which accounts for several finite-size and edge effects.
TL;DR: Spectroscopy of discrete Landau levels (LLs) in bulk-insulating three-dimensional topological insulators in perpendicular magnetic field characterizes the Dirac nature of their surface sta... as discussed by the authors.
Abstract: Spectroscopy of discrete Landau levels (LLs) in bulk-insulating three-dimensional topological insulators (3D TIs) in perpendicular magnetic field characterizes the Dirac nature of their surface sta...
TL;DR: The Joint Density Functional Theory is applied in the context of Grand Canonical Kohn-Sham theory to calculate the global and local softness of pristine and N-substituted graphene structures and it is found that global chemical softness is proportional to the total capacitance measured in the experiments.
Abstract: The joint density functional theory (JDFT) is applied in the context of the grand canonical Kohn-Sham theory to calculate the global and local softness of pristine and N-substituted graphene structures. A comparison is established between the different theoretical approaches to evaluate total capacitance, revealing that the JDFT approach presents the closest result of this property with experimental data. A model of series capacitors is used to determine the quantum and nonquantum contributions of total capacitance, which enables us to determine the limitations of the rigid band approximation for the studied systems. It is found that global chemical softness is proportional to the total capacitance measured in the experiments, when the geometry relaxation is neglected. In this context, it is possible to obtain quantum and total capacitance (and consequently softness) from an average number of electrons vs applied potential plots and the model of series capacitors. Likewise, the relation of capacitance and softness gives rise to a new definition of local capacitance within the JDFT formalism. The evaluation of global and local softness paves the way to analyze electrochemical surface reactivity as a function of applied potential for a solid-electrolyte interface.
TL;DR: In this paper, a gate-defined few-electron quantum dot in bilayer graphene is used to read out individual charge states in a gate defined few electron quantum dot, where an LC resonator with a resonance frequency close to 280 MHz is directly coupled to an ohmic contact of the quantum dot device.
Abstract: We demonstrate dispersive readout of individual charge states in a gate-defined few-electron quantum dot in bilayer graphene. We employ a radio frequency reflectometry circuit, where an LC resonator with a resonance frequency close to 280 MHz is directly coupled to an ohmic contact of the quantum dot device. The detection scheme based on changes in the quantum capacitance operates over a wide gate-voltage range and allows to probe excited states down to the single-electron regime. Crucially, the presented sensing technique avoids the use of an additional, capacitively coupled quantum device such as a quantum point contact or single electron transistor, making dispersive sensing particularly interesting for gate-defined graphene quantum dots.
TL;DR: This work experimentally probe and model the electronic density of states (DOS) in thin layers of BiSbTeSe2 by capacitance experiments both without and in quantizing magnetic fields and shows that a large fraction of the electrons filled via field effect into the system ends up in (localized) bulk states and appears as a background DOS.
Abstract: BiSbTeSe2 is a 3D topological insulator (3D-TI) with Dirac type surface states and low bulk carrier density, as donors and acceptors compensate each other. Dominating low-temperature surface transport in this material is heralded by Shubnikov-de Haas oscillations and the quantum Hall effect. Here, we experimentally probe and model the electronic density of states (DOS) in thin layers of BiSbTeSe2 by capacitance experiments both without and in quantizing magnetic fields. By probing the lowest Landau levels, we show that a large fraction of the electrons filled via field effect into the system ends up in (localized) bulk states and appears as a background DOS. The surprisingly strong temperature dependence of such background DOS can be traced back to Coulomb interactions. Our results point at the coexistence and intimate coupling of Dirac surface states with a bulk many-body phase (a Coulomb glass) in 3D-TIs.