Quantum capacitance

About: Quantum capacitance is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 24165 citations.

Trade-off between quantum capacitance and thermodynamic stability of defected graphene: an implication for supercapacitor electrodes

Abstract: Defects are inevitable most of the times either at the synthesis, handling or processing stage of graphene, causes significant deviation of properties. The present work discusses the influence of vacancy defects on the quantum capacitance as well as thermodynamic stability of graphene, and the nitrogen doping pattern needs to be followed to attain a trade-off between these two. Density Functional Theory (DFT) calculations have been performed to analyze various vacancy defects and different possible nitrogen doping patterns at the vacancy site of graphene, with an implication for supercapacitor electrodes. The results signify that vacancy defect improves the quantum capacitance of graphene at the cost of thermodynamic stability, while the nitrogen functionalization at the vacancy improves thermodynamic stability and quantum capacitance both. It has been observed that functionalizing all the dangling carbons at the defect site with nitrogen is the key to attain high thermodynamic stability as well as quantum capacitance. Furthermore, the results signify the suitability of these functionalized graphenes for anode electrode of high energy density asymmetric supercapacitors.

Shedding Light on Pseudocapacitive Active Edges of Single-Layer Graphene Nanoribbons as High-Capacitance Supercapacitors

Abstract: In the field of energy storage by high-rate supercapacitors, there has been an upper limit for the total interfacial capacitance of carbon-based materials. This upper limit originates from both quantum and electric double-layer capacitances. Surpassing this limit has been the focus of intense research in this field. Here, we precisely investigate the effect of chemical functional groups and physical confinement on the electrochemical performance of graphene nanoribbons. We present the results of a quasi-one-dimensional single-layer graphene nanoribbon (120 nm in width and ∼100 μm in length) microelectrode fabricated by mechanical exfoliation of graphite, followed by electron beam lithography process and oxygen plasma etching treatment. We directly measure the interfacial capacitance as a function of frequency at different potentials in an aqueous electrolyte using a three-electrode electrochemical system. Electrochemical impedance spectroscopy and cyclic voltammetry tests show an average capacitance of 75...

Band tail interface states and quantum capacitance in a monolayer molybdenum disulfide field-effect-transistor

Abstract: Although MoS2 field-effect transistors (FETs) with high-k dielectrics are promising for electron device applications, the underlying physical origin of interface degradation remains largely unexplored. Here, we present a systematic analysis of the energy distribution of the interface state density (Dit) and the quantum capacitance (CQ) in a dual-gate monolayer exfoliated MoS2 FET. The CQ analysis enabled us to construct a Dit extraction method as a function of EF. A band tail distribution of Dit with the lowest value of 8*1011 cm-2eV-1 suggests that Dit is not directly related to the sharp peak energy distribution of the S vacancy. Therefore, the Mo-S bond bending related to the strain at the interface or the surface roughness of the SiO2/Si substrate might be the origin. It is also shown that ultra-thin 2D materials are more sensitive to interface disorder due to the reduced density of states. Since all the constituents for the measured capacitance are well understood, I-V characteristics can be reproduced by utilizing the drift current model. As a result, one of the physical origins of the metal/insulator transition is suggested to be the external outcome of interface traps and quantum capacitance.

Quantum C-V modeling in depletion and inversion: accurate extraction of electrical thickness of gate oxide in deep submicron MOSFETs

Abstract: Presented in this paper is a quantum capacitance-voltage (C-V) modeling in depletion and inversion, incorporating the gate-depletion effect. The model enables fast and accurate extraction of the electrical thickness of gate oxide in deep submicron MOSFETs. The main quantum effect consists of the inversion capacitance of two-dimensional (2-D) electrons masking the true gate-oxide thickness, t/sub OX/. The quantum mechanical and gate depletion effects necessitate 6-10 /spl Aring/ equivalent oxide thickness correction, which is important for a t/sub OX/ of 4 nm or less. The classical C-V analysis is compared with the quantum results in the light of the data, highlighting the difference between the models. The model is shown in good agreement with experiments and also with numerically calculated results.

Probing Defect-Induced Midgap States in MoS2 Through Graphene–MoS2 Heterostructures

Abstract: Crystalline defects in MoS2 may induce midgap states, resulting in low carrier mobility. These midgap states are usually difficult to probe by conventional transport measurement. The quantum capacitance of single-layer graphene is sensitive to defect-induced states near the Dirac point, at which the density of states is extremely low. It is reported that the hexagonal-boron nitride/graphene/MoS2 sandwich structure facilitates the exploration of the properties of those midgap states in MoS2. Comparative results of the quantum capacitance of pristine graphene indicate the presence of several midgap states with distinct features. Some of these states donate electrons while some states lead to localization of electrons. It is believed that these midgap states originate from intrinsic point defects such as sulfur vacancies, which have a significant impact on the property of the MoS2/graphene interface. They are responsible for the contact problems of metal/MoS­2 interfaces.