Quantum capacitance

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

Modeling and analysis of intrinsic gate capacitance for carbon nanotube array based devices considering variation in screening effect and diameter

Abstract: An accurate analytical model for intrinsic gate capacitance of carbon nanotube array based back-gated FET is proposed. The model accounts for electrostatic capacitive coupling between nanotubes as well as screening effect for any given number of nanotubes, their diameter, and pitch. Analysis using this model shows that as the number of nanotubes increases, although the overall electrostatic capacitance per nanotube decreases by up to 50%, the electrostatic capacitance becomes the dominant factor over the quantum capacitance. Furthermore, applicability of the proposed model in presence of practical fabrication process variations such as variation in diameter of carbon nanotubes is demonstrated using a probabilistic approach.

The Role of Modelling and Simulation in the Achievement of Next-Generation Electrochemical Capacitors

Abstract: Modelling and simulation have greatly assisted in the provision of expressions and guidelines to find the practical thickness of electrodes, optimum charging current and materials utilization in cells of specific practical conductivity of electrodes and electrolyte for new-generation electrochemical capacitors (ECs) or ultracapacitors. Improved performance of ultracapacitors is attainable due to guidelines obtained via modelling, because this will eliminate materials (electrodes) underutilization, increased inefficiencies and potential drops. Optimizing electrodes and electrolyte morphology experimentally is mainly through trial and error method, which is very strenuous due to numerous parameters and contesting processes required, thus modelling and simulation are inevitable. The dependence of ECs performance on electrode and electrolyte fabricating conditions, such as mass ratio of electrode, electrode type, materials reaction, potential window of electrolyte and capacitance, has been presented from modelling and simulation. This gives absolute comprehension of the effects of various operating conditions, constructional design parameters and self-discharge on device performance, which guides in obtaining optimal design and fabrication of new-generation ultracapacitors. Perfecting the knowledge of the effects of the electrodes and separator's structural parameters, electrolyte effective conductivities and the operation conditions is inevitable in design and fabrication of new-generation ultracapacitors. Modelling provides an overall framework which permits the different factors that affect the ultracapacitors performance and implementation of the EDL differential capacitance while considering capacitance that is dependent on either potential or concentration. MD simulation results have the capacity to give the blueprints for optimizing energy density within carbon-based electrodes at microscopic level through concurrent optimization of EDL capacitance and quantum capacitance. Determination of minimum impurity or redox species concentration and the optimum total thickness of separator and anode are achievable through modelling and simulation. A theoretical guideline using optimum electrodes and potential window ratios for design and fabrication of symmetric electric double layer capacitors (EDLCs) that operate as asymmetric capacitors has been acquired through modelling. Also, useful guidelines and requirements to determine the optimum electrodes and potential window ratios, proper organic electrolyte for optimal performance, and entire design and fabrication of electrochemical energy storage devices with enhanced energy and power with a reduction in device mass and volume via modelling were presented. These guidelines and requirements aid in production of asymmetric ultracapacitors with the optimum battery-type mass ratio, potential range ratio, maximum potential range ratio and ratio of capacitance of capacitor type. Density functional theory (DFT) calculations and other types of modelling play a vital role in the discovery, synthesis, optimization and fabrication of numerous new electrode and electrolyte materials, which can help in the new-generation electrochemical capacitors with improved performance. Modelling and simulation are therefore very crucial in making great progress in area of electrodes material synthesis, optimization and fabrication, electrolytes synthesis and optimizations, separators synthesis and fabrications. Subsequently, an optimized design of the new-generation ultracapacitors with enhanced performance will be achievable by employing the electrochemical capacitors’ blueprint obtained from improved electrodes, electrolytes and separators acquired via modelling and simulation.

Memory Behaviour and Distributed Capacitive Coupling Model for Low Frequency Inversion Capacitance of a Quantum Dot Flash Memory Gate Stack

Abstract: Initially, FGMOS gate stack is examined for satisfactory memory behaviour. Later, we present a simple analytical model for the low frequency capacitance of a quantum dot based flash memory gate stack. The model makes use of simple parallel combination of capacitances offered by differentiating regions formed in the gate stack of a flash memory. The model describes overall capacitance where dimensions, number of dots and inter-dot spacing do not affect the validity of the model. With this model, it is possible to develop expressions for static behaviour and dynamic charging of the memory device. The results are compared with the simulation outputs. There is a close matching.