Negative Quantum Capacitance of Carbon Nanotube Field-Effect Transistors

TL;DR

This study uses atomistic DFT calculations to explore quantum capacitance in carbon nanotube FETs, revealing negative quantum capacitance effects due to exchange interactions, which influence screening properties.

Contribution

It demonstrates the occurrence of negative quantum capacitance in CNTs and highlights the role of exchange contributions beyond the density of states.

Findings

Negative quantum capacitance observed at low electron densities.

Quantum capacitance can enhance or limit screening in CNTs.

Exchange interactions dominate the quantum capacitance behavior.

Abstract

Atomistic density functional theory (DFT) calculations of the capacitance between a metallic cylindric gate and a carbon nanotube (CNT) are reported. Results stressing the predominant effect of quantum capacitance in limiting or even enhancing screening properties of the CNT are shown. Other contributions to the quantum capacitance beyond the electronic density of state (DOS) are pointed out. Negative values of the quantum capacitance are obtained for low-density systems, which correspondingly over-screen the gate field. This unconventional behavior of the quantum capacitance is related to the predominance of the exchange contribution in the total electronic energy of the CNT.