Transmission Line Impedance of Carbon Nanotube Thin Films for Chemical Sensing

TL;DR

This study investigates the impedance characteristics of carbon nanotube thin films used in chemical sensing, revealing that resistance changes significantly with analyte pressure while capacitance remains unaffected by gate bias or chemical adsorption.

Contribution

It models CNT films as RC transmission lines and demonstrates that resistance, not capacitance, is the key parameter affected by chemical analytes.

Findings

Resistance is highly sensitive to low-pressure analyte exposure.

Capacitance remains constant regardless of gate bias or chemical adsorption.

CNT film acts as an RC transmission line with impedance changes driven by resistivity.

Abstract

We measure the resistance and frequency-dependent gate capacitance of carbon nanotube (CNT) thin films in ambient, vacuum, and under low-pressure (10E-6 torr) analyte environments. We model the CNT film as an RC transmission line and show that changes in the measured capacitance as a function of gate bias and analyte pressure are consistent with changes in the transmission line impedance due to changes in the CNT film resistivity alone; the electrostatic gate capacitance of the CNT film does not depend on gate voltage or chemical analyte adsorption. However, the CNT film resistance is enormously sensitive to low pressure analyte exposure.