Gas sensing with carbon nanotube networks

Abstract

Carbon nanotubes are an exciting new material with exemplary mechanical and electronic properties. Carbon nanotubes can be either metallic or semiconducting; either type has properties which rival conventional materials. The one-dimensional electronic nature of these materials leads to extreme sensitivity to the local energy landscape, a desirable property for a sensing element. Production of carbon nanotubes currently has no method of growing nanotubes with a speci c electronic property, any di erentiation occurs through processing a heterogenous ensemble. Recently, networks of carbon nanotubes have shown attractive properties for electronic applications. The self-selecting current path has properties averaged from the ensemble of nanotubes providing repeatability in addition to exibility and transparency. This thesis is a study of the transport properties of thin and thick networks of single-walled carbon nanotubes and their electrical response to oxygen adsorption in both a simple resistive geometry and as the gate layer in a nanotube-metal-oxide-silicon capacitor. The thickness of network was found to determine the electrical characteristics of the network ensemble, thin networks displaying semiconducting transport characteristics, thick networks becoming more metallic. The response of the nanotube networks to oxygen exposure was found to be dependent on UV treatment. UV-desorbed networks exhibited an increased conductance upon oxygen-exposure, adsorbed networks exhibited a decrease in conductance upon further oxygen-exposure. Thinner, more semiconducting nanotube networks exhibited a greater change in conductance upon oxygen exposure. The nanotube-metal-oxide-semiconductor capacitor also showed a greater change in at-band capacitance for thin nanotube networks. The capacitance of the nanotube device at the nanotube network at-band voltage is shown to be in uenced by both oxygen and nitrogen gases. The origin of the behaviour of the at-band voltage is attempted to be understood and future work is suggested. 4