Defects and gas sensing properties of carbon nanotube-based devices

In this work we report on the development of back-gated carbon nanotube-field effect transistors (CNT-FETs), with CNT layers playing the role of the channel, and on their electrical characterisation for sensing applications. The CNTs have been deposited by electrophoresis on an interdigitated electrode region created on a SiO2/Si substrate. Different kinds of CNTs have been used (MWCNTs by arc discharge in liquid nitrogen and MWCNTs by chemical vapour deposition, CVD) and the electrical characterisation of the devices was performed in a NH3and NO2-controlled environment. Preliminary data have shown an increase in the channel resistance under NH3 exposure, whereas a decrease is observed after exposure to NO2, and the sensitivity to each gas depends on the kind of CNTs used for the device. Furthermore, the defect formation by Si ion implantation on CNTs was investigated by high-resolution transmission electron microscopy (TEM) and Raman analysis. The behaviour observed for the different devices can be explained in terms of the interaction between structural or chemical defects in CNTs and the gas molecules.