Mechanism of NO2 detection in carbon nanotube field effect transistor chemical sensors

We report an experimental method that clearly determines the sensing mechanism of carbon-nanotube field effect transistors. The nanotube/electrode contacts are covered with a thick and long passivation layer that hinders their exposure to chemicals in a controlled fashion, leaving only the midsection of the nanotube exposed. In the case of nitrogen dioxide, a considerably delayed response is fully consistent with the diffusion of the gas through the passivation layer. The results clearly indicate that nitrogen dioxide detection is due to changes at the interfaces between the nanotube and the electrodes and not to molecules adsorbed on the nanotube surface.