Complex impedance characterization of highly sensitive carbon nanotube gas sensors

Complex impedance spectroscopy is used to characterize carbon nanotube (CNT) based gas sensors under the exposure of different concentrations of NH₃ (10 ppm, 25 ppm, 50 ppm and 100 ppm). The characterization is performed in a frequency range between 20 Hz and 2 MHz. The frequency response of the CNT film showed high dependence on the film resistance. The variation in the normalized response of the sensor with the frequency might suggest a change in the sensing mechanism at certain frequencies. Moreover, we investigated the effect of different temperatures on the frequency response of the CNT film. Finally, the feasibility of obtaining selective CNT gas sensors based on the sensor recovery characteristics for three different gases (NH₃, CO and ethanol) is demonstrated.