In-plane impedancemetric ammonia sensing of solution-deposited, highly semiconductor-enriched single-wall carbon nanotube submonolayer network gas sensors

We present the impedancemetric operation of ammonia gas sensors based on drop-deposited, 99% semiconductor-enriched single-walled carbon nanotube networks. Impedance spectroscopic data for these devices exhibit a complex impedance over a range of frequencies (0.5 Hz to 300 kHz) and are well fit with a proposed equivalent electrical circuit model. The effect of NH₃ on the high-frequency arc resistance is described by a linear law at all NH₃ concentrations, indicating the possibility of utilizing the impedance spectra as the main sensing signal. The impedancemetric operation mode demonstrates a sensitivity of 3.70%/ppm at 3.6-41.4 NH₃ concentration, which is equivalent to an improvement in sensitivity of 2.1 times compared to conventional direct current (dc) measurement. Furthermore, impedancemetric sensing is much less susceptible than conventional dc to noise problems in the very low frequency or dc due to ionic contamination or dissociated NH₃ molecules.