Trace level ammonia sensing by SWCNTs (network/film) based resistive sensor using a simple approach in sensor development and design

Highly stable and sensitive detection of trace level (approximately 1 ppm) of NH3 gas at room temperature is demonstrated for single wall carbon nanotube (SWCNT)-based resistive sensor. The sensor device was comprised of two planer Au electrodes deposited on carbon nanotubes (CNTs) by thermal evaporation method followed by patterning with photolithography process. For the growth of high-quality SWCNTs, multiple catalysts were deposited by co-sputtering method, and the yielded CNTs were in the diameter range of 0.8 to 1.5 nm. The CNTs were characterized by various techniques including Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. As-grown SWCNTs-based resistive sensor showed an excellent variation in sensor response in the trace sensing range from 1 to 50 ppm of NH3 where the sensor response linearly increased with NH3 concentration. The sensing mechanism was attributed to the electron transfer to the SWCNTs as a result of NH3 oxidation on the nanotube surface. The sensor was found to have good sensitivity with a response time of a few minutes at room temperature. Sensor recovery posed a great problem at room temperature, and the fast and complete recovery was successfully achieved by using appropriate thermal treatment protocol.