NO² gas sensitivity of carbon nanotubes obtained by plasma enhanced chemical vapor deposition

Carbon nanotubes (CNTs) thin films deposited by plasma enhanced chemical vapor deposition on Si/Si3N4 substrates provided with platinum interdigital electrodes have been investigated as resistive gas sensors towards NO, oxidizing gas. The electrical response has been measured exposing the films to sub-ppm NO2 concentrations (10-100 ppb in dry air) at different operating temperatures ranging between 25 and 215 degreesC. The response to NO2 has been found to be at maximum at around 165 degreesC. Upon exposure to NO2 the electrical resistance of randomly oriented CNTs is found to decrease. Gas sensitivity, response time and reproducibility of the electrical response resulted to be dependant from the preparation conditions and film thickness. The prepared films show fast dynamic of the electrical response and high reproducibility of the electrical properties. The resistance decrease of the CNTs when exposed to NO2 gas and the sensor response to concentrations as low as 10 ppb NO2, suggest the possibility to utilize CNTs as new sensors for air-quality monitoring