Sensitivity to NO2 and cross-sensitivity analysis to NH3, ethanol and humidity of carbon nanotubes thin film prepared by PECVD

The NH3, H2O, and C2H5OH cross-sensitivities to the NO2 electrical response of carbon nanotubes (CNTs) thin films for gas sensing applications is reported. CNTs have been deposited by plasma enhanced chemical vapor deposition (PECVD) on Si3N4/Si substrates provided with Pt electrodes. Microstructural features as determined by SEM, TEM (electronic scanning and transmission microscopy) and Raman spectroscopy have highlighted the growth of well developed tubular carbon structures of 30-40 nm diameter and 100-200 nm length. CNTs have shown a p-type response with decrease in resistance upon exposure to NO2 gas (10-100 ppb) and the highest sensitivity at 165 degreesC working temperature. The NO,) gas sensitivity has resulted to be improved by annealing the as-grown films at temperatures higher than 330degrees. No response has been found by exposing the films to CO and CH4 in the working temperature range 25-250 degreesC. An amount of 500 ppm of NH3 and ethanol, as well as 80% relative humidity (RH), have resulted to increase the electrical resistance of the films. Cross-sensitivity test have highlighted strong interference of ethanol and ammonia gases to the NO2 response, while negligible cross-sensitivity effects have been found with humidity at 80 RH. The reproducibility of the electrical response to NO2 is also reported. (C) 2003 Elsevier B.V. All rights reserved.