Investigation of the NO_2 sensitivity properties of muItiwalled carbon nanotubes prepared by plasma enhanced chemical vapor deposition

摘要

In the present work, multiwalled carbon nanotube (MWNT) thin films deposited by plasma enhanced chemical vapor deposition have been investigated as resistive gas sensors towards NO_2. The sensor design is a platinum interdigitate electrode, fabricated by photolithography upon Si_3N_4 deposited on silicon, over which the MWNTs are deposited. Microstructural features as determined by scanning electron, transmission electron, and Raman spectroscopies have highlighted the growth of tubular carbon structures of 20―30 nm diameter and 150―200 nm length. Carbon nanotubes have shown a decreasing of their resistance upon exposure to NO_2 gas (10-100 ppb) and the highest sensitivity at 165 ℃ working temperature. The time evolution of the electrical resistance at 165 ℃ as the sample was cycled through 500 ppm of NH_3, 100 ppm of C_6H_6, water vapor, and 500 ppm of ethanol gases and dry air has been also reported. The variation of conductance in the presence of oxidizing or reducing gases is explained on the basis of charge transfer between the adsorbates and the nanotubes.