Effects of oxygen annealing on cross sensitivity of carbon nanotubes thin films for gas sensing applications

The H2O and NH3 cross sensitivity to NO2 gas of carbon nanotubes (CNTs) thin films have been evaluated in view of their different preparation conditions. Carbon nanotubes have been deposited by plasma enhanced chemical vapor deposition onto Si3N4/Si substrates provided with Pt electrodes. Effects of air oxidative treatment show that semiconducting nanotubes can be converted into metal CNTs through oxidizing procedure. The cross sensitivity from metallic oxidized CNTs sensitively depends on the annealing process. In particular a significant cross sensitivity has been found by exposing the as deposited (AS) CNTs thin films to H2O and NH3 gases while less pronounced H2O and NH3 cross sensitivity to NO2 has resulted for the oxidized CNTs. Our results suggest that carbon nanotubes can survive selectively during the oxidative annealing process indicating that intrinsic properties measured on as prepared nanotubes depend on annealing purification process of carbon nanotubes.