Carbon nanotubes gas sensors: current status and future prospects

CNT thin film sensors have been prepared by PECVD techniques on Si/Si₃N₄ micromachined substrates. The role of the preparation conditions on the intrinsic electrical properties of the CNTs (i.e. metallic or semiconductor nature) the role of the structural defects on the CNT gas response (i.e. sensitivity, selectivity and stability) the interaction mechanisms of oxidizing and reducing molecules with the CNT surface (i.e physisorption or chemisorption), are analysed and discussed by means of experimental measurements (microstructural and electrical characterizations) and theoretical simulations (density functional calculations). CNT films demonstrated their fitness for oxidizing gases monitoring (NO₂ and O₃), had good selectivity when water vapor and reducing gases are the interfering species, and good stability. Surface modifications and hybrid CNT structures are presented as possible routes to improve gas response.