Carbon Nanotubes and Graphene - Research and Applications

We investigate the impact of the tailored load of gold (Au) nanoclusters functionalizing the sidewalls of the carbon nanotubes (CNTs) networks on gas sensing performance of a chemiresistor, operating at a working temperature in the range of 20–250 °C. CNTs networked films have been grown by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) technology onto low-cost alumina substrate, provided with 6 nm nominally thick cobalt (Co) growth-catalyst. Nanoclusters of Au have been deposited by sputtering onto CNTs networks with a controlled loading of equivalent thickness of 2.5, 5 and 10 nm. Microstructure and morphology of the CNTs have been characterized by FE-SEM and TEM with diameter of the bundles of nanotubules of 10–40 nm. CNTs and Au-modified CNTs exhibit a p-type response with a decrease in electrical resistance upon exposure to oxidizing NO₂ gas and an increase in resistance upon exposure to reducing gases (NH₃, CO, N₂O, H₂S, SO₂). Negligible response has been found for CNTs and Au-modified CNTs sensors exposed to CO, N₂O, SO₂. In the contrast, significantly enhanced gas response of NO₂, H₂S and NH₃, up to a low limit of sub-ppm level, has been measured for Au-functionalized CNTs-chemiresistors. Highest gas sensitivity to NO₂, H₂S and NH₃ has been found by CNTs functionalized with Au loading of 5 nm, at 200 °C. An optimal operating temperature for each Au-modified CNTs-sensor exposed to NO₂ gas has been recorded. Good repeatability of the electrical response to 200 ppb NO₂ is also reported, at 200 °C. These results demonstrate the efficiency of the CNTs-chemiresistors functionalized with Au nanoclusters for selective air-pollutants environmental monitoring applications.

(M. Penza, R. Rossi, M. Alvisi, G. Cassano and E. Serra, Sensors and Actuators B: Chemical, Article in Press, 2009, doi:10.1016/j.snb.2009.04.008)