Metal-Functionalized and Vertically-Aligned Multiwalled Carbon Nanotube Layers for Low Temperature Gas Sensing Applications

Abstract

Vertically-aligned carbon nanotubes (CNTs) films have been grown by radiofrequency plasma-enhanced chemical vapor deposition system onto alumina substrates, coated with 2.5 nm thick Fe catalyst, for NO₂, H₂ and C₂H₅OH gas sensing applications, at sensor temperatures from room-temperature to 150°C. The CNTs appear in the form of forest-like structure. Nanoclusters of noble metals with nominal thickness of 5 nm of Pt, Ru and Ag have been sputtered on the top-surface of the vertically-aligned CNTs layers to enhance the gas sensitivity. It was demonstrated that the gas sensitivity of the metal modified CNTs-sensors significantly improved by a factor up to an order of magnitude through a spillover effect, and a broader selectivity was provided. The gas sensing properties of the CNTs-sensors, including the metal-modified CNTs, are characterized by a change of the electrical conductivity in a model of the charge transfer with a semiconducting p-type character. The metal-functionalized CNTs-sensors exhibit high sensitivity, fast response, reversibility, good repeatability, sub-ppm range detection limit. A practical application of the CNTs-sensors for monitoring landfill gas is presented.