The effect of metal cluster coatings on carbon nanotubes

The electrical transport and chemical sensing properties of single-walled carbon nanotube field effect transistors (SWNT-FETs) coated with metal clusters have been investigated. The source-drain current passing through an SWNT-FET coated with Pd nanoparticles showed no change over a range of gate voltages. Nevertheless, the magnitude of the current was still sensitive towards NO2, NH3 and H-2 exposure. The Pd nanoparticles coating on the nanotube generated hole carriers, which either became diluted upon NH3 or H-2 adsorption, or enhanced upon NO2 adsorption. Unlike the ohmic behaviour demonstrated by SWNT-FETs coated with Pd nanoparticles, the transfer characteristics of SWNT-FETs coated with Al nanoparticles revealed Schottky barrier formations at the metal-nanotube contacts. Here, the conductance through the nanotube decreased, while the device sensitivity towards NO2 and NH3 gases improved greatly. We suggest that coating SWNT-FETs with metal nanoparticles could be exploited for the development of highly sensitive nanotube-based molecular sensors.