AVS 50th International Symposium
    Nanotubes Wednesday Sessions
       Session NT-WeA

Paper NT-WeA10
Gas Adsorption on Multi-walled Carbon Nanotubes: An Experimental and Theoretical Study

Wednesday, November 5, 2003, 5:00 pm, Room 317

Session: Properties of Carbon Nanotubes
Presenter: S. Picozzi, University of L'Aquila, Italy
Authors: S. Picozzi, University of L'Aquila, Italy
L. Lozzi, University of L'Aquila, Italy
C. Cantalini, University of L'Aquila, Italy
L. Valentini, Universita di Perugia, Italy
I. Armentano, Universita di Perugia, Italy
J.M. Kenny, Universita di Perugia, Italy
S. Santucci, University of L'Aquila, Italy
Correspondent: Click to Email
The effects of environment gases (such as O2, NO2, NH3) on the electronic and transport properties of carbon nanotubes have recently attracted great interests.@footnote 1@ In this work a combined experimental and theoretical study on CNT-based system for gas sensing applications is reported. Carbon nanotubes thin films have been deposited by plasma enhanced chemical vapor deposition on Si3N4/Si substrates provided with Pt electrodes. Microstructural features as determined by SEM, TEM and Raman spectroscopy highlight the growth of defective tubular carbon structures. CNTs show a p-type response with decreasing electrical resistance upon exposure to NO2 gas (100 ppb) and the highest sensitivity at 165° C working temperature. No response has been found by exposing the film to CO gas in the temperature range between 25 and 250° C. In order to obtain a theoretical validation of the experimental results, the equilibrium position, charge transfer and density of states are calculated from first principles for the CNT+CO and CNT+NO2 systems.@footnote 2@ Our spin-unrestricted density functional calculations show that NO2 retains its spin-polarized state upon adsorption. Both CO and NO2 molecules adsorb weakly on the tube wall, with essentially no charge transfer between the tube and the molecules. The electronic properties of CNTs are sensitive to the adsorption of NO2, due to an acceptor-like peak close to the tube valence band maximum, while they are insensitive to the CO adsorption. According to the experimental findings, our theoretical results suggest that gas-induced modification of the density of states close to the Fermi level might significantly affect the transport properties of nanotubes. @FootnoteText@@footnote 1@ J. Kong, N.R. Franklin, C. Zhou, M.G.Chapline, S. Peng, K. Cho and H. Dai, Science 287, 622 (2000).@footnote 2@ B. Delley, J. Chem. Phys. 113, 7756 (2000).