AVS 51st International Symposium
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS-TuP

Paper NS-TuP15
Theoretical and Experimental Studies on the Adsorption of Oxidizing Gas on Carbon Nanotubes Thin Films

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: L. Lozzi, University of L'Aquila, Italy
Authors: L. Lozzi, University of L'Aquila, Italy
L. Valentini, University of Perugia, Italy
S. Picozzi, University of L'Aquila, Italy
C. Cantalini, University of L'Aquila, Italy
S. Santucci, University of L'Aquila, Italy
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In this work a combined theoretical and experimental study on CNT-based system for gas sensing applications is reported. Carbon nanotubes thin films have been deposited by 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. The electrical resistivity of the CNT film shows a temperature dependence semiconducting-like and a p-type response with decreasing electrical resistance upon exposure to NO2 gas and O3. No response has been found by exposing the film to CO gas, while some other concomitan gases may have an interfering behavior [1]. 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 and CNT+O3 systems. Our density functional calculations show that Both CO and NO2 and O3 molecules adsorb weakly on a defect free 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 and O3 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. The role of the defects on the wall of CNT is also discussed and related to the experimental results. In particular the anomalous adsorption of O3 that produces a consumption of the CNT film also at low temperatures is explained as the effect of the chemisorption of this gas onto defective sites. [1] C.Cantalini, L.Valentini, I.Armentano, L.Lozzi, J.M.Kenny and S.Santucci. Sensors and Actuators B 95, 195 (2003).