Highly sensitive and selective sensors based on carbon nanotubes thin films for molecular detection

In the present work, the electrical response of carbon nanotubes (CNTs) thin films to NO2, CO, NH3, H2O and C2H5OH for gas sensing applications is reported. The sensor design is a CNT serpentine resistor, fabricated by photolithography defining Pt electrodes upon Si3N4, and then growing CNTs upon the Si3N4 structure The electrical response has been measured exposing the films to the interfering gases at different operating temperatures between 25 and 250 degreesC. Upon exposure to NO2 (10-100 partsper-billion (ppb)) the electrical resistance of CNTs is found to decrease. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by a fast recovery at 165 degreesC. No response has been found by exposing the films to CO in the investigated working temperature range. On the contrary, NH3, ethanol as well as 80% relative humidity, have resulted to increase the electrical resistance of the films. The experimental findings revealed that p-type semiconductor behaviour is present in our CNTs. (C) 2003 Elsevier B.V. All rights reserved.