On the potential of long carbon nanotube forest for sensing gases and vapors

Ensembles of contacting carbon nanotubes (CNTs) undergo changes of electrical resistance at exposition to an ambient gas atmosphere due to the sensitivity of their electronic structure to adsorbed molecules. This phenomenon has been studied in dependence on temperature, the purity of carrier gas and operational history using a sensor-like device prepared by means of a vertically aligned multi-walled CNT forest. The CNT ensemble was grown by aerosol-assisted chemical vapor deposition using a ferrocene–acetonitrile solution. The sensitivity to O2, CO2, NH3, CH4 and C2H4 was measured at different temperatures. The presented study allows the conclusion that the high sensitivity of the carbon surface to changes of temperature, vaporized water and oxygen present in the air or to contaminations of the carrier gas decreases the potential of carbon-based devices for practical sensing applications. A possible mechanism of working of CNT-based sensing devices is discussed.

Research highlights
► Sensing device based on a vertically aligned multi-walled carbon nanotube (CNT) forest.
► Temperature dependence of electrical resistance.
► Electrical resistance of the CNT forest is mainly determined by the contact resistance between neighboring CNTs.
► The purity of the carrier gases has a strong influence on the accuracy of the sensor output. Sensing device is highly sensitive to its prehistory. Long freestanding CNTs serve as a reservoir for adsorbed molecules.
► The performance of CNT-based device is determined both by its morphology and its surface chemistry.