(518d) High Sensitive and Reversible Response of Nanotube Chemical Sensors in Poole-Frenkel Conduction Regime

In this study, we find that the applied electric field has an unexpectedly large effect on the sensitivity and reversibility of nanotube chemical sensors. It is shown that nanotube sensors are insensitive to gas adsorption at low applied voltages and remains low until a critical potential is reached. The sensor response then rapidly increases over a small range of voltage. The critical voltage roughly corresponds to the barrier for electron hopping between defect sites. These results show that the Poole-Frenkel (P-F) conduction regime is so important to sensing with nanotubes. In this regime, nanotube defects as low-energy sorption sites for chemical vapors significantly contribute to the response of a sensor.

It is also shown that at P-F conduction regime, a new desorption mode arises where the current through the sensor stimulates adsorbates to desorb without heating the sensor significantly. The recovery time of a nanotube sensor is reduced by over a factor of 300 and the method is general: alcohols, aromatics, amines and phosphonates were all found to desorb. The process is analogous to electron stimulated desorption, but it differs in that electrons being conducted through the nanotube, rather than an external source of electrons is used to stimulate the desorption. To our knowledge this is the first time that desorption of molecules has been found to occur via stimulation by the current through a material.