Controlled fabrication of carbon nanotube NO2 gas sensor using dielectrophoretic impedance measurement

The authors have previously demonstrated an electrokinetic fabrication method of a carbon nanotube (CNT) gas sensor using dielectrophoresis. One advantage of the technique was that one could quantify the amount of trapped nanotubes on a real time basis by monitoring electrical impedance of the sensor (dielectrophoretic impedance measurement, DEPIM). In the present study, we extended the DEPIM technique to controllable assembly of the carbon nanotube gas sensor. This realized a production of CNT gas sensors with identical electrical properties such as initial conductance. The gas sensor response to ppm--level nitrogen dioxide (NO2) gas was investigated with various values of the initial conductance. It was found that relative conductance change of the CNT gas sensor after NO2 exposure increased almost proportionally with the initial conductance for a constant NO2 concentration. This enabled to define intrinsic sensitivity of CNT sensors by normalization. It was found that a single--wall CNT gas sensor had higher normalized sensitivity than a multi--wall CNT sensor.