Application of dielectrophoresis to fabrication of carbon nanohorn gas sensor

This paper describes an electrokinetic fabrication method for a gas sensor composed of single-wall carbon nanohorns (SWCNHs) using dielectrophoresis (DEP). The authors have previously demonstrated that DEP manipulation of carbon nanotubes (CNTs) can be applied to the fabrication of a CNT gas sensor. In the present study, we further explored the possibility of electrokinetic manipulation of SWCNHs. The latter have different structures and properties compared to CNTs. The SWCNHs were synthesized using the ‘arc in water with gas injection’ method. The SWCNH aggregates were dispersed in ethanol and trapped in an interdigitated microelectrode gap under the action of positive DEP. After the DEP process, the ethanol was evaporated and the microelectrode retaining the SWCNHs was exposed to nitrogen dioxide (NO2) or ammonia (NH3) gas while the electrode impedance was monitored. It was found that conductance of the DEP-fabricated SWCNH sensor increased or decreased upon exposure to ppm-levels of NO2 or NH3, respectively. These results were similar to those previously obtained for CNT gas sensors and suggest that the SWCNH aggregate behaves as a p-type semiconductor. The comparison reveals that intrinsic NO2 sensitivity of the SWCNHs is lower than that of single-wall CNTs (SWCNTs) but comparable with the intrinsic sensitivity of multiple-wall CNTs (MWCNTs).