of the filter were measured using condensation particle counters (TSI Inc. model 3022A). Submicrometer particles entering the counters are grown into micrometer sized droplets by condensation of a supersaturated vapor of 1-butanol onto the particles, then counted by laser light scattering. The particle concentrations were averaged over ten measurements at each particle size. Filter experiments were repeated at least twice to ensure reproducibility. The pressure drop after filtration was also measured using previously described methods.

We have used field-effect transistor (FET) devices with semiconducting single-walled carbon nanotubes (SWNTs) as the conducting channels to study interactions of aromatic compounds with SWNTs. Electronic detection occurs through charge-transfer effects, monitored as the change of the gate voltage (V g) dependence of the source-drain current I sd. For monosubstituted benzene compounds, we find that the shift of the I sd − V g characteristic is proportional to the Hammett sigma values (σp) of their substituents.

Sequential CVD and CMOS processes were used to make a FET that has single walled carbon nanotubes to serve as the conducting source to drain channel. This structure can be decorated to provide gas and liquid responses and herein is evaluated as a humdity sensor. The Na , K, and Ca 2 ion-exchanged Nafion polymer acts as the chemically sensitive layer in this electrochemical sensor. The effect of gate voltage on the charge-sensitive NT structure was found to be RH dependent over the range of 12 ± 93% RH with msec response time.