Sensing NO2 with individual suspended single-walled carbon nanotubes

We report on the fabrication and measurements of first NO2gas sensors based on individual suspended single-walled carbon nanotubes (SWNTs). Transient current response of NO2 exposed semiconducting SWNTs in dry air are analyzed. Both types of suspended SWNTs show a strong chemiresistor like transient response and clearly rule out a strong influence of the SiO2 substrate to the sensing mechanism of SWNT gas sensors. Furthermore, we analyze the dynamic gate sweep behavior that is highly dominated by hysteresis. When exposed to NO2 the gate characteristics show significant changes, which are discussed in detail. We measure the decay times of the dynamic hysteretic charge traps of more than 1400 s. A hysteresis free gate measurement shows a clear shift of the threshold voltage. This paper shows that NO2 sensing with SWNTs involves both, static and dynamic effects.