Superior enhancement of NO2 gas response using n-p-n transition of carbon nanotubes/SnO2 nanowires heterojunctions

Abstract

The enhancement of sensor performances for the detection of highly toxic NO2 gas is one of the most important technological issues in the realization of devices for environmental pollution monitoring. Herein, the n-p-n heterojunctions of carbon nanotubes (CNTs) and SnO2 nanowires (NWs) are designed and fabricated by a facile method to investigate their NO2 gas-sensing performance. The designed devices are easily realized by first growing the SnO2 NWs on Pt electrodes using a thermal chemical vapour deposition method and then spray coating the single-walled carbon nanotubes (SWCNTs) and/or multi-walled carbon nanotubes (MWCNTs) to make a connection between the two electrodes. The MWCNTs/SnO2 NWs device has much higher NO2 responsiveness compared to the SWCNTs/SnO2 NWs and the pristine SnO2 NWs devices. The fabricated devices showed ultrahigh enhancement in gas sensing performance for NO2, whereas these characteristics do not significantly improve for H2S gas. At a low working temperature of 100°C, the fabricated sensors are able to detect the NO2 gas concentration down to 20ppb. We also clarify the sensing mechanism of the fabricated devices.