Atmospheric pressure fabrication of SnO2-nanowires for highly sensitive CO and CH4 detection

In this paper we report on a new approach for the fabrication of ultra-long single crystalline SnO2-nanowires for gas sensing applications based on a combined spray pyrolysis and annealing process. The SnO2-nanowires are grown on SiO2-coated Si-substrates and exhibit diameters of 30–400 nm and lengths up to several 100 μm. The whole SnO2-nanowire fabrication procedure is performed at atmospheric pressure and requires no vacuum. The experimental results suggest a competing evaporation and condensation process, which converts the nanocrystalline SnO2-films into single crystalline SnO2-nanowires directly on the chip. For the realization of gas sensors the SnO2-nanowires are transferred to another SiO2-coated Si-substrate. Evaporation of Ti/Au contact pads on both ends of single SnO2-nanowires enables their direct use as sensing elements. The devices are very sensitive, are able to detect humidity, and concentrations of CO and CH4 as low as a few ppm at operating temperatures of 200–250 °C. We believe that our fabrication procedure might be the technology of choice for the controlled fabrication of SnO2-nanowires as highly sensitive gas sensing elements on a wafer scale.