Density-controllable growth of SnO2 nanowire junction-bridging across electrode for low-temperature NO2 gas detection

The junction-bridging structure of metal oxide nanowires (NWs) improves gas-sensing properties. In this study, an on-chip growth method was used to fabricate gas sensors, it easily and effectively controls NW junctions. SnO2 NWs were synthesized by thermal evaporation at 800 A degrees C with tin powder as the source. The density of the NW junctions was controlled by changing the mass of the source material. A source material with large mass yielded high-density NW junctions. With electrode spacing of 20 mu m, NW junctions were formed from the source material of larger than 2 mg. Gas sensing results revealed that the junction sensors exhibited a good response to NO2 gas at a concentration of 1-10 ppm. The sensors exhibited a good response to NO2 gas at low temperature of up to 100 A degrees C and short response-recovery time (similar to 20 s). The sensors also had good selectivity to NO2 gas. The response (R (gas) /R (air)) to 1 ppm NO2 was as high as 22 at 100 A degrees C, whereas the cross gas responses (R (air) /R (gas)) to 10 ppm CO, 10 ppm H2S, 100 ppm C2H5OH, and 100 ppm NH3 were negligible (1.1-1.3).