Comparison of the gas sensing performance of SnO2 thin film and SnO2 nanowire sensors

In order to optimize the performance of gas sensor devices, nanocrystalline SnO2 thin film and single crystalline SnO2 nanowire sensors have been characterized for the target gases CO, CH4, H2, CO2, SO2 and H2S. At optimum operating temperature – varying from 250 °C to 400 °C – the SnO2 thin film sensor detects CO, CH4, CO2 and SO2 with responses in the range of 23–34%, H2 and H2S with responses above 80%. The SnO2 nanowire sensor shows responses in the range of 1–8% for CO, H2 and SO2, 29% for H2S, while CH4 and CO2 are not detected. Taking into account that the exposed surface area of the thin film sensor is 800 times larger than that of the single nanowire, we have correlated the number of CO gas molecules impinging the sensors’ surface with the number of electrons, which are actually detected as sensors’ response for the target gas CO. In case of the thin film sensor a single detected electron requires ∼2760 gas molecules impinging the sensorʹs surface. For the nanowire sensor only ∼86 gas molecules are required for a single detected electron. The SnO2 nanowire sensor thus has a detection efficiency more than 30 times higher than the SnO2 thin film sensor, which we attribute to a lack of grain boundaries. From our measurements we conclude that single crystalline SnO2 nanowire sensors provide a higher sensitivity and an improved cross-sensitivity than their nanocrystalline counterpart.