Influence of oxygen vacancies on the performance of SnO2 gas sensing by near-ambient pressure XPS studies

Modulation of oxygen vacancy (V & sdot;& sdot;O) concentrations in SnO2 is an efficient strategy for improving its NO2 sensing performance. However, due to the complex reaction process between NO2 and adsorbed oxygen species on the surface of metal oxide, the role of V & sdot;& sdot;O is still unclear without in-situ characterization. Here, SnO2 nanowires (NWs) were synthesized via chemical vapor deposition method, and the V & sdot;& sdot;O concentration in SnO2 NWs was enhanced by removing adsorbed H2O on the surface of precursor during the growth process. The V & sdot;& sdot;O-abundant SnO2 NWs exhibited large improvement in NO2 sensing performance with ultralow detection limit (2 ppb NO2) and high response value towards 1 ppm NO2 (49.5 at 50 degrees C). Near-ambient pressure X-ray photoelectron spectroscopy was used to reveal the in-situ sensing reactions occurred on the surface of SnO2 NWs. The results revealed that V & sdot;& sdot;O provided active sites for adsorption of oxygen species and confirmed the formation of NO. This work demonstrates an easy route to grow SnO2 NW with tunable V & sdot;& sdot;O concentration, and provides a direct evidence for deeper understanding of the effect of V & sdot;& sdot;O in sensing process.