Investigation of the hydrogen response characteristics for sol–gel-derived Pd-doped, Fe-doped and PEG-added SnO2 nano-thin films

This report describes the preparation of undoped, polyethylene glycol (PEG-400)-added, Fe-doped, Pd-doped and Fe-, Pd-doped, PEG-400-added SnO2 thin films using sol–gel technology. The gas-sensing properties of the five abovementioned structures were investigated over a range of 50–2000 ppm H2. The linear response magnitude (S) response profile of Fe-, Pd-doped, PEG-400-added SnO2 thin film toward H2 concentration (C) was observed, and a concise formula without any transformation was expressed as S = 1.724 + 0.046 C (correlation coefficient (R) = 0.99803, probability (P) < 0.0001). The selectivity of Fe-, Pd-doped, PEG-400-added SnO2 thin film toward H2 in CO and CH4 defined as S(H2)/S(CO) and S(H2)/S(CH4) was 17.3 and 40.4, respectively, which was better than those of undoped SnO2 (2.6 and 5.3, respectively) at 225 °C. A volcano-shaped correlation was observed in Fe-, Pd-doped, PEG-400-added SnO2 thin film approaching 2000 ppm within a range of 75–275 °C, and the filmʹs response magnitude measured up to 55.75, even at a low temperature of 75 °C. The consistency and reproducibility of undoped SnO2 thin films were investigated and found to be acceptable when considering the mass sensor production. Two important phenomena related to gas response time profile and a “fluctuation” that appeared at the bottom of every gas response profile were observed and qualitatively analyzed for the first time in this study.