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

Abstract This report describes the preparation of undoped, polyethylene glycol (PEG-400)-added, Fe-doped, Pd-doped and Fe-, Pd-doped, PEG-400-added SnO 2 thin films using sol–gel technology. The gas-sensing properties of the five abovementioned structures were investigated over a range of 50–2000 ppm H 2 . The linear response magnitude ( S ) response profile of Fe-, Pd-doped, PEG-400-added SnO 2 thin film toward H 2 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 )  2 thin film toward H 2 in CO and CH 4 defined as S (H 2 )/ S (CO) and S (H 2 )/ S (CH 4 ) was 17.3 and 40.4, respectively, which was better than those of undoped SnO 2 (2.6 and 5.3, respectively) at 225 °C. A volcano-shaped correlation was observed in Fe-, Pd-doped, PEG-400-added SnO 2 thin film approaching 2000 ppm within a range of 75–275 °C, and the film's response magnitude measured up to 55.75, even at a low temperature of 75 °C. The consistency and reproducibility of undoped SnO 2 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.