Chemiresistive trimethylamine sensor using monolayer SnO2 inverse opals decorated with Cr2O3 nanoclusters

Abstract

Two-dimensional SnO2 inverse opal (2D IO) structures with uniform surface decoration of Cr2O3 nanoclusters were prepared using a Sn-solution-dipped sacrificial polystyrene monolayer template method and were employed for chemiresistive gas-sensor applications. The responses (resistance ratio) of the pure SnO2 2D IO sensor to 5 ppm trimethylamine (TMA) and ethanol were as high as 209.5 and 242.3, representing improvements of two orders of magnitude compared with that of a dense SnO2 thin film sensor. The high gas response of the porous SnO2 IO sensor is attributed to the superior gas accessibility as well as the large chemiresistive variation at the thinnest neck region of the 2D IO structures. Further enhancements of the TMA selectivity and response were achieved by decorating the surface of the SnO2 IO structure with Cr2O3 nanoclusters. The control of the TMA-sensing characteristics of the SnO2 2D IO sensor through the decoration with Cr2O3 nanoclusters was explained by the change of the electron-depletion layer in the SnO2 particles due to the formation of the p(Cr2O3)-n(SnO2) junction, as well as the catalytic promotion of the gas-sensing reaction by Cr2O3. The oxide 2D IO films with high gas accessibility and chemiresistive neck structures are promising nanoarchitectures for gas-sensor applications, and the formation of hetero-nanostructures via decoration with different oxide semiconductor nanoclusters having dissimilar work functions and catalytic activity allows the enhancement of the selectivity toward a specific gas, as well as the gas response.