Methane detection is extremely difficult, especially at low temperatures, due to its high chemical stability. Here, WO₃ nanosheets loaded with SnO₂ nanoparticles with a particle size of about 2 nm were prepared by simple impregnation and subsequent calcination using SnO₂ and WO₃·H₂O as precursors. The response of SnO₂-loaded WO₃ nanosheet composites to methane is about 1.4 times higher than that of pure WO₃ at the low optimum operating temperature (90 °C). Satisfying repeatability and long-term stability are ensured. The dominant exposed (200) crystal plane of WO₃ nanosheets has a good balance between easy oxygen chemisorption and high reactivity at the dangling bonds of W atoms, beneficial for gas-sensing properties. Moreover, the formation of a n–n type heterojunction at the SnO₂-WO₃ interface and additionally the increase of specific surface area and defect density via SnO₂ loading enhance the response further. Therefore, the SnO₂-WO₃ composite is promising for the development of sensor devices to methane.

The excellent and promising gas sensors not only have high response, but also can be easily integrated with other semiconductor devices to form an intelligent chip. In order to realize this goal, an effective strategy is proposed to combine the magnetron sputtering and Ar plasma treatment. As a result, a high-performance sensor based on Au-ZnO films is achieved at the optimal technology parameter, with high response (R_a/R_g) of 190 to 100 ppm isopropanol (IPA), rapid response/recovery speed of 1 s/18 s, and low detection limit of 100 ppb at 300 °C. Moreover, the mechanisms of the improvement on the sensing properties of the as-fabricated sensor are discussed. The present work provides new ideas for the future development of integrating gas sensors with functional circuits to form a smart chip that can perform data acquisition, processing and storage.

Ag-doped SnO2 nanoflowers (NFs) are prepared via a simple one-step hydrothermal method and subsequent Ag-doping using AgNO3 solution as precursors. The crystal structure, morphology and elements of the Ag-doped SnO2 NFs are investigated in detail. The maximal response of Ag-doped SnO2 sensor with 1.0 wt.% Ag doping to 500 ppm methane is increased by a factor of 1.6 as compared to that of pure SnO2 sensor. The long-term stability and the selectivity of the SnO2-based sensor are improved by Ag-doping as well. Meanwhile, pre-adsorption of oxygen molecules on the surface of the SnO2-based substrate is studied in-depth with the method of first-principle calculation. Ag doping lowers adsorption energy for all the adsorption sites, demonstrating a higher adsorption stability of chemisorbed oxygen ions on the Ag-doped SnO2 as compared to the pristine phase. More electron transfer from the semiconductor to the chemisorbed oxygen is revealed by the Mulliken charge analysis and the electron density difference for the Ag-doped SnO2, explaining the better sensitivity of gas sensors based on Ag-doped SnO2 nanostructures as compared to its undoped counterpart.