Engineered SnO2-based thin films for efficient CO2 gas sensing at room temperature

• Non-stoichiometric SnO-SnO 2 thin films were formed through electron beam evaporation. • Thin film forms a native SnO-SnO 2 structure, which serves as an active p-n junction. • The as-deposited SnO-SnO 2 heterojunction demonstrates an enhanced response to CO 2 . • Enhancement is due to the depletion layer, increasing surface free electron number. • Femtosecond laser was first applied in room-temperature gas sensor operations. Tin oxide (SnO 2 )-based thin films were deposited on alumina printed circuit boards via electron beam evaporation to fabricate CO 2 gas sensors operating at room temperature. Femtosecond laser surface nanotexturing was applied as a novel approach to optimize key gas sensitivity parameters, including surface roughness and grain size. Raman and X-ray photoelectron spectroscopy revealed that the sensitive layer consists of a 1 µm SnO film with a non-stoichiometric SnO 2 upper layer for the as-deposited film. The electronic disparity between these layers forms a native SnO-SnO 2 interface, creating a p-n junction that enhances sensor sensitivity. This sensor shows a sensing response ranging from 7 % to 20 % for CO 2 concentrations of 1000 to 2000 ppm, and up to 40 % at 5000 ppm. Laser irradiation introduced periodic surface structures (∼ 800 nm), increasing the roughness and the number of active sites for the gas sensing. Although no significant improvements were observed in terms of sensitivity, the fs-laser treated sensor exhibited enhanced stability and reproducibility, indicating its potential for low-energy consumption gas sensing platforms for indoor air quality applications.