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

Tin oxide (SnO₂)-based thin films were deposited on alumina printed circuit boards via electron beam evaporation to fabricate CO₂ 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 SnO₂ upper layer for the as-deposited film. The electronic disparity between these layers forms a native SnO-SnO₂ interface, creating a p-n junction that enhances sensor sensitivity. This sensor shows a sensing response ranging from 7 % to 20 % for CO₂ 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.