Engineered SnO2-based thin films for efficient CO2 gas sensing at room temperature
Eleonora Bolli, A. Bellucci, Matteo Mastellone, Alessio Mezzi, S. Orlando, Riccardo Polini, Raffaella Salerno, A. Santagata, Veronica Valentini, D.M. Trucchi
Abstract
• 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.