Ultrasensitive yttrium modified tin oxide thin film based sub-ppb level NO2 detector

Considering the adverse effect of rising air pollution on environment and human health, highly selective and trace level sensors are needed. Herein, yttrium (Y) incorporated tin oxide (SnO2) thin film gas sensors have been developed for sub-ppb level detection of NO2 at room-temperature. The undoped and Y-doped (1, 3 and 5 wt%) thin films have been prepared via electron beam deposition technique. The XPS studies confirmed the substitution of Sn with Y in SnO2 lattice. The morphological and structural characterizations reveal smooth and crystalline thin films, while Raman and PL spectroscopic studies confirm the presence and growth of oxygen vacancies (OVs), specifically in-plane OVs, in doped samples. Moreover, narrowing of electron absorption spectra in doped samples implied the formation of mid-gap states in energy bandgap of SnO2 leading to enhanced electron transfer. The 3 wt% Y-doped SnO2 sensor exhibited excellent sensing response with high selectivity towards NO2 in 15–240 ppb range. The sensors also showed high stability and repeatability along with humidity insensitivity. Notably, the sensor was observed to be highly sensitive to 0.6 ppb NO2 exhibiting a 26 % response along with response/recovery time of 4/2 min. The improved sensing characteristics have been ascribed to reduced crystallite size, elevated in-plane OVs, enhanced charge transfer and increased specific surface area due to Y integration.