Nitrogen-Dioxide Sensing Properties of Solution Precursor Plasma Sprayed Zinc Oxide Coatings with Oxygen Vacancies

This study investigates the feasibility of using solution precursor plasma sprayed (SPPS) zinc oxide to fabricate NO₂ gas sensors. In the experiments, thin ZnO layers were deposited on Al₂O₃ substrates that had been printed with interdigitated gold electrodes. FE-SEM images show that the as-sprayed films are highly porous and nanostructured as desired. Diffuse reflectance measurements reveal that significant absorption occurs in the visible light range. In gas sensing tests, the SPPS ZnO films were responsive to concentrations of NO₂ gas down to 0.4 ppm. The performance is attributed to the porous nanostructure and the presence of oxygen vacancies, or mid-bandgap defects, as confirmed by XPS analysis.