Room-temperature ammonia gas sensor based on Ti-doped ZnO thin films prepared via wet chemical synthesis using drop casting technique

This study investigates the preparation of pristine and ZnO: Ti thin films through drop casting technique, with titanium (Ti) concentrations of 1 %, 3 %, and 5 % by weight. The prepared samples were analyzed using powder X-ray diffraction (XRD), UV-Vis spectroscopy, photoluminescence studies and gas sensing analysis. The powder XRD results confirmed that the ZnO:Ti thin films exhibited a hexagonal wurtzite structure. The lattice parameters and unit cell volumes were determined, and the film exhibited negligible microstrain. Surface morphology analysis revealed voids with interconnected network structures, which enhanced the surface adsorption of oxygen species and contributed to an improved gas sensing response for the ZnO:Ti thin film with 3 % Ti. According to UV-Vis spectroscopy, the optical band gap of the synthesized ZnO: Ti thin films ranged from 3.37 to 3.39 eV. Photoluminescence studies indicated that deep-level emissions in the visible region of the electromagnetic spectrum are attributed to defects, such as interstitials and vacant sites within the lattice. The gas sensing properties demonstrated a gas response of 74, with a response time of 10.4 s and a recovery time of 6.4 s for 250 ppm ammonia gas, indicating high gas response for the ZnO: Ti 3 % thin film. This film also exhibited remarkable selectivity towards ammonia and a linear response to ambient relative humidity. Repeatability and stability studies confirmed reliable sensing performance and good aging properties, making the 3 % Ti-doped ZnO film suitable for ammonia gas sensing applications.