Synthesis and characterization of WO3:TiO2 nanostructured thin films for NH3 sensing application

Abstract

Nanostructured WO3 and WO3:TiO2 thin films were fabricated through pulsed laser ablation in liquid followed by spin coating to investigate the influence of TiO2 incorporation on room-temperature NH3 sensing. Structural characterization confirmed that the pristine WO3 film was predominantly tetragonal, with an average crystallite size of 39 nm. Introducing TiO2 produced broader diffraction peaks, slight peak shifts, and a reduction in crystallite size to nearly 32 nm, reflecting defect generation and local lattice distortion. Morphological analyses revealed finer surface features and increased surface roughness, thereby providing a larger effective surface area for NH3 adsorption. PL measurements further verified the formation of defect-related states, including oxygen vacancies and Ti3+ centers, which facilitate charge separation and enhance surface reactivity. These structural and electronic modifications were directly reflected in the sensing performance. At room temperature, the WO3:TiO2 composite exhibited a sensitivity of 55.3% toward 5 ppm NH3, whereas pristine WO3 produced only 0.17%, together with faster response and recovery characteristics. The superior sensing behavior is attributed to the combined effects of defect-assisted charge transport, increased adsorption sites, and heterointerface interactions between WO3 and TiO2, demonstrating the potential of the composite film for reliable ammonia detection under ambient conditions.