Highly selective and fast-response NH₃ gas sensor based on Ag-doped WO₃ thin films prepared by spray pyrolysis

Undoped and Ag-doped tungsten oxide (WO₃) sensors were synthesized using the spray pyrolysis technique. The thin films are characterized by various techniques like XRD, UV–Visible spectroscopy, SEM and FTIR. The UV–Visible analysis confirmed the modification of optical properties of tungsten oxide due to silver doping and effective reduction in band gap from 2.76 to 2.70 eV. XRD analysis showed the decrease in crystallite size of tungsten oxide (from 13.98 to 11.39 nm) due to Ag-doping. The SEM analysis revealed the spherical shaped nanoparticles of pure and Ag-doped tungsten oxide with the embedded flakes like structures. The study of sensing characteristics revealed that 7 % Ag-doped WO₃ shows the highest selectivity and response (98.5) to NH₃ gas having the limit of detection (LOD) 18.31 ppb. The material also shows quick response (12 s) and recovery (36 s) times as well as the enhanced long term stability for the period of 30 days.