Influence of Al doping on NiO thin films for NH₃ gas sensing of low PPM concentration

We present a study on aluminum-doped nickel oxide nanostructured thin films synthesized via spray pyrolysis for ammonia gas sensing applications. Structural analysis confirms the polycrystalline nature of NiO, with the most intense diffraction peak along the (111) plane. Al doping induces variations in surface roughness and optical bandgap, as evidenced by morphological and optical studies. The presence of defects, including oxygen and nickel vacancies, is confirmed through room-temperature photoluminescence and Raman spectroscopy, with x-ray photoelectron spectroscopy further validating an increase in defect concentration upon doping. Gas sensing measurements demonstrate sensor responses of 1.07 and 0.95 for 4% and 6% Al-doped NiO films, respectively, at a low NH₃ concentration of 4 ppm.