E Elaboration and Characterization of Doped NiO Thin Films Prepared by Spray Pyrolysisand Their Application in Gas Sensor Devices

Abstract

Abstract—NiO thin films were deposited on glass substrates using the spray pyrolysis technique at a fixed temperature of 450 °C, employing nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) as the precursorThe primary objective of this study is to compare fluorine-, copper-, and aluminum-doped NiO thin films prepared via spray deposition. To achieve this, ammonium fluoride (NH₄F) was used with an F/Ni ratio of 0.05 for fluorine doping, copper acetate (Cu(CH₃COO)₂) with a Cu/Ni ratio of 0.03 for copper doping, and aluminum nitrate (Al(NO₃)₃) with an Al/Ni ratio of 0.03 for aluminum doping.
Using a fixed NiO solution volume of 5 mL, we examined the structural, optical, and electrical properties of the thin films. The F‑, Cu‑, and Al‑doped NiO films all crystallized in a monocrystalline cubic phase with a preferred (111) orientation, and the largest crystallite size (12.51 nm) was observed for the Al‑doped samples. Optically, every doped film exhibited high transmittance in the visible region, with the F‑doped NiO reaching about 84%. Furthermore, the F‑doped films showed the smallest optical band gap (3.55 eV) and the lowest electrical resistivity 231 Ω·cm.