Influence of annealing temperature on the structural, morphological, and optical properties of nanocrystalline NiO and Cu-doped NiO thin films and its application in acetone gas sensing

In this research, the nanocrystalline pure and Cu-doped NiO (NiO:Cu) films were prepared by reactive DC magnetron sputtering onto silicon and quartz substrates. The effect of annealing temperature on the structural, morphological, and optical properties of prepared samples was thoroughly investigated by different identification methods. The XRD results verified the formation of NiO in a cubic structure with (200) preferred orientation, and the crystallite size was reduced compared to the undoped sample. The optical investigation showed a decrease in the optical band gap of NiO:Cu films compared with the pure NiO films. The PL spectra of all samples after annealing reveal three characteristic peaks with different intensities at 421, 488, and 538 nm. FESEM images reveal that the surface morphology is homogeneous with good adhesion to the substrate. The electrical measurements showed that the sheet resistance of NiO film decreased after Cu doping. Additionally, the ability of NiO and NiO:Cu films to sense acetone gas concentrations in terms of the time working and the different temperatures were studied and reported. The results exhibited that the samples can detect the acetone gas at different temperatures however, the NiO sample was more sensitive to acetone relative to NiO:Cu.