Investigating the influence of Ni doping on the CuO thin films deposited via ultrasonic spray pyrolysis: Structural, optical and H2 gas sensing analyses

Abstract

Pure and nickel doped copper oxide thin films were successfully grown on a soda lime glass substrates including various amounts (1, 2, 4, and 8%) of nickel dopants via ultrasonic spray pyrolysis method. The effects of the different impurity doping concentrations on the structural, morphological, optical, and H2 gas sensing properties of the prepared samples were assessed by performing X-ray Diffraction, scanning electron microscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy, gas sensing measurements, and X-ray photoelectron spectroscopy. The structural observations revealed that the grown films have polycrystalline nature with monoclinic cubic crystal structure of copper oxide with no secondary phases present, and grain sizes increased in general as the doping percentage increased except for the 4% nickel doped sample. The morphological analysis showed that the impurities clearly led to modifications in the shapes of the grown copper oxide nanocrystals. In the optical measurements, it was uncovered that the ideal impurity level can enhance the absorbance features of the copper oxide material, and a slight increase in bandgap occurred due to the first level of impurity doping, but then the bandgap decreased as the impurity contents increased. A gradual decrease in the intensity of luminescent emissions was observed in the photoluminescence spectra as the doping concentration increased, which may be associated with the defects caused by the added nickel ions into the copper oxide lattices. Gas sensor measurements disclosed that the produced films were responsive when exposed to H2 gas, and enhanced responsivity was realized by the nickel doping compared to that of pure copper oxide sample. X-ray photoelectron spectroscopy confirmed the presence of aimed chemical compositions in the prepared thin films.