Effect of substrate temperature and precursor salt molarities on the nickel oxide physical properties

This paper investigates the effects of substrate temperature and precursor salt molarities on the nickel oxide (NiO) thin film physical properties. The NiO thin films were deposited on glass substrates via spray pyrolysis at different temperature (from 400 to 650 °C) with two different molarities (0.05 M and 0.1 M) of the precursor nickel acetate. The structural and morphological properties of the films were studied by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The optical properties of the films were characterized using UV–visible transmission spectroscopy. Electronic defects were investigated using photoluminescence (PL) measurements. The obtained results reveal that regardless of the salt molarity, films prepared at low substrate temperatures are amorphous. With an increase in the substrate temperature, the film crystallinity is improved, while the grain size is enlarged but remains in the nanocrystalline range. In the intermediate temperature range of 500–600 °C, both Raman and XRD analyses suggested that the films were composed of a mixture of oxalate (NiOx) and NiO. At high substrate temperature, the obtained film is a pure NiO. Films prepared at 500 and 600 °C exhibit lower transmission in the visible region due to their large surface roughness. PL measurements revealed only the presence of Ni interstitial defect in the forbidden band gap. At low molarity, this defect concentration increases with substrate temperature, whereas it is reduced when using higher salt molarity.