Substrate temperature-dependent properties of sprayed cobalt oxide thin films

Cobalt oxide (Co₃O₄) thin films were deposited onto amorphous glass substrates using a home-made pneumatic spray pyrolysis system (SPT) from aqueous solution of cobalt chloride salt (CoCl₂) as a source of cobalt. The films were deposited at different substrate temperatures ranging from 250 to 450 °C in steps of 50 °C. The effect of substrate temperature on structural, electrical and optical properties was studied. The characterization of samples was carried out by X-ray diffraction (XRD), UV–Vis spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy and four probe points measurements. The XRD study showed that all the films were polycrystalline consisting of Co₃O₄ spinel cubic phase. The preferred orientation of the crystallites changed from (311) to (111) when the substrate temperature increases. The average calculated grain size was about 40.38 nm. Morphological studies exposed that the films surface morphology is almost homogeneous and well-covered. Peaks associated with Co and O elements are present in EDS analysis witch confirm the composition of the films. The optical transmittance and the band gaps energy increase with the increase of substrate temperature. The measured electrical conductivity at room temperature was found in the order of 10⁻¹ (Ω cm)⁻¹.