Substrate type effect on the structural, morphological and optical band gap of spray deposited CuO thin films

In the present work, the effect of substrate types -glass, quartz, and FTO (SnO2:F)- on the crystal growth, structure, morphology, and optical properties of copper oxide (CuO) nanocrystalline thin films was investigated. The spray pyrolysis method was used to deposit CuO films at a substrate temperature of 350 °C. X-ray analysis revealed that the deposited films are polycrystalline with a monoclinic phase. The crystallite size increased when the substrate changed from glass to quartz and FTO: (23–28) nm and (20–49) nm for the (002) and (111) orientations, respectively, while crystal defects and lattice strain decreased. The impact of the substrate type on the average Roughness R a , Root mean Square Roughness RMS and the grain size of the on the CuO surface topography was investigated by atomic force microscopy AFM. The grain size of the CuO film deposited on glass, quartz and FTO substrates are about 137 nm, 104 nm and 96 nm respectively. The R a , the RMS and the grain size values of the samples vary according to the type and nature of the substrate related to the mismatching between the substrate surface and the deposited CuO thin films. The film surfaces contain nanostructures and nanoparticles uniformly distributed as hierarchical (pyramidal-shaped) structures of varying shapes and sizes depending on the substrate type, fully covering the substrates. Optical results showed that the transmittance of CuO/glass films is lower (∼40%) than that of films on quartz and FTO (about 70%). The optical absorption edge blue-shifted toward lower wavelengths when the substrate was changed from glass to quartz and FTO. The energy gap values are 1.59 eV, 1.85 eV, and 1.901 eV for CuO films deposited on glass, quartz, and FTO substrates, respectively. Therefore, CuO thin film characteristics can be controlled by the substrate type, which plays an important role in film crystal growth and suitability for a wide range of applications.