Aqueous chemical growth of ZnO/CdO nanocomposite thin films: effect of volume ratio and annealing on structural, morphological and optical properties

Structural, morphological and optical characteristics of ZnO/CdO nanocomposite films synthesized via successive ionic layer adsorption and reaction (SILAR) technique with different ratios of ZnO/CdO: 30:50 ml, 40:40 ml and 50:30 ml has been investigated. Structural studies indicated a mixed phase of hexagonal ZnO and cubic CdO with low intensities. Variation of identified crystal phases, crystallinity and crystallites sizes responded strongly with varying precursor ratios and thermal annealing. SEM micrographs show nanoparticles of varying particle sizes in the range of 32.9–57.7 nm, governed by CdO content in the film and thermal annealing. Optical studies indicated that the synthesized materials have predominantly ultraviolet (UV) absorption which was significantly enhanced into the visible spectrum due to annealing. Bandgap shrinked from 3.80 to 2.72 eV as a result of annealing and variation of precursor ratio. The materials demonstrated very low reflectance, which confirmed their good absorption quality. The refractive index of the material indicated abnormal and normal dispersion regions with uniform peaks, which were slightly blue-shifted upon annealing. High optical conductivity in the order of 10¹¹ S⁻¹ were measured, which confirmed the good photoresponse of the films. The absorption and extinction coefficients of the materials were in good agreement with the high ultraviolet–visible (UV–Vis) absorption observed. Finally, the synthesized materials were adjudged to be suitable for photovoltaic (PV) application, photocatalysis, thermoelectrics, photo diodes, disinfectants, antibacterial activity, gas sensing and optical communication.