Correlation between the optical and microstructural characteristics and surface wettability transition of In2O3:Sn/ZnO nanostructured bilayer system for self-cleaning application

Abstract

In this research, in the Glass/In2O3: Sn/ZnO nanostructured bilayers system, In2O3: Sn and ZnO thin films were deposited onto glass using thermal evaporation and spray pyrolysis, respectively. The thin films were annealed at 350, 400‚ 450‚ 500‚ and 550 °C for 90 min. The primitive purpose of this study was to explain the effect of annealing temperature on the wettability, optical, microstructural, and morphological properties of the bilayers using UV–vis spectrophotometer, advanced x-ray diffraction (XDA) analysis, atomic force microscope (AFM), and scanning electron microscope (SEM). Various parameters were determined, including the transmission and reflection coefficients, optical energy band gap, extinction coefficient, refractive index, lattice strain, dislocation density, root mean square roughness, and water contact angle for the samples before UV exposure. The wettability results showed that the hydrophobicity of the In2O3: Sn/ZnO nanostructured thin films without UV radiation was improved by increasing the annealing temperature due to the increase in root mean square (RMS) roughness. Microstructural analysis indicated that increasing the annealing temperature increased crystallite size and decreased the lattice strain. The contact angles of the samples were significantly reduced, and the surface wettability of the layers changed from hydrophobic to hydrophilic after the UV treatment. Finally, the correlation between the optical, microstructural, morphological, and wettability features of the samples was determined. The effective optical band gap was observed to have a linear, inverse square, and quadratic correlation with strain, crystallite size, and dislocation density, respectively.