Transparent ZnO thin films deposited by dip-coating technique: Analyses of their hydrophobic properties

Abstract

Highly transparent ZnO films were deposited on clean glass substrates via the sol-gel technique. The films were prepared by varying the zinc concentration of the precursor solution (0.25, 0.50, 1.00 and 1.25 M) and using annealing temperatures chosen based on the experimental 24 factorial design with 3 replicates. The crystallinities and preferential orientations of the films were influenced by the deposit conditions; at low temperatures, the films showed preferential orientation in the (002) plane, while at high concentrations, the grain lengths were increased. The UV‒Vis spectra showed that the transmittances of the ZnO thin films exceeded 90%, especially for low concentration deposition, which resulted from low light scattering at grain boundaries due to the large grain sizes. The behaviors of the ZnO films matched Wenzel's model, as greater roughness generated a larger effective area and consequently a smaller water contact angle (WCA). The experimental design analysis showed high significance for the WCA results, demonstrating the effects of the concentration and the annealing temperature on the wettability of the film.