SILAR synthesized nanocrystalline ZnO thin films: Role of varying dipping cycles on engineering the structural properties and optical band gap

The accumulation of nanocrystalline ZnO thin films on microscopic glass substrate was achieved using a straightforward and affordable SILAR procedure with altered dipping cycles ranging from 50 to 80. Nanocrystalline ZnO thin films are produced using 0.1 M ZnSO4.H2O aqueous solution as the cationic precursor, 25% ammonia solution was used to adjust the pH to 10.5 and deionized water at 90oC as the oxidizing solution. In this specific research, multiple batches of ZnO films with 50, 60, 70 and 80 SILAR dipping cycles were fabricated. An investigation of crystallographic, morphological, and optoelectronic properties of ZnO thin films was carried out using XRD, SEM, UV-VIS double beam spectrophotometer (JASCO V-630) and two-probe method. XRD analysis revealed well crystallized films oriented predominantly along (1 0 0), (0 0 2) and (1 0 1) planes. A polycrystalline ZnO structure with a hexagonal wurtzite arrangement was found to be present in the films. From the SEM pictures it is seen that the number of SILAR dipping sessions has affected the surface properties of the nanocrystalline ZnO thin films. The fabricated films exhibit interconnected nanosheets featuring an extremly porous interface. UV-Vis spectroscopic examination performed at ambient temperature indicates that the films exhibit varied spectral band gap values with different dipping cycles, and the value of optical band-gap varies between 3.27 eV to 3.19 eV. Two-probe experiment revealed that the number of SILAR dipping cycles affected the electrical resistance of ZnO thin films that were nanocrystalline.