Spray-Deposited Coral-Like ZnO Micro/Nano Thin Films on Glass Substrates

In this work, coral-like micro/nano zinc oxide (ZnO) thin films are synthesized onto glass substrates using the low-cost spray pyrolysis (SP) method without using a metal catalyst or surfactant. The films are prepared at substrate temperature T s = 350 ± 3°C, using oxygen as the carrier gas. The structure, surface morphology, composition, and optical properties of the as-deposited thin films are characterized using x-ray diffraction (XRD), scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM–EDS), and UV–VIS spectroscopy, respectively. ImageJ software is used to produce the plot profiles and surface occupancy plots. The XRD diffractogram showed that the films are polycrystalline with hexagonal (wurtzite) structure. SEM observations revealed the formation of coral-like products of different shapes with a wide range of dimensions. The EDS spectrum showed that the films contain Cl in addition to Zn and O. Absorbance is used to infer the transmittance and to estimate the band gap energy, which is found to be E g = 3.37 eV. The fourth derivative of the absorbance revealed the three free exciton peaks A, B, and C. In addition, a strong broad absorption band with several sharp lines is detected in the energy range 1.77–2.50 eV and a weaker absorption band in the energy range 2.48–2.80 eV. This non-catalyst production of coral-like ZnO micro/nano thin films on glass substrates may have potential applications in the industry of nanoelectronic and nanooptical devices, optoelectronics, sensors, nanoscale mechanics research, and solar cells.