Catalyst-Free Synthesis of ZnO Nanorods by Thermal Oxidation of Zn Films at Various Temperatures and Their Characterization

We synthesized ZnO nanostructures on glass substrates by using the thermal oxidation of Zn films and investigated their structural and optical properties. The scanning electron microscopy images showed the structural changes induced in the Zn films, which transformed into oxidized ZnO thin films at 500 and 600 °C, and into oxidized ZnO nanorods at 700 °C. In the X-ray diffraction, the Zn films oxidized at 200, 300, and 400 °C did not exhibit any ZnO-related diffraction peaks, whereas the Zn films oxidized at 500, 600, and 700 °C exhibited the ZnO diffraction peaks. The full width at half maximum (FWHM) values of the ZnO nanostructures prepared at 500, 600, and 700 °C were 0.38°, 0.21°, and 0.17°, respectively. The decrease in the FWHM value with the increase in the oxidation temperature meant that the crystalline quality of the ZnO nanostructures improved with the increasing oxidation temperature. In the Photoluminescence spectra, the intensity of near- band-edge (NBE) emission gradually increased with increasing oxidation temperature to 700 °C and especially the ZnO nanostructures prepared at 600 and 700 °C exhibited broad green emissions which were attributed to the oxygen vacancies and surface defects.