Synthetics of ZnO nanostructures by thermal oxidation in water vapor containing environments

Metallic Zn films deposited on glass were wet or dry oxidized at 390 °C in pure N2 or O2 to understand the effects of water vapor in different oxygen partial pressure on growth of ZnO nanostructure during thermal oxidation. As-prepared ZnO oxides were characterized by a scanning electron microscope (SEM), an X-ray diffractometer (XRD), and a transmission electron microscope (TEM). Optical and electric properties of these ZnO films were characterized by photoluminescence (PL) and resistance measurements, respectively. It was found that the oxygen partial pressure and water vapor of environment significantly affect the morphologies of ZnO nanostructures. Decreasing oxygen partial pressure in dry oxidation can enhance a green light peak at 500 nm on PL spectra arising from defect-related emission and reduce the resistivity of the oxide films. High H2O(g)/O2 ratio in wet oxidation will significantly increase the intensity of a green light peak and reduce the resistivity of the oxide films. The effect of oxygen partial pressure and H2O(g)/O2 ratio on the PL spectra and resistivity of ZnO films are explained by the theory of defects equilibrium during oxidation.