Direct and catalyst-free synthesis of ZnO nanowires on brass by thermal oxidation

In this research work, nanowires were grown on brass (Cu - 37.2 wt% Zn) substrate by thermal oxidation process. The substrate was oxidized at temperature ranging from 350-600 °C in the presence of varying concentrations of O2 in N2 (1-100%) flown at a rate of 200 sccm. The oxidized brass surface was characterized by field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectroscope and transmission electron microscope (TEM). Four different types of morphological variations such as thin, thick with branches, circular-flake and flat-cone shape were observed during oxidation at different conditions. However, the prevalence of thin, thick morphology with branches was more prominent and found in all growth conditions. The length and diameter of the nanowires were varied from 1-30 µm and 50-500 nm, respectively whereas the length of the branches varied from 1-3 µm. The composition of the nanowires was ZnO possessing of hexagonal wurtzite structure. The selected area diffraction confirms that the nanowires grew along <1 1 0> directions. Based on the results, a stress induced based mechanism is proposed for the growth of ZnO nanowires on Cu - 37.2 wt% Zn substrate.