Effect of the O2/N2 ratio on the morphology of ZnO nanostructures grown by a thermal evaporation technique

ZnO nanostructures were synthesized by thermal evaporation of Zn powder in an oxygen and nitrogen gas environment at 1000 °C. No substrates or catalysts were used for the formation of the ZnO nanostructures. The ZnO nanostructures were synthesized inside crucibles with Zn source powder. ZnO nanoneedles began to be found at O2/N2 ratios of less than 60/40. As the O2/N2 ratio increased to 80/20, the ZnO nanostructures mainly grew in the longitudinal direction. Upon increasing the O2/N2 ratio to 100/0, the ZnO nanostructures grew mainly in the transverse direction. CL spectra showed that ZnO with a high crystalline quality was obtained at a O2/N2 ratio of 80/20.