The effect of oxygen pressure in the synthesis of ZnO nanostructures through thermal evaporation of Zn powder was investigated. The thermal evaporation process was carried out in oxygen ambient for 1 hr at 1,000℃ under different pressures. The oxygen pressure was changed in range of 0.5 ? 900 Torr. Any nanostructure was not formed on the specimens prepared at oxygen pressures lower than 10 Torr. When oxygen pressure was 100 Torr, ZnO nanowires were observed. With increasing the oxygen pressure to 500 Torr, the morphology of ZnO nanostructures changed from wire to tetrapod. For all the samples, room temperature photoluminescence spectra show a strong green emission peak at around 550 nm.

ZnO nanostructures with tetrapod, needle and multipod shapes were synthesized without catalysts through a simple thermal oxidation of metallic Zn powder in alumina crucible under air atmosphere. X-ray diffraction data revealed that the ZnO nanostructures had wurtzite structure of hexagonal phase. Energy dispersive X-ray (EDX) spectra showed that the ZnO was of high purity. After the oxidation of Zn powder, white colored product was mainly observed and yellow colored product was observed only a very little on the surface of the oxidized source materials. The white product consisted of tetrapods, while yellow product was composed of needles and multipods. Cathodoluminescece spectra showed that the crystalline quality of tetrapods was better that those of needles and multipods.