Optimal Zn/O ratio in vapor phase for the synthesis of high quality ZnO tetrapod nanocrystals via thermal evaporation of Zn in Air

Abstract

Tetrapod-shaped ZnO nanocrystals were synthezised via thermal evaporation of Zn powder in air. The Zn powder was oxidized at 930°C for 60min. To investigate the optimal Zn/O molar ratio in such vapor phase synthesis, the Zn content was varied in range of 0.1–0.75g. When the Zn content was 0.1g, no nanocrystals were formed. Above 0.25g Zn, growth of ZnO nanocrystals started without clear tetrapod like morphology. Beyond Zn content of 0.50g, clear tetrapod-shaped ZnO nanocrystals were detected. These results establish that there is a certain required ratio of zinc and oxygen in vapor phase for generation of tetrapod-shaped ZnO nanocrystals. Such Zn:O ratio is also calculated theoretically from the ideal gas law. Clear tetrapod type ZnO nanocrystals prepared with Zn content of 0.5g exhibited the highest intensity of the ultraviolet emission centered at 380nm which also confirms the high crystalline quality of such ZnO nanocrystals.