Field emission from zinc oxide nanotowers: the role of the top morphology

Arrays of novel nanometer-scale tower-shaped structures of zinc oxide (ZnO nanotowers) were synthesized by a simple thermal evaporation method. Due to the difference in fabrication conditions, ZnO nanotowers with similar body structure but different top morphologies were obtained. These ZnO nanotowers with different top morphologies showed obvious disparity in field emission, despite their overall field enhancement factor and density being the same. The nanotowers with the sharpest top had the lowest turn-on and threshold electric field. This disparity is attributed to the different local field enhancement factors at the nanotower tops, which were calculated both from the field emission data and by simulation. The above results have demonstrated the essential importance of the top morphology of a ZnO nanostructure in field emission.