Fabrication of a novel hierarchical assembly of ZnO nanowires on WOx nanowhiskers for highly efficient field electron emission

Abstract

A novel hierarchical heteronanostructure of ZnO nanowires/WO_x nanowhiskers was fabricated using a simple two-step process called the thermal evaporation and solution reaction. A high density of thin ZnO nanowires was uniformly deposited on a WO_x nanowhisker backbone. The density and morphology of the ZnO nanowires were observed to be tunable as a function of reaction parameters, such as reaction time, growth temperature and solution composition. A solution-mediated solid (SS) growth mechanism was proposed for the formation of the ZnO/WO_x hierarchical heteronanostructures. The developed schematic model is consistent with the experimental results as shown in SEM and TEM analyses. Our hierarchical ZnO/WO_x heteronanostructures demonstrated enhanced field electron emission properties in comparison to pristine WO_x nanowhiskers. The turn-on-field voltage and field enhancement factor were comparable to other nanostructured materials, suggesting that ZnO/WO_x hierarchical nanostructures are promising electron emitters in future field emission devices.