Low temperature growth of aligned ZnO nanowires and their application as field emission cathodes

Aligned ZnO nanowires have been synthesized by annealing gold deposited zinc foil in air at 400 °C. The X-ray diffraction pattern indicates formation of ZnO possessing hexagonal wurtzite structure along with binary phases like Au3Zn and AuZn3. The scanning electron microscope images depict presence of densely distributed aligned ZnO nanowires, having length of several microns and diameter in the range of 40–80 nm. The transmission electron microscope and selected area electron diffraction analysis confirms the nanocrystalline nature of the ZnO wires exhibiting preferential growth along the [0 0 1] direction. Based on the microscopic analysis a possible growth mechanism of the ZnO nanowires is presented. From the field emission studies, the value of the turn-on field corresponding to an emission current density of 0.1 μA cm−2 is found to be 2.4 V μm−1 and a current density of 100 μA cm−2 is obtained at an applied field of 3.4 V μm−1. The field emission current stability investigated over a period of 3 h at the preset value of 1 μA is found to be promising. The simplicity of the synthesis rout coupled with the promising field emission properties offer unprecedented advantage for the use of ZnO field emitters for high current density applications.