Synthesis of Ni-doped ZnO nanostructures by low-temperature wet chemical method and their enhanced field emission properties

Abstract

In this study, we report an enhancement in the field emission (FE) properties of ZnO nanostructures obtained by doping with Ni at a base pressure of ∼1 × 10⁻⁸ mbar, which were grown by a simple wet chemical process. The ZnO nanostructures exhibited a single-crystalline wurtzite structure up to a Ni doping level of 10%. FESEM showed a change in the morphology of the nanostructures from thick nanoneedles to nanoflakes via thin nanorods with an increase in the Ni doping level in ZnO. The turn-on field required to generate a field emission (FE) current density of 1 μA cm⁻² was found to be 2.5, 2.3, 1.8 and 1.7 V μm⁻¹ for ZnO (Ni0%), ZnO (Ni5%), ZnO (Ni7.5%) and ZnO (Ni10%), respectively. A maximum current density of ∼872 μA cm⁻² was achievable, which was generated at an applied field of 3.1 V μm⁻¹ for a Ni doping level of 10% in ZnO. Long-term operational current stability was recorded at a preset value of 5 μA for a duration of 3 h and was found to be very high. The experimental results indicate that Ni-doped ZnO-based field emitters can open up many opportunities for their potential use as an electron source in flat panel displays, transmission electron microscopy, and the generation of X-rays. Thus, the simple low-temperature (∼80 °C) wet chemical synthesis approach and the robust nature of the ZnO nanostructure field emitter can provide prospects for the future development of cost-effective electron sources.