Role of work function in field emission enhancement of Au island decorated vertically aligned ZnO nanotapers

•Hydrothermally synthesized nanotapers were decorated by gold corrugation using simple evaporation techniques for large area applications.•A significantly enhanced field emission properties of nanotapers were achieved.•The metal induced midgap states formed at the ZnO-Au interface and the reduced effective work function are responsible for low turn-on field.•TUNA measurements revealed a very uniform spatial emission profile in the Au decorated nanotapers.

In this report, we demonstrate significantly enhanced field emission properties of ZnO nanotapers achieved via a corrugated decoration of Au. Field emission experiments on these Au-decorated ZnO nanotapers showed emission current densities comparable to the best results in the literature. Au decoration of 5 nm also reduced the effective turn-on field to ∼0.54 V/μm, compared to the as grown ZnO nanotapers, which showed a turn-on field of ∼1.1 V/μm. Tunneling atomic force microscopy measurements revealed a very uniform spatial emission profile in the 5 nm Au decorated nanotapers, which is a basic requirement for any large scale application. We believe that metal induced mid-gap states formed at the ZnO-Au interface are responsible for the observed low turn-on field because such interface states are known to reduce the effective work function. A direct measurement of effective work function using Kelvin probe force microscopy indeed showed more than 1.1 eV drop in the case of 5 nm Au decorated ZnO nanotapers compared to the pristine nanotapers, supporting the above argument.