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.