Enrichment of the field emission properties of NiCo2O4 nanostructures by UV/ozone treatment

Abstract

Herein, UV/O₃ treatment was imposed on the hydrothermally synthesized spinel NiCo₂O₄ urchin like structure to study its enhancement effect on the field electron emission properties. The FE studies revealed that UV/O₃ treated NiCo₂O₄ possesses a 4.38 V μm⁻¹ turn on field at 1 μA and an emission current density of 386 μA cm⁻², whereas pristine NiCo₂O₄ retains 5.69 V μm⁻¹ turn on field at 1 μA and 168 μA cm⁻² emission current density. The enhancement in the FE characteristics of UV/O₃ treated NiCo₂O₄ is attributed to the change in the electronic structure of the emitter due to UV/O₃ treatment. Experimental data were supported through electronic structure simulations using Density Functional Theory technique. We have achieved the modification of the electronic properties of spinel NiCo₂O₄ due to the oxygen vacancy created by UV/O₃ treatment. There is an enhancement of electronic states near the Fermi level due to oxygen vacancy. The computed work function reduces when oxygen vacancy is introduced on the surface of pristine NiCo₂O₄ which justifies the enhancement in the field electron emission after UV/O₃ treatment. Due to O vacancy, there is charge gain by the 3d orbital of Ni and Co whereas there is a charge loss by the 2p orbital of the O atom near the vacancy. The results suggest UV/O₃ treatment can be practiced in the field electron emission investigation to retain a good current density for practical applications.