Field emission behavior of vertically aligned ZnO nanowire planar cathodes

Abstract

A field emission (FE) study by scanning anode field emission microscopy was performed to evaluate the FE properties of vertically aligned zinc oxide (ZnO) nanowire arrays electrodeposited on a plane conductive surface. The specific FE behaviors of the cathode observed experimentally are (1) a turn-on macroscopic field of about 6 V/μm for a FE current density JFE = 5 × 10−4 A/cm2, (2) a stable FE characteristics for 5 × 10−4 < JFE < 5 × 10−2 A/cm2, and (3) a brutal shut down of FE when JFE crossed a limiting value of ∼0.05 A/cm2 due to a rapid evolution of the nanowires toward a bulbous tip geometry or a complete melting. A physical process of FE from ZnO nanostructures is proposed from the experimental data analyses. An effective surface barrier of about 1 eV was determined from the experimental Fowler–Nordheim plot and the presence of a Zn enriched surface was assumed in considering the possibility of important modifications of the crystallography and charge transfers at the surface of ZnO nanowires during the application of the strong electric field required for FE.