Effect of ion bombardment on the field emission of a zinc oxide cathode

The effects of ion bombardment on the field emission of screen printed tetrapod zinc oxide cathodes are reported. The field emission characteristics of this cathode degrade strongly after Ar ion bombardment for 10min at an energy of 3keV and ion current of 5µA. The emission current density decreases from 1.65 to 0.32mA/cm
²
at 4.50V/µm field strength, while the turn-on field increases from 2.16 to 3.11V/µm at a current density of 0.1µA/cm
²
. This result demonstrates that the field emission of the ZnO emitters severely degrades upon ion bombardment. The emission degradation can be attributed to a lower value of the field enhancement factor β, which is caused by changes of the morphology, and a higher work function ϕ, which is caused by changes of the surface composition of ZnO.