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 10 min at an energy of 3 keV and ion current of 5 muA. The emission current density decreases from 1.65 to 0.32 mA/cm² at 4.50 V/mum field strength, while the turn-on field increases from 2.16 to 3.11 V/mum at a current density of 0.1 muA/cm². 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 beta, which is caused by changes of the morphology, and a higher work function phi, which is caused by changes of the surface composition of ZnO.