Re-Generable Field Emission Cathodes Part I: Surface Morphology of In2O3 Emitter Apex

Abstract

This is the first part of a two-part paper that focuses on a field-emission cathode for use in Electric Propulsion (EP) that has the potential for very long lifetime due to its ability to be re-generated when the emitter tip become damaged. The field-emitting tips were formed by the application of an ion-extracting electric potential applied to a heated indium-coated tungsten needle, known as a liquid metal ion source (LMIS). The LMIS is then cooled, freezing in a solid nanotip at the apex. When the modified needle was then subjected to electron-extracting potentials stable and long-lived electron emission was observed. The focus of this investigation was to operate and quench a LMIS at ion emission currents from 2 to 25 A to acquire micrographs of the surface morphology as a function of the ion emission current at quench. The LMISs were also operated at selected ion emission currents for 1’s to 10’s of seconds between quenching to observe the temporal change in emitter tip surface morphology as a function of ion emission current. Micrographs of the quenched emitter tips yielded Taylor-cone-shaped structures. The quenched emitters exhibited multiple nanoprotrusions on the surface of the micro-scale Taylor cone, which were capable of electron field emission.