Field electron emission from metal surfaces irradiated with helium plasmas

Field emission properties on several different metal surfaces irradiated with helium plasmas were measured. Field emission currents from nanostructure, pinhole, and loop-like tantalum surfaces were significantly higher than that from polished tantalum (Ta) surface. Before and after the micro-breakdown, where the current density was under ~1 μA/mm2, field enhancement factor showed slight increase. On the other hand, significant increase of field enhancement factor was measured after breakdown, where the current density increased up to ~100 μA/mm2. In the scanning electron microscope observation, melted cathode spots were detected. The increment of field enhancement factor after the breakdown may be induced by thermo-field electron emission from the melted spots.