Electron Emission Preceding Electrical Breakdown in Vacuum

Abstract
An applied field of 105 V/cm produces electron emission from apparently smooth surfaces at room temperature. It is found experimentally that this prebreakdown emission is independent of emitter temperature up to 1000°K. Using a shadow electron microscope, projections about 2 μ high capable of producing field enhancements on the order of 100 have been found on optically polished cathodes at prebreakdown emission sites. This, with other evidence, strongly indicates that prebreakdown emission is Fowler—Nordheim field emission, due to a geometrical field enhancement.