The Energy Analysis of Electrons Emitted from Localised Sites on Extended-Area High Voltage Electrodes

Abstract

An advanced high resolution hemispherical electron spectrometer has been used to measure the energy spectra of the pre-breakdown electron currents emitted from localised sites on broad-area high voltage electrodes under U.H.V. (~ 10-10 torr) conditions. Four electrode materials have been examined which are of interest in the industrial application of high voltage vacuum insulation. The energy spectra of these electron currents are shifted to low energies by ~ 100-500meV compared to that normally obtained from a metallic field emission source. This displacement is characteristic of the electron energy spectra of semiconducting microtip emitters. A qualitative model for the emission mechanism at these sites has therefore been proposed which involves electron tunnelling through a semiconducting/insulating oxide or impurity microstructure overlaying the metallic electrode surface. This model also accounts for other important properties of the emission sites such as their apparently high field enhancement (β) factor as predicted from the Fowler-Nordheim graphs and their very localised existence. Complementary electron optical and X-Ray analysis studies have also been carried out which provide supporting evidence for this interpretation.