An instrument for experimental secondary electron emission investigations, with application to the spacecraft charging problem.

摘要

Secondary electron emission (SEE) and incident-particle backscattering are important processes accompanying the impact of energetic electrons and ions on surfaces. The phenomena play a key role in the build-up of electrical charge on spacecraft surfaces, and are therefore of particular interest to scientists attempting to model spacecraft charging. In response to a demonstrated need for data, a technique for determining total secondary electron (SE) and backscatter (BS) yields {dollar}delta{dollar} and {dollar}eta{dollar}, and associated scattering-angle-resolved, scattering-energy-resolved, and simultaneous angle-energy-resolved yields has been developed. Further, an apparatus capable of making the necessary measurements for experimental determination of these quantities--for conducting materials in a UHV environment--has been designed, constructed, and partially tested. The apparatus is found to be in working order, though in need of fine-tuning, and the measurement technique successful.; Investigations using a 1-3 keV beam of monoenergetic electrons normally incident on bulk Al have been undertaken with the new apparatus. Electron-stimulated desorption of surface contaminants has been observed, as has been beam-induced carbon deposition, and an empirical model describing the resulting dynamic evolution of {dollar}delta{dollar} is presented. Total {dollar}delta{dollar} and {dollar}eta{dollar} values obtained in the present investigation are found to be in qualitative agreement with the results of previously reported investigations, though quantitative disagreement of {dollar}delta{dollar}-values is substantial. Specifically, evidence is presented suggesting that previously reported SE yields for clean Al under electron bombardment (in the 1-3 keV energy range) are in error by as much as 30%.