Date of Award:

1996

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Physics

Advisor/Chair:

J.R. Dennison

Abstract

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 buildup 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, techniques for determining total secondary electron (SE) and backscatter (BS) yields (del) and (neu), and associated scattering-angle-resolved,scattering-energy-resolved, and simultaneous angle-energy-resolved yields have been developed. Further, an apparatus capable of making the necessary measurements for experimental determination of these quantities---for conducting materials in an ultra-high vacuum 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 AI 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 (del)is presented. Totalb and 11 values obtained in the present investigation are found to be in qualitative agreement with the results of previously reported investigations, though quantitative disagreement of b-values is substantial. Specifically, evidence is presented suggesting that previously reported SE yields for clean AI under electron bombardment (in the 1-3 Kev energy range) are in error by as much as 30 %.

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