Date of Award:

5-2014

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Physics

Committee Chair(s)

JR Dennison

Committee

JR Dennison

Committee

D. Mark Riffe

Committee

Eric Held

Committee

James S. Dyer

Abstract

Spacecraft charging is the accumulation of an electrical charge on orbiting spacecraft induced by the space plasma environment and has harmful effects on the electrical functionality of a spacecraft. This is studied extensively, particularly in the Materials Physics Group (MPG) at Utah State University (USU). During charging studies performed by the MPG, another potentially problematic effect of the space plasma environment on spacecraft was observed: light emanating from the sample undergoing electron beam bombardment. Space-based observatories are one type of spacecraft on which this luminescence may occur. If the luminescence from the material caused by the space plasma is within the field of view of the collection optics on the observatory or emanating from the collection optics themselves, the observatory images will be tainted by this light contamination. This problem provides the main motivation behind these experiments. It can also have applications in microelectronics, geological dating, and other fields.

The process of electron-induced luminescence, or cathodoluminescence, provides information on and insight into the electronic band structure of the material undergoing radiation. The energetic incident electrons excite electrons within the material from low-energy states to high-energy states. From there, electrons can undergo light emitting relaxation into trapped states residing in the material’s band gap. Trapped states exist in the band gap because there are defect sites (doping sites or other sites, which deviate from the crystalline structure) within the structure of the material. The cathodoluminescence intensity and wavelength range behaviors in disordered SiO2 are the focus of this thesis. The intensity has been shown to change as incident electron current density and energy change and as temperature varies. Further, wavelength spectral data show there are multiple defect bands available for relaxation.

The Utah State Materials Physics Group, with the funding of the NASA James Webb Space Telescope project and a NASA Space Technology Research Fellowship, is currently studying this phenomenon for disordered SiO2 (as is presented here) and is extending their work to other materials.

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