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The effects of atomic oxygen on space coatings
Abstract
Amorphous silicon dioxide and aluminum oxide films are being considered by NASA for application on low earth orbit solar space reflectors as oxidation protective coatings. Using monolayer sensitive Variable Angle Spectroscopic Ellipsometry (VASE) the author has investigated the diffusion of atomic oxygen through deposited films of these materials. Atomic oxygen was generated in an RF plasma chamber using pure oxygen. Conversion of silver to silver oxide was used for the detection of atomic oxygen. Mainly, the grain boundary diffusion of oxygen was attributed to the diffusion of atomic oxygen through a deposited film. A new proposal, made by the author for improving the protective layer quality, was to deposit a thin aluminum layer on top of silver before depositing the silver oxide were also determined by VASE technique. To investigate the mechanisms of atomic oxygen diffusion through (grown) silicon dioxide films, the growth of silicon dioxide on top of silicon(111), caused by atomic oxygen diffusion, was monitored using VASE. A "kink" at about 30 Angstroms of silicon dioxide thickness was observed in the oxide growth curve for each of the plasma powers used by the author. Various theories were investigated for explaining the experimental data. The Murali and Murarka theory was found to be in reasonable agreement with the data. For an alternative explanation, a theory involving the formation of pores during the initial stages of oxide growth is proposed by the author. Development of these pores was probed using the VASE technique, and above about 30 Angstroms of oxide thickness, no further pore growth was found. The temperature and pressure dependencies of silicon dioxide growth were also investigated by the author. Finally the effects of atomic oxygen on Indium Tin Oxide (ITO) films were studied by the author using X-ray diffraction, optical transmission, VASE and resistivity measurements. It was found that increased ashing results in lower resistivity and increased optical absorption of the film, before reaching a saturation point.
Subject Area
Condensation|Optics
Recommended Citation
De, Bhola Nath, "The effects of atomic oxygen on space coatings" (1990). ETD collection for University of Nebraska-Lincoln. AAI9108217.
https://digitalcommons.unl.edu/dissertations/AAI9108217