Spectroscopic Ellipsometry Characterization of Polymers Modified by Atomic Oxygen and Ultraviolet Radiation
Atomic oxygen (AO) and ultraviolet (UV) radiation-induced surface modifications of several space application polymers are investigated with spectroscopic ellipsometry (SE). The polymers studied include Kapton® polyimide, FEP Teflon®, CV-1144-0 silicone and polyarylene ether benzimidazole (PAEBI). Using in situ and ex situ SE covering a large spectral range from 190 nm to 14 μm, various parameters and trends of the polymers are measured as they are exposed to AO and/or UV light.
UV light greater than 200 nm wavelength is used to modify the surface of PAEBI and Kapton. Thickness and index of refraction as a function of depth of the UV-modified surface layers is quantified. The modified layers are optically-modelled assuming an exponentially graded layer, as opposed to standard models that often use either a single homogenous layer or linearly-graded layer. Measurements show that UV light causes a decrease in the index of refraction in both materials. The damaged layer in Kapton is approximately 500 nm into the polymer and approximately 200 nm in the PAEBI.
Two oxide forming polymers, CV-1144-0 silicone and PAEBI, are exposed to AO in an oxygen plasma. Protective oxide layers that form on the polymers are studied using SE. Oxide formation trends, rates of oxidation, amount of porosity, volume percentage of water, and change in optical properties as a function of AO exposure are quantified. Furthermore, studying the change in molecular bond vibrations in the infrared allowed a quasi-chemical analysis of the silicone.
Single wavelength ellipsometry over a large range of incident angles is used to measure changes in potical density of aluminizedFEP Teflon after being exposed to the Low Earth Orbit environment aboard the Hubble Space Telescope. The purpose of the study is to help support physical density measurements acquired by NASA Lewis Research Center. The optical density measurements are in good agreement with physical density measurements. These measurements are in good agreement with excessive heating was a major contributor to increases in density of the FEP returned from the second servicing mission.
KeywordsPorosity Quartz Anisotropy Argon Hydroxide
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