Spectroscopic ellipsometry as a sensitive monitor of materials contamination

Spectroscopic ellipsometry is demonstrated to be extremely sensitive to contamination layers in the thickness range from 0.1 nm to 10 microns. In the present experiments we deposit either a thin lubricating oil (WD-40) or mineral oil continuously onto Ir, Cu, Al, Au, and V substrates from a bubbler, and monitor its thickness growth from sub-nanometer to tens of nanometers as a function of time. Re-evaporation of contaminant oils is also monitored in real-time by ellipsometry

LEO degradation of graphite and carbon-based composites aboard Space Shuttle Flight STS-46

Six different types of carbon and carbon-boron nitride composites were exposed to low Earth orbit aboard Space Shuttle flight STS-46. The samples received a nominal atomic oxygen fluence of 2.2 x 10(exp 20) atoms/sq cm in 42 hours of exposure. Pyrolytic graphite and highly oriented pyrolytic graphite showed significant degradation, and the measured erosion yield was within a factor of two of published values. The erosion yield of pyrolytic boron nitride was found to be 2.6 x 10(exp 26) cu cm/atom in plasma asher exposure, over 42 times lower than that of pyrolytic graphite. This low erosion yield makes graphite plus boron nitride mixtures quite resistant to low Earth orbit exposure. Evidence suggests that the graphitic component was preferentially etched, leaving the surface boron nitride rich. Degradation resistance increases with boron nitride composition. Carbon fiber/carbon composites degraded in low Earth orbit, and the carbon pitch binder was found to etch more easily than the graphite fibers which have much higher degradation resistance

Degradation of Thin Films: Comparison Between Low Earth Orbit Experiments and Laboratory Simulations of the Space Environment

The low Earth orbit (LEO) environment exposes spacecraft materials to atomic oxygen, UV light, meteroid impact and thermal cycling. The purpose of this paper is to report on progress towards evaluating damage done to candidate space materials, and ways to protect materials on future long-term space missions in LEO. Specifically, we prepared and characterized sets of samples for flights on the US Space Shuttle missions STS-46 and STS-51, and evaluated samples returned from STS-46. In addition, laboratory simulations of the LEO environment are shown to present interesting problems and challenges