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22 January 1993 Effect of oxygen atom bombardment on the reflectance of SiC mirrors in the extreme-ultraviolet region
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Chemical vapor deposited (CVD) silicon carbide mirrors were exposed to bombardment by 8 km/s (5.2 eV) oxygen atoms that simulated exposure in low earth orbit for periods up to 7.5 years. The reflectances of four mirrors were measured before and after exposure at 584, 736, 1048, 1216, and 1610 angstroms and at eleven angles of incidence ranging from 5 degree(s) to 80 degree(s). The oxygen exposure reduced the normal incidence reflectances by factors of 1.5 to 4.5 in the VUV but had no effect on the visual appearance. The optical constants and thicknesses of the surface layers present on the SiC substrates were determined from reflectance measurements. This analysis indicated that before exposure the surface layers were composed of SiOx (where x approximately equals 1.5) with thicknesses of 8 - 18 angstroms. After exposure the thicknesses had increased to 35 - 45 angstrom. There were no systematic differences in the reflectances after simulated space exposures of 1.5, 4.5, and 7.5 years. This implied that most of the growth in thickness of the SiOx layers occurred early in the exposure and stabilized at thicknesses of 35 - 45 angstroms. The optical results were consistent with x-ray photoelectron spectroscopy of the four mirrors after oxygen exposure.
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John F. Seely, Glenn E. Holland, William R. Hunter, Robert P. McCoy, Kenneth F. Dymond, and Michael R. Corson "Effect of oxygen atom bombardment on the reflectance of SiC mirrors in the extreme-ultraviolet region", Proc. SPIE 1764, Ultraviolet Technology IV, (22 January 1993);


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