Impact damage as a function of crystal orientation in Ge IR windows employing durable phosphide coatings

Michael Wilson; Marshal Thomas; Ignacio M. Perez; D. Price

doi:10.1117/12.187333

28 September 1994 Impact damage as a function of crystal orientation in Ge IR windows employing durable phosphide coatings

Michael Wilson, Marshal Thomas, Ignacio M. Perez, D. Price

Author Affiliations +

Proceedings Volume 2286, Window and Dome Technologies and Materials IV; (1994) https://doi.org/10.1117/12.187333
Event: SPIE's 1994 International Symposium on Optics, Imaging, and Instrumentation, 1994, San Diego, CA, United States

Abstract

The erosion resistance of thin film epitaxial phosphide coatings has been shown to be affected by substrate crystal orientation when deposited on Ge substrates. GaP was systematically studied using optical microscopy, FTIR spectrophotometry, image analysis and x-ray diffraction. Microstructural aspects of the surface fractures indicated a clear crystallographic preference for erosion. X-ray diffraction identified the (111) plane as having the preferred crystal orientation for erosion resistance and variations of the (100) as the erosion prone planes. Removal of the hard carbon coating was observed in a large number of samples resulting in measurable damage to the GaP layer. Crack morphology was distinctly different in (111) and {100} crystals. (111) planes displayed erosion as discrete isolated pits and {100} planes developed very intricate orthogonal crack networks with pits at the intersections. Depth of damage varied as a function of crystal orientation and non (111) coating sections suffered some substrate exposure. Subsections of (111) protected Ge had an average depth of damage (measured vertically) of 0.47 mm and non (111) subsections had an average depth of damage of 2.3 mm. In most specimens, complex crack networks developed within 10 minutes of exposure to the simulated rain environment. The resultant GaP coating loss averaged 18 percent.

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Michael Wilson, Marshal Thomas, Ignacio M. Perez, and D. Price "Impact damage as a function of crystal orientation in Ge IR windows employing durable phosphide coatings", Proc. SPIE 2286, Window and Dome Technologies and Materials IV, (28 September 1994); https://doi.org/10.1117/12.187333

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