Coatings technology for CVD diamond optics

Tim P. Mollart; Keith L. Lewis; Christopher J. H. Wort; Charles S. James Pickles

doi:10.1117/12.439176

7 September 2001 Coatings technology for CVD diamond optics

Tim P. Mollart, Keith L. Lewis, Christopher J. H. Wort, Charles S. James Pickles

Proceedings Volume 4375, Window and Dome Technologies and Materials VII; (2001) https://doi.org/10.1117/12.439176
Event: Aerospace/Defense Sensing, Simulation, and Controls, 2001, Orlando, FL, United States

Abstract

CVD diamond optics are now available for far infrared airborne applications in both flat plate and dome geometries. For many applications, these require durable coatings for antireflection and/or oxidation protection. With a high characteristic modulus, diamond may allow the use of relatively weaker materials for such coatings provided that the coatings are well-adhered to the substrate. Single layer and two-layer designs have been assessed based on yttria, ytterbia and silicon. Magnetron sputtered examples have been assessed with single layer coatings reducing single surface reflectivities by 12%, whilst maintaining transmission to 13.5 micrometers . The erosion properties of these coated optics, assessed by water jet impact testing (MIJA), are found to be exceptional, with damage thresholds > 350 ms^-1 achieved, with a 0.8 mm jet size. The pre-deposition treatment of the diamond has been found to influence the strength of the diamond/coating interface and thus the durability of the coatings. The nature of the diamond surface and the effects of oxidizing pre-deposition treatments have been investigated by X-ray electron spectroscopy (XPS). Strong oxidizing etches conventionally used to clean diamond can leave the surface rich in chemisorbed oxygen with a range of valence states evident in XPS data. In comparison, the valence states of the carbon atoms at hydrogen terminated surfaces have a much narrower distribution. The type of carbon oxygen bonding on the surface of the diamond is critical to adhesion of transition metal oxide based coatings.

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Tim P. Mollart, Keith L. Lewis, Christopher J. H. Wort, and Charles S. James Pickles "Coatings technology for CVD diamond optics", Proc. SPIE 4375, Window and Dome Technologies and Materials VII, (7 September 2001); https://doi.org/10.1117/12.439176

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