14 December 1992 Diamond layers for the protection of infrared windows
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In comparison with presently available LWIR (8 - 12 micrometers ) window materials, diamond has unsurpassed optical and thermomechanical properties. However, the manufacture of bulk diamond optical components is still in its infancy and many years effort are required to develop the technologies necessary to the fabrication of large windows and domes. In the short term the coating of current LWIR materials (particularly ZnS) with a protective layer of polycrystalline diamond would result in a significant improvement in performance. At GMMTL a high temperature microwave plasma assisted chemical vapor deposition (MPACVD) system has been developed which produces excellent quality diamond films on silicon. It is not so easy to apply this technique to the coating of ZnS since atomic hydrogen in the microwave plasma attacks and rapidly etches the ZnS surface and, in addition, there is a large thermal expansion mismatch between ZnS and diamond that causes decohesion of the film. To solve this problem an advanced physical vapor deposition (PVD) process has been used to deposit interlayers of various LWIR transparent materials onto ZnS to give protection from the plasma and also allow some thermal stress relief. The interlayers have been found to be extremely robust with respect to current nucleation treatments and have allowed continuous diamond films of thickness in excess of 1 micron to be formed onto ZnS. The significance of nucleation treatment and diamond morphology are discussed in the context of gaining the optimal performance both in terms of layer adhesion and IR properties.
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David A. Tossell, David A. Tossell, Mark C. Costello, Mark C. Costello, Crofton J. Brierley, Crofton J. Brierley, } "Diamond layers for the protection of infrared windows", Proc. SPIE 1760, Window and Dome Technologies and Materials III, (14 December 1992); doi: 10.1117/12.130804; https://doi.org/10.1117/12.130804

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