12 May 2015 Low-stress coatings for sputtered-sliced Fresnel zone plates and multilayer Laue lenses
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The application of thin film coating processes for the fabrication of diffractive X-ray optical elements like sputteredsliced zone plates or multilayer Laue lenses (MLL) is a very promising approach for X-ray focusing down to spot sizes of < 10 nm. However, for practical useful focal length in the order of several millimeters or a few centimeters, multilayer thicknesses of several 10 μm up to a few 100 μm are necessary in order to have large enough numerical apertures of the lenses. Currently one of the main challenges is to coat low-stress multilayers with large total thicknesses in the order of 100 μm. Usually sputter deposition results in thin films with significant compressive stress. With new material combinations such as Mo/MoSi2/Si/MoSi2 and W/WSi2/Si/WSi2 the overall stress can be reduced to almost zero if the individual thicknesses are properly adapted. In the case of these four-layer-systems only the period thickness dp follows the zone plate law. In case of Mo/MoSi2/Si/MoSi2, stress-free multilayers are obtained with dMo = 0.5*dp, dMoSi2 = 0.16*dp and dSi = 0.34*dp.
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Stefan Braun, Adam Kubec, Peter Gawlitza, Maik Menzel, Andreas Leson, "Low-stress coatings for sputtered-sliced Fresnel zone plates and multilayer Laue lenses", Proc. SPIE 9510, EUV and X-ray Optics: Synergy between Laboratory and Space IV, 95100L (12 May 2015); doi: 10.1117/12.2178851; https://doi.org/10.1117/12.2178851

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