Coatings for FEL optics: preparation and characterization of B4C and Pt

Large X-ray mirrors are required for beam transport at both present-day and future free-electron lasers (FELs) and synchrotron sources worldwide. The demand for large mirrors with lengths up to 1   m single layers consisting of light or heavy elements has increased during the last few decades. Accordingly, surface finishing technology is now able to produce large substrate lengths with micro-roughness on the sub-nanometer scale. At the Helmholtz-Zentrum Geesthacht (HZG), a 4.5   m-long sputtering facility enables us to deposit a desired single-layer material some tens of nanometers thick. For the European XFEL project, the shape error should be less than 2   nm over the whole 1   m X-ray mirror length to ensure the safe and efficient delivery of X-ray beams to the scientific instruments. The challenge is to achieve thin-film deposition on silicon substrates, benders and gratings without any change in mirror shape. Thin films of boron carbide and platinum with a thickness in the range 30 – 100   nm were manufactured using the HZG sputtering facility. This setup is able to cover areas of up to 1500   mm × 120   mm in one step using rectangular sputtering sources. The coatings produced were characterized using various thin-film methods. It was possible to improve the coating process to achieve a very high uniformity of the layer thickness. The movement of the substrate in front of the sputtering source has been optimized. A variation in B4C layer thickness below...

Source: Journal of Synchrotron Radiation - December 7, 2017 Category: Physics Authors: St ö rmer, M. Siewert, F. Horstmann, C. Buchheim, J. Gwalt, G. Tags: FEL X-ray mirrors FEL optics coatings research papers Source Type: research