TY - CHAP A1 - Döhring, Thorsten A1 - Probst, Anne-Catherine A1 - Stollenwerk, Manfred A1 - Emmerich, Florian A1 - Stehlíková, Veronika A1 - Inneman, Adolf ED - Hudec, René ED - Pina, Ladislav T1 - Prototyping iridium coated mirrors for X-ray astronomy T2 - Proceedings of the International Society for Optics and Photonics N2 - X-ray astronomy uses space-based telescopes to overcome the disturbing absorption of the Earth´s atmosphere. The telescope mirrors are operating at grazing incidence angles and are coated with thin metal films of high-Z materials to get sufficient reflectivity for the high-energy radiation to be observed. In addition the optical payload needs to be light-weighted for launcher mass constrains. Within the project JEUMICO, an acronym for “Joint European Mirror Competence”, the Aschaffenburg University of Applied Sciences and the Czech Technical University in Prague started a collaboration to develop mirrors for X-ray telescopes. The X-ray telescopes currently developed within this Bavarian- Czech project are of Lobster eye type optical design. Corresponding mirror segments use substrates of flat silicon wafers which are coated with thin iridium films, as this material is promising high reflectivity in the X-ray range of interest. The deposition of the iridium films is based on a magnetron sputtering process. Sputtering with different parameters, especially by variation of the argon gas pressure, leads to iridium films with different properties. In addition to investigations of the uncoated mirror substrates the achieved surface roughness has been studied. Occasional delamination of the iridium films due to high stress levels is prevented by chromium sublayers. Thereby the sputtering parameters are optimized in the context of the expected reflectivity of the coated X-ray mirrors. In near future measurements of the assembled mirror modules optical performances are planned at an X-ray test facility. KW - X-ray KW - iridium KW - mirror KW - lightweight optic KW - Lobster Eye KW - Iridium KW - Röntgenastronomie KW - Spiegelteleskop Y1 - 2017 U6 - https://doi.org/10.1117/12.2265931 VL - 2017 IS - 10235 SP - 1023504-1 EP - 1023504-8 PB - SPIE International Society for Optics and Photonics CY - Bellingham WA ER - TY - JOUR A1 - Probst, Anne-Catherine A1 - Stollenwerk, Manfred A1 - Emmerich, Florian A1 - Büttner, Andre A1 - Zeising, Sebastian A1 - Stadtmüller, Johannes A1 - Riethmüller, Franziska A1 - Stehlikova, Veronika A1 - Mingwu, Wen A1 - Proserpio, Laura A1 - Damm, Christine A1 - Rellinghaus, Bernd A1 - Döhring, Thorsten T1 - Influence of sputtering pressure on the nanostructure and the X-ray reflectivity of iridium coatings JF - Surface and Coatings Technology N2 - Reflective mirror coatings made of iridium are used in X-ray telescopes of the Chandra X-ray Observatory (CXO) launched in 1999 by the National Aeronautics and Space Administration (NASA) to investigate astronomical sources at photon energies below 10. keV. These coatings were produced in a DC magnetron sputtering process and have so far proven their suitability for space-based applications. We are considering in the present paper the processing of thin iridium films for lightweight telescopes using the radio frequency magnetron sputtering technique with an oblique angle deposition. The coating development presented here is focused on the influence of total sputtering pressure on film properties as well as on its impact on the mirror's performance. Characterisation methods such as X-ray diffractometry, X-ray reflectometry, atomic force microscopy and transmission electron microscopy have been used. Correlations between morphology, density, surface micro-roughness, crystal structure of the iridium layer and the expected reflectivity of the X-ray mirror are described and discussed. KW - Iridium KW - sputtering KW - microstructure KW - coating KW - X-ray KW - Iridium KW - Röntgenteleskop Y1 - 2017 UR - https://doi.org/10.1016/j.surfcoat.2017.10.062 SN - 0257-8972 VL - 2017 IS - 343 SP - 101 EP - 107 ER - TY - JOUR A1 - Büttner, Andre A1 - Probst, Anne-Catherine A1 - Emmerich, Florian A1 - Damm, Christine A1 - Rellinghaus, Bernd A1 - Döhring, Thorsten A1 - Stollenwerk, Manfred T1 - Influence of Sputtering Pressure on the Microstructure and Layer Properties of Iridium Thin Films JF - Thin Solid Films N2 - Iridium layers with low stress, high density, and low surface roughness find widespread use in different high-technology applications. This paper presents a study of the influence of the sputtering pressure on the properties of iridium thin films and of its effect on the substrate surface microstructure. We analysed the dependence of the microstructure, crystalline structure, electrical resistivity, and deposition rate on the sputtering pressure and surface defects of the substrate. For the latter, plasma etching of the substrate was performed for different processing times and its effect on the surface roughness of substrates and, subsequently, on the grown iridium films, was examined. The sputtering pressure and the substrate plasma etching time both had a strong influence on the microstructure and surface roughness. These microstructural changes are in good agreement with the tendency described in the Thornton Structure-Zone Model for different sputtering pressures and the microstructure phase map of Alvarez. The electrical resistivity, deposition rate, and crystalline structure were highly dependent on the sputtering pressure. KW - Iridium KW - microstructure KW - TEM KW - sputtering KW - thin films KW - Iridium KW - Dünne Schicht Y1 - 2018 UR - https://doi.org/10.1016/j.tsf.2018.06.056 SN - 0040-6090 VL - 2018 IS - 662 SP - 41 EP - 46 ER - TY - CHAP A1 - Döhring, Thorsten A1 - Probst, Anne-Catherine A1 - Emmerich, Florian A1 - Stollenwerk, Manfred A1 - Stehlikova, Veronika A1 - Friedrich, Peter A1 - Damm, Christine T1 - Development of iridium coated X-ray mirrors for astronomical applications T2 - Proceedings of the International Society for Optics and Photonics (SPIE) N2 - Future space-based X-ray observatories need to be very lightweight for launcher mass constraints. Therefore they will use a reduced mirror thickness, which results in the additional requirement of low coating stress to avoid deformation of the initial precisely shaped mirror substrates. Due to their excellent reflection properties iridium coatings are sometimes applied for grazing incidence mirrors in astronomical X-ray telescopes. At Aschaffenburg University of Applied Sciences the coating of thin iridium films by an RF-magnetron sputtering technique is under development. The work is embedded in collaborations with the Max-Planck-Institute for Extraterrestrial Physics in Germany, the Czech Technical University in Prague, the Osservatorio Astronomico di Brera in Italy, the German Leibniz Institute for Solid State and Materials Research in Dresden, and the French Institute Fresnel. Sputtering with different parameters leads to iridium films with different properties. The current work is focused on the microstructure of the iridium coatings to study the influence of the substrate and of the argon gas pressure on the thin film growing process. Correlations between coating density, surface micro-roughness, the crystalline structure of the iridium layers, and the expected reflectivity of the X-ray mirror as well as coating stress effects are presented and discussed. The final goal of the project is to integrate the produced prototype mirrors into an X-ray telescope module. On a longer timescale measurements of the mirror modules optical performance are planned at the X-ray test facility PANTER. KW - X-ray KW - telescope KW - mirror KW - iridium KW - coating KW - Iridium KW - Röntgenteleskop Y1 - 2017 U6 - https://doi.org/10.1117/12.2273988 VL - 2017 IS - 10399 SP - 103991C-1 EP - 103991C-8 PB - SPIE ER - TY - JOUR A1 - Probst, Anne-Catherine A1 - Begou, Thomas A1 - Döhring, Thorsten A1 - Zeising, Sebastian A1 - Stollenwerk, Manfred A1 - Stadtmüller, Johannes A1 - Emmerich, Florian A1 - Lumeau, Julien ED - Publishing OSA, T1 - Coating stress analysis and compensation for iridium-based x-ray mirrors JF - Applied Optics N2 - Iridium-based coatings for mirrors of x-ray telescopes are studied. In particular, stress-induced deformation is characterized and shown to be compressive and equal to −1786  MPa. Two methods for stress compensation are then studied. One relies on the deposition of silica on the back surface of the substrate and a second one relies on the deposition of a chromium sublayer. Advantages and drawbacks of each of these techniques are presented. KW - iridium KW - coating stress KW - X-ray KW - mirror KW - astronomy KW - Röntgenteleskop KW - Iridium KW - Spiegelteleskop Y1 - 2018 UR - https://doi.org/10.1364/AO.57.008775 VL - 2018 IS - 57 (29) SP - 8775 EP - 8779 ER -