@article{ProbstStollenwerkEmmerichetal.2017, author = {Probst, Anne-Catherine and Stollenwerk, Manfred and Emmerich, Florian and B{\"u}ttner, Andre and Zeising, Sebastian and Stadtm{\"u}ller, Johannes and Riethm{\"u}ller, Franziska and Stehlikova, Veronika and Mingwu, Wen and Proserpio, Laura and Damm, Christine and Rellinghaus, Bernd and D{\"o}hring, Thorsten}, title = {Influence of sputtering pressure on the nanostructure and the X-ray reflectivity of iridium coatings}, series = {Surface and Coatings Technology}, volume = {2017}, journal = {Surface and Coatings Technology}, number = {343}, issn = {0257-8972}, pages = {101 -- 107}, year = {2017}, abstract = {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.}, subject = {Iridium}, language = {en} } @inproceedings{DoehringProbstEmmerichetal.2017, author = {D{\"o}hring, Thorsten and Probst, Anne-Catherine and Emmerich, Florian and Stollenwerk, Manfred and Stehlikova, Veronika and Friedrich, Peter and Damm, Christine}, title = {Development of iridium coated X-ray mirrors for astronomical applications}, series = {Proceedings of the International Society for Optics and Photonics (SPIE)}, volume = {2017}, booktitle = {Proceedings of the International Society for Optics and Photonics (SPIE)}, number = {10399}, publisher = {SPIE}, doi = {10.1117/12.2273988}, pages = {103991C-1 -- 103991C-8}, year = {2017}, abstract = {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.}, subject = {Iridium}, language = {en} } @article{ProbstBegouDoehringetal.2018, author = {Probst, Anne-Catherine and Begou, Thomas and D{\"o}hring, Thorsten and Zeising, Sebastian and Stollenwerk, Manfred and Stadtm{\"u}ller, Johannes and Emmerich, Florian and Lumeau, Julien}, title = {Coating stress analysis and compensation for iridium-based x-ray mirrors}, series = {Applied Optics}, volume = {2018}, journal = {Applied Optics}, number = {57 (29)}, editor = {Publishing OSA,}, pages = {8775 -- 8779}, year = {2018}, abstract = {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.}, subject = {R{\"o}ntgenteleskop}, language = {en} }