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Development and qualification of X-ray reflective mirror coatings for the NewAthena mission is progressing with a focus on enabling scientific capabilities of the telescope, given the updated requirements of the redefined mission. In this work, we consider both design and development of Ir/C multilayer coatings optimised to ensure the required performance across the spectral range, facilitating the mission science objectives. We present demonstration of manufacturing capability for the optimised Ir/C multilayer coatings, and compatibility with the Silicon Pore Optics (SPO) technology. Characterisation of X-ray mirror coatings is performed using X-ray reflectometry with a focus on mirror design qualification and long-term stability.

This work investigates the importance of substrate quality and contamination of thin film coatings, essential for high-energy reflective mirrors used in astronomical missions and other applications, focusing on the manufacturing process from substrate selection to final assembly of the optics. Characterization of thin film coatings is crucial for evaluating the performance of X-ray mirrors. Multifaceted and synergized methodologies utilizing Xray reflectometry (XRR), X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM) are presented. Herein, we discuss coating performance, encompassing substrate preparation, coating deposition, and storage conditions. XRR scans provide detailed insights into thin film properties, however, the dependence on accurate a priori knowledge necessitates a robust model for solving the inverse problem. Addressing this limitation, XPS proves invaluable in revealing the chemical composition of thin films, improving the accuracy of the XRR model. Combined characterization through OM and XRR is very useful to find visual insights into surface contamination-induced changes when mirrors are stored for long periods in a clean room environment, as might be the case for some astronomical missions. The synergy among these techniques is pivotal for evaluating coating quality for high-energy astronomical telescopes, with a specific focus on NewAthena and upcoming missions. This research not only advances methodologies in this field but also highlights the collaborative power of XRR, XPS, and OM in providing a comprehensive understanding of thin film coatings, emphasizing the importance of pre-coating mirror quality and mitigating contamination effects throughout the optics production process to ensure optimal performance.

NewAthena (New Advanced Telescope for High–Energy Astrophysics) has been endorsed by the European Space Agency in November 2023 and the mission is entering a pre–industrialization phase prior to the foreseen adoption early 2027. A key aspect of the thin film coating development for the NewATHENA X–ray optics, is to determine the adhesion efficiency and the residual stress limitation of the coatings on silicon substrates. To do so, we magnetron sputtered different layer thicknesses of chromium layers underneath iridium/carbon bilayer and linear graded multilayer coatings. The samples were characterized using X–ray Reflectometry (XRR) to derive the thickness and micro–roughness. The residual stress was assessed by profilometry using a Dektak 150 stylus profilometer. The curvature of the samples before and after coating, along with the total film thickness derived from XRR, was used to evaluate the residual stress.