Performance and time stability of Ir/SiC X-ray mirror coatings for ATHENA

Abstract

Excellent X-ray reflective mirror coatings are key in order to meet the performance requirements of the ATHENA telescope. The baseline coating design of ATHENA was initially formed by Ir/B 4 C but extensive studies have identified critical issues with the stability of the B 4 C top layer which shows strong evolution over time and appears incompatible with the industrialization processes required for the production of mirror modules. Motivated by the need for a compatible top layer material to improve the telescope performance at low energies and based on simulated performance, a SiC top layer has been selected as the best substitute to B 4 C. We report the latest development of Ir/SiC bilayer coatings optimized for ATHENA and the characterization of coating performance and stability.

LEXR: A low-energy X-ray reflectometer for characterization of ATHENA mirror coatings

“…They are required to have high performance in the energy range from 0.3 to 12 keV which is obtained by utilizing mirror substrates coated with a combination of high and low-Z materials. The current baseline coating for ATHENA is an Ir/SiC bilayer design optimized for the energy band in question 3,4 . Previous studies performed at DTU Space have established that the requirement for effective area can be achieved at both 1 keV and at 6 keV using a combination of bilayer coatings and/or linear graded multilayers 5,6 .…”

Status of the silicon pore optics technology

“…In 2018 we commissioned a fully automated plate coating machine [19,20], discussed elsewhere in these proceedings. It is already able to coat up to 100.000 plates per year.…”

Development and manufacturing of SPO X-ray mirrors

“…After wedging, a final processing step is necessary to boost the reflectivity of the SPO mirror plates. Metal coatings such as iridium and low-Z overcoatings such as SiC or B4C are currently under investigation as materials for obtaining the required X-ray reflectivity for Athena [16,17]. Patterning of the metal layer is needed to ensure bondability of the silicon mirror plates during the stacking process.…”

“…This report details the process steps utilized in the manufacture of silicon mirror plates for SPO [10,[12][13][14][15][16][17][18]. The plate manufacturing process begins with double-sided polished 300 mm wafers, and ends with diced, ribbed, wedged, and coated SPO plates which can be subsequently stacked to form an optical unit [1,2].…”