As part of the thin film development for the Athena X-ray telescope and X-ray optics in general, we investigated the residual stress in iridium and chromium thin films deposited using direct current magnetron sputtering. Residual stresses in thin films can affect the performance and adhesion properties of the fabricated thin film coated X-ray optics. We characterized the thin films using X-ray reflectometry to determine the thin film thicknesses and stylus profilometry to determine the residual film stresses. To counterbalance the compressive stress identified in the iridium thin films, we introduced a chromium thin film layer for which the residual stress is tensile beneath the iridium film. However, chromium thin films are known to exhibit a grainy growth resulting in a high surface roughness which was also observed in this work. In this paper, we evaluated the effect on the iridium surface roughness when introducing a chromium underlayer and discussed the effect on the X-ray optics performance.
We present a number of example studies of telescope optics using the latest version of the AstroX add on toolbox for McXtrace. Among which are first, a benchmark study of effective area and vignetting for the Chandra X-ray Observatory which we find to match well with literature. Second, a convenient way of building a telescope model (in this case NuSTAR) with many similar optical elements scripted using python module. This lends itself well to be included in online notebooks and/or for teaching. Third, we show a new AstroX module for lobster eye optics, and fourth, a study of the proposed solar axion telescope BabyIAXO.
The mirror coatings for the Athena X-ray telescope assumes Ir/SiC bilayer thin films as a baseline design. Adding the soft overcoat to the Ir X-ray mirror coatings for the Athena optics is used to improve the low energy performance necessary to achieve the telescope effective area requirements. The Athena mirror is based on silicon pore optics technology, for which the manufacturing process involves a sequence of wet chemical and thermal post-coating treatments of the mirror plates. Establishing compatibility of the thin film material candidates following exposure to these processes is critical for the Athena mission since the specific coating quality will influence the performance of the X-ray telescope. We present an investigation of Ir and Ir/SiC thin films exposed to post-coating treatments based on coatings produced at DTU Space. The current status of the chemical procedures is presented with representative coatings from the Athena-dedicated coating facility.
A state-of-the-art Low-Energy X-ray Reflectometer (LEXR) is in operation at DTU Space with the main purpose of characterizing coatings for the Advanced Telescope for High-ENergy Astrophysics (ATHENA), a selected Lclass ESA mission. In particular, soft materials are difficult to characterize at higher energies so the 1.487 keV beamline compliments our existing 8.048 keV reflectometer, allowing for a more complete understanding of thinfilm X-ray characteristics. Documenting and qualifying the as-deposited coatings for X-ray telescope optics is of crucial importance, both to ensure that the effective area requirements are met, but also to quantify any temporal evolution in coating characteristics as well as the impact of manufacturing process parameters on mirror performance. It is notably relevant in the case of ATHENA, as there is a desire to enhance the low-energy performance by using a low-Z material overcoating on top of the Ir coating. We report on the commissioning and qualify the performance of the as-built 1.487 keV reflectometer as well as discuss measurement repeatability and system limitations.
Multilayer (ML) thin film coatings have shown promise in achieving hard x-ray nanofocusing with high reflectivity and high resolution. The chemical, structural, and long-term stability of Ir/B4C MLs, which are of great interest to the synchrotron and astrophysics communities, are not yet fully understood. The evolution of the x-ray performance of Ir/B4C ML mirrors was monitored over 5 years, and the chemical and structural properties were investigated in depth. Reflectivity scans reveal significant alteration in the energy range of 3.4 to 10 keV over this period. Furthermore, thickness and density degradation of B4C layers were observed in scanning electron transmission microscopy results. The oxidation of B4C occurs only for the top layers, whereas the buried B4C layers go through various complex chemical modifications. The x-ray reflectivity model of Ir/B4C structure was modified, based on the experimental findings, and resulted in good understanding of the long-term reflectivity performance of the x-ray mirror coatings.
Qualification of coating performance at the low-energy range of the Advanced Telescope for High Energy Astrophysics (ATHENA) is important to ensure that the mirror coatings satisfy the performance criteria required to meet ATHENA's science objectives. We report on the design, implementation, and expected performance of a state-of-the-art Low-Energy X-ray Reflectometer (LEXR) acquired with the purpose of qualifying the soft energy X-ray performance of mirror coatings for ATHENA. The reflectometer components are housed in a vacuum chamber and utilizes a microfocus Al source with custom made Kirkpatrick-Baez mirrors and W/Si monochromator to produce a collimated beam of 1.487 keV photons. The system has been designed with source interchangeability, allowing reconfiguration to an 8.048 keV reflectometer using a Cu source or other energies with sources such as Fe, Mg, etc. Several mirror samples can be mounted on a motorized stage, and a 2D CCD camera is used to obtain spatially resolved detection.
X-ray reflectivity (XRR) characterization of X-ray mirrors is an essential step for designing space telescopes and instruments. We report on production and characterization of platinum thin films coated onto a at thick glass substrate for evaluating measurement results obtained using several XRR systems. The main objective of this study is to compare the XRR results measured using facilities at the Technical University of Denmark, DTU Space, and BESSY II for the Advanced Telescope for High-ENergy Astrophysics (ATHENA) mission funded by the European Space Agency, ESA. This sample will be used as a reference sample for testing and calibrating similar measurements at relevant X-ray facilities. This information demonstrates the stable performance of the platinum mirror as a reference sample. Also, the overlayer effect on mirror performance is investigated.
We present the latest progress on the industrial scale coating facility for the Advanced Telescope for High-ENergy Astrophysics (ATHENA) mission. The facility has been successfully commissioned and tested, completing an important milestone in preparation of the Silicon Pore Optics (SPO) production capability. We qualified the coating facility by depositing iridium and boron carbide thin films in different configurations under various process conditions including pre-coating in-system plasma cleaning. The thin films were characterized with X-Ray Reectometry (XRR) using laboratory X-ray sources Cu K-α at 8.048 keV and PTB's four-crystal monochromator beamline at the synchrotron radiation facility BESSY II in the energy range from 3.6 keV to 10.0 keV. Additional X-ray Photoelectron Spectroscopy (XPS) measurements were performed with Al K-α radiation to analyze the composition of the deposited thin films.
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/B4C but extensive studies have identified critical issues with the stability of the B4C 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 B4C. We report the latest development of Ir/SiC bilayer coatings optimized for ATHENA and the characterization of coating performance and stability.