Improved X-Ray Filters with Al-Sc Alloys and Nanoparticle-Doped Polyimide

The next generation of detectors for high energy observatories needs a significant improvement in filter technology, as identified in the SBIR solicitation and as a PCOS technology gap. We propose a two-fold change in the state of the art of thin film EUV and x-ray filters, using Al-Sc alloy in place of Al and adding Au nanoparticles to polyimide. Al-Sc alloys show smaller grain sizes that should translate to increased strength and decreased optical/IR transmission, even for alloying fractions <1% that would not noticeably impact the x-ray spectrum. Surface plasmon resonances (SPR) in Au nanoparticles allow tunable absorption peaks for optical thermal control and baking. Since SPRs effectively enlarge the absorption cross section of nanoparticles, we expect to achieve a narrowband visible optical depth of ~0.2 with an x-ray transmittance of >95% (nanoparticles only). We lay out a fabrication and testing plan to push these technologies from TRL2 to TRL4 by the end of Phase I by demonstrating heating of doped films, optical and infrared density of alloyed films, and beamline measurements of x-ray transmittance and density of constituent species in integrated Al-Sc/doped polyimide filters.