Investigation of NiV-based multilayers for the High Energy X-ray Probe

The High Energy X-ray Probe (HEX-P) is a NASA probe-class mission concept that will combine high spatial resolution X-ray imaging (<10 arcsec FWHM) and broad spectral coverage (0.1−150 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. Optimized nanometer-thin Ni-based multilayer coatings enable high performance of focusing X-ray telescopes to energies up to 150 keV and beyond, though current fabricated Ni-based coatings contain high interfacial roughness which will affect the predicted performance of the telescope. As part of the thin film coating development for the High Energy X-ray Probe, we report on the current development of reducing the coating roughness in periodic NiV/Si multilayer coatings. The multilayers are fabricated using the direct current magnetron sputtering coating facility at DTU Space, using different types of sputtering collimators and different reactive sputtering gas concentrations, optimized for the production of low interfacial roughness. The multilayers are characterized using X-ray reflectometry and X-ray photoelectron spectroscopy. More information on HEX-P, including the full team list, is available at hexp.org.