Recent development of cryogenic detectors enabled high resolution
diagnostics of emission line and absorption line/edge
structures. These studies are quite important to investigate physics
of interstellar/intergalactic plasma and dynamics of matters around
black holes, for example.
Soft X-ray telescopes for such purpose, sensitive up to 10 keV, are
usually designed using Au, Pt, or Ir for their large electron density
and large critical angle. However in fact, these materials are not
very suitable in a few to 8 keV region, because they have wide and
deep M-shell absorption edge structures in 2--4 keV region.
Considering absorption edges and also thin-film characteristics, C or
Ni can be alternatives. However, these materials alone cannot be a
good mirror, again from absorption edges in the energy region of
interest (0.1-10 keV). We designed composite structure consisting of
C, Ni and Pt with thickness of 30 to 300 A, to get smooth and high
reflectivity all across the energy region. Test fabrication showed
interfacial roughness is as low as expected, indicating match of
materials is also good.
We applied this result to the baseline design of NeXT/Soft X-ray
Telescope, by substituting current material (Au) with C-Ni-Pt
composite, and obtained 20% larger effective area in 2-8 keV region.
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