Grazing incidence specular reflectance and near specular scattering of uncoated and multilayer coated substrates are measured at Al-K(alpha) (1.486 keV) and Cu-K(alpha) (8.047 keV). Substrates included superpolished fused silica, SiO<SUB>2</SUB> wafer, superpolished and precision ground Zerodur, float polished BK7 glass, and precision ground silicon carbide. Surface topography of these substrate had been measured with the Scanning Probe Microscope (SPM) and a Talystep mechanical profiler. The results showed that roughnesses obtained from 100 micrometer X 100 micrometer SPM images and 100 micrometer Talystep profiles were in good agreement with that calculated from the Al-K(alpha) X-ray measurements. X-ray measurements of the multilayers deposited on these substrates are very important. The results of this study can be used as a foundation of calculating the X-ray specular reflectance and diffuse scattering at grazing incidence from multilayer coated mirrors. We coated these substrates with Pt/C multilayers. Its periodical length were 40 angstrom and number of layer pairs was 40. The measured reflectivity showed no significant correlation between interfacial roughness of multilayers and the substrate surface roughness. The interfacial roughness of most samples scattered around 3 - 4 angstrom except for the precision ground silicon carbide and the precision ground Zerodur. The surface roughness of these exceptional substrates are considerably larger value of 6 angstrom and 9 angstrom rms from Talystep measurement. When the surface roughness of the substrate is small enough, typically less than 3 angstrom interfacial roughness of multilayers are considered to be independent from substrates.
We present a current status of the development of hard x-ray telescope using Pt/C multilayer supermirror. The telescope system is to be made by combining thin foil replication technology for high throughput mirror and multilayer supermirror coating technology for hard x-ray reflection. After the successful multilayer coating on the replica foil mirror, we made the performance demonstration model of this type of telescope, having 20 replica foil supermirrors, 10 primary and 10 secondary reflectors, with focal length of 4.75 m and radius of 100 mm. Pt/C multilayer supermirror structure was designed and optimized to have high and flat reflectivity for x-ray energy from 25 through 40 keV. After some efforts to avoid heat damage of replica foil mirror during the deposition process of multilayer by DC sputtering system, we could establish the fabrication method of supermirror structure on replica foil mirror. Based on the x-ray measurement, we found that this demonstration model showed the half power diameter of 1.9 arcmin for had x-rays and nearly the same reflectivity and energy band width as expected. In this paper, we present the design of graded multilayer as the supermirror, the fabrication and the performance of this demonstration model.
In the fabrication of the x-ray reflector using the replication method, Au was thought as the only material which can be used as the surface of reflector. However, if we could use the Pt or Ir, these has higher electron density than Au, as the surface, we can obtain higher reflectivity especially in the hard x-ray band. Furthermore, direct replication of the multilayer is very useful for the high reflectivity and mass-production process. We used the Au replica foil as the substrate of the multilayer. However, the epoxy layer of the replica foil was easily damaged by the heat during the deposition. This is a serious problem for the mass-production process, since we must take a long time to deposit the multilayer to keep the high reflectivity. We studied the direct replication of the multilayer, and successes to obtain the reflectivity as high as original one. Furthermore, we keep the trying to improve the quality of the reflector as flight quality. We will report the results and feature prospects of the replication of the multilayer and its application to the hard x-ray telescope.
We present new results in the development of high throughput hard x-ray telescopes with multilayer supermirror coatings. Basic techniques to make the supermirror are at first developed in deposition of constant d spacing multilayers. The reflector of multilayer on the float glass achieves high reflectivity, limited by the surface roughness of substrate, while, we need more improvement in getting comparable reflectivity of multilayers on the replica foil. We put the mask just in front of sample, it reduced the nonuniformity of the thickness less than 2%. In order to maximize the effective area and field of view, we have optimized the supermirror parameters; d spacing, number of layer pairs, and thickness ratio of heavy and light element. Multiblock method is introduced to design the supermirror, and it gives high reflectivity of approximately 30% in the 25 - 40 keV band. A test supermirror sputtered on a glass sample exhibits reasonable reflectivities of about 20 - 30%. We designed a telescope system with 45 cm diameter, 20 cm mirror length in two stage, and focal length of 8 m. The effective area of four such telescopes is 320 cm<SUP>2</SUP> for the x rays between 25 and 40 keV. We plan the application of this type of telescope to the balloon experiment named InFOC(mu) S to reveal hard x-ray images of clusters of galaxies or supernova remnants.