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Proceedings Paper

Design and optimization of multilayer coatings for hard x-ray mirrors
Author(s): Adrian Ivan; Ricardo J. Bruni; Kyung Wha Byun; Finn Erland Christensen; Paul Gorenstein; Suzanne E. Romaine
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Paper Abstract

We present the results from a systematic study of several different material combinations for multilayer coatings on flat silicon and fused silica substrates. To obtain high reflectivity in a broad energy bandpass for hard X-rays (greater than 10 keV), a graded d-spacing multilayer structure must satisfy a set of conditions, e.g., low surface and interface roughness/diffuseness, good layer thickness uniformity, low residual stresses, etc. The coating process must be stable and accurately controlled over long deposition times, and allow good reproducibility from one run to another. The deposition method used was DC magnetron sputtering at low argon pressures (1.5 to 3.5 mT). The materials selected for the reflector/spacer pair were W/Si, W/C, Ni/C, and Pt/C. The initial work consisted in calibrating the deposition rate and optimizing the process parameters (argon backpressure, target to substrate distance, and cathode current). The main characterization methods used were: Atomic Force Microscopy in tapping mode, stylus profilometry, and specular X-ray reflectivity. In the next stage of the study, constant and graded d-spacing multilayers were deposited on Si and float glass substrates, with the design structure based on a computer modeling of the X-ray reflectivity dependence with grazing angle and energy. A specular reflectivity scan was performed for each sample at 8.05 keV (and also at higher energies for some samples) and was fitted using the IMD software. Cross-sectional TEM was performed on a limited number of samples to offer additional information. The analyses completed for W/Si, W/C, Pt/C, and Ni/C show for the best samples good uniformity and high reflectivity at 8.05 keV. The work in progress for Cu/Si and Mo/Si will be presented at the conference and will conclude this study of candidate materials and optimized designs for hard X-ray multilayer optics.

Paper Details

Date Published: 16 November 1999
PDF: 6 pages
Proc. SPIE 3773, X-Ray Optics Design, Performance, and Applications, (16 November 1999); doi: 10.1117/12.370082
Show Author Affiliations
Adrian Ivan, Smithsonian Astrophysical Observatory and Massachusetts Institute of Technology (United States)
Ricardo J. Bruni, Smithsonian Astrophysical Observatory (United States)
Kyung Wha Byun, Smithsonian Astrophysical Observatory and Harvard Univ. (United States)
Finn Erland Christensen, Smithsonian Astrophysical Observatory and Danish Space Research Institute (Denmark)
Paul Gorenstein, Smithsonian Astrophysical Observatory (United States)
Suzanne E. Romaine, Smithsonian Astrophysical Observatory and Radcliff College (United States)

Published in SPIE Proceedings Vol. 3773:
X-Ray Optics Design, Performance, and Applications
Ali M. Khounsary; Andreas K. Freund; Tetsuya Ishikawa; George Srajer; Jonathan C. Lang, Editor(s)

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