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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: James C. Wyant
  • Vol. 47, Iss. 23 — Aug. 10, 2008
  • pp: 4196–4204

Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics

Fredrik Eriksson, Naureen Ghafoor, Franz Schäfers, Eric M. Gullikson, Samir Aouadi, Susanne Rohde, Lars Hultman, and Jens Birch  »View Author Affiliations


Applied Optics, Vol. 47, Issue 23, pp. 4196-4204 (2008)
http://dx.doi.org/10.1364/AO.47.004196


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Abstract

Cr/Sc and Ni/V multilayers, intended as normal incidence soft x-ray mirrors and Brewster angle polarizers, have been synthesized by employing a novel modulated low-energy and high-flux ion assistance as a means of engineering the interfaces between the subnanometer layers on an atomic scale during magnetron sputter deposition. To reduce both roughness and intermixing, the ion energy was modulated within each layer. The flat and abrupt interfaces yielded soft x-ray mirrors with near-normal incidence reflectances of R = 20.7 % at the Sc 2 p absorption edge and R = 2.7 % at the V 2 p absorption edge. Multilayers optimized for the Brewster angle showed a reflectance of R = 26.7 % and an extinction ratio of R s / R p = 5450 for Cr/Sc and R = 10 % and R s / R p = 4190 for Ni/V. Transmission electron microscopy investigations showed an amorphous Cr/Sc structure with an accumulating high spatial frequency roughness. For Ni/V the initial growth mode is amorphous and then turns crystalline after 1 / 3 of the total thickness, with an accumulating low spatial frequency roughness as a consequence. Elastic recoil detection analyses showed that N was the major impurity in both Cr/Sc and Ni/V with concentrations of 15 at. % and 9 at. %, respectively, but also O (3 at. % and 1.3 at. %) and C (0.5 at. % and 1.9 at. %) were present. Simulations of the possible normal incidence reflective properties in the soft x-ray range of 100 600 eV are given, predicting that reflectivities of more than 31% for Cr/Sc and 5.8% for Ni/V can be achieved if better control of the impurities and the deposition process is employed. The simulations also show that Cr/Sc is a good candidate for mirrors for the photon energies between the absorption edges of B ( E = 188 eV ) and Sc ( E = 398.8 eV ).

© 2008 Optical Society of America

OCIS Codes
(230.1480) Optical devices : Bragg reflectors
(230.4170) Optical devices : Multilayers
(240.0310) Optics at surfaces : Thin films
(310.1620) Thin films : Interference coatings
(340.7470) X-ray optics : X-ray mirrors

ToC Category:
Optical Devices

History
Original Manuscript: April 7, 2008
Revised Manuscript: July 3, 2008
Manuscript Accepted: July 4, 2008
Published: August 4, 2008

Virtual Issues
Vol. 3, Iss. 9 Virtual Journal for Biomedical Optics

Citation
Fredrik Eriksson, Naureen Ghafoor, Franz Schäfers, Eric M. Gullikson, Samir Aouadi, Susanne Rohde, Lars Hultman, and Jens Birch, "Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics," Appl. Opt. 47, 4196-4204 (2008)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-47-23-4196


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