Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R=14.5% at a grazing angle of 87.5° measured at the wavelength λ=3.11 nm , which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of σ=0.34 nm and an exceptionally small layer thickness drift of ~1.6×10-5 nm/multilayer period throughout the stack. Simulations show that a reflectivity of R=25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Sc sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (λ=3.374 nm) from a laser plasma source was verified.
© 2003 Optical Society of America
(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
Fredrik Eriksson, Göran A. Johansson, Hans M. Hertz, Eric M. Gullikson, Ulrich Kreissig, and Jens Birch, "14.5% near-normal incidence reflectance of Cr Sc x-ray multilayer mirrors for the water window," Opt. Lett. 28, 2494-2496 (2003)