We have fabricated periodic multilayers that comprise either Si/Tb or SiC/Tb bilayers, designed to operate as narrowband reflective coatings near 60 nm wavelength in the extreme ultraviolet (EUV). We find peak reflectance values in excess of 20% near normal incidence. The spectral bandpass of the best Si/Tb multilayer was measured to be 6.5 nm full width at half-maximum (FWHM), while SiC/Tb multilayers have a more broad response, of order 9.4 nm FWHM. Transmission electron microscopy analysis of Si/Tb multilayers reveals polycrystalline Tb layers, amorphous Si layers, and relatively large asymmetric amorphous interlayers. Thermal annealing experiments indicate excellent stability to 100°C (1 h) for Si/Tb. These new multilayer coatings have the potential for use in normal incidence instrumentation in a region of the EUV where efficient narrowband multilayers have not been available until now. In particular, reflective Si/Tb multilayers can be used for solar physics applications where the coatings can be tuned to important emission lines such as O V near 63.0 nm and Mg X near 61.0 nm.
© 2005 Optical Society of America
(230.4170) Optical devices : Multilayers
(310.1620) Thin films : Interference coatings
(310.6860) Thin films : Thin films, optical properties
(340.0340) X-ray optics : X-ray optics
(350.1260) Other areas of optics : Astronomical optics
David L. Windt, John F. Seely, Benjawan Kjornrattanawanich, and Yu. A. Uspenskii, "Terbium-based extreme ultraviolet multilayers," Opt. Lett. 30, 3186-3188 (2005)