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Thorium-Based Thin Films as Highly Reflective Mirrors in the EUV

  • Jed E. Johnson (a1), David D. Allred (a2), R. Steven Turley (a3), William R. Evans (a4) and Richard L. Sandberg (a5)...


As applications for extreme ultraviolet (EUV) radiation have been identified, the demand for better optics has also increased. Thorium and thorium oxide thin films (19 to 61 nm thick) were RF-sputtered and characterized using atomic force microscopy (AFM), spectroscopic ellipsometry, low-angle x-ray diffraction (LAXRD), x-ray photoelectron spectroscopy (XPS), and x-ray absorption near edge structure (XANES) in order to assess their capability as EUV reflectors. Their reflectance and absorption at different energies were also measured and analyzed at the Advanced Light Source in Berkeley. The reflectance of oxidized thorium is reported between 2 and 32 nm at 5, 10, and 15 degrees from grazing. The imaginary component of the complex index of refraction, β, is also reported between 12.5 and 18 nm. Thin films of thorium were found to reflect better between 6.5 and 9.4 nm at 5 degrees from grazing than all other known materials, including iridium, gold, nickel, uranium dioxide, and uranium nitride. The measured reflectance does not coincide with reflectance curves calculated from the Center for X-Ray Optics (CXRO) atomic scattering factor data. We observe large energy shifts of up to 20 eV, suggesting the need for better film characterization and possibly an update of the tabulated optical constants.



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2. Takemoto, K., et al. , “Transmission x-ray microscopy with 50 nm resolution in Ritsumeikan synchrotron radiation center,” X-ray Microscopy AIP Conference Proceedings 446–51 (2–6 Aug 1999).
3. Allred, D. D., Squires, M. B., Turley, R. S., Cash, W., and Shipley, A.. “Highly reflective uranium mirrors for astrophysics applications,” Proc. SPIE 4782, 212223 (2002).
4. Lunt, S., “Determining the indices of refraction of reactively sputtered uranium dioxide thin films from 46 to 584 angstroms,” M.S. Thesis (BYU, Provo, UT, 2000).
8. Johnson, J. E., “Thorium Based Mirrors for High Reflectivity in the EUV,” Undergraduate Thesis (Brigham Young University, Provo, UT, 2004).
9. Windt, D., “IMD-software for modeling the optical properties of multiplayer films,” American Institute of Physics 12 (4), 360370 (1998).
10. Sandberg, Richard L., Allred, David D., Lunt, Shannon, Urry, Marie K., Steven Turley, R., “Optical Properties and Application of Uranium-based Thin Films for the Extreme Ultraviolet and Soft X-ray Region,” in Optical Constants of Materials for UV to X-Ray Wavelengths,” edited by Soufli, Regina, and Seely, John F., Proceedings of SPIE, Vol. 5538, (SPIE, Bellingham, WA, 2004) 107118.
11. Smith, J.F., Carlson, O.N., Peterson, D.T., and Scott, T.E., THORIUM: Preparation and Properties, 1st ed. (The Iowa State University Press, Ames IA, 1975,) p. 324.
12. Storms, Edmund K., The Refractory Carbides, (Academic Press, New York, 1967).
14. Henke, B.L., Gullikson, E.M., and David, J.C., “X-ray Interactions,” Atomic Data and Nuclear Data Tables, 54(2), (1993) see ref 230 on p. 342.



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