Ultra-short-period W/B{sub 4}C multilayers for x-ray optics-microstructure limits on reflectivity

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Multilayer thin films are used as Bragg reflectors for soft x-rays in the energy range 50eV < E < 1000eV in many x-ray optics applications such as x-ray microscopes and telescopes, reducing optics for extreme ultraviolet (EUV) lithography, and x-ray polarizers and phase retarders. Applications often depend critically on reflectivity, which has not been systematically characterized for multilayer periods below 20{angstrom}. For this study, W/B{sub 4}C multilayers were fabricated by magnetron sputtering on Si(111), with periods from 48{angstrom} to as little as 4.7{angstrom}. The x-ray reflectivity measured at {lambda} = 1.54{angstrom} and at 45{degrees} incidence (289 eV < E < ... continued below

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145 p.

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Walton, C.C. December 1, 1997.

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  • Walton, C.C. Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

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Multilayer thin films are used as Bragg reflectors for soft x-rays in the energy range 50eV < E < 1000eV in many x-ray optics applications such as x-ray microscopes and telescopes, reducing optics for extreme ultraviolet (EUV) lithography, and x-ray polarizers and phase retarders. Applications often depend critically on reflectivity, which has not been systematically characterized for multilayer periods below 20{angstrom}. For this study, W/B{sub 4}C multilayers were fabricated by magnetron sputtering on Si(111), with periods from 48{angstrom} to as little as 4.7{angstrom}. The x-ray reflectivity measured at {lambda} = 1.54{angstrom} and at 45{degrees} incidence (289 eV < E < 860 eV) was found to decrease sharply for multilayer periods less than 15-20{angstrom}. Examination by high-resolution transmission electron microscopy (HRTEM) showed an expansion of the thickness of the W-rich layers of 30-40% from the nominal values, consistent with intermixture of the two materials during sputter growth, and discontinuous W-rich layers for multilayer periods below about 15{angstrom}. The experimental data for the specular reflectivity in the hard and soft x-ray regimes and the diffuse scattering fit well to a model of multilayer roughness. The model is expressed as a power-law dependence of roughness on spatial frequency. Analysis of small-angle scattering in transmission from multilayers grown on freestanding Si{sub 3}N{sub 4} membranes confirms the onset of discontinuity at periods between 14{angstrom} and 22{angstrom}. Spectroscopy studies by x-ray absorption (NEXAFS) and electron energy loss (EELS) at the boron K-edge (188eV) are consistent with changes in the average boron bonding environment, as the multilayer period decreases and the W-rich layers are increasingly thin and dispersed. A discrete W-rich phase is present for periods at least as small as 6.3{angstrom}.

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145 p.

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OSTI as DE98052657

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  • Other Information: TH: Thesis (Ph.D.)

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  • Other: DE98052657
  • Report No.: LBNL--41425
  • Grant Number: AC03-76SF00098
  • Office of Scientific & Technical Information Report Number: 588555
  • Archival Resource Key: ark:/67531/metadc690686

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • December 1, 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • April 5, 2016, 11:06 a.m.

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Walton, C.C. Ultra-short-period W/B{sub 4}C multilayers for x-ray optics-microstructure limits on reflectivity, thesis or dissertation, December 1, 1997; California. (digital.library.unt.edu/ark:/67531/metadc690686/: accessed October 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.