PROPERTIES OF Ni/C AND Ni_xSi_y/C MULTILAYERED REFLECTION COATINGS

Abstract
We present results of measurements on multilayered reflection coatings (multilayers), and discuss the possibility to use multilayers as a dispersive element in a double crystal monochromator. The multilayers discussed are produced at the FOM-Institute AMOLF in Amsterdam, and have appr. 160 layers with 4Å thicknesses of Ni or Ni_xSi_y, and 18Å C. The use of multilayers offers a tool for the monochromatization of synchrotron radiation in the soft x-ray region. The throughput spectrum of a monochromator, equipped with a pair of identical multilayers, will be shown. From oscillations present at the high energy side of the Ni-L_2,3 edge (at about 850 eV) in the throughput spectra, we determined bondlengths in the interfaces between 1.8 and 2.3 Å. The bondlength of 1.8 Å is assigned to Ni - C [1], 2.1 Å to Ni - Si [2] and 2.3 Å to Ni - Ni [1]. We found strong evidence that the stoichiometry of the Ni_xSi_y layer is Ni₂Si. Ni_xSi_y/C coatings deposited in a 10^-6 torr H₂ atrnosphere show a better resolution than those without. The difference is ascribed to H₂ preventing the formation of silicides and the diffusion of the Ni into the carbon, resulting in more amorphous layers.