Structure and scattering properties of Ni80Nb20-MgO water-window multilayer mirrors.

Abstract

Ni80Nb20-MgO multilayers with d spacing that varies from 2.50 to 3.07 nm were prepared by pulsed laser deposition under conditions of ultrahigh vacuum (UHV) and argon. The morphological and atomic structure in the multilayers was determined by hard-x-ray scattering. It was found that the interface roughness in both cases, UHV and argon deposition, is <0.4 nm, whereas the lateral and longitudinal correlation lengths in the case of argon deposition, 5.0 and 1.0 nm, respectively, are an order of magnitude lower. This is due to a reduction in kinetic energy of the condensing species in argon by orders of magnitude due to multiple collisions, which reduces the lateral relaxation probability. Hence the soft-x-ray reflectance of [Ni80Nb20-MgO]10 multilayers deposited in argon was determined at 413 eV (3.00 nm), middle of the water window. The reflectance has a peak at approximately 35.2 degrees with a half-width of 3.5 degrees and 0.19% maximum value. These results agree well with the simulation results performed by use of the structural parameters obtained from hard-x-ray scattering. The atomic structure determined by high-angle x-ray diffraction shows that both Ni80Nb20 and MgO are amorphous in the as-deposited condition.