Periodic and depth-graded Cu/Si multilayer films for hard x-ray optics

We describe the growth and characterization of periodic and depth-graded Cu /Si multilayer structures for use as coatings in hard x-ray optics. Films h ave been grown by dc magnetron sputtering, and were characterized by grazin g-incidence x-ray (8 keV) reflectance analysis. The x-ray reflectance of bo th periodic and depth-graded structures was found to be high, and stable at room temperature over a period of at least several months. The interface w idths determined from fits to the x-ray reflectance data were found to lie in the range 0.23-0.3 nm. X-ray diffraction revealed no crystalline phases present in any of the films, only broad peaks indicating either an amorphou s Cu or possibly copper-silicide phase. As a result of the small measured i nterface widths and the low x-ray absorption of Cu just below, and also far above the Cu K edge (similar to 9 keV), highly efficient depth-graded Cu/S i multilayer coatings can now be used for broadband, grazing-incidence x-ra y mirrors, for x-ray energies greater than at least 100 keV. (C) 1999 Ameri can Institute of Physics. [S0003-6951(99)04119-4].