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 have been grown by dc magnetron sputtering, and were characterized by grazing-incidence x-ray (8 keV) reflectance analysis. The x-ray reflectance of both 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 widths 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 amorphous Cu or possibly copper–silicide phase. As a result of the small measured interface widths and the low x-ray absorption of Cu just below, and also far above the Cu K edge ( ∼ 9 keV), highly efficient depth-graded Cu/Si multilayer coatings can now be used for broadband, grazing-incidence x-ray mirrors, for x-ray energies greater than at least 100 keV. © 1999 American Institute of Physics.