Reflectance and resolution of multilayer monochromators for photon energies from 400 - 6000 eV

This paper deals with multilayer monochromators for synchrotron beamlines that are produced by magnetron and ion beam sputter deposition (MSD and IBSD). Different material combinations (W/B4C, W/Si, Mo/B4C, MO/Si) with period thicknesses between I rim and 10 nm have been fabricated and measured at the synchrotron BESSY II (optics and KMC1 beamlines). The main challenge for the deposition of nanometer multilayers is to find growth conditions where the interfaces between adjacent layers are abrupt (no interdiffiasion sigma(d)) and smooth (no roughness sigma(r)). The interface width sigma (sigma(2) = sigma(2)(d) + sigma(2)(r)) becomes increasingly important for smaller period thicknesses. One decisive point for the interface formation is the kinetic energy distribution of the particles arriving on the substrate surface. In MSD, the sputter gas pressure is the main parameter for influencing the kinetic energy of the particles. In IBSD, an assist ion beam source can be used to bombard the growing film with inert gas atoms of a specific energy. Using this option, the best compromise between low interdiffusion and low roughness can be found for every material combination. Investigations of the reflection of W/B4C multilayers with period thicknesses of 1.2 nm and number of periods N = 50, 300 and 600 show that no roughness increase occurs with increasing N. Typical values for the interface widths are sigma = 0.27...0.28 nm.