MULTILAYER REFLECTIVITY CALCULATIONS APPLIED TO THE ENERGY-DISPERSIVEMETHOD

The specular reflectivity of periodic multilayers illuminated by a whi te parallel X-ray beam is calculated versus photon energies over a ran ge of 4 keV to 40 keV for fixed grazing incidence angles. The influenc e of the anomalous dispersion and absorption terms in the atomic scatt ering factors, respectively Delta f' and Delta f '' on the reflectivit y profiles is discussed, Calculations show that the use of an X-ray tu be as source and a Si(Li) diode as detector for peak reflectivity, ban d pass and overlapping orders measurements is justified. By choosing t he incidence angle, the Bragg peaks can be set at any energy, in parti cular close to an absorption edge in order to observe the step reflect ivity change due to abrupt index variations. Spiller's rules are invok ed to explain these variations.