GIXR measurements for (a, b) N = 6, (c) N = 16 and (d) aperiodic multilayers on gratings in classical mounting. RCWA model of the multilayer grating and IMD simulation of the multilayer on a flat SiO₂ substrate are also plotted in each case. (b) is a close view of the total reflection plateau of (a) and shows an IMD simulation of the multilayer on a flat SiO₂ substrate with a top EMA layer to account for the surface profile.