In situ study of multilayer reflectivity upon heat treatment under synchrotron radiation

Periodic multilayers deposited by Distributed Electron Cyclotron Resonance (DECR) sputtering were studied with synchrotron radiation at the ESRF bending magnet beam line BM5. In situ reflectivity measurements at a photon energy of 20keV have been carried out on these samples during a specific heat treatment. A dedicated furnace has been developed to heat the multilayers under vacuum from room temperature up to 550°C. [Ru/B4C]70 and [W/B4C]40 samples with repetition periods of about 4nm were chosen. Simulations of reflectivity measurements were performed to understand the evolution of layer thicknesses and interface widths. Additional ex-situ reflectivity measurements were done at 8keV before and after the annealing experiments to investigate irreversible effects. We will discuss the heat impact on the layered structure and in which way multilayer optics could be thermally pre-treated before their installation on synchrotron beam lines.