Improvement of the microstructure and X-ray performance of ultrathin Ru/C multilayer mirror after high temperature treatment

Abstract

Ru/C multilayer mirrors with a period of 2.5 nm and 150 bilayers were studied under hightemperature annealing and long-term storage. A general increase in the reflectivity was observed after annealing at different temperatures from 300 to 700 °C, during which a maximum enhancement of around 14% was obtained at 600 °C. The highest reflectance measured at 8 keV reached 69% after 600 °C annealing. This was accompanied by a 6% expansion of the layer period, which could be mainly attributed to carbon layers. The surface roughness was not affected by the annealing, whereas the polycrystallization of Ru with crystallographic planes parallel to the layer interfaces was enhanced. Combining the transmission-electron microscopy measurements, it was found that the interdiffusion at the C-on-Ru interface was significantly suppressed. The decreased interdiffusion, enhanced optical contrast, and larger multilayer period were the main reasons for the increased reflectance. The 600 °C annealed Ru/C multilayer remained intact after 13 months of storage in air, which also demonstrated significant temporal stability.