Soft X-ray reflectivity and structure evaluation of CoCr/C multilayer X-ray mirrors for spectral region around 6 nm

The development of highly-reflective multilayer mirrors for use in the 6-nm region is desired for X-ray photoemission spectroscopy for inner-shell excitation using a Schwarzschild objective. For this application, reflectivity is the most critical parameter determining the performance of multilayer mirrors, because the reflectivities of multilayers in the 6-nm region are generally very low. We have designed CoCr/C multilayer mirrors with a comparatively high reflectivity at around normal incidence and have fabricated them by magnetron sputtering. The measured peak reflectivity is about 11.5% at a wavelength of around 6 nm and an incident angle of 88°. Thermal annealing was found to markedly improve the reflectivity, and a high value of 13% was obtained by annealing at 400 in an Ar atmosphere for 1 h.