Optical constants of beryllium from photoabsorption measurements for x-ray optics a

摘要

Abstract: Beryllium (Be) has been recently receiving considerable attention as the key material for a range of potential applications in the extreme ultraviolet (EUV) and x-ray region. Most notably, it has been successfully implemented as the spacer material in beryllium-based multilayer mirrors for EUV lithography, achieving experimental reflectivities of about 70% at wavelengths around 11.4 nm. Knowledge of the absorptive and dispersive properties of this material thus becomes important for the modeling of these optics. Experimental photoabsorption results in the region 40 - 250 eV, derived from transmission measurements on free-standing beryllium foils, are presented in this work. The measured absorption in the region extending a few tens eV below the K edge (111.7 eV) appears to be significantly (up to 50%) lower than the tabulated values. Fine structure above the K edge is also demonstrated in the measurements. These data are incorporated in an updated set for the atomic scattering factors of beryllium, obtained in the range 0.1 - 30,000 eV. Finally, the Bragg reflectivity of Mo/Be multilayer optics is modeled using the new experimental results. !15