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In this work, the refractive index of beryllium in the photon energy range 20.4–250 eV was experimentally determined. The initial data include measurements of the transmittance of two free‐standing Be films with thicknesses of 70 nm and 152 nm, as well as reflectometric measurements of similar films on a substrate. Measurements were carried out at the optics beamline of the BESSY II synchrotron radiation source. The absorption coefficient β was found directly from the transmission coefficient of the films, and the real part of the polarizability δ was calculated from the Kramers–Kronig relations. A comparison is carried out with results obtained 20 years ago at the ALS synchrotron using a similar methodology. [ABSTRACT FROM AUTHOR]

An extended model for the reconstruction of multilayer nanostructures from reflectometry data in the X-ray and extreme ultraviolet ranges is proposed. In contrast to the standard model approach, where the transitional region is defined in advance as a specific function, the transition layer is sought as a linear combination of several functions at once in the extended model. This allows one to describe a much wider class of multilayer structures with different dominant physical mechanisms for the formation of transition regions. The extended model occupies an intermediate position between the classical model approach and the so-called model-free methods. The efficiency of the described method is illustrated in detail in numerical simulations and in a real experiment on the annealing of a multilayer Mo/Be mirror. [ABSTRACT FROM AUTHOR]

Mo/Be multilayers are promising optical elements for extreme ultraviolet (EUV) lithography and space optics. Experimentally derived optical constants are necessary for accurate and reliable design of beryllium-containing optical coatings. We report optical constants of beryllium derived from synchrotron radiation-based reflectivity data of Mo/Be multilayers. Results are in good agreement with available data in the literature obtained from the well-known absorption measurements of beryllium thin films or foils. We demonstrate synchrotron based at-wavelength reflectometry as an accurate and non-destructive technique for deriving EUV optical constants for materials that are difficult or unstable to make thin foils for absorption measurements. [ABSTRACT FROM AUTHOR]