ABSTRACT
We have developed a new method for the determination of photoabsorption at extreme ultraviolet wavelengths longer than 20 nm, where reliable refractive index values are sparse or non-existent. Our method overcomes the obstacle of multiple reflections that occur inside thin films in this spectral range, which up until now has prevented the accurate determination of photoabsorption from transmittance measurements. We have derived a mathematical expression that is independent of internal reflection amplitudes, while taking advantage of the transmittance oscillations stemming from such reflections. The method is validated on measurements of aluminum thin films. This advance will enable accurate refractive index values for many important materials for optical instrumentation, thus facilitating high-priority research on topics including coherent light sources, planetary and solar physics, and semiconductor manufacturing.
ABSTRACT
This manuscript presents the first systematic study of non-periodic, broadband Mo/Si multilayer coatings with and without B 4C interface barrier layers for hard x-ray applications with large field of view. The photon energy of operation in this work is 17.4 keV, the Mo Kα emission line. The coatings involve layers with varying thicknesses in the nanometer scale and the behavior at the layer interfaces plays a crucial role in their performance. Reflectivity measurements and modeling at 8.05 keV and 17.4 keV, Transmission Electron Microscopy (TEM), as well as thin film stress measurements, are employed to examine and optimize the reflective performance of these coatings and the physics of their constituent layers and interfaces. Mo/Si with B 4C barrier layers on the Mo-on-Si interface is shown to produce the highest reflectivity among all design configurations considered in this work.
ABSTRACT
This paper demonstrates that highly reflective Cr/B4C multilayer interference coatings with nanometric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable reflective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B4C multilayers is also examined, with emphasis on the B4C-on-Cr interface where a significant diffusion layer is formed and on the oxide in the top B4C layer. Multiple characterization techniques (X-ray reflectivity at different photon energies, X-ray photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B4C layer structure.
