W-based multilayer soft X-ray Bragg optics: Synthesis and characterization

This work is dedicated to thin film reflective multilayer optics working in the range between the O Ka and the Al Ka absorption edges (525 eV-1486 eV) to be used in spectroscopic applications. The main requirements for multilayer optics in spectroscopy are a high peak reflectance and a narrow bandwidth. The periodicity of the multilayer system designed for such an energy range is only 2.5 nm with individual layers being thinner than 1 nm. This makes the performance of such systems extremely sensitive to any imperfection at the interfaces. Analysis of such short period structures is very challenging due to the limitations of conventional methods that are commonly used for multilayer systems with larger periodicities. Therefore, this research faced two main challenges: engineering and analysis. In the engineering part, to improve the optical contrast and the quality of the interfaces various techniques such as ion beam polishing of layers, alternative working gas, and the use of alternative material combinations were applied. The analysis part required a combination of several state-of-the-art analytical methods in order to obtain reliable information about interfaces and film growth.

A comprehensive analysis of the short-period W/Si and W/B multilayer systems was carried out in this work. A combination of various state-of-the-art analysis techniques was used to obtain reliable information about the internal structure of the multilayers. Understanding the physics of thin-film growth at the atomic scale helped to define the next steps in improving the performance of such systems as discussed in the "valorization and outlook" section. This thesis is a basis for further studies on this type of multilayer mirrors.