Investigation of soft X-ray optical properties and their correlation with structural characteristics of zirconium oxide thin films

Highlights: • Optical performances of zirconium oxide films evaluated near O K-edge. • Hard X-ray reflectivity reveals similar density of the films. • X-ray diffraction data shows two different phases of the films. • Local environment of the films inferred from Extended X-ray absorption. • Correlation between the optical performance and the local environment is established. Oxide-based compound materials serve as a suitable coating material for soft X-ray optical applications. The optical performances of such materials depend on various properties like oxygen (O)/metal ratio, O-vacancies, defects, and crystallinity. In this study, we have investigated the soft X-ray optical properties and their correlation with structural characteristics of zirconium oxide thin films of thickness ~10 and 50 nm. The soft X-ray optical properties of the films were measured using Indus-2 soft X-ray reflectivity beamline BL-03 covering the O K-edge. To understand the influence of structural parameters, crystallinity, and the local environment of the films on the optical performance, multiple techniques like grazing incidence X-ray reflectivity, diffraction and Extended X-ray Absorption Fine Structure Spectroscopy are used. It was found that a marginal variation in O/Zr ratio, O- vacancies, and a change in distortion and co-ordination number of the Zr-O and Zr-Zr bonding in the two films of different thicknesses does not influence much the behaviour of soft X-ray optical response near O K-edge region. Details of the results are discussed.