“…Figure 7 shows the spectral reflectivity calculated from ellipsometric data for boride coatings and for the corresponding bulk hexaborides. Due to the highly disordered microstructure of these coatings, their electronic and, consequently, their optical properties differ from those of the bulk values (21,30,(86)(87)(88)(89). Structural defects like interstitials, vacancies, and impurities which are typical for coatings grown by low-temperature PVD processes are expected to affect the shape of the plasma oscillation edge in rare-earth hexaborides (90).…”