Low reflectivity materials for the vacuum UV: Mg and Ag surfaces

We have developed absorptive Mg coatings for the Vacuum UV (VW) wavelength range. The total hemispherical reflectivity at normal incidence was measured at 121.6 nm. The reflectivity of the Mg coating produced by magnetron sputtering (presumably from the vapor phase) is close to 1%, comparable to the best known coatings. In contrast to the latter they are mechanically robust. After storage in air for 2 years the reflectivity increased by a factor 2. The reflectivity of Mg and Ag coatings produced by thermal evaporation was observed to be about 2 - 3%. The reflectivity of the Ag coatings proved to be stable over a period of 58 months in air.