In-depth analysis of elements and properties of hydrated subsurface layers on optical surfaces of a SiO2-BaO-B2O3 glass with SIMS, IBSCA, RBS and NRA Part 2. Discussion of results

Abstract

In the second part of this contribution it was derived from the comparison of the sputter yields with the specific energy losses within the bulk glass and within the various subsurface layers, that the differences in the matrix effects for SIMS and IBSCA between the bulk glass and the subsurface layers are caused by a decrease of the atomic densities and of the mean atomic bond energies within the subsurface layers as well. The knowledge of the matrix effects and their origin was most important for the interpretation of the SIMS and IBSCA in-depth profiles recorded for samples prepared with variations of the production parameters. E. g., various degrees of hydration and swelling could be distinguished by the influence of the different matrix effects on the in-depth profiles of the elements. The variations in the degrees of hydration of the subsurface layers could be ascribed to the influence of the thermal treatment before coating, to the interaction with slurries of different pH values and to the duration of storage before coating with λ/4-MgF2 layers. It is of importance for the fabrication of optical surfaces that the analysis results and the optical properties of the subsurface layers could be correlated with each other and with respective changes of the production parameters. The results illustrate that the properties of hydrated subsurface layers depend sensitively on a great variety of parameters which may be difficult to keep constant during processing. It is recommended, therefore, that such subsurface layers should be avoided whenever possible in optical fabrication to make it easier to attain the high reproducibility required for the optical properties.