Placido Garcia-Juan

MgF2 antireflective coatings by sol–gel processing: film preparation and thermal densification

Magnesium fluoride sols for the wet chemical processing of porous MgF2 antireflective coatings were prepared by the reaction of MgCl2 with HF. The formation and crystallisation of MgF2 nanoparticles were followed by 19F NMR spectroscopy, X-ray diffraction (XRD) and dynamic light scattering (DLS) in the liquid phase. The crystallization of the resulting films was monitored by XRD experiments. At temperatures exceeding 550 °C the film material and glass substrates undergo a chemical reaction, MgO is formed and SiF4 evaporates as a volatile product. Microstructure and optical properties were characterized as a function of the annealing temperature. The mechanical stability of MgF2 films was evaluated by the Crockmeter test using both felt and steel wool. It is shown that porous MgF2 films prepared by this synthesis have a vast potential for the large-area processing of antireflective coatings.

Porous MgF2 antireflective λ/4 films prepared by sol–gel processing: comparison of synthesis approaches

Porous MgF2 is a highly promising film material for the preparation of durable antireflective coatings. Synthesis routes based on Mg(OMe)2 and Mg(OAc)2 precursors are described, and the resulting sol–gel films and their thermal consolidation are compared using thermal analysis (TGA/DTA), scanning electron microscopy, ellipsometric porosimetry and X-ray diffraction. Due to their constant viscosity, Mg(OAc)2-based coating solutions are superior from the practical point of view. The porous films are stable against degradation under the steady-state temperature humidity life test (85/85), and they can successfully be integrated into TiO2–MgF2–TiO2 interference filters.Graphical AbstractPorous MgF2 antireflective λ/4 coatings were prepared by sol–gel processing. Synthesis routes based on Mg(OMe)2 and Mg(OAc)2 precursors are established, and the properties of the resulting film materials are compared, respectively.