Solubility of porous MgF2 films in water: Influence of glass substrates

MgF2 antireflective coatings exposed to cold water show an increase of porosity and film delamination after prolonged soaking times. The related structural changes within the material were characterized by scanning electron microscopy and ellipsometric porosimetry. The glass substrate type used, namely its sodium content, has a pronounced effect on the film microstructure and its long-term solubility. The stability of MgF2 films could significantly be improved by Na-doping of the coating solutions.