Mesoporosity in silica films studied by a slow positron beam and ellipsometry

Porous silica films were synthesized via a sol-gel method using a nonionic amphiphilic triblock copolymer F127 as the structural template. Mesoporosities of the prepared silica films were investigated by Doppler broadening of positron annihilation radiation (DBAR) spectroscopy, positron annihilation gamma-ray energy spectroscopy based on a slow positron beam, and ellipsometry. For the mesoporous silica films, the variation of positron annihilation line shape parameter reveals that the porosity of the silica films increases with loading more F127, which is also confirmed by a decrease of refractive index n. Little variation in positron 3γ-annihilation fraction is found for the silica films prepared with F127 loading less than 15 wt%, whereas a remarkable increment is seen for the films with higher loading. This indicates the pore percolation in porous silica films occurs around a loading of F127 with 15 wt%.