Detailed study of the pore-filling processes during nanocasting of mesoporous films using SnO2/SiO2 as a model system

Mesoporous SnO2 films synthesized using mesoporous silica thin films as molds in a nanocasting process have been used as a model system in order to study the mechanism of the exotemplating process. A systematic study of the infiltration capability of the porous mold is presented, which also is suggested to shed some light on the general process of nanocasting from solution. The silica films were repeatedly dip-coated in an ethanolic SnCl4 solution and the films were calcined between each impregnation cycle. The structural evolution during the process was followed by Environmental Ellipsometry Porosity (EEP), and the SnO2 films were additionally studied by SEM-FEG, TEM. GI-SAXS and XRD. The SnO2 films have a high porosity (over 60%) after leaching Of SiO2, and are of optical quality. Furthermore, the SnO2 is present in the form of nanocrystallites about 5 nm in diameter. Despite the fact that the films were very homogeneous and showed a high mechanical stability, the results show that not all the mesopores in the SiO2 films can be filled by SnO2 before formation of a layer of nonporous SnO2 on top of the SiO2 films occur. A tentative model for the pore filling events is presented based on the experimental findings. (c) 2009 Elsevier Inc. All rights reserved,