Preparation and application of alumina- and titania- nanocrystals-dispersed thin films via sol-gel process with hot water treatment

A process to prepare nanocrystals-dispersed thin films at low temperatures using a hot water treatment of the gel films, and application of these nanocomposite thin films were demonstrated. When amorphous Al₂O₃ gel films were immersed in a hot water, we found that boehmite nanocrystals were formed on the surface of the films. In the hot water treatment of Al₂O₃-ZnO amorphous films, Zn-Al layered double hydroxide (LDH) was found to be formed on the films. When the SiO₂-TiO₂ gel films containing poly(ethylene glycol) were treated in a hot water, anatase nanocrystals were formed on the surface and inside of the films, and for the gel films without an organic polymer, the anatase nanocrystals were formed only on the surface of the films. In the hot water treatment of SiO₂-TiO₂ gel films under a vibration, titania nanosheets were found to be precipitated, instead of anatase nanocrysltals. Since formation of nanocrystals on the substrates using a hot water treatment is very mild conditions as the precipitation of crystals, we believe this process will open new application fields of nanocystals-dispersed thin films.