Fabrication of TiO2/SiO2 multilayer film structure by the sol-gel process with efficient thermal treatment methods

Multilayer structure of thin films by the sol-gel process attracts great attention for versatile applications. However, the multilayer structure often shows undesirable morphologies such as cracks or delaminations resulted from non-wettability of the coating solution with the pre-deposited hydrophobic layer, especially in the case of SiO2 layers. The hydrophobic surface is originated from residual alkoxy groups in the layer after sintering step. For the sintering process, introducing the heating-up period from the room temperature to the target temperature is very effective in removing residual alkoxy groups from the SiO2 film by hydrolysis with remaining water molecules. The well-defined TiO2/SiO2 multilayer structure is successfully fabricated at a sintering temperature of 300 °C by forming a hydrophilic SiO2 layer with the heating-up period.

► TiO2 films morphologies on the hydrophobic SiO2 films. ► The TiO2/SiO2 multilayer structure formation on the hydrophilic SiO2 film. ► Heating-up period included in the sintering process. ► Residual alkoxy groups removed effectively with the gradual-sintering method. ► The TiO2/SiO2 multilayer fabricated at 300 °C with the heating-up period.