Advances in the synthesis of large-area 3D ordered macroporous titania film photonic crystals by silica colloidal crystal templating

The recent advances of the authors' study on the synthesis of large-area 3D ordered macroporous titania film photonic crystals by using silica colloidal crystals as templates were presented. The main procedure of the preparation was described as follows. Firstly, the silica colloidal crystal template was deposited onto a glass micro slide through a convective assembly process in which monodispersive silica spheres of 309nm were used. Secondly, after sintered at 600 degrees C for 1h the crystalline template was immersed vertically into a TiO2 sol for the infiltration of the template. Thirdly, the resulting titania-opal composite film was immersed in an aqueous NaOH solution for 24h to remove the silica template. By means of the systematical study of the processes and application of some innovative processing techniques such as silica colloidal crystal templating technique, alkali based template-etching technique, the highly ordered macroporous TiO2 film photonic crystals with sizes of centimeters were successfully fabricated. The results show that the shrinkage of the macroporous framework with a filling rate of 17.4% is less than 3%. The XRD pattern shows that the porous framework consists of nanocrystallites of anatase mixed with a magneli phase (Ti5O9). The optical property measurements of the films indicate that the film photonic crystal has strong photonic bandgap behavior.