Fabrication of ordered TiO2 porous thin films by sol-dipping PS template method

Monolayer polystyrene spheres (similar to 400 nm) array templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS and porous TiO2 thin films were prepared by using sol-dipping template method to fill TiO2 sol into the interstices among the close-packed PS templates and then annealing to remove the PS templates. The effects of TiO2 precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed pore size of the ordered TiO2 porous thin film depended mainly on PS size and partly on TiO2 sol concentration. The shrinkage of pore diameter was about 10% for 0.2 M and 20% for 0.4 M TiO2 sol concentrations. X-ray diffraction (XRD) spectra indicated the porous thin film was anatase structure. The transmittance spectrum showed that optical transmittance of the porous thin film kept above 70% beyond the wavelength of 430 nm. Optical band-gap of the porous TiO2 thin film (fired at 550 degrees C) was 3.12 eV.