Fabrication and characterization of TiO₂ thin film prepared by a layer-by-layer self-assembly method

Titanium dioxide (TiO₂) thin films assembled with TiO ₂ nanoparticles and oppositely charged polyelectrolytes or titanium (IV) bis(ammonium lactato) dihydroxide (TALH) were successfully fabricated via a layer-by-layer (LBL) self-assembly method at room temperature. Especially, by using the quartz crystal microbalance (QCM) to monitor the in-situ deposition phenomenon of TALH that is saturated and then separated from the film before and after the deposition of 30 s at low pH, the anatase TiO₂ multilayer films fabricated with 30 s deposition in TALH adjusted to pH 2.5 showed a higher refractive index (ca. n = 1.75), a denser film growth, and a lower surface roughness (ca. 10.5 nm) than those of the films deposited in different conditions. This film showed a high transmittance in visible range for optical applications and photocatalytic properties by decomposing methyl orange molecules gradually according to UV irradiation time. In addition, as the pH of TALH was decreased from pH 5.5 to 2.0, the thickness of (TiO₂ / TALH)₃₀ film was increased from ca. 85 nm to ca. 442 nm.