Formation of Transparent Nanoporous Titanium Oxide Films on Glass Substrates using an Anodization Process

We report on an experimental study on transparent nanoporous titanium oxide films on glass substrates using an anodization process. Ti thin films of 50-90 nm have been deposited on glass substrate by dc sputtering (1.82.10(-3)Pa, 100 W) followed by a thermal treatment of 500 C for 30 min. in order to improve the adhesion to the glass substrate. Then an anodization process was applied in order to obtain TiO2 thin nanoporous layers using a cell consisted of three electrodes and aqueous electrolyte solution of 1% NH4.F concentration, monoethyleneglycol and DI water. After anodization the samples were annealed at 450 degrees C for 45 min using nitrogen gas. The layers have a nanoporous structure with pore dimensions in the range of 50-80 nm. FTIR and micro-Raman spectroscopy were used to identify the crystalline phase of the TiO2 layers. Raman scattering spectra clearly identify the anatase phase on the basis of Eg modes at similar to 146 cm(-1) of the TiO2. The FTIR spectrum showed only the peak at 614 cm(-1) which can be associated with the characteristic vibrational mode of TiO(2)anatase. The optical properties of TiO2 thin films have been determined by ellipsometric measurements in the spectral range (0.2-0.8 mu m) and a value of 2.41-2.45 was obtain for refractive index at 632 nm. Spectrophotometric measurements showed a transmittance over 70% and an optical band gap of 3.3-3.5 eV was determined.