Transparent titania nanotubes of micrometer length prepared by anodization of titanium thin film deposited on ITO

Transparent TiO2 nanotube arrays of micrometer lengths were prepared by anodization of titanium thin film RF sputtered on indium tin oxide (ITO) which was coated on glass substrate. The sputtering process took place at elevated temperature of 500 °C. The structures of the films were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the optical properties of the films were investigated using UV–visible spectroscopy. Two types of electrolytes were used in this work: an aqueous mixture of acetic acid and HF solution and a mixture of NH4F and water dissolved in ethylene glycol. The concentration of NH4F, voltage and the thickness of the sputtered titanium film were varied to study their effect on the formation of TiO2 nanotube arrays. It is demonstrated in this work that the nanoporous layer is formed on top of the ordered array of TiO2 nanotubes. Furthermore, the optical transmittance of TiO2 nanotubes annealed at 450 °C is much lower than the non annealed TiO2 nanotubes in the visible wavelength region.