Synthesis of anodic TiO 2 nanotubes on indium tin oxide coated glass electrodes

Abstract

Highly ordered transparent thin films of TiO2 with nanotube (TNT) arrays were synthesized by electrochemical anodization of titanium thin films that had been radio-frequency magnetron deposited on glass substrates covered with indium tin oxide (ITO) thin film. Ti film anodic oxidation was carried out in fluorine and aqueous electrolytes. The samples were sintered at 450°C for two hours in the air in order to change the amorphous TiO2 structure into a crystalline one. Scanning electron microscope, x-ray diffractometry, spectroscopic ellipsometry, ultraviolet–visible spectroscopy spectrophotometry, and Raman spectroscopy were used to analyze the morphological, structural, and optical characteristics of the samples. Highly ordered TNT arrays of 40 to 45 nm pore diameter with a high degree of optical transmission were obtained. It has been established that anodization time affects the surface morphology and regularity of the pores. The longer the anodization time, the more regular the porous structure. An x-ray diffraction pattern of the TiO2/ITO structure has shown the existence of the anatase phase of polycrystalline TiO2. Polyform phases of rutile and brookite were not revealed. The films display high ultra violet absorption with a wavelength shorter than 360 nm and are transparent in the 360 to 900 nm range with the transmission of roughly 70% to 80% of light. Only the anatase phase was confirmed by the Raman spectra. Based on ellipsometric studies, an optical model was created for the experimentally obtained glass/ITO/TiO2 structure, which consists of five layers of different thicknesses and compositions.