Effects of titanium foil thickness on TiO2 nanostructures synthesized by anodization

During anodic oxidation (i.e. anodization) synthesis of titanium dioxide (TiO2) nanostructures on a titanium (Ti) foil surface, the interfacial barrier layer properties play a major role in the growth of TiO2 nanostructures. In the present investigation, three cases of Ti foil thickness (0.5 mm, 0.25 mm and 0.127 mm) were chosen, to study its effect on barrier layer properties, under the same anodization conditions, finally leading to different TiO2 nanostructures (nanoparticular type for thicker Ti foil and nanotubular type for thinner Ti foil thickness). The in situ growth mechanism of barrier layer formation on the Ti foil surface is examined by monitoring the current with respect to time. Nanoindentation studies of the barrier layer formed on these three different Ti foil surfaces were carried out. At 300 nm and 500 nm indentation depths, the hardness of the thicker barrier layer on thicker Ti foil surface was found to be approximately three times greater than that of the thinner barrier layer on thinner Ti foil. After annealing, the surface morphology and characteristic features of TiO2 nanostructures grown on a barrier layer were explored by scanning electron microscopy (SEM) and field emission-transmission electron microscopy (FE-TEM), respectively. Crystalline TiO2 nanostructure phases were characterized by X-ray diffraction (XRD), Raman spectroscopy, selected area electron diffraction, SAED patterns and diffraction lines, which indicate the presence of anatase and rutile phases. UV-visible absorption spectra showed that the thicker barrier layer forming TiO2 nanoparticles causes a blue shift and the thinner barrier layer forming TiO2 with nanotubular morphology causes a red shift.