Raman spectroscopic study of the influence of voltage-time on titania growth-fast anodized nanostructures

Abstract

TiO2 nanotubes were prepared by the anodization process of a set of titanium foils in order to study the influence of time and voltage on the morphology of them under a 1.2 wt % NH4F salt concentration, taking advantage of this percent and remarking the great importance of the oxide growth-dissolution speed with this electrolyte concentration. The anodization process consists of an organic media of ethylene glycol, a voltage from 5 to 30 V for a time period from 1 to 6 hours, a constant potential of 30 V for a time lapse from 10 to 360 minutes and 5 to 480 seconds. All anodized samples are rinsed and annealed to 400°C for 3 hours to obtain an anatase crystalline structure. The morphological characterization was carried out by Field Emission Scanning Electron Microscopy (FESEM) to verify the presence of the main nanostructures: nanopores, nanotubes, and nanograss. Raman spectroscopy was used for optical characterization in order to identify the changes in the signal of the Eg(v6) vibrational mode. It was observed the Raman Eg(v6) vibrational mode suffers a redshift at the initial anodization stage with the contribution of the stress between the substrate-oxide layer and the stoichiometry defects. The diameter and tube length have a strong correlation with the oxide thickness (ascendant slope), moreover, this oxide is compared and related to the Raman intensity of the Eg(v6) mode, from this fact, it is easy to define some time periods and a voltage range for each titania nanostructures observed.