TiO2 nanotubes with tunable morphologies

Abstract

Titanium anodic oxide layers with a bottle shaped nanotubular structure have been grown in an electrolyte containing NH₄F, applying voltage steps. The grown layers were analyzed using scanning and transmission electron microscopy (SEM and TEM), and Rutherford backscattering spectroscopy (RBS). The results show that a concentration of 0.15 M of NH₄F in the anodizing bath, and a step of 10 to 20 V produces an oxide with a double morphology comprised of nanotubes at the oxide/metal interface and nanopores at the oxide/electrolyte interface of the anodic layer. Higher concentration of F⁻ in the bath, 0.3 and 0.45 M NH₄F, enhanced the chemical dissolution of the anodic layer resulting in nanotubular structures along the oxide layer. Therefore, the bottle shaped nanotubular structures that show a well defined morphology are obtained in a bath containing a concentration of 0.3 M NH₄F and applying a voltage step of 10–20 V.