Formation of Self-Ordered TiO2 Nanotubes by Electrochemical Anodization of Titanium in 2-Propanol/NH4F

TiO2 nanotubes (TiNTs) were formed by the electrochemical anodization of titanium in 2-propanol/water containing 0.14 M NH4F as the supporting electrolyte. The effects of the water content, time of anodization, and potential on the growth behavior of TiNT were studied. At the optimum solvent composition of 16 vol % water/84 vol % 2-propanol, the reaction was kinetically controlled. The TiNTs obtained under optimum conditions had heights of up to 1800 nm and inner diameters of about 90 nm. Increasing the potential beyond 20 V did not improve the quality of the nanotubes because of the introduction of disordering. The scanning electron microscopy and X-ray diffraction analysis revealed a preferred growth direction of the TiNTs relative to the substrate surface. A thin barrier layer existed at the nanotubes/metal interface, which was also confirmed by ellipsometry. This barrier layer was enriched with the rutile phase, whereas the nanotubes were enriched with the anatase phase. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3232246] All rights reserved.