TiO2 nanotubes: Tailoring the geometry in H3PO4/HF electrolytes

In the present work, we investigate the formation of self-organized titanium oxide nanotube layers at different fluoride concentrations and potentials in H3PO4 electrolytes. We demonstrate that in optimized phosphate/HF electrolytes, in contrast to other electrolytes the tube length and diameter can be controlled over a wide range by the applied potential. It was found that for potentials between 1 and 25 V tubes could be grown with any desired diameter ranging from 15 to 120 nm combined with tube length from 20 nm to 1 μm. The diameter and the length depend linearly on the voltage. These findings represent an unprecedented level of control in the geometry of anodic TiO2 nanotubes.