Fabrication and characterization of smooth high aspect ratio zirconia nanotubes

In the present work, we report formation of high aspect ratio zirconia nanotubes by electrochemical anodization of zirconium in a 1 M (NH4)2SO4 electrolyte containing 0.5 wt% NH4F. Highly self-organized zirconia nanotubes can be formed with a diameter of ≈50 nm and a length of ≈17 μm, i.e. with an aspect ratio of more than 300. The nanotubes show a distinct smooth and straight morphology. XRD investigation reveals that the nanotubes have a cubic crystalline structure directly after anodization, that is, without any further annealing.