Non-chapped, vertically well aligned titanium dioxide nanotubes fabricated by electrochemical etching

Thu Loan Nguyen, Thi Dieu Thuy Ung and Quang Liem Nguyen

Abstract

This paper reports on the fabrication of non-chapped, vertically well aligned titanium dioxide nanotubes (TONTs) by using electrochemical etching method and further heat treatment. Very highly ordered metallic titanium nanotubes (TNTs) were formed by directly anodizing titanium foil at room temperature in an electrolyte composed of ammonium fluoride (NH₄F), ethylene glycol (EG), and water. The morphology of as-formed TNTs is greatly dependent on the applied voltage, NH₄F content and etching time. Particularly, we have found two interesting points related to the formation of TNTs: (i) the smooth surface without chaps of the largely etched area was dependent on the crystalline orientation of the titanium foil; and (ii) by increasing the anodizing potential from 15 V to 20 V, the internal diameter of TNT was increased from about 50 nm to 60 nm and the tube density decreased from 403 tubes μm⁻² down to 339 tubes μm⁻², respectively. For the anodizing duration from 1 h to 5 h, the internal diameter of each TNT was increased from ~30 nm to 60 nm and the tube density decreased from 496 tubes μm⁻² down to 403 tubes μm⁻². After annealing at 400 °C in open air for 1 h, the TNTs were transformed into TONTs in anatase structure; further annealing at 600 °C showed the structural transformation from anatase to rutile as determined by Raman scattering spectroscopy