Titanium oxide nanotube arrays prepared by anodic oxidation

Titanium oxide nanotubes were fabricated by anodic oxidation of a pure tita nium sheet in an aqueous solution containing 0.5 to 3.5 wt% hydrofluoric ac id. These tubes are well aligned and organized into high-density uniform ar rays. While the tops of the tubes are open, the bottoms of the tubes are cl osed, forming a barrier layer structure similar to that of porous alumina. The average tube diameter, ranging in size from 25 to 65 nm, was found to i ncrease with increasing anodizing voltage, while the length of the tube was found independent of anodization time. A possible growth mechanism is pres ented.