Abstract
We report on the growth of anodic oxide nanotubes grown on a simple Ti45Nb alloy that show self-organization on two sizescales. The well-ordered nanotube layers consist of large and small diameter tubes that are arranged in an alternating two-dimensional (2D) structure. This bimodal morphology and the thickness of the nanotube layer are affected by the electrochemical conditions used. The bimodal feature can be obtained over a wide potential range (between 15 and 55 V), resulting in a linear diameter variation from 80 to 330 nm for the larger and 50-180 nm for the smaller tubes. The organization into two size-scales takes place during the first hour of the anodization process. This result of flexible two size-scale self-organization using a simple two element alloy is of significant importance not only for fundamental research but also for specific applications that can benefit from bimodal properties. (c) 2007 Elsevier B.V. All rights reserved.