Figure 2

AFM images of TNAs at various stages of their fabrication process taken with 3 µm scan length: (A) 1st anodization, (B) dimpled substrate without as-grown nanotubes, (C) 2nd anodization, (D) annealing, (E) dimpled film without nanotubes, (F) plot of the structure function (bifractal characteristics) of the TNAs at the final stage. Arrows in (E) mark the boundary separating the structures with dominant rings (A) and chains (B).