Shape irregularity and size dispersion exhibited by TiO2 nanotube arrays (TNAs) is a disadvantage for size-selective applications such as flow-through membranes, cell differentiation and drug delivery, and for photonic applications such as photonic crystals and metallodielectric metamaterials, where size and shape dispersity are sources of defects and scattering. We show that achieving extremely smooth Ti films is more critical than a large Ti grain size in attaining highly ordered nanotube arrays with minimal dispersity in shape and size, and obtain the insight that uniform pore nucleation is determinative of the quality of the nanostructures that result following electrochemical anodization. TiO2 nanotubes formed by anodization of highly smooth Ti films on single crystal silicon wafers in electrolytes with high water concentrations had only circular pores with a narrow dispersion of pore diameters, and exhibited uniform cross-sections along the tube-axis. Pattern order was evaluated using 2D-FFT analysis .
TiO2 nanotubes on Si wafers with a (a) narrow and (b) wide dispersion in shape and size.