Size-effects in TiO2 nanotubes: Diameter dependent anatase/rutile stabilization

In the present work we demonstrate that amorphous anodic TiO2 nanotubes show upon annealing a tube diameter dependent phase stabilization. For tube diameters < 30 nm the formation of rutile is observed while for larger diameters anatase is formed. This effect is induced by the presence of the metallic substrate — in its absence all tube diameters are converted to anatase. As the nature of the stable phase strongly affects electronic, optical and biomedical properties of TiO2, the finding is of a high significance for many applications of TiO2 nanotubes.

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► Anodic TiO2 nanotubes show, upon annealing, tube diameter dependent phase stabilization.
► For small diameter TiO2 nanotubes (< 30 nm) rutile is formed while for larger diameters (> 30 nm) anatase is formed.
► Effect on size dependent anatase/rutile phase stabilization is induced by the presence of the metallic substrate.
► In absence of a substrate all tube diameters are converted to anatase.