Formation of quasi-spherical AU48-198 clusters in anodic titania nanotubes grown on Ti-Au alloys

The effect of alloying sputter-deposited Ti with 2 at.% of Au on the growth of anodic nanotubes was studied in monoethylene glycol electrolyte containing 1.0 mol dm(-3) of water and 0.1 mol dm(-3) of ammonium fluoride. The classic shape of nanotubes modified with quasi-spherical clusters of Au48-198 was obtained on Ti-Au (2 at.%). The results were compared to the formation of a barrier-type anodic film which suggested that gold located at the alloy/anodic film interface is enriched as a consequence of the preferential oxidation of titanium during the prior anodizing period and transported to the cell boundary region of the nanotubular film in the form of quasispherical clusters of Au48-198. A consequence of the inclusion of Au48-198 in the structure of the nanotubes was a reduction in the rate of nanotubular film growth due to the generation of oxygen catalysed on the clusters. A further increase in gold content up to 8 at.% in the alloy resulted in the formation of sponge-like or nanoporous anodic layers, with the structure depending on electrolyte composition.