Atomic Layer Deposition Al(2)O(3) Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO(2) Nanotube Layers

[Image: see text] We report on a very significant enhancement of the thermal, chemical, and mechanical stability of self-organized TiO(2) nanotubes layers, provided by thin Al(2)O(3) coatings of different thicknesses prepared by atomic layer deposition (ALD). TiO(2) nanotube layers coated with Al(2)O(3) coatings exhibit significantly improved thermal stability as illustrated by the preservation of the nanotubular structure upon annealing treatment at high temperatures (870 °C). In addition, a high anatase content is preserved in the nanotube layers against expectation of the total rutile conversion at such a high temperature. Hardness of the resulting nanotube layers is investigated by nanoindentation measurements and shows strongly improved values compared to uncoated counterparts. Finally, it is demonstrated that Al(2)O(3) coatings guarantee unprecedented chemical stability of TiO(2) nanotube layers in harsh environments of concentrated H(3)PO(4) solutions.