Atomic Layer Deposition Al₂O₃ Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO₂ Nanotube Layers

High Resolution Image Download MS PowerPoint Slide 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.