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Atomic Layer Deposition Al 2 O 3 Coatings Significantly Improve Thermal, Chemical, and MechanicalStability of Anodic TiO 2 Nanotube Layers

View Article: PubMed Central - PubMed

ABSTRACT

We report on a verysignificant enhancement of the thermal, chemical,and mechanical stability of self-organized TiO2 nanotubeslayers, provided by thin Al2O3 coatings of differentthicknesses prepared by atomic layer deposition (ALD). TiO2 nanotube layers coated with Al2O3 coatingsexhibit significantly improved thermal stability as illustrated bythe preservation of the nanotubular structure upon annealing treatmentat high temperatures (870 °C). In addition, a high anatase contentis preserved in the nanotube layers against expectation of the totalrutile conversion at such a high temperature. Hardness of the resultingnanotube layers is investigated by nanoindentation measurements andshows strongly improved values compared to uncoated counterparts.Finally, it is demonstrated that Al2O3 coatingsguarantee unprecedented chemical stability of TiO2 nanotubelayers in harsh environments of concentrated H3PO4 solutions.

No MeSH data available.


Hardness of differentTiO2 nanotube layers determinedby nanoindentation measurements. Except for the sample marked “uncoated”,all nanotube layers were annealed at 870 °C for 1 h.
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fig4: Hardness of differentTiO2 nanotube layers determinedby nanoindentation measurements. Except for the sample marked “uncoated”,all nanotube layers were annealed at 870 °C for 1 h.

Mentions: The mechanicalintegrity of theTiO2 nanotube layers is of significant importance, especiallyfor synthesis of devices based on flow-through membranes utilizingnanotube layers opened on both sides.51 Even though some nanoindentation analyses of the TiO2 nanotube arrays were already carried out,52−59 nanotube layers modified with additional coatings, as in the presentcase, have not yet been analyzed. Figure 4 shows hardness of TiO2 nanotubelayers with Al2O3 coatings of different thicknessesas well as two reference nanotube layers. If not denoted otherwise,all nanotube layers were annealed at 870 °C for 1 h as the lastprocessing step. The obtained hardness values show two prominent features.First, the uncoated amorphous (i.e., did not undergo annealing) TiO2 nanotube layer displayed lower hardness value than the annealeduncoated counterpart, fully rutile structure comprised. That was expectedas the crystal structure has (as a rule of thumb) higher hardnessthan amorphous mass of the same compound. Second, the annealed Al2O3-coated TiO2 nanotube layers exhibitedlarger hardness with the increasing Al2O3 coatingthickness. This can be ascribed to increasing content of rutile (Table 1) and to an increasingAl2O3 mass within the nanotubes.


Atomic Layer Deposition Al 2 O 3 Coatings Significantly Improve Thermal, Chemical, and MechanicalStability of Anodic TiO 2 Nanotube Layers
Hardness of differentTiO2 nanotube layers determinedby nanoindentation measurements. Except for the sample marked “uncoated”,all nanotube layers were annealed at 870 °C for 1 h.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382572&req=5

fig4: Hardness of differentTiO2 nanotube layers determinedby nanoindentation measurements. Except for the sample marked “uncoated”,all nanotube layers were annealed at 870 °C for 1 h.
Mentions: The mechanicalintegrity of theTiO2 nanotube layers is of significant importance, especiallyfor synthesis of devices based on flow-through membranes utilizingnanotube layers opened on both sides.51 Even though some nanoindentation analyses of the TiO2 nanotube arrays were already carried out,52−59 nanotube layers modified with additional coatings, as in the presentcase, have not yet been analyzed. Figure 4 shows hardness of TiO2 nanotubelayers with Al2O3 coatings of different thicknessesas well as two reference nanotube layers. If not denoted otherwise,all nanotube layers were annealed at 870 °C for 1 h as the lastprocessing step. The obtained hardness values show two prominent features.First, the uncoated amorphous (i.e., did not undergo annealing) TiO2 nanotube layer displayed lower hardness value than the annealeduncoated counterpart, fully rutile structure comprised. That was expectedas the crystal structure has (as a rule of thumb) higher hardnessthan amorphous mass of the same compound. Second, the annealed Al2O3-coated TiO2 nanotube layers exhibitedlarger hardness with the increasing Al2O3 coatingthickness. This can be ascribed to increasing content of rutile (Table 1) and to an increasingAl2O3 mass within the nanotubes.

View Article: PubMed Central - PubMed

ABSTRACT

We report on a verysignificant enhancement of the thermal, chemical,and mechanical stability of self-organized TiO2 nanotubeslayers, provided by thin Al2O3 coatings of differentthicknesses prepared by atomic layer deposition (ALD). TiO2 nanotube layers coated with Al2O3 coatingsexhibit significantly improved thermal stability as illustrated bythe preservation of the nanotubular structure upon annealing treatmentat high temperatures (870 °C). In addition, a high anatase contentis preserved in the nanotube layers against expectation of the totalrutile conversion at such a high temperature. Hardness of the resultingnanotube layers is investigated by nanoindentation measurements andshows strongly improved values compared to uncoated counterparts.Finally, it is demonstrated that Al2O3 coatingsguarantee unprecedented chemical stability of TiO2 nanotubelayers in harsh environments of concentrated H3PO4 solutions.

No MeSH data available.