The self-organized TiO₂ nanotube layers have attracted considerable scientific and technological interest over the past 10 years motivated for their possible range of applications including photo-catalysis, solar cells, hydrogen generation and biomedical uses [1]. The synthesis of 1D TiO₂ nanotube structure is carried out by a conventional electrochemical anodization of valve Ti metal sheet. The main drawback of TiO₂ is its applicability in the UV light (wavelengths < 390 nm). In order to enhance the efficiency, TiO₂ has been doped by N [2] or C [3] o to shift its absorption into the visible light.

Except of doping, one of the major issues to extend the functional range of nanotubes is to coat homogenously tube interiors by a secondary material. It has been shown that additional ultrathin surface coating of TiO₂ by secondary materials such as Al₂O₃ [4], ZnO [5] or MgO [6] annihilates electron traps at the TiO₂ surface and thus increases the photogenerated concentration of charge carriers. Recently, it has been demonstrated that just a single cycle of Al₂O₃ [7] or ZnO [5] deposited by atomic layer deposition (ALD) efficiently improve charge transport properties of the heterostructure while gradual passivation appears with increasing ZnO thickness due to stronger band-bending [5].

The presentation will focus in detail on the coating of the nanotube arrays by secondary materials using ALD. The deposited materials influence strongly photo-electrochemical properties of nanotube films. Experimental details and some very recent photocatalytic [8] and sensing [9] results will be presented and discussed.

References:

[1] J. M. Macak et al., Curr. Opin. Solid State Mater. Sci. 1-2 (2007) 3.

[2] C. Burda et al., Nano Lett. 3 (2003) 1049.

[3] S. Sakthivel et al., Angew. Chem., Int. Ed. 42 (2003) 4908.

[4] R. Zazpe et al., Langmuir, in press, DOI: 10.1021/acs.langmuir.6b03119.

[5] A. Ghobadi et al., Scientific Reports 6 (2016) 30587

[6] H. Park, et al., Journal of Electroceramics 23 (2009) 146.

[7] J-Y. Kim et al., Nanotechnology 25 (2014) 504003.

[8] M. Krbal et al., Ms submitted.

[9] S. Ng et al., Ms in preparation.