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 [1,2]. 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).

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 [3], ZnO [4] or MgO [5] 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 [6] or ZnO [4] deposited by atomic layer deposition (ALD) efficiently improves charge transport properties of the heterostructure while gradual passivation appears with increasing ZnO thickness due to stronger band-bending [4].

The presentation will focus in on the coating of the nanotube arrays by various secondary materials using ALD. The deposited materials influence strongly photo-electrochemical properties of nanotube layers. Experimental details and some recent photocatalytic [7, 8] results will be presented and discussed.

References:

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

[2] K. Lee et al., Chem. Rev., 2014, 114, 9385.

[3] R. Zazpe et al., Langmuir, 2017, 33, 3208.

[4] A. Ghobadi et al., Sci. Rep., 2016, 6, 30587.

[5] H. Park, et al., J. Electroceram., 2009, 23, 146.

[6] J-Y. Kim et al., Nanotechnology, 2014, 25, 504003.

[7] H. Sopha et al., Appl. Mater. Today, 2017, 9, 104.

[8] S. Ng et al., Adv. Mater. Interfaces 2017, 1701146.