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 , ZnO  or MgO  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  or ZnO  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 .
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  results will be presented and discussed.
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