Ultrafast Anodic Growth of TiO2-Nanotubes with Semi-Metallic Properties

Abstract

Self organized nanotubular structures of transition metal oxides grown on their metallic substrates, especially titanium [1], have attracted great scientific and technological interest due to the possibility to exploit their functional properties (such in photo-catalysis, electro-catalysis, solar energy conversion and as host for Li storage) in a nanotubular morphology. In contrast to the conventional way to grow anodic TiO2 nanotubes, which is an optimized electrochemical treatment of Ti in fluoride containing electrolyte (for an overview see [2]) this work reports on the growth of nanotubes by so-called RBA (rapid breakdown anodization).[3] This nanotube growth-process is in comparison extremely fast (seconds instead of hours) and leads to surface coatings consisting of dense packed bundles of nanotubes with very high aspect ratios (tube length up to 50 micrometer, tube diameter of ~40 nanometer). In addition, this method provides a new route for an insitu electrochemical doping during the growth of TiO2 nanotubular layers with various transition metals to adjust i.e. the photocatalytic activity [4]. The second part of the presentation will demonstrate that alternatively the electronic and optical properties [5] of these TiO2 nanotubes can be significantly modified, showing semi-metallic behavior by a high temperature reduction treatment in acethylene or ammonia creating a suitable platform for highly conductive surface area electrodes which is important i.e. sensing applications. [6] Literature: [1] V. Zwilling, M. Aucouturier, E. Darque-Ceretti, Electrochim. Acta, 45, 921 (1999).[2] S. Berger, R. Hahn, P. Roy, P. Schmuki Phys. Status Solidi B247, 10, 2424 (2010).[3] R. Hahn, J. M. Macak, P. Schmuki, Electrochem. Commun.,9, 947 (2007).[4] M. Stark, R. Hahn, M.S. Killian, P. Schmuki Catal. Sci. Technol., 3, 1765 (2013).[5] R. Hahn, F. Schmidt-Stein, J. Salonen, S. Thiemann, Y.Y. Song, J. Kunze,V.-P. Lehto, P Schmuki, Angewandte Chemie - International Edition 48 (39), 7236 (2009).[6] R. Hahn et al submitted