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Spectroscopic Properties of adjoined TiO2 Nanocrystals

Michael J. Elser 1Thomas Berger 1Johannes Bernardi 2Erich Knoezinger 1Oliver Diwald 1

1. Institute of Materials Chemistry, Vienna University of Technology (TU), Veterinärplatz 1, Wien 1210, Austria
2. University Service Centre for Transmission Electron Microscopy (USTEM), Wiedner Hauptstraße 8-10/138, Wien 1040, Austria


To include particle attachment and porosity in the discussion of the electronic properties of nanostructured oxide materials is indispensable for deeper insights into electronic conduction across grain boundaries and thus essential to electronics, sensor technology and photovoltaics. We investigated the aggregation of isolated TiO2-nanocrystals which results from the application of a simple hydration-dehydration cycle. After contact with water and subsequent dehydration and adsorbate removal under high vacuum conditions the powder containing isolated nanocrystals [1] is transformed into a monolithic solid which consists of a mesoporous particle network. These monoliths show significant changes in the optical absorption properties as investigated by UV-diffuse reectance spectroscopy. Vacuum annealing at temperatures T > 870 K induces oxygen anion vacancy formation on isolated TiO2-nanocrystals. The electrons left behind form paramagnetic states which can be tracked by electron paramagnetic resonance (EPR) spectroscopy. On aggregated TiO2-nanocrystals EPR measurements reveal that vacancy formation occurs at significantly lower temperatures than T = 870 K. In addition, polarizable conduction band electrons [2] have only been observed in the network of adjoined TiO2-nanocrystals [3]. Changes in the spectroscopic properties resulting from solvent-mediated particle aggregation and particle network formation as well as the facilitated defect formation process will be discussed in the light of the associated structural data.

[1] T. Berger, M. Sterrer, O. Diwald, E. Knözinger, Chem.Phys.Chem. 2005, 6, 2104

[2] E. Serwicka, M. W. Schlierkamp, R. N. Schindler, Z. Naturforschung 1981, 36a, 226

[3] M. J. Elser, T. Berger, D. Brandhuber, J. Bernardi, O. Diwald, E. Knözinger, J. Phys. Chem. B 2006, 110, 7605


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Related papers

Presentation: Oral at E-MRS Fall Meeting 2007, Symposium A, by Michael J. Elser
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 20:29
Revised:   2009-06-07 00:44