Transition of molecule orientation during adsorption of terephthalic acid on rutile TiO2(110)

  • chair: Rahe, P. / Nimmrich, M. / Nefedov, A. / Naboka, M. / Wöll, C. / Kühnle, A. (2009)

  • place: J. Phys. Chem. C 113 (2009), 17471-17478

  • Date: 2009
  • Rahe, P. / Nimmrich, M. / Nefedov, A. / Naboka, M. / Wöll, C. / Kühnle, A. (2009): „Transition of molecule orientation during adsorption of terephthalic acid on rutile TiO2(110)“. In: J. Phys. Chem. C 113 (2009), 17471-17478


The coverage-dependent mode of adsorption of terephthalic acid [C6H4(COOH)2, TPA] on rutile TiO2(110) was investigated by means of noncontact atomic force microscopy (NC-AFM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy under ultrahigh vacuum conditions at room temperature. Individual molecules are observed to adsorb in an disordered, flat-lying geometry at low coverages up to ~0.3 monolayer (ML).

The molecules are immobile at room temperature, implying a diffusion barrier larger than 0.8 eV. This rather high value might be explained by anchoring to surface defect sites. A transition from flat-lying to upright-oriented molecules is revealed by NEXAFS when saturation coverage is achieved. High-resolution NC-AFM images reveal two different structures at coverages between ~0.8 and 1 ML: (i) a well-ordered (2 × 1) structure and (ii) a structure of single and paired rows oriented along the [001] crystallographic direction.

The latter structure might originate from a pairwise interaction of two neighboring molecules through the top carboxyl groups. Further increase in the exposure results in a saturation of the corresponding signal in the NEXAFS spectra, revealing that the growth of TPA on TiO2(110) at room temperature is self-limiting.


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