| AVS 56th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session I and Mort Traum Finalists |
| Presenter: | A. Nefedov, Ruhr University of Bochum, Germany |
| Authors: | A. Nefedov, Ruhr University of Bochum, Germany P. Rahe, University of Osnabruck, Germany M. Nimmrich, University of Osnabruck, Germany M. Naboka, Ruhr University of Bochum, Germany A. Kuehnle, University of Osnabruck, Germany Ch. Woell, University of Bochum, Germany |
| Correspondent: | Click to Email |
Chemically functionalized surfaces play an important role in many nanotechnological applications. However, only few attempts have been made so far to create a chemically functionalized metal oxide surface by adsorption of organic molecules, even though metal oxide surfaces provide anisotropy and specific adsorption sites that lead to well-ordered monolayers. Terephthalic acid (TPA) is a versatile molecular linker and has, consequently, received considerable attention with regard to the assembly of three-dimensional self-assembling porous frameworks stabilized by metal-carboxylate bonds, as well as in two-dimensional supramolecular architectures at surfaces. In particular, TPA/TiO2 is a promising system to create an overlayer of upright oriented molecules exposing an organic surface terminated by carboxyl groups.
The coverage-dependent adsorption of terephthalic acid on rutile TiO2 was investigated by means of non-contact atom force microscopy (NC-AFM) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy [1, 2] under ultra-high vacuum conditions at room temperature. Experiments were performed in two separate systems, one for performing the NC-AFM measurements and the second UHV system using synchrotron radiation for the NEXAFS experiments, which were carried out at the HE-SGM beamline of BESSY II.
Individual molecules are observed to adsorb in a flat-lying geometry at low coverages up to ~0.3 monolayer (ML). The molecules are immobile at room temperature, implying a diffusion barrier of larger than 0.8 eV. This rather high value might be explained by an 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 ML and 1 ML: (i) a well-ordered (2×1) structure and (ii) a mixed structure of molecular 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 of the exposure results in a saturation of the corresponding signal in the NEXAFS spectra revealing that the growth of TPA on TiO2 at room temperature is self-limiting.
1. S. Reiss, H. Krumm, A. Niklewski, V. Staemmler, Ch. Wöll, J. Chem. Phys. 116, 7704, (2002).
2. D. Käfer, L. Ruppel, G. Witte, Ch. Wöll; Phys. Rev. Lett., 95, 166602 (2005).