Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 36: Postersitzung (Elektronische Struktur, Grenzfl
äche fest-flüssig, Halbleiteroberfl
ächen und -grenzfl
ächen, Nanostrukturen, Oberfl
ächenreaktionen, Teilchen und Cluster, Struktur und Dynamik reiner Oberfl
ächen)
O 36.4: Poster
Montag, 7. März 2005, 15:00–18:00, Poster TU F
Adsorption of benzoic acid and its OH–substituted derivatives on MgSO4· H2O(100) — •C. Tegenkamp1, V. Maslyuk1, T. Bredow2, and H. Pfnür1 — 1Institut für Festkörperphysik, Abteilung Oberflächen, Appelstr. 2, 30167 Hannover, Germany — 2Theoretische Chemie, Im Kleinen Felde 30, 30167 Hannover, Germany
The adsorption of organic molecules on the MgSO4 · H2O(100) surface has been investigated theoretically using ab inito and semi–empirical methods. For the ab initio method a combination of Hartree–Fock and density functional theory, using the Perdew Wang exchange potential, has been used. As already demonstrated for the clean surface, both methods reveal comparable results and agree well with experimental data. The semi-empirical MSINDO package was “calibrated“ by means of the ab initio method and can be successfully used to describe large unit cells. Here we present results about the adsorption of the organic molecules, benzoic acid, saliclyic acid (SA), and para-salicylic acid. Both the geometry and the electronic structure have been calculated. For all three acids, the energetically most favorable position is above the Mg-atom with the molecules bound to the surface by the carboxylic O-atom. This leads to dramatic changes in the remaining molecule structure, e.g. the quasi-aromatic system of the SA is distorted. Furthermore, all acids generate new occupied and unoccupied states within the band gap of the insulator and the band gap is reduced to 0.1eV and 1eV depending on the molecule. The origin of these states can be assigned to specific parts of the molecule. The impact of the change in the electronic structure will be discussed in the context of contact charging between insulators.