Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 55: Poster Session III - MA 141/144 (Methods: Atomic and Electronic Structure; Particles and Clusters; Heterogeneous Catalysis; Semiconductor Substrates: Epitaxy and Growth+Adsorption+Clean Surfaces+Solid-Liquid Interfaces; Oxides and Insulators: Solid-Liquid Interfaces+Epitaxy and Growth; Phase Transitions; Metal Substrates: Adsorption of Inorganic Molecules+Epitaxy and Growth; Surface Chemical Reactions; Bimetallic Nanosystems: Tuning Physical and Chemical Properties; Oxides and insulators: Adsorption; Organic, polymeric, biomolecular films; etc.)
O 55.67: Poster
Mittwoch, 27. Februar 2008, 18:30–19:30, Poster F
Contact charging between insulators by organic molecule adsorption — •Wei Chen, Christoph Tegenkamp, and Herbert Pfnuer — Leibniz-Universität Hannover, Institut für Festkörperphysik, Appelstr. 2, 30167 Hannover, Germany
It has been shown that adsorption of simple organic acids on wide band gap insulators can introduce unoccupied electronic states in the band gap. These unoccupied states of adsorbates can lower electron excitation energy significantly, which makes it possible for charge exchanges between insulators. The adsorbates are thus decisive for contact charging problems as the electronic states of the surfaces are well defined by the them.
In this paper, the electronic states of benzoic acids attached to various functional groups are investigated by density functional theory calculations. The results show that salicylic acid (SA) and anthranilic acid (AA) are ideal for contact charging between insulators because of their higher binding energy of the uppermost πz orbital of the COOH group. The corresponding anti-bonding state (i.e. the LUMO) is thus located closer to the VB edge of the insulators, resulting a smaller effective band gap. Moreover, the HOMO-LUMO separation of AA is 0.12 eV smaller compared to SA. Further, we represent first results of atomic force microscopy measurements which are performed on organic molecule adsorbed NaCl surface using KCl coated cantilevers in order to study contact charging between the alkali chlorides.