Regensburg 2004 – wissenschaftliches Programm

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SYOH: Organic and Hybrid Systems for Future Electronics

SYOH 5: Poster

SYOH 5.31: Poster

Donnerstag, 11. März 2004, 18:00–21:00, B

Band gap engineering of insulating films due to defects and adsorption of organic molecules — •C. Tegenkamp and H. Pfnür — Institut Für Festkörperphysik, Appelstr.2 D-30167 Hannover,Germany

For possible applications of organic molecules in electronic circuits, the functionality of a chemically designed molecule can be significantly changed due to fundamental interactions of the molecule with a surface after adsorption. Generally, the strength of the chemical bond should depend on serveral parameters like substrate, orientation of the surface and defects.
As an example of functional organic molecules, we will present results about the problem of contact charging between insulators. Therefore, we have studied the adsorption of OH-substituted benzoic acids on insulating films like NaCl(100) and KCl(100) in the multilayer, monolayer and submonolayer regime using photoelectron- and electron energy loss spectroscopy. The experiments were performed on both defect–free surfaces and on surfaces decorated with anion vancancies. In accordance with DFT claculations, there are specific molecular orbitals which are in resonance with the valence band structure of the alkali halides. Interestingly, defects like anion vancancies only strengthen the bond by polarization effects. A reactivity of these centers in form of a dissociation of the molecules as for water has not been found. Although the molecules are chemisorbed in presence of defects, this is not reflected in energetic shifts of molecular orbitals of the functional acid- and phenoli OH–groups, which are most important for our model of contact charging. Our experimental results are supported by simple DFT calculations.