Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 24: Postersitzung (Epitaxie und Wachstum, Oxide und Isolatoren, Elektronische Struktur, Oberfl
ächenreaktionen, Adsorption an Oberfl
ächen, Organische Dünnschichten)
O 24.36: Poster
Mittwoch, 26. März 2003, 14:30–17:30, P1
Charge transfer and dynamic screening effects in PTCDA monolayers on Ag substrates — •Ying Zou1, Achim Schöll1, Thomas Schmidt1, Rainer Fink2, and Eberhard Umbach1 — 1Exp. Physik II, Univ. Würzburg, 97074, Würzburg, Germany — 2Phys. II, Univ. Erlangen-Nürnberg, Egerlandstr. 3, 91058, Erlangen, Germany
Due to a large charge separation energy many organic substances are regarded as Mott-Hubbard compounds if a solid state description is used. For PTCDA monolayers adsorbed on various low-index Ag surfaces (Ag(111), Ag(110)) a gap state is detected in UPS spectra. In NEXAFS spectra, we observe that the intensity of the lowest unoccupied molecular orbital (LUMO) of the molecular substance is reduced or even disappears for PTCDA/Ag(111)[1] and PTCDA/Ag(110), respectively. Comparing the UPS and NEXAFS data with recent HREELS experiments for these adsorbates and for potassium doped PTCDA films [2], we are able to clarify the modifications of the electronic structure upon charge transfer. Upon adsorption, the (original) PTCDA LUMO splits into two Hubbard bands. The observed changes are interpreted as a gradual reduction of Coulomb repulsion energy (Hubbard U) with increasing bonding between metal and PTCDA molecules. We will present a consistent picture of the electronic structure for the various systems. This work is funded by the BMBF under contract 05 KS1WWA-5.
[1] E. Umbach, R. Fink, Proc.Internat.School of Physics, IOS Press, Amsterdam (2002)
[2] V. Shklover, et al., Surf. Sci. 482-485(2001)1241-1248