Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P313
High-resolution PES and NEXAFS investigation of organic molecules and
interfaces
Achim Schöll 1 , Ying Zou 1 , Thomas Schmidt 1 , Rainer Fink 2 , Eberhard
Umbach 1
1 Experimentelle Physik II, Universität Würzburg – 2 Physikalische Chemie II, Univer-
sität Erlangen
Metal-organic contacts are of fundamental interest and of crucial importance for all organic
electronic applications. The bonding between the organic molecules of the active
layer and the metal contact surface does not only have a key influence on the charge
carrier transport through the interface but also on the morphology and structure of
the organic film. By using high-resolution PES and NEXAFS spectroscopy we are able
to characterize this interface in details that are not accessible by other techniques. As
example, we present investigations on model molecules (PTCDA, NTCDA) in different
adsoption states on Ag(111) and Au(111) surfaces. We find that the molecules interact
much stronger with the Ag(111) surface, where PTCDA and NTCDA are chemisorbed
which can clearly be derived by the high quality of the spectroscopic data. Moreover,
the rich finestructures of the monolayer PES spectra exhibit substantial differences for
the same molecule in different adsorption states. Changes in the relative intensity of
satellite features can be interpreted in terms of different charge transfer screening probabilities
due to differences in the interface coupling [1]. The bonding is assigned to the
interaction of the molecular aromatic pi-system with Ag d-states and significant charge
transfer from Ag into the NTCDA/PTCDA LUMO can be observed. In contrast, the
investigated molecules show mainly physisorptive bonding to the Au(111) surface. In
addition, the vibronic fine structure in high-resolution NEXAFS data, analysed in
detail for NTCDA, reveals interesting information on the electron-vibron coupling in
complex organic compounds [2].
This project is financed by the BMBF under contract 05KS4WWC/2.
[1] A. Schöll et al., Journal of Physical Chemistry B 108, 14741 (2004).
[2] A. Schöll et al., Physical Review Letters 93 (2004).