Dresden 2011 – scientific programme

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DS: Fachverband Dünne Schichten

DS 65: Organic Thin Films IV

DS 65.4: Talk

Friday, March 18, 2011, 16:45–17:00, GER 38

Electronic Coupling and Charge Transfer between Metals and Epitaxial Organic Layers — •Roman Forker and Torsten Fritz — Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Max-Wien-Platz 1, 07743 Jena, Germany

When molecules are adsorbed on metals, several processes may occur, such as the “push-back-effect”, chemical interaction, the formation of interface states or even charge transfer (CT) between substrate and adsorbate. The strength and in part also the direction of such effects strongly depend on the molecule–metal combination and, additionally, on the specific structure(s) formed [1].

Here we investigate epitaxial mono- and multilayers of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) in situ on various metal surfaces by a variant of optical absorption spectroscopy. During film growth we observe pronounced changes in the spectra from the first monolayer (ML) to 2 ML and higher film thicknesses. While our results suggest the formation of radical cations in the second ML of PTCDA on Au(111) and Au(100) [2], the situation on Ag(111) is somewhat different. There, no clear indications for charged molecules were observed. On aluminum surfaces we conclude that the direction of the charge transfer is reversed, i.e., the spectral signature of PTCDA anions becomes visible. This gives rise to the interpretation that the electronic properties of the metal substrate, in particular the work function, determine the occurrence of charge transfer.

[1] S. Braun et al., Adv. Mater. 21 (2009), 1450.

[2] R. Forker et al., Org. Electron. 10 (2009), 1448.