Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 64: Metal Substrates: Adsorption of Organic/Bio Molecules IV

O 64.5: Talk

Thursday, February 28, 2008, 12:15–12:30, HE 101

Voltage-dependent contrast of Co-Tetraphenylporphyrin Molecules on Ag(111) — •Florian Buchner, Karmen Comanici, Ken Flechtner, Thomas Lukasczyk, J. Michael Gottfried, Hubertus Marbach, and Hans-Peter Steinrück — Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen

The self-assembly of molecules on single-crystal surfaces is an approach towards the creation of novel materials with outstanding properties. Porphyrins represent a group of molecules which are of great interest for applications as well as for fundamental research. In this contribution, it will be shown that the appearance of tetraphenylporphyrins (TPP) in scanning tunneling microscopy (STM) topographs strongly depends on the applied bias voltage. Here we report the observation and identification of certain features in STM images of CoTPP layers on Ag(111). A significant portion of an ordered monolayer of CoTPP appears as depression at bias voltages around -1 V. At reduced negative bias voltages, the contrast of the depressions fade and at bias voltages around +1 V, the contrast is inverted. Investigating the electronic structure of CoTPP and 2HTPP layers by means of ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS), the contrast mechanism could be clarified, enabling us to interpret the depressions as 2HTPP. Additional evidence could be provided by imaging layers of different mixtures and by high-resolution STM images of the features in CoTPP. This work has been funded by the DFG through Sonderforschungsbereich 583.