Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 52: Metal substrates: Adsorption of organic / bio molecules VII
O 52.9: Talk
Thursday, March 26, 2009, 17:00–17:15, SCH A118
Fingerprints of large organic molecules: on the interior of tetraphenyl-porphyrins in scanning tunneling microscopy — Florian Buchner1,3, Karl-Georg Warnick2,3, Thorsten Wölfle2,3, Wolfgang Hieringer2,3, Andreas Görling2,3, Hans-Peter Steinrück1,3, and •Hubertus Marbach1,3 — 1Lehrstuhl für Physikalische Chemie II — 2Lehrstuhl für Theoretische Chemie — 3Interdisciplinary Center of Molecular Materials (ICMM), Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91056 Erlangen
The appearance of a constant current scanning tunneling microscopy (STM) image is determined by both the topography and the electronic structure of the investigated object. The discrimination of these effects and the understanding of the bias dependent appearance of different adsorbed species represents a major challenge. We investigate an intermixed tetraphenylporphyrin (TPP) layer consisting of 2HTPP, CoTPP and FeTPP molecules on Ag(111), to allow for a direct in situ comparison. By a combined experimental and theoretical analysis, we find that at lower bias voltages the appearance of CoTPP in the STM image is dominated by electronic effects, while at high bias a combination of both electronic and topographic effects is observed. For 2HTPP and FeTPP the images are dominated by topographic effects. The detailed interpretation of the bias dependence is performed by means of high quality density-functional calculations, which allow to reproduce the experimentally observed STM images with very high accuracy and to trace back the observed features to individual molecular orbitals. Supported by the DFG through SFB 583.