Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 51: Organic-Inorganic Systems II: Energy Level Alignment
O 51.6: Talk
Wednesday, March 9, 2016, 12:00–12:15, S054
Optical transition energies of isolated molecular monomers and weakly interacting 2D aggregates — •Roman Forker1, Thomas Dienel2, Andreas Krause3, Marco Gruenewald1, Matthias Meissner1, Tino Kirchhuebel1, Oliver Gröning2, and Torsten Fritz1 — 1Institute of Solid State Physics, Friedrich Schiller University Jena, Helmholtzweg 5, 07743 Jena, Germany — 2Nanotech@surfaces Laboratory, EMPA - Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Duebendorf, Switzerland — 3NaMLab gGmbH, Noethnitzer Str. 64, 01187 Dresden, Germany
We analyze the S0→S1 fundamental transition energies observed for 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) as a function of coverage on various surfaces with substantially dissimilar dielectric properties. Surprisingly, only two different spectral positions are found: (i) PTCDAHE basically mimics the behavior of isolated monomers on the surface, while (ii) PTCDALE, red-shifted by approx. 70 meV, is attributed to a densely packed monolayer (ML) in a two-dimensional herringbone arrangement. This red-shift is in remarkable accordance with previous investigations for PTCDA on NaCl(100) and thus likely arises from the same physical effects, namely the formation of 2D excitonic bands and the polarizability of neighboring molecules within the ML. Possible contributions from substrate-induced molecular distortions and chemical interactions are discussed. Contrary to earlier studies, we conclude that the polarizability of the substrate is not the dominant factor responsible for the reported spectral positions.