Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 29: Metal substrates: Adsorption of organic / bio molecules II

O 29.5: Talk

Tuesday, March 27, 2012, 11:30–11:45, MA 043

Investigation of Pentacene Submonolayers Adsorbed on Cu(110)-(2×1)O and Cu(110)-c(6×2)O — •Johannes Gall, Mariella Denk, Günther Weidlinger, Daniel Queteschiner, Lidong Sun, Michael Hohage, and Peter Zeppenfeld — Institut für Experimentalphysik, Johannes Kepler Universität Linz, 4040 Linz, Österreich

We have investigated the sub-monolayer adsorption behavior of pentacene molecules on both the Cu(110)-(2×1)O and the Cu(110)-c(6×2)O surface with RDS (reflectance difference spectroscopy), STM/STS (scanning tunneling microscopy and spectroscopy) and LEED (low energy electron diffraction).

In case of the Cu(110)-(2×1)O surface it was found that pentacene sub-monolayers undergo a temperature-dependent phase transition from a (densely packed) condensed phase at low temperatures to a (dilute) 2D-gas phase at higher temperatures. The characteristics of this phase transition could also be well reproduced by Monte Carlo simulations. From the experiments we were able to derive important adsorption parameters, such as the effective lateral molecule-molecule interaction energy, which also agree with the simulation results.

For the Cu(110)-c(6×2)O surface the situation is quite different: pentacene molecules were not observed to condense into densely packed islands at low temperature. Instead, a low-density frozen 2D-gas phase was observed. We attribute this behavior to a repulsive interaction between adsorbed species. Furthermore, we found strong evidence that those species in the 2D-gas phase actually consist of pentacene dimers.