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O: Fachverband Oberflächenphysik

O 88: Metal substrates: Adsorption of organic / bio molecules IX

O 88.5: Vortrag

Donnerstag, 17. März 2011, 18:15–18:30, PHY C213

Temperature Induced Phase Transition of Pentacene Sub-Monolayers on Cu(110)-(2×1)O — •Johannes Gall, Michael Hohage, Lidong Sun, Daniel Queteschiner, Günther Weidlinger, Mariella Denk, and Peter Zeppenfeld — Institute of Experimental Physics, Johannes Kepler University, Linz, Austria.

A reversible temperature induced phase transition of pentacene sub-monolayer films on the Cu(110)-(2×1)O reconstructed substrate was observed by means of Reflectance Difference Spectroscopy (RDS). It is interpreted as a transition from a 2D condensed phase (stable at low temperatures) to a molecular 2D gas phase at high temperatures.

In the present study, we have performed Monte Carlo (MC) and Kinetic Monte Carlo (KMC) simulations in the framework of a rectangular two dimensional lattice-gas model with nearest neighbor interactions to reproduce the phase transition behavior.

From adsorption isotherm experiments of pentacene on Cu(110)-(2× 1)O, the 2D-sublimation energy of pentacene was found to be 87 meV. In contrast, from simulations, the sum of the lateral molecule-molecule interaction energies of pentacene was determined to be 101 meV.

However, from the RD spectra and Scanning Tunneling Microscopy (STM) images evidence was found that the gas phase actually consists of pentacene dimers. Therefore, the influence of these dimers on the phase transition is dicussed.