Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 52: Metal substrates: Adsorption of organic / bio molecules VII

O 52.3: Talk

Thursday, March 26, 2009, 15:30–15:45, SCH A118

Temperature and thickness dependent adsorption studies of azobenzene molecules on Cu(100) — •Alex Krüger, Marten Piantek, Cristina Navio, Jorge Miguel, Matthias Bernien, and Wolfgang Kuch — Institut für Experimentalphysik, Freie Universität Berlin

Here we present a study of the influence of temperature and coverage on the ordering of dimetacyano-azobenzene (DMC) ultrathin layers adsorbed on Cu(001). Near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) provided information on the molecular geometry relative to the substrate and on the nature of molecule adsorption to the surface, respectively. From XPS data we determine that DMC molecules evaporated onto Cu(001) at room temperature are chemisorbed, but a dramatic change in the angle-dependent C- and N-K edge NEXAFS between 0.5 and 1 ML (monolayer) indicates that strong intermolecular interactions provoke a conformational change. On a second step, we studied the temperature dependence of 1 ML DMC on Cu(001). At 150 K, about half of the molecules are physisorbed in a planar conformation parallel to the surface. As the temperature increases, the NEXAFS data shows a strong change in the molecular conformation at 230 K, concurrent with the formation of a bond between one of the azo nitrogen atoms to the surface, as seen by XPS. These results are supported by density functional theory calculations. We conclude that both intermolecular and molecule-substrate interactions can give rise to the observed conformational change.