Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 89: Metal substrates: Adsorption of organic / bio molecules V

O 89.10: Vortrag

Freitag, 30. März 2012, 12:45–13:00, A 053

X-ray induced reversible switching of azobenzene derivatives, adsorbed on Bi(111) — •Alex Krüger, Matthias Bernien, Ch. Felix Hermanns, and Wolfgang Kuch — Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, 14195 Berlin

The adsorption of the photoswitch dimetacyano-azobenzene (DMC) on Bi(111) after deposition at 110 K was studied for different coverages by angle-dependent near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. For the adsorption of one monolayer of molecules we find the molecules physisorbed in a nearly planar conformation parallel to the surface. By illumination with intense x rays two orders of magnitude higher in flux density than used for the NEXAFS measurements at a photon energy corresponding to the azo N 1s → LUMO transition at 399 eV, the angle dependence of the π ^* resonances of N-K as well as C-K NEXAFS spectra changes significantly. The effect can be interpreted as a switching of at least 20% of the DMC molecules from the trans to the cis conformation. The process is reversible, as the NEXAFS spectra become identical to the spectra before the illumination after waiting for 1 h in darkness at 110 K, indicating a thermally induced back reaction. Using off-resonant x rays with an energy of 270 eV for the illumination, no modifications of the NEXAFS N-K and C-K spectra were observed. A comparable effect with an even higher percentage of switched molecules occurs also in multilayers of DMC molecules on Bi(111).
This work is supported by the DFG through Sfb 658.