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O: Fachverband Oberflächenphysik

O 58: Poster Session III (Solid/liquid interfaces; Metals; Semiconductors; Oxides and insulators)

O 58.33: Poster

Mittwoch, 28. März 2012, 18:15–21:45, Poster B

Chemical transformations drive complex self-assembly of uracil on close packed coinage metal surfaces — •Anthoula C. Papageorgiou, Sybille Fischer, Joachim Reichert, Katharina Diller, Florian Blobner, Florian Klappenberger, Francesco Allegretti, and Johannes V. Barth — Physik Department E20, Technische Universität München, 85748 Garching, Germany

We address the interplay between adsorption, chemical nature and self-assembly of uracil on Ag(111) and Cu(111) surfaces as a function of molecular coverage and temperature. We find that the metal surface acts both as a template and a catalyst for the resulting self-assembled structures. With a combination of STM, synchrotron XPS and NEXAFS studies, we unravel a molecular phase map on Cu(111) consisting of three phases, in stark contrast to what is observed for the case of uracil on the more inert Ag(111) surface. On Ag(111) uracil adsorbs flat, intact and forms close packed two-dimensional islands. The self-assembly is driven by stable hydrogen bonded dimers with poor two-dimensional order. On Cu(111) complex structures are observed and we determine these phase transformations to be driven by gradual deprotonation of the uracil molecules. Our XPS study reveals the tautomeric signature of uracil in the contact layer and its deprotonation site. Our data show a dependence between molecular coverage and molecule-metal interaction, as the molecules tilt at higher coverages in order to accommodate for a higher packing density. After deprotonation of both uracil N atoms, the observed adsorption geometry can be understood only with significant charge redistribution in the molecule.