Dresden 2006 – wissenschaftliches Programm

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O: Oberflächenphysik

O 9: Organic films I

O 9.9: Vortrag

Montag, 27. März 2006, 17:00–17:15, TRE Phys

On the Origin of a Phase Transition in clean Porphyrin Films on a Silver (111) Surface — •H. Marbach, K. Comanici, F. Buchner, F. Maier, and H.-P. Steinrück — Lehrstuhl für Physikalische Chemie ll, Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91056 Erlangen

Organic molecules play a prominent role for the development of new materials and molecular devices. An important group of such molecules are porphyrins. Their versatility and distinct chemical and electronic properties make them promising candidates for tailored catalytic processes and as building blocks for nanoscaled electronic devices. The properties of porphyrins can be modified e.g. by introducing or changing a central metal atom and different ligands. We studied different porphyrins on a silver (111) surface by means of scanning tunneling microscopy (STM) in ultra high vacuum (UHV). The preparation of the porphyrin layers was done in UHV via sublimation techniques. Different ordered phases and spatiotemporal behaviors were observed for different central metal atoms and porphyrin ligands. In particular for a specific Cobalt porphyrin (Co-TTBPP) two different phases (square and hexagonal) were observed. In a time series of STM images the transition from the hexagonal to the square phase was studied. Based on these observations and the comparison with the ordered square structures of similar porphyrins the underlying mechanism is interpreted as an activated process.