Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 56: Metal substrates: Adsorption of organic / bio molecules III

O 56.9: Talk

Wednesday, March 28, 2012, 18:45–19:00, A 053

Free-base porphine on Ag(111): Repulsive interaction and substrate mediated phase transitions. — •Felix Bischoff, Willi Auwärter, David Écija, Saranyan Vijayaraghavan, Sushobhan Joshi, Knud Seufert, and Johannes V. Barth — Physik Department, E20, TU München, Germany

Motivated by nature, porphyrins have been established as useful building blocks in functional nano-architectures. A key issue is the tailoring of porphyrin building blocks with desired properties, yet a detailed understanding of the influences of different constituents, such as meso-substituents and central metal ions, is still lacking. To advance the control of surface-confined porphyrins, we studied the simplest molecule - the porphine - that is the basic macrocyclic body of all porphyrins. We present systematic low-temperature STM experiments of free-base porphines (2H-P) on Ag(111). At low coverages, porphines exhibit a disordered phase, indicating repulsive electrostatic interactions that could arise from charge-transfer bonds with the metal substrate. The molecules are selectively chemisorbed at specific adsorption sites. This also causes substrate-mediated phase transitions with increasing coverage from a disordered lattice gas, to a liquid-like phase, to a regular solid and finally to a glassy layer that shows an average positional, but no orientational order.