Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 59: Poster Session II (Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: arrays; Nanostructures at surfaces: Wires, tubes; Nanostructures at surfaces: Other; Plasmonics and nanooptics; Metal substrates: Epitaxy and growth; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsoprtion of organic / bio molecules; Metal substrates: Adsoprtion of inorganic molecules; Metal substrates: Adsoprtion of O and/or H; Metal substrates: Clean surfaces; Density functional theory and beyond for real materials)

O 59.88: Poster

Wednesday, March 24, 2010, 17:45–20:30, Poster B1

Porphyrin based molecular switches and quantum corrals — Felix Bischoff, •Willi Auwärter, Knud Seufert, Daniel Heim, and Johannes V. Barth — Physik Department, E20, Technische Universität München, James-Franck Str. 1, D-85748 Garching, Germany

Porphyrin molecules exhibit an intriguing variety of functional properties, which are exploited in both biological and artificial systems. Hereby, particular interest lies on the porphyrin macrocycle, which can act as a chemical pocket and host either two hydrogen atoms or a metal ion. Here, we present first results on the tautomerization of free-base tetraphenylporphyrin molecules (H2-TPP) anchored on a Ag(111) surface. STM experiments proof that the switching of the two H's in the porphyrin pocket can be induced by voltage pulses. This process is directly monitored by current versus time (I-t) spectra, which exhibit two characteristic current levels. In addition, a tip induced process can be applied to remove one H atom from the porphyrin pocket. As a result, the remaining H atom can be switched between four possible positions (the four nitrogen atoms of the macrocycle).

In a different set of experiments, we show that the TPP's chemical pocket plays a non-neglibible role for the interaction of the porphyrin with the electronic structure of the supporting surface. By STM manipulation, individual TPP molecules are removed one-by-one from highly ordered TPP arrays on Ag(111), to construct artifical structures confining the Ag(111) surface state electrons. Hereby, the chemical nature of the corral walls, i.e. the use of either H2-TPP or Co-TPP arrays, affects the electron confinement and the coupling of resonators.