Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 2: Organische Dünnschichten I

O 2.8: Talk

Friday, March 4, 2005, 12:30–12:45, TU EB301

Transfer and amplification of chirality in hydrocarbon monolayers — •Karl-Heinz Ernst, Manfred Parschau, Roman Fasel, and Sara Romer — Empa-Materials Science and Technology, 8600 Duebendorf, Schweiz

We present a new form of chirality transfer and amplification observed in two-dimensional monolayers. In the first case, a special surface enantiomorphism is observed via STM after adsorption of the enantiomers of a helical aromatic hydrocarbon on Cu(111) at 50 K. Instead of crystallization into homochiral domains on the surface, racemic mirror domains are observed, i.e., they possess an equimolar content of left- and right-handed molecules. In this situation, a small excess of one chiral species is sufficient to create domains of a single handedness throughout the whole surface layer. In the second case, homochirality was induced in monolayers of achiral molecules after chiral doping. Achiral molecules can become chiral when adsorbed at surfaces because of the reduced symmetry in the molecule or the adsorbate lattice. Adsorbed on Cu(110), succinic acid forms equal numbers of left- and right-handed domains and the surface is globally achiral. Doping with small amounts of left- or right-handed tartaric acid, however, creates homochirality and the opposite mirror domains are not observed anymore in the LEED pattern. Our findings are explained by cooperative interactions and will be discussed in the frame of a one-dimensional random-field Ising model.