Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 15: Single Molecules
CPP 15.2: Vortrag
Dienstag, 26. Februar 2008, 17:15–17:30, C 230
Molecular Wires in Single Molecule Junctions: Charge Transport and Vibrational Spectra — •Stefan Ballmann1, Daniel Secker1, Heiko B. Weber1, Wolfgang Hieringer2, and Andreas Görling2 — 1Lehrstuhl für Angewandte Physik, Universität Erlangen-Nürnberg, Staudtstrasse 7, 91058 Erlangen — 2Lehrstuhl für Theoretische Chemie, Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen
Quantum transport through single molecules is accompanied by internal molecular vibrations, detectable in principle as vibronic sidepeaks in the conductance spectra. We use the mechanically controllable break-junction (MCBJ) technique for the investigation of single-molecule contacts. The molecules under investigation are oligoynes, with a string-like atomic chain unit consisting of eight carbon atoms with alternating single and triple bonding, spanned between two platinum atoms and protected by bulky ligands. In our experiments, suppressed conductance at low bias, characteristic step-like features at higher voltages and strong sample-to-sample fluctuations are observed in the I-V-characteristics. In order to obtain a better understanding of the experimental results, density functional theory (DFT) calculations were performed. The experimental data show strong indications for the observation of vibrational features as peaks in dI/dV at a temperature of 75 Kelvin. In comparison to the theoretically observed values for the vibrational frequencies of the carbon chain, the peaks are in excellent agreement with the four energetically lowest-lying longitudinal modes.