Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 105: Nanostructures at surfaces: 1D and 2D structures and networks III

O 105.2: Talk

Thursday, March 15, 2018, 17:30–17:45, MA 141

Crossover in the inelastic spectra of highly-conducting conjugated molecules — •Enrique Montes, Giuseppe Foti, and Héctor Vázquez — Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, Prague, Czech Republic

We use inelastic electron tunnelling spectroscopy (IETS) first-principles simulations [1] to identify and characterise the different vibrational modes of single conjugated molecules bonded to Au metal electrodes. The molecules are polyphenyls (with 1 to 4 benzene units) bonded to Au via highly conducting direct Au-C bonds. The short molecule shows near resonant elastic transmission, with a crossover to tunnelling for the longer backbones [2].

The calculated inelastic spectra exhibit dips for the short molecule, and peaks for the longer molecules, in the second derivative of the current. We first characterize the inelastic spectra in terms of IETS selection rules [3]. We then analyze the observed trends as a function of molecular length. In particular, we characterize the modes whose inelastic signal increases with the number of phenyl units, the modes where it decreases, and the modes where IETS dips change to peaks.

[1] T. Frederiksen, M. Paulsson, M. Brandbyge, and A.-P. Jauho. Phys. Rev. B 75, 205413 (2007).

[2] W. Chen, J. R. Widawsky, H. Vázquez, S. T. Schneebeli, M. S. Hybertsen, R. Breslow, and L. Venkataraman. J. Am. Chem. Soc. 133, 17160 (2011).

[3] M. Paulsson, T. Frederiksen, H. Ueba, N. Lorente, and M. Brandbyge. Phys. Rev. Lett. 100, 226604 (2008).