Raman Spectroscopy on Single Molecule Junctions

Dr. Joachim Reichert, University of Münster

Electronic transport measurements on single molecules which are immobilized by self-assembling techniques between two metallic electrodes have proven the ability of organic molecules to act as functional parts in nano-scale-devices. Recent developments and advances in atomic-scale imaging and manipulation techniques enables access to a new field of single molecule experiments. Especially scanning near field optical microcopy (SNOM) with its ability to apply an optical field to a molecular system in a controlled manner enlarges the range of experimentally available properties in metal-anchored molecular junctions. A novel method to contact single molecules with a SNOM-tip has been developed. In parallel it has been shown, that Raman spectroscopy on a molecular level of adsorbates on Au using the same kind of tetrahedral SNOM-tip is possible. We propose to combine these two experiments to perform Raman spectroscopy and conductance measurements at the same time. Analysis of the vibrational spectrum of a molecule in between two metallic electrodes would verify that the desired and only the desired molecular species is present. Such an analysis would furthermore lead to physical insights that as far as known have not been studied yet.
Certain aspects of electron transport through single molecules are poorly described by the Landauer-approach. The strongly broadened peaks at room temperature and especially the decreasing line width at lower temperatures indicate, that inelastic processes might play an important role in the non-equilibrium-situation of electron transport. In electron transfer theory, resonant inelastic tunneling in molecular junctions including strong electron-phonon coupling can strongly influence and broaden the observed structure. By looking at the current- and temperature-dependence of the vibrational-spectrum we expect to be able to study a strong non-equilibrium situation.