Seminar "Single molecule junctions under high bias: Limitations of the single-level model"

Title: Single molecule junctions under high bias: Limitations of the single-level model

Speaker: Prof. Elke Scheer, Department of Physics, University of Konstanz, Germany

Abstract:

Contacting single molecules with metallic electrodes is challenging because of their small size of roughly a nanometer and the limitations in nanofabricating electrode pairs with this size. Over the last years several techniques have been put forward, among others,  electromigrated electrode pairs, scanning tunneling microscope techniques or mechanically controllable breakjunctions (MCBJ). A second challenge consists in verifying that the contact is indeed formed by a single molecule bridging an electrode gap. Several methods are established to gather information about the nature of the electronic transport and the contact configuration, including the analysis of the current-voltage characteristics (IVs), inelastic electron tunneling spectroscopy (IETS), and noise spectroscopy. To analyze the IVs usually the single(resonant) level model (SLM) is applied which assumes that the current is dominated by the transport through a single channel formed by one molecular orbital in contact with the Fermi seas of the electrodes [1-4]. Although the model is successfully applied in many cases, it also has its limitations due to approximations made to derive and due to the real energy landscape of the molecular junction. In this talk I will show examples of successful and unsuccessful fitting with the SLM and possible extensions taking into account Fermi level pinning or electrc field effects in the junction.

[1] Zotti et al, Small 6, 1529 (2010)
[2] Kirchner et al.,  Acta Phys. Pol. 121, 410 (2012)
[3] Thijssen & van der Zant, phys. stat. sol. (b) 245, 1455 (2008)
[4] Huisman et al.,  Nano Lett. 9, 3909 (2009)