Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 90: Methods: Scanning Probe Techniques II
O 90.3: Vortrag
Freitag, 29. Februar 2008, 10:45–11:00, MA 042
Alignment of molecular energy levels between two biased metal electrodes — •Nikolai Severin1, Hua Liang1, Stefan Hecht2, Ragnar Stoll2, Klaus Müllen3, Igor M. Sokolov1, and Jürgen P. Rabe1 — 1Department of Physics, Humboldt University Berlin, Newtonstr 15, D-12489, Germany — 2Department of Chemistry, Humboldt University Berlin, Brook-Taylor-Str. 2, D-12489, Germany — 3Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
Understanding the alignment of molecular energy levels in a monolayer of molecules located between two biased metal electrodes in a tunneling contact is of paramount importance in the fast developing field of molecular electronics. Current rectification in such systems has been described taking into account a strong dependence of the energy levels on the relative position of the molecules between the electrodes. However, to our knowledge such dependence has not been experimentally examined yet; it is also not self-evident, since also different simple pictures of energy level alignment may be rationalized. Here we report on the dependence of the current rectification ratio on the relative position of different molecules between a highly ordered pyrolytic graphite substrate and a Pt/Ir scanning tunneling microscope tip immersed in 1-phenyloctane. The variation of the relative position of the molecules within the gap is achieved by the variation of the tip-surface distance. We find that the variation of current rectification ratio is substantially different for different molecules. We propose a simple model which rationalizes the experimental observations.