Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 10: Metal substrates: Adsorption of organic / bio molecules II
O 10.5: Vortrag
Montag, 14. März 2011, 16:00–16:15, TRE Phy
Engineering Negative Differential Conductance in a single-C60 tunnel junction — •Benjamin W. Heinrich1,2, Mircea V. Rastei1, Deung-Jang Choi1, Jean-Pierre Bucher1, Thomas Frederiksen3, and Laurent Limot1 — 1Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, Strasbourg, France — 2Institut für Experimentalphysik, Freie Universität Berlin, Germany — 3Donostia International Physics Center, San Sebastián, Spain
Negative differential conductance (NDC) occurs when a voltage increase across an electronic device produces a decreasing current. The last two decades have seen a revived interest in this field following the observation of NDC at the atomic scale and in hybrid metal-organic junctions, which are potentially interesting for molecular electronics. The NDC characteristics in molecular systems are usually attributed to localized energy states, but can also result from inelastic or chemical processes.
Here we use a cryogenic STM to engineer an NDC with a single C60 molecule attached to the tip of the microscope. The original aspect of the observed NDC is that it results from electrons tunneling between the LUMO+1 of C60 and the dispersive Shockley surface states of Cu(111). The NDC intensity can then be tuned by varying the barrier thickness or by changing the C60 orientation up to complete extinction. In particular, this study underlines how the k-dependence of the tunneling process may be altered through the orientation of a molecular orbital: a single molecule acts as a k-filter for tunneling electrons.