Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 8: Metal Substrates: Adsorption of Organic/Bio Molecules I
O 8.8: Vortrag
Montag, 25. Februar 2008, 13:45–14:00, MA 041
Electron transport across single phthalocyanide (Pc) molecules — •Florian Witt1, Albert Takacs1,2, Timofey Balashov1, and Wulf Wulfhekel1,2 — 1Physikalisches Institut, Universität Karlsruhe, Wolfgang-Gaede Strasse 1, 76131 Karlsruhe, Germany — 2CFN-DFG Centrum für Funktionelle Nanostrukturen
Recently molecular electronics is discussed as a future replacement of semiconductor electronics. A detailed knowledge of the electronic properties of the molecules i.e. the HOMO-LUMO gap, the density of states and the conductance is necessary. Scanning Tunneling Microscopy (STM) in combination with Scanning Tunneling Spectroscopy (STS) has become one of the most important methods for studying these molecular properties. We present results on single molecule contact measurements obtained with STM at 4K. A small amount of H2Pc and CoPc molecules was evaporated on clean Cu(111) and Co/Cu(111). By laterally positioning the STM tip over isolated molecules and approaching the tip towards the molecules we measured the conductance as function of distance. Initially, an exponential increase was observed reflecting electron tunneling. Below a critical distance both H2Pc and CoPc molecules have a tendency to lift from the surface and jump to contact with the tip. After the jump, the conductance only weakly varies with the distance. On Cu(111) typical conductances of 0.1 G0 were found while on Co/Cu(111) the conductance is higher by a factor of 3. STS measurements in the tunneling regime revealed strong vibrational modes located on the organic side groups of Pc which are most likely responsible for the jump to contact.