MSC Colloquium Herre van der Zant
|03 March 2005||FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Herre van der Zant|
|Affiliation:||Kavli Institute of Nanoscience, Delft University of Technology|
|Title:||Three-terminal molecular junctions|
|Date:||Thu Mar 3, 2005|
|Start:||16.00 (Doors open and coffee available at 15.30)|
With electrochemical etching nanogaps have been made with a high yield and atomic resolution. Small organic molecules of different lengths (sulphur end functionalized oligo(cyclohexylidenes) which possess sigma-pi-sigma conjugation) have been trapped between the electrode pairs. Transport measurements show that the molecules are strongly coupled to the leads (level broadening of the same order as the charging energy) because of their unconventional gate effect. Surprisingly, we find that at low temperatures smaller molecules are worse conductors than longer ones. Quantum chemistry calculations confirm the experimental findings. The oligocyclohexylidenes link chemistry (orbitals) to quantum transport and derivatives are available to test and refine the models. For example, asymmetric molecular junctions with a strong sulphur-gold bonding only on one side, show current-voltage characteristics with steps.
In the opposite, weak coupling limit current flow is limited by the contacts. The molecular devices can now be viewed as molecular quantum dots. Coulomb-blockade and Kondo physics dominate. We use electromigration of gold wires on top of aluminum gates to measure the properties of the single molecule magnet Mn-12 (S = 10 ground state) and OPV-3. Different samples share common features. Excitations in the Mn-12 system are believed to be due to vibrational modes; others may be related to spin excitations. The OPV-3 molecular junctions show Kondo behavior.
|Last modified:||22 October 2012 2.30 p.m.|