"Smart sandwich enables fundamental studies in molecular electronics".

"Smart sandwich enables fundamental studies in molecular electronics".

Research in molecular electronics is working towards the bottom-up fabrication of single-molecule devices. However, the electronic properties of such devices may depend as much on the chemical structure of the molecule as on the electrode-molecule interface. To attain a better understanding of molecular electronics it is necessary to tune both the electrical potential and the geometry of metal-molecule-metal junctions. Researchers in the Netherlands based at Delft University of Technology and Leiden University have now developed a new type of gated mechanical break junction (MCBJ) that enables such studies.

Their devices build on the mechanical break junction principle, in which a flexible substrate is bent to stretch and break a metal wire on its top. As the suspended wire breaks at a prefabricated constriction, two fresh fracture surfaces are formed. If the wire is made of gold – the standard electrode material in molecular electronics – the breaking leads to two atomically sharp tips that are small enough to contact a single molecule. The bending of the substrate can then be used to control the distance between the electrodes with subangstrom precision.

The Dutch team used advanced nanolithography to fabricate such a gold wire directly on top of a gate insulator and a gate electrode. Thanks to this sandwich-type architecture, the devices are exceptionally stable and versatile. The gold electrodes can be broken and tuned independently of the gate, which makes it possible to actively contact single molecules in a three-terminal configuration.

Initial low-temperature measurements on a nanoscale cluster indicate that charge transport can be tuned independently in the new devices, both by bending the substrate and by applying a voltage to the gate electrode. In the future, the gated mechanical break junctions will be used to unravel structure-property relations in large conjugated molecules.

More information:
"Smart sandwich enables fundamental studies in molecular electronics".
Christian A Martin, Jan M van Ruitenbeek and Herre S J van der Zant.
Nanotechnology 21 (2010) 265201 (8pp). doi:10.1088/0957-4484.