"This research highlights the importance of the metal-molecule contact in determining the charge-transport characteristics of a molecular electronic device," Jim Kushmerick of the Center for Bio/Molecular Science and Engineering at the Naval Research Laboratory told nanotechweb.org. "When the molecule is chemically linked at both ends with thiol groups to gold electrodes it acts as a molecular wire, conducting charge equally well for both bias voltage polarities. In contrast diode-like characteristics are measured when the molecule is chemically linked at only one end."
The researchers used a crossed-wire tunnel junction consisting of two 10-µm diameter wires, one modified with a self-assembled monolayer of the OPE molecules under test. Bringing the wires together formed a junction at the contact point. The scientists claim they are the first to measure electron transport across organic monolayers in this way.
The experiment tested two types of OPE molecule, one with thioacetyl functional groups on both ends, and the other with a thioacetyl group on only one end of the molecule. As a result, junctions made with the second type of molecule were inherently asymmetric.
"We are currently exploring other metal-'alligator clip' [the chemical-linkage group that connects a molecule to a metal contact] combinations as well as different molecular cores in order to elucidate the basic physics that control charge transport in molecular electronic devices," added Kushmerick.
The scientists reported their work in Physical Review Letters.