Two experimental approaches for controlling current flowing through metal-molecules-metal junctions

Two exptl. approaches that enable control of current flow through metal-mols.-metal junctions are described. A no. of studies using two-electrode metal-mols.-metal junctions have shown that the current between the electrodes depends on the structures of the incorporated mols. When a tunneling mechanism dominates electron transport through org. mols., the mols. behave similar to resistors with resistivities that can be controlled by changing the structure. Incorporation of mols. with increasing conjugation into Hg-based junctions increases the current flow dramatically. Alternatively, by using four-electrode electrochem. junctions that allow the potential of the electrodes to be controlled with respect to the energy levels of the incorporated mols., it is possible to change the mechanism of electron transfer and produce abrupt increases in the current flow. These signals, analogous to solid-state diodes, are particularly significant for mol. electronics. Electrochem. junctions also permit prediction of the value of the applied potential at which the current will start taking off and to identify the mechanism of charge transport. New and recently published results obtained using junctions based on Hg electrodes in an "electrochem." mode show that two junctions incorporating redox centers by different interactions behave as current switches, with the current flow dominated by different charge-transport mechanisms.