Single-molecule 'wires' show highly efficient modes of charge transport
Researchers at the University of Illinois Urbana-Champaign have shown that molecular wires exhibit a highly efficient mode of charge transport across a wide range of different molecular compositions. The work -- published this month in Nano Letters – provides a direct experimental observation of the transition to resonant transport in single-molecule junctions.
Resonant transport will enable efficient, long-range charge transport in single-molecule junctions, which is essential for developing new high-performance molecular electronic devices that have long been of interest to quantum chemists, physicists, materials scientists, electrical engineers and microelectronics researchers.
The paper also describes a method to determine the transition to resonance, as well as a physical model that allows for the prediction of the transition to resonant transport in molecular wires. Above the resonant transition, the resistance of molecular wires significantly decreases and allows current to flow more easily. For these reasons, understanding the transition to resonant transport will aid in the design high-performance molecular devices with switchable properties.
“Our work provides a new fundamental understanding and general design strategy for building molecular wires to achieve efficient resonant transport,” said Charles Schroeder, a James Economy Professor in The Grainger College of Engineering’s Department of Materials Science & Engineering.
To experimentally measure charge transport through the molecule wires, the team used a technique known as the scanning tunneling microscopy-break junction method. In these experiments, a single-molecule junction is formed between two metal electrodes, and the resulting current flowing through the molecule is measured for a given applied bias.
“Interestingly, we also demonstrate transient, time-dependent charge transport measurements for single molecules, where a single-molecule junction is held at a fixed position and the current is measured as a function of time while applying step changes to the bias across the molecule,” said first-author Songsong Li, a recent doctoral alumnus from the Schroeder group. These experiments show that the resonant transition is reversible in single-molecule junctions.
The research was a collaboration between the Schroeder Group and Jeffrey Moore and Martin Burke’s groups in the Department of Chemistry and the Beckman Institute for Advanced Science and Technology at Illinois. The research was supported by the Joint Center for Energy Storage Research (an Energy Innovation Hub funded by the U.S. Department of Energy), the Department of Defense Multi-University Research Initiative and the Defense Advanced Research Projects Agency’s Accelerated Molecular Discovery Program.