Scientists Advance Toward Single-Molecule Electronics
Researchers from Columbia University and Berkeley Lab’s Molecular Foundry have developed a single-molecule diode that outperforms the best of its predecessors by a factor of 50. The scientists describe the development as a major milestone in molecular electronics.
The research is published in Nature Nanotechnology with the title “Single-molecule diodes with high rectification ratios through environmental control.”
Unprecedented Molecular Control of Nanoscale Electronics
Diodes are basic electronic devices that allow electric current to flow in only one direction. Typically, diodes are implemented with junctions between semiconductor crystals with different properties (“p-n junction”). Previous single-molecule diodes, developed through the chemical synthesis of special asymmetric molecules that are analogous to a p-n junction, had low efficiency, but the new device presents a spectacular improvement.
The researchers demonstrated current rectification – unidirectional flow – in symmetric single-molecule junctions using two electrodes of the same metal, but breaking symmetry by exposing considerably different electrode areas to an ionic solution. This allowed the scientists to control the junction’s electrostatic environment in an asymmetric fashion by simply changing the bias polarity.
“Using an ionic solution, two gold electrodes of dramatically different exposed surface areas, and a single symmetric molecule specially designed by the Luis Campos’ group at Columbia, we were able to create a diode that resulted in a rectification ratio, the ratio of forward to reverse current at fixed voltage, in excess of 200, a record for single-molecule devices,” says Latha Venkataraman, Associate Professor of Applied Physics at Columbia University.
In 1974 researchers at IBM and New York University proposed a “unimolecular rectifier“, a single organic molecule that works as a rectifier (one-way conductor) of electric current. The unimolecular rectifier was the first concrete theoretical proposal in the field of molecular electronics. Since then, single-molecule electronics has been pursued by many researchers, because extreme miniaturization permits higher performance electronics.
“With the increasing level of experimental control at the single-molecule level, and improvements in theoretical understanding and computational speed and accuracy, we’re just at the tip of the iceberg with what we can understand and control at these small length scales,” said Molecular Foundry Director Jeff Neaton.
The researchers are persuaded that their new approach to a single-molecule diode provides a general route for tuning nonlinear nanoscale-device phenomena that could be applied to systems beyond single-molecule junctions and two-terminal devices.
“We expect the understanding gained from this work to be applicable to ionic liquid gating in other contexts, and mechanisms to be generalized to devices fabricated from two-dimensional materials,” says lead author Brian Capozzi.
Beyond devices, these tiny molecular circuits are petri dishes for revealing and designing new routes to charge and energy flow at the nanoscale.
Recently, in another important advance that open the way to more and more precise control of molecular electronics, an international team of scientists built a tiny transistor with a single molecule and a small number of atoms.
Images from Columbia University and Brian Capozzi et al./Nature Nanotechnology.