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Single-molecule diode outperforms predecessors by a factor of 50

30 July 2015

A team of researchers has passed a major milestone in molecular electronics with the creation of the world's highest-performance single-molecule diode.

Schematic of the molecular junction created using asymmetric area electrodes, which functions as a diode (image: Berkeley Lab and Columbia University)

Working at Berkeley Lab's Molecular Foundry, the team (from Berkeley Lab and Columbia University) used a combination of gold electrodes and an ionic solution to create a single-molecule diode that outperforms the best of its predecessors by a factor of 50.

"Using a single symmetric molecule, an ionic solution and two gold electrodes of dramatically different exposed surface areas, 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, which is a record for single-molecule devices," says Jeff Neaton, Director of the Molecular Foundry and a senior faculty scientist with Berkeley Lab's Materials Sciences Division.

"The asymmetry necessary for diode behaviour originates with the different exposed electrode areas and the ionic solution," he says. "This leads to different electrostatic environments surrounding the two electrodes and superlative single-molecule device behaviour."

Single-molecule devices represent the ultimate limit in electronic miniaturisation. In 1974, molecular electronics pioneers Mark Ratner and Arieh Aviram theorised that an asymmetric molecule could act as a rectifier. Since then, development of functional single-molecule electronic devices has been a major pursuit with diodes being at the top of the list.

Scientists have previously fashioned single-molecule diodes either through the chemical synthesis of special asymmetric molecules that are analogous to a p-n junction; or through the use of symmetric molecules with different metals as the two electrodes. However, the resulting asymmetric junctions yielded low rectification ratios, and low forward current. Neaton and his colleagues at Columbia University have discovered a way to address both deficiencies.

The Berkeley Lab-Columbia University team believes 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.

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