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World’s smallest diode consists of a single molecule

For decades scientists have looked for ways to fulfill the vision of Arieh Aviram and Mark Ratner, who back in 1974 came up with the theory of getting a molecule to function as a one-way conductor of electric current, also known as a rectifier.

Now, the Indian-American scientist Latha Venkataraman, Associate Professor of Applied Physics at Columbia Engineering, has succeeded in creating a nanoscaled device just like that.

Over 50 different designs so far, all preceding this one, have failed to be useful for real world applications. Even if they did function with a low efficiency grade, they didn’t allow enough current to pass through the different molecule-sized experiments.

As explained by Brian Capozzi, a PhD student who also worked with Venkataraman on the project: “A well-designed diode should only allow current to flow in one direction – the ‘on’ direction – and it should allow a lot of current to flow in that direction.”

The solution used was a direct response to the difficulties of getting asymmetric molecules to perform in a predictable and useful manner. Together with her colleagues, Jeffrey Neaton’s group at the Molecular Foundry at UC Berkeley and Chemistry Assistant Professor Luis Campo’s group at Columbia, Professor Latha Venkataraman decided to create an asymmetric environment for the molecule. By surrounding the active molecule with an ionic solution as well as contacting the molecule with gold metal electrodes of varying sizes, they achieved rectification ratios at a level of 250.

This solution allows for more than 0.1 microamps to flow through the single molecule diode, which makes it applicable to any kind of nanoscaled devices – even graphene electrode ones.

Previous experiences in the research of using single-molecules have shown that when attaching the molecules to metal electrodes, they can be used as different types of circuit elements, like transistors, resistors, switches and diodes.

Professor Venkataraman talks about the discovery that has beaten a lot of other enthusiastic researchers to the finish line: “It’s amazing to be able to design a molecular circuit, using concepts from chemistry and physics, and have it do something functional… This goal… represents the ultimate in functional miniaturization that can be achieved for an electronic device.”

The results are published in Nature Nanotechnology, May 25, under the title “Single-Molecule Diodes with High On-Off Ratios through Environmental Control”.

Image: Geoffrey Fairchild