Researchers have now found a way to manufacture single-molecule diodes that can perform 50 times better than previous diode designs.

In a study published in the journal Nature Nanotechnology, researchers led by Latha Venkataraman from Columbia Engineering came up with a new technique that results in a single-molecule diode with a high "on" current and level of rectification. Producing a single-molecule device has long been a dream in nanoscience since the idea was introduced in 1974 by Arieh Aviram and Mark Ratner.

According to Aviram and Ratner, it's possible for a molecule to act as a one-way conductor for electric current. Following this theory, researchers have been exploring molecular charge-transport properties and have shown that single molecules connected metal electrodes can be manipulated to mimic a number of circuit elements. As a diode functions like an electricity valve, it has to be made asymmetrically, allowing electricity flowing in a direction to experience a different environment compared to what electricity flowing in the other direction is experiencing.

The problem with an asymmetric diode is that it produces low current flows in both directions. A proper diode is one that allows current to flow not only in just one direction but lets a lot of current flow in that one direction. To address this concern, researchers surrounded an active molecule with an ionic solution before using electrodes made of gold metal to touch the molecule. This resulted in high rectification and high current flows in the "on" direction.

Aside from addressing the issue with asymmetric diodes, this solution is also easy to implement, making it possible to apply it to various types of nanoscale devices, including those produced with graphene electrodes.

"It's amazing to be able to design a molecular circuit, using concepts from chemistry and physics, and have it do something functional," said Venkataraman.

She explained that such a length scale so small translates to quantum mechanical effects that are integral to the device, believing that it was a big feat to produce something that will never be physically seen and yet behaves the way it is intended.

Venkataraman and her colleagues are now doing further research to gain a better understanding of the physics behind single-molecule diodes and are trying to boost rectification ratios even more with the help of new molecular systems.

The study received funding support from the Packard Foundation, the Department of Energy and the National Science Foundation. Brian Capozzi, Luis Campos, Jianlong Xia, Jeffrey Neaton, Olgun Adak, Jeffrey Taylor, Emma Dell and Zhen-Fei Liu also contributed.

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