For the First Time, Signal Transfer Between Molecules Has Been Achieved

Molecular computing reaches another milestone

STM image of all the initial β-form molecules in the middle row that changed into the α-form owing to a single manipulation
Image: Nanchang University/Nature Nanotechnology
STM image of all the initial β-form molecules in the middle row that changed into the α-form owing to a single manipulation

The history of molecular computing and electronics has been a long and twisting road—one that was meticulously catalogued on the pages of IEEE Spectrum two years ago. While the future of molecular electronics and computing remains somewhat up in the air, a great deal of research is still being focused on the field.

There have been proof-of-concept molecular switches, molecular data storage bits, and diodes.  However, one fundamental issue that has not been resolved is the transfer and exchange of signals between molecular devices for complex signal processing at room temperature.

Now researchers at Nanchang University in China have described, in the journal Nature Nanotechnology, a device that uses a particular kind of molecule that takes on two specific geometries when in contact with a copper surface. These two geometries can serve as the “0” and “1” of digital logic.

The work is based on a phenomenon known as in-plane molecular orientation, which occurs when an organic molecule lands on a solid surface. This adsorbed molecule might take different adsorption geometries. These adsorption geometries can be classified into several groups.

“In our case, the molecule we used has two distinguished adsorption geometries on a copper surface,” explained Li Wang, professor of physics at Nanchang University, in an e-mail interview with IEEE Spectrum. “One is left-handed, the other is right handed.” For the purposes of data storage or transfer, “We define left-handed geometry as ‘1’ and the right-handed geometry as ‘0’,” added Wang.

Wang and his colleagues discovered that the in-plane orientation of a molecule could be controlled by the in-plane orientations of two neighboring molecules due to their intermolecular interactions. The researchers exploited this intermolecular interaction as a way to build a logic gate in which an output signal is controlled by two input signals.

“For the first time, we have succeeded in realizing signal transfer and operation between molecules,” said Wang. “Our findings prove that a single molecule can present a certain signal and such signal can be utilized as a conventional signal to carry useful information to transfer and take part in complex operation processing.”

From this stepping stone, Wang believes in principle that as long as the molecules are coupled to each other in some way, much more complicated functions can be achieved, such as molecular computing.

The molecular devices that Wang and his colleagues fabricated in the lab were built by manipulating molecules one by one. For this kind of work to go beyond a mere prototype, it will de necessary to assemble the molecules into designed configurations with the expected intermolecular interactions, according to Wang.

In ongoing research, Wang and his colleagues intend to build more molecular devices with which they can exploit the intermolecular interactions in order to carry out different functions. “We will try to connect variable molecular devices into a whole system to achieve computing as common electronic devices can do,” he added.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.