A single molecule switch

fullerene switch

Artist’s rendering of a fullerene switch with incident electrons and incident red laser light pulses. Credit: 2023 Yanagisawa et al.

A unique carbon molecule was found to have the ability to operate as multiple high-speed switches simultaneously.

An international team of researchers, including the Institute for Solid State Physics at the University of Tokyo, has made a groundbreaking discovery. They have successfully demonstrated the use of a single molecule called fullerene as a switch, similar to a transistor. The team achieved this by using a precisely calibrated laser pulse, which allowed them to steer the path of an incoming electron in a predictable manner.

The switching process enabled by fullerene molecules can be significantly faster than the switches used in microchips, with a speed increase of three to six orders of magnitude, depending on the laser pulses used. Using fullerene switches in a network could lead to the creation of a computer with capabilities beyond what is currently achievable with electronic transistors. In addition, they have the potential to revolutionize microscopic imaging devices by offering unprecedented levels of resolution.

More than 70 years ago, physicists discovered that molecules in the presence of electric fields emit electrons and later specific wavelengths of light. The electron emissions produced patterns that aroused curiosity but defied explanation. However, that has changed thanks to a new theoretical analysis whose ramifications could not only lead to new high-tech applications but also improve our ability to study the physical world itself.

How the fullerene switch works like a railroad track

A simple analogy of how the fullerene switch works like a track switch. The light pulse can change the path of the incoming electron, represented here by a train. Credit: 2023 Yanagisawa et al.

Project researcher Hirofumi Yanagisawa and his team theorized how the emission of electrons from excited fullerene molecules should behave when exposed to certain types of laser light, and testing their predictions found them correct.

“What we’ve succeeded in doing here is controlling the way a molecule steers the path of an incoming electron with a very short pulse of red laser light,” Yanagisawa said. “Depending on the light pulse, the electron can either stay on its given course or be deflected in a predictable way. So a bit like the points on a track or an electronic transistor, only much faster. We believe we can achieve a switching speed 1 million times faster than a classic transistor. And this could translate into real computing power. But just as importantly, if we can tune the laser to cause the fullerene molecule to switch in multiple ways at once, it could be like having multiple microscopic transistors in a single molecule. That could increase the complexity of a system without increasing its physical size.”

The fullerene molecule on which the switch is based is related to the perhaps more familiar carbon nanotube, although fullerene is not a tube but a sphere of carbon atoms. When placed on a point of metal—essentially the end of a needle—the fullerenes orient themselves in a specific way, allowing them to predictably steer electrons. Fast laser pulses in the range of femtoseconds, billionths of a second or even attoseconds, quintillionths of a second, are focused on the fullerene molecules to trigger the emission of electrons. This is the first time laser light has been used to control the emission of electrons from a molecule in this way.

“This technique is similar to the way a photoelectron emission microscope produces images,” Yanagisawa said. “However, these at best achieve resolutions of around 10 nanometers, i.e. ten billionths of a meter. Our fullerene switch amplifies this, enabling resolutions of around 300 picometers, or three hundred trillionths of a meter.”

In principle, since multiple ultrafast electronic switches can be combined into a single molecule, only a small network of fullerene switches would be required to perform computational tasks potentially much faster than traditional microchips. But there are still some hurdles to overcome, such as the miniaturization of the laser component, which would be essential for the development of this new type of integrated circuit. So it may be many years before we see a fullerene switch-based smartphone.

Reference: “Light-Induced Subnanometric Modulation of a Single-Molecule Electron Source” by Hirofumi Yanagisawa, Markus Bohn, Hirotaka Kitoh-Nishioka, Florian Goschin and Matthias F. Kling, March 8, 2023, Physical Verification Letters.
DOI: 10.1103/PhysRevLett.130.106204

The study was funded by PRESTO and the German Research Foundation.

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