Switch developed from a single molecule

An international team of researchers, including those from the University of Tokyo’s Institute for Solid State Physics, has demonstrated a switch, analogous to a transistor, made from a single molecule called fullerene. By using a carefully tuned laser pulse, the researchers used fullerene to switch the patch of an incoming electron in a predictable way. This switching process can be three to six orders of magnitude faster than switches in microchips, depending on the laser pulses used. Fullerene switches in a network can produce a computer beyond what is possible with electronic transistors, and they could also enhance the resolution in microscopic imaging devices.

Over 70 years ago, physicists discovered that molecules emit electrons in the presence of electric fields, and later on, certain wavelengths of light. The electron emissions created patterns that eluded explanation. However, this has changed due to a new theoretical analysis, which could lead to new high-tech applications. Project researcher Hirofumi Yanagisawa and his team theorised how the emission of electrons from excited molecules of fullerene should behave when exposed to specific kinds of laser light and when testing their predictions, found they were correct.

Yanagisawa said that the researchers have managed to control the way a molecule directs the path of an incoming electron using a very short pulse of red laser light. Depending on the pulse of light, the electron can either remain on its default course or be redirected in a predictable way.

“It’s a little like the switching points on a train track, or an electronic transistor, only much faster. We think we can achieve a switching speed 1 million times faster than a classical transistor. And this could translate to real-world performance in computing. But equally important is that if we can tune the laser to coax the fullerene molecule to switch in multiple ways at the same time, 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,” Yanagisawa said.

The fullerene molecule underlying the switch is related to the carbon nanotube, though instead of a tube, fullerene is a sphere of carbon atoms. When placed on a metal point — essentially the end of a pin — the fullerenes orientate a certain way so they will direct electrons predictably. Fast laser pulses on the scale of femtoseconds (quadrillionths of a second) or even attoseconds (quintillionths of a second) are focused on the fullerene molecules to trigger the emission of electrons.

Image caption: Changing tracks. A simple analogy as to how the fullerene switch works like a train track switching point. The light pulse can alter the path taken by the incoming electron, here represented by a train. Image credit: 2023 Yanagisawa et al.

“This technique is similar to the way a photoelectron emission microscope produces images. However, those can achieve resolutions at best around 10 nanometres, or ten-billionths of a metre. Our fullerene switch enhances this and allows for resolutions of around 300 picometres, or three-hundred-trillionths of a metre,” Yanagisawa said.

In principle, as multiple ultrafast electron switches can be combined into a single molecule, it would only take a small network of fullerene switches to perform computational tasks potentially faster than conventional microchips. But there are hurdles to overcome, such as how to miniaturise the laser component, which could be necessary to create this new integrated circuit. So, it could be many years before fullerene switch-based smartphones are developed. The research findings were published in the journal Physical Review Letters.

Top image caption: Fullerene switch. An artist’s rendering of a fullerene switch with incoming electron and incident red laser light pulses. Image credit: 2023 Yanagisawa et al.