The switch made from a single molecule

A special carbon molecule can function as multiple high-speed switches at once.

For the first time, 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 are able to use fullerene to switch the path 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 could produce a computer beyond what is possible with electronic transistors, and they could also lead to unprecedented levels of 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 enticed curiosity but eluded explanation. But this has changed thanks to a new theoretical analysis, the ramification of which could not only lead to new high-tech applications, but also improve our ability to scrutinize the physical world itself. Project Researcher Hirofumi Yanagisawa and his team theorized 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.

“What we’ve managed to do here is control the way a molecule directs the path of an incoming electron using a very short pulse of red laser light,” said Yanagisawa. “Depending on the pulse of light, the electron can either remain on its default course or be redirected in a predictable way. So, 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.”

The fullerene molecule underlying the switch is related to the perhaps slightly more famous 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. 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,” said Yanagisawa. “However, those can achieve resolutions at best around 10 nanometers, or ten-billionths of a meter. Our fullerene switch enhances this and allows for resolutions of around 300 picometers, or three-hundred-trillionths of a meter.”

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 much faster than conventional microchips. But there are several hurdles to overcome, such as how to miniaturize the laser component, which would be essential to create this new kind of integrated circuit. So, it may still be many years before we see a fullerene switch-based smartphone.

Journal article: Hirofumi Yanagisawa, Markus Bohn, Hirotaka Kitoh-Nishioka, Florian Goschin, and Matthias F. Kling. “Light-induced subnanometric modulation of a single-molecule electron source”, Physical Review Letters.

Funding:
This work was supported by the Murata Science Foundation, the Sumitomo Foundation, Research Foundation for Opto-Science and Technology, the Precise Measurement Technology Promotion Foundation (PMTP-F), the Research Center for Biomedical Engineering, Japan Science and Technology Agency via PRESTO project (Grant No. 1082208), the PETACom project financed by the European Research Council via the FET Open H2020 program, the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via DFG project funding (Project No. 389759512).

Useful links:
The Institute for Solid State Physics – https://www.issp.u-tokyo.ac.jp/index_en.html

Research contact:
Hirofumi Yanagisawa
The Institute for Solid State Physics, The University of Tokyo,
Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8581, Japan
hirofumi.yanagisawa@issp.u-tokyo.ac.jp

Press contact:
Mr Rohan Mehra
Public Relations Group, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
press-releases.adm@gs.mail.u-tokyo.ac.jp

About The University of Tokyo
The University of Tokyo is Japan’s leading university and one of the world’s top research universities. The vast research output of some 6,000 researchers is published in the world’s top journals across the arts and sciences. Our vibrant student body of around 15,000 undergraduate and 15,000 graduate students includes over 4,000 international students. Find out more at www.u-tokyo.ac.jp/en/ or follow us on Twitter at @UTokyo_News_en.

Journal: Physical Review Letters
Method of Research: Experimental study
Subject of Research: Not applicable
Article Title: Light-induced subnanometric modulation of a single-molecule electron source