In the presence of electric fields and specific wavelengths of light, molecules emit electrons, creating patterns that arouse curiosity but elude explanation. A new theoretical analysis has changed this: the effects of this could increase our ability to explore the physical world and offer new high-tech applications.

An international team of researchers, including those from the University of Tokyo’s Institute for Solid State Physics, theorized how the emission of electrons from excited fullerene molecules should behave when exposed to specific types of laser light.

Using a single molecule called fullerene, the team has demonstrated a switch analogous to a transistor. With a properly calibrated laser pulse, the researchers can predictably change the route of an incoming electron into fullerene. Depending on the laser pulses used, this switching process can be three to six orders of magnitude faster than switches in microchips.

Networks of fullerene switches could create computers more powerful than those made with electronic transistors and enable microscopic imaging devices to reach previously unheard-of levels of brightness.

Project researcher Hirofumi Yanagisawa said: “What we’ve been able to do here is determine how 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 stay on its standard course or be predictably diverted. So it’s a kind of like the switching points on a train track or an electronic transistor, only much faster. We think we can achieve a switching speed that is 1 million times faster than a conventional transistor.”

“This could translate into real-world computing performance. But equally important, if we can tune the laser to coax the fullerene molecule to switch in multiple ways at once, it could be as if there were multiple microscopic transistors are contained in a single molecule, which could increase the complexity of a system without increasing its physical size.”

The fullerene molecule underlying the switch is similar to the better-known carbon nanotube, but fullerene is a sphere of carbon atoms rather than a tube. The fullerenes align themselves in a specific way so they will predictably route electrons when placed on a metal tip, which is basically the end of a pin.

To cause the emission of electrons from the fullerene molecules, fast laser pulses on the order of femtoseconds, quadrillionths of a second, or even attoseconds, quintillionths of a second, are directed at them. It is the first time that the emission of electrons from a molecule has been controlled in this way using laser light.

Yanagisawa said: “This technique is similar to how a photoelectron emission microscope produces images. However, those can reach resolutions of about 10 nanometers, or ten-billionths of a meter, at best. Our fullerene switch improves on this and enables resolutions of about 300 picometers or three hundred trillionths of a meter.”

Magazine reference:

  1. 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: March 8, 2023, DOI: 10.1103/PhysRevLett. 130.106204