Fullerene as an ultrafast electron switch

Fast sphere: Fullerenes can be converted into electronic switches that are up to a million times faster than the transistors in conventional microchips, as an experiment with the hollow spheres made of carbon atoms has now demonstrated. Targeted laser pulses change the electrochemical state of the fullerene, causing the electrons to either be deflected or fly on. Theoretically, the “buckyballs” could enable faster and more powerful microelectronics in the future.

Carbon is one of the most versatile elements in the periodic table, it can form countless structural variants – from diamond to graphite to single-layer graphene , the versatile carbon nanotubes or the spherical Buckminster fullerenes. These hollow spheres consist of 60 carbon atoms arranged in a lattice of pentagons and hexagons. They are regarded as promising catalysts and semiconductors in organic solar cells, but also as transport molecules and radical scavengers in medicine.

Fullerene deflects electrons in a controlled manner

Physicists working with Hirofumi Yanagisawa from the University of Tokyo have now discovered another promising application. In preliminary tests, they had already established that fullerenes emit electrons in specific patterns when they are applied to a thin metal tip and exposed to an electric field. In their current experiment, the physicists used ultra-short laser pulses to specifically influence the state of excitation and the orientation of the hollow carbon spheres.

It turned out that the fullerene excited by the laser acts like a switch. Depending on the light pulse, it either deflects incoming electrons in a controllable manner or lets them pass undeflected – similar to a switch on a railway track. “This allows us to control how the molecule directs incoming electrons,” explains Yanagisawa. In principle, the fullerene works in a similar way to a transistor used as a switch – but is much smaller.

Up to a million times faster than a common transistor

The decisive factor, however, is that this switching process takes place at enormous speed. In the experiment, the fullerene switched the electrons several orders of magnitude faster than circuits in conventional microchips. “We could achieve a switching speed with the fullerene that is a million times faster than with a classic transistor,” says Yanagisawa. This could make electronic circuits faster and smaller in the future.

“However, it is just as important that we could use targeted laser pulses to get the fullerene to carry out several switching operations at the same time,” explains the physicist. “It’s like having several microscopic transistors combined in a single molecule.” Such a molecular multi-switch could increase the complexity of a circuit without having to make it physically larger.

According to the researchers, fullerene switches open up new possibilities for making computers and other electronics faster and smaller. Theoretically, only a small network of fullerene switches would then be needed to complete arithmetic tasks faster than conventional microchips. However, it will probably be a long time before there are actually fullerene-based transistors and circuits. This is because the lasers required for switching must first be miniaturized and integrated into chips. (Physical Review Letters, accepted )