molecular switch 18.03.2023

An international team of researchers, including those from the Institute of Solid State Physics at the University of Tokyo, has made a groundbreaking discovery. They successfully demonstrated the use of a single molecule called a fullerene as a transistor-like switch. The team achieved this by applying a finely calibrated laser pulse that allowed them to predictably control the path of the input electron.

The switching process provided by fullerene molecules can be significantly faster than switches used in microchips, with speed increases of three to six orders of magnitude depending on the laser pulses used. The use of fullerene switches on a network could result in a computer with capabilities beyond what is available with electronic transistors. In addition, they have the potential to revolutionize microscopic imaging devices, delivering unprecedented levels of resolution.

More than 70 years ago, physicists discovered that molecules emit electrons in the presence of electric fields and then certain wavelengths of light. The emission of electrons produced patterns that aroused curiosity but eluded explanation. But that has changed thanks to 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.

A simple analogy of how a fullerene switch works like a train switch. A light pulse can change the path taken by an input electron, represented here by a circuit.

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 after testing their predictions, they found that they were correct.

Depending on the momentum of the light, the electron can either stay on its default course or be redirected in a predictable way. So, it's a bit like switching points on a railroad track or an electronic transistor, only much faster. Scientists believe that we can achieve switching speeds 1 million times faster than a classic transistor. And this can lead to real performance in computing. But just as important, if we can tune the laser to make the fullerene molecule switch in multiple ways at the same time, it could be like having multiple microscopic transistors in a single molecule.

The fullerene molecule at the heart of the switch is related to the perhaps slightly better known carbon nanotube, although instead of a tube, the fullerene is a sphere of carbon atoms. When placed on a metal dot—essentially the end of a hairpin—the fullerenes orient themselves in a certain way to guide the electrons in a predictable way. Fast laser pulses on the scale of femtoseconds, quadrillionths of a second, or even attoseconds, quintillionths of a second, are focused on fullerene molecules to cause electrons to be emitted. This is the first time laser light has been used to control the emission of electrons from a molecule in this way.

In principle, since several ultra-fast electronic switches can be combined into a single molecule, only a small network of fullerene switches would be needed to perform computational tasks much faster than conventional chips. But there are a few hurdles to overcome, such as how to miniaturize the laser component that will be needed to create this new kind of integrated circuit. So, it could be many years before we see a smartphone based on a fullerene switch.