Switch of only one molecule

First test for the smallest electrical switch

Schematic representation of an azobenzene molecule bound to two metallic electrodes (carbon nanotubes) © Franz Stadler / University of Regensburg
Read out

Scientists have now tested the smallest electrical switch in a simulation. As they report in the journal Nature Nanotechnology, they used an isomer, a molecule that can exist in two spatial structures.

"Smaller, ever more efficient" is the motto when it comes to the development of computers and other electronic devices. The components have long been moving in unimaginably small dimensions; For example, a silicon-based transistor today has a side length of 90 nanometers. And the development continues: orders of magnitude of one nanometer - that is a billionth of a millimeter - should have the components of the future. They would be as small as molecules.

But can molecules act as electronic devices? You can, say those scientists who are at the frontier of quantum physics and electronics in the young field of "molecular electronics" leader. Among them, the Regensburg junior research group funded by the Volkswagen Foundation with 960, 000 euros. Gianaurelio Cuniberti and scientists from the University of Madrid: They recently simulated a circuit in which a single organic molecule acted as an electrical switch. The results of the experiments are published in the current March issue of the journal Nature Nanotechnology.

Isomers as switch candidates

Azobenzene is the name given to the molecule used by the researchers to simulate one of the smallest electrical switches so far. Azobenzene belongs to the class of molecules that exist in different spatial structures. Such states of a molecule, also referred to as isomers, can have qualitatively different properties. For example, they react very differently to an electric field. This circumstance is to be exploited in molecular electronics. To investigate the electrical transport properties of the azobenzene molecule and its isomers, physicists in Regensburg chose complex computer simulation techniques.

Molecular structure influences conduction properties

In the model, the molecule was chemically bound to two metallic nanotubes - consisting of carbon atoms - that act as nanoelectrodes. When an electrical voltage was applied, charges could flow through the molecule. The simulation showed that both isomers have completely different electrical conduction properties. A change in the spatial molecular structure - induced, for example, by laser light of different wavelengths - could thus dramatically change the flow of electric current and thus realize a switching function on the molecular scale. display

An important result: Switchability is particularly influenced by the chemical groups that bind the molecule to the electrodes. Cuniberti and his team plan further investigations to test the efficiency and stability of this molecular switch. Their results will provide important information for developing state-of-the-art electronics. With all confidence, the researchers also know: "The molecular computer will have to wait a while yet."

(Volkswagen Foundation, 07.03.2007 - NPO)