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Abstract:
Molecular electronics is a wonderful and exciting concept: imagine the ave-inspiring power of chemical synthesis combined with nanoelectronic circuits, the backbone of the information society!!!! Molecules that switch devices, or even *are* the devices. Unfortunately, molecules are very, very small and difficult (to say the least) to trap and control even with the finest nanolithography in existence. Methods to create molecular electronics exist, but are challenging. The hardest problem is to control how the molecules bind to the electrodes, because in nanotechnology, the details of the contacts have a massive impact on how a device works.

A molecular switch at the edge of graphene

Kgs. Lyngby, Denmark | Posted on July 27th, 2018

A team of italian, spanish and danish researchers have worked out a far simpler way to put molecules to work in electronic switches.

Jose Caridad, assistant professor at DTU Nanotech, recently discovered that edges of graphene - which are just 0.3 nm thick and a thousand times sharper than a razor blade - give water molecules a well-defined place to bind, while somehow allowing them to switch orientation (see illustration below) in response to an electrical field. These relatively few molecules (maybe about 10000) attached along the edge, control the resistance and capacitance of surprisingly large graphene devices (5 x 5 µm device is about 1 billion carbon atoms). The graphene devices were encapsulated - leaving just the edges exposed and accessible to the molecules.

The water molecules at the edge can be switched "up" or "down" with a gate electrode, similar to those used for MOSFETs in computer chips.
The molecules respond collectively to the external electric field. Not only that, they keep their alignment after the field has been removed, just like a toggle switch stay in position after flipped it. Not only that (!), they communicate with the charge carriers in the graphene, which the researchers saw as a persistent shift in the conductance and capacitance. The switching strength depend on how polar the molecules are, making water the best he tried so far.

José Caridad now wants to use this for sensors and memory devices, which are important for future internet of things and neuromorphic computing.

Peter Bøggild, Prof. at DTU Nanotech, is excited: "The key thing is to control which atoms terminate the graphene edge, even before the water molecules arrive. If they are fluorine, nothing happens. If we replace them with oxygen, it comes to live. We can basically dial in a wide range of responses depending on which atom we put on the carbon atoms."

The experiments were backed up by theoretical calculations led by my colleague Prof. Mads Brandbyge, who worked with molecular electronics for many years: "We tried with polar molecules, and immediately we have a memory device. What about larger molecules, with special electronic properties? Can they switch orientation as well? The graphene edge is a perfect molecule trap, and there are so many interesting possibilities."

The work was done in collaboration with our great colleagues from Politecnico Milano, Universidade Do Minho and Università di Catania, and you can read more here: "A Graphene-Edge Ferroelectric Molecular Switch" in Nano Letters.

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Contacts:
Peter Bøggild
Address: DTU Nanotech, Technical University of Denmark, Building 345C
City: Kgs. Lyngby
State:
Zip: 2800
Country: Denmark
Phone: 21362798

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