A team of researchers from Denmark, Italy and Portugal recently discovered a new mechanism that allows graphene to be used to control electronic devices using molecules.
The researchers have shown that the ferroelectric ordering of polar molecules attached to the edge of graphene can be ‘toggle-switched’ by an electrostatic gate and can be used for memory devices and sensors. This research shows that it is possible to use graphene to control electronic devices using molecules.
Molecular electronics aims to use individual molecules to control electronics. The vast amount of molecules and techniques to modify them can create sophisticated. The normal hindrance is the small size of the molecules.
As reported by Graphene-info, it is possible to create molecules, but they are incredibly difficult to handle. It is almost impossible to manipulate small enough features in ordinary materials to electrically connect with individual molecules.
Jose Caridad from Technical University of Denmark came up with very a different approach to the usual and most common approach – the so-called mechanical break junction, which relies on creating ‘cracks’ in wires small enough to bridge individual molecules. The new approach involves using something that is already atomically small to trap the molecules: the 0.3 nm wide edge of graphene.
Graphene to control electronic devices using molecules
The researchers inserted graphene layers in hexagonal boron nitride (hBN) crystals. They then carved square shaped devices using common etching processes that cuts through the hBN-graphene-hBN sandwich and leaves the 1 atom thin graphene edge exposed.
While these devices are not sensitive to the environment, the researchers found a way to make the graphene device react to water molecules. The researchers attached different atoms to the graphene edges and then exposing them water vapor and other polar molecules.
A series of experiments showed that polar molecules can be aligned by a user-controlled electrical field in two positions (just like a toggle switch). This changes the electron distribution in the graphene layer, and thereby the resistance and capacitance of the device.
The aligned water molecules kept their orientation even when removing the field, creating exactly the type of hysteresis needed for new memory devices.
As reported by nanowerk, Peter Bøggild, Professor at DTU Nanotech said: “There are two important things we have learned. First: even for quite large devices – 5 µm in size – the behaviour is completely controlled by a few molecules sitting along the edge. Using graphene edges to manipulate molecules is a fantastic way to trap molecules and explore new device functionalities. It also tells us that we have to [be] careful; we are not always interested in devices changing their behaviour in this way. We may think that we have protected the graphene, but if the edges are still exposed, all bets are off. Graphene is a nanomaterial where every atom counts – and the treatment of those delicate edges is absolutely crucial for any future electronics based on graphene”.
The research was funded by the Danish National Research Foundation and the Horizon 2020 Graphene Flagship and has been published in the journal Nano Letters.