Multilayer graphene has interesting electronic properties

Two articles, one published in the journal “Carbon” and one in the journal “Nano Letters”, describe research on the electronic properties of graphene. Two teams of researchers coordinated by the University of Linköping (LiU), Sweden, focused on the possibilities of multilayer graphene for a range of applications connected to electronics, for the possibility of using it as a superconductor and in the production of sustainable fuels.

Graphene has been indicated for several years as an extraordinary material due to its electrical characteristics. So far the high costs of quality graphene have slowed the development of devices based on it but it’s a matter of time and various production techniques were proposed, including one at an industrial level that’s supposed to be cheap. It’s produced in sheets formed by a single layer of atoms bound together but graphene’s electronic properties are even more interesting when this material is produced in several layers, howhever that adds further complications.

An ideal multilayer graphene sheet has the various layers with the cells formed by their carbon atoms aligned but getting that result is difficult. If the layers are not aligned, their edges end with a sort of microscopic staircase in which the cells form nanosteps and this has consequences on the sheet’s properties. The authors of this new research found a way to eliminate this problem by creating graphene at a carefully controlled temperature. This technique also allows to control the number of graphene layers of the sheet.

The researchers had already developed a technique to produce silicon carbide, also known as carborundum, a material that combines carbon and silicon, and monolayer graphene over this material. In the article published in the journal “Carbon” they describe a progress that allows to produce quality cubic multilayer graphene as well with well-aligned layers on a silicon carbide surface.

The photo (courtesy Thor Balkhed/LiU, all rights reserved) shows Jianwu Sun, one of the researchers who was part of the two teams who conducted these studies, while inspecting the equipment that produces the silicon carbide on which his team subsequently produce monolayer or multilayer graphene.

Among the applications of multilayer graphene there are those connected to electronics but this research is also oriented to the production of renewable fuels. That’s because multilayer graphene could be used in a process of conversion of water and carbon dioxide into compounds such as ethanol and methanol, which can be used as fuels with the advantage of being more sustainable than those produced with other processes precisely because in this case the carbon dioxide introduced into the atmosphere wouldn’t be greater than that absorbed in their production. That’s not an ideal solution but at least in short-term it could be an alternative to fossil fuels.

The article published in the journal “Nano Letters” focuses on the possibilities of activating the superconducting properties of multilayer graphene produced on silicon carbide. In April 2018, a MIT team showed the possibility to obtain that result with a double layer of graphene when the two hexagonal cell nets are twisted against each other by an angle of 1.1°. At the University of Linköping they experimentally proved that a certain positioning of the layers allows to obtain a form of superconductivity in graphene.

This type of result brings together two branches of research that are important for technological advances, since both the common adoption of graphene and the achievement of a superconductivity at room temperature would represent considerable progress in the field of electronics. Another team of researchers also conducted experiments with the superconductivity of double layer graphene, reported in an article published in the journal “Science Advances”.

In recent years there have been a lot of news concerning the development of graphene production techniques but often the problem arrived in the transition from the laboratory to mass production. Unfortunately, the practical problems, with the related costs, must be solved and only then the real potential connected to the revolution promised years ago can be assessed.

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