Writing in the journal Science, Manchester team has revealed more about the electronic properties of its slightly fatter cousin – bilayer graphene.
The researchers, from the universities of Manchester, Lancaster (UK), Nijmegen (the Netherland) and Moscow (Russia), have studied in detail the effect of interactions between electrons on the electronic properties of bilayer graphene.

 

They used extremely high-quality bilayer graphene devices which are prepared by suspending sheets of the material in vacuum. This way most of the unwanted scattering mechanisms for electrons in graphene could be eliminated, thus enhancing the effect of electron-electron interaction.  The latter could be seen as strong changes in the low-energy electronic spectrum – it becomes strogly anysotropic. This is the first effect of its kind where the interactions between electrons in graphene can be clearly seen.

 

The reason for such unique electronic properties is that quasiparticles (electrons and holes, which carry electric current) in this material are very different from those in any other metals. They possess chiral symmetry (a symmetry between electrons and holes) of the sort which exist between particles and antiparticles in high-energy physics. Graphene is a novel two-dimensional material which can be seen as a monolayer of carbon atoms arranged in a hexagonal lattice. When two layers of graphene are bonded in a certain manner, they form bilayer graphene – a very interesting and unusual material in its own right.

Both graphene and bilayer graphene possesses a number of unique properties, such as extremely high electron and thermal conductivities due to very high velocities of electrons and high quality of the crystals, as well as mechanical strength. 

 

Professor Andre Geimhas modified graphene to make fluorographene – a one-molecule-thick material chemically similar to Teflon.

Fluorographene is fully-fluorinated graphene and is basically a two-dimensional version of Teflon, showing similar properties including chemical inertness and thermal stability.

The team hope that fluorographene, which is a flat, crystal version of Teflon and is mechanically as strong as graphene, could be used as a thinner, lighter version of Teflon.
Professor Geim and his team have exploited a new perspective on graphene by considering it as a gigantic molecule that, like any other molecule, can be modified in chemical reactions. Teflon is a fully-fluorinated chain of carbon atoms. These long molecules bound together make the polymer material that is used in a variety of applications including non-sticky cooking pans.

The Manchester team managed to attach fluorine to each carbon atom of graphene. To get fluorographene, the Manchester researchers first obtained graphene as individual crystals and then fluorinated it by using atomic fluorine. To demonstrate that it is possible to obtain fluorographene in industrial quantities, the researchers also fluorinated graphene powder and obtained fluorographene paper.

Fluorographene turned out to be a high-quality insulator which does not react with other chemicals and can sustain high temperatures even in air.

One of the most intense directions in graphene research has been to open a gap in graphene’s electronic spectrum, that is, to make a semiconductor out of metallic graphene. This should allow many applications in electronics. Fluorographene is found to be a wide gap semiconductor and is optically transparent for visible light, unlike graphene that is a semimetal.