Graphene is a single, flat sheet of carbon arranged in a honeycombed lattice. Since the material was first created in 2004, its unique electronic and mechanical properties have amazed researchers, who say that it could even replace silicon as the future material of choice in applications like ultrafast transistors. This is because the free electrons in graphene behave like relativistic particles with no rest mass, which means that they whiz through the material at extremely high speeds. Indeed, graphene has intrinsic carrier mobilities as high as between 3000 and 200000 cm2V–1s–1.

Making real-world devices from graphene depends on controlling how “edges” are formed in graphene sheets. The shape of these edges (smooth or rough) is responsible for the material's electronic properties. Adding oxygen to graphene in any chemical form at the edges, to produce graphene oxide, removes electronic states at the Fermi level, and thus turns graphene into an insulator. This normally means that there are no free electrons available in graphene oxide.

Yves Chabal's team at the University of Texas at Dallas with colleagues at Rutgers University in New Jersey have observed a surprisingly strong infrared absorption band at 800 cm-1 when graphene oxide is reduced. According to the team, such absorption is only possible when all oxygen-containing chemical species are removed from regions adjacent to the edges of defective areas in graphene oxide, that is, from clean graphene patches.

This giant absorption is a new phenomenon, unique to graphene, said Chabal, and the applications that derive from this are very exciting, he told The effect cannot be explained by simple infrared absorption mechanisms and can only happen if free, mobile electrons are induced in reduced graphene oxide – something that has never been observed before.

The researchers say that the effect may also occur in other systems like unzipped carbon nanotubes.

The work was reported in Nature Materials.