Given the edge

Researchers at the University of Illinois at Urbana-Champaign have shown in experiments that the molecular structure of graphene’s edges significantly influences the material’s electronic properties.

Graphene, which was first isolated and studied in Europe, is a single-atom-thick sheet of carbon that is said to have a great deal of potential in future nanoelectronics applications.

Graphene consists of a hexagonal lattice of carbon atoms. While scientists have predicted that the orientation of atoms along the edges of the lattice would affect the material’s electronic properties, the prediction had not been proven experimentally.

‘Our experimental results show, without a doubt, that the crystallographic orientation of the graphene edges significantly influences the electronic properties,’ said Joseph Lyding, a professor of electrical and computer engineering. ‘To utilise nanometre-size pieces of graphene in future nanoelectronics, atomically precise control of the geometry of these structures will be required.’

To carry out their work, the researchers developed a method for cutting and depositing nanometre-size pieces of graphene on atomically clean semiconductor surfaces such as silicon. Then they used a scanning tunnelling microscope to probe the electronic structure of the graphene.

‘From this emerged a clear picture that edges with so-called zigzag orientation exhibited a strong edge state, whereas edges with armchair orientation did not,’ added Lyding.

‘We found that pieces of graphene smaller than about 10 nanometres with predominately zigzag edges exhibited metallic behaviour rather than the semiconducting behaviour expected from size alone,’ Lyding said. ‘This has major implications in that semiconducting behaviour is mandatory for transistor fabrication.’

Unlike carbon nanotubes, graphene is a flat sheet, and therefore compatible with conventional fabrication processes used by today’s chipmakers. Based on the researchers’ experimental results, controlled engineering of the graphene edge structure will be required for obtaining uniform performance among graphene-based nanoelectronic devices.