In Nature July 22, 2010, scientists from Empa and the Max Planck Institute for Polymer Research report how they have managed for the first time to grow graphene ribbons that are just a few nanometres wide, using a simple surface-based chemical method.

Graphene ribbons are considered to be hot candidates for future electronics applications because their properties can be modified by adjusting width and edge shape. Scientists from Empa, the Max Planck Institute for Polymer Research in Mainz (Germany), ETH Zürich and the Universities of Zürich und Bern have now developed a new method for creating graphene ribbons with band gaps.

To date, graphene ribbons have been cut from larger graphene sheets. Or carbon nanotubes were slit open lengthwise and unfurled. This gives rise to a band gap  – an energy range that cannot be occupied by electrons and that determines the physical properties, such as the switching capability. The width (and edge shape) of the graphene ribbon determines the size of the band gap and thereby influences the properties of components constructed from the ribbon.

If extremely narrow graphene ribbons (under 10 nanometers wide) that also have well-defined edges could be manufactured, they might allow for components exhibiting specific optical and electronic properties: depending on requirements, adjustment of the band gap could be used to fine-tune the switching characteristics of a transistor.

Growing graphene ribbons

In the Nature article, the scientists describe a simple surface-based chemical method for creating such narrow ribbons without the need for cutting, using a bottom-up approach. To achieve this, they spread specifically designed halogen-substituted monomers on gold and silver surfaces under ultrahigh vacuum conditions. These are linked to form polyphenylene chains in a first reaction step.

In a second reaction step, initiated by slightly higher heating, hydrogen atoms are removed and the chains interconnected to form a planar, aromatic graphene system. This results in graphene ribbons of the thickness of a single atom that are one nanometer wide and up to 50 nm in length, exhibiting an electronic band gap, so they possess switching properties – a first and important step for the shift from silicon microelectronics to graphene nanoelectronics.

Citation: Atomically precise bottom-up fabrication of graphene nanoribbons», J. Cai, P. Ruffieux, R. Jaafar, M. Bieri, T. Braun, S. Blankenburg, M. Muoth, A.P. Seitsonen, M. Saleh, X. Feng, K. Müllen, R. Fasel, Nature, 22 July 2010, Vol. 466, No. 7305, pp 470-473, doi:10.1038/nature09211

More info: Swiss Federal Laboratories for Materials Testing and Research news