Graphene nanoribbons (also called nano-graphene ribbons), often abbreviated GNRs, are thin strips of graphene or unrolled single-walled carbon nanotubes. The graphene ribbons were originally introduced as a theoretical model by Mitsutaka Fujita et.al. to examine the edge and nanoscale size effect in graphene.
Their electronic states largely depend on the edge structures (armchair or zigzag). Zigzag edges provide the edge localized state with non-bonding molecular orbitals near the Fermi energy. They are expected to have large changes in optical and electronic properties from quantization. Calculations based on tight binding predict that zigzag GNRs are always metallic while armchairs can be either metallic or semiconducting, depending on their width. However, recent DFT calculations show that armchair nanoribbons are semiconducting with an energy gap scaling with the inverse of the GNR width. Indeed, experimental results show that the energy gaps do increase with decreasing GNR width. However, to date no experimental results have measured the energy gap of a GNR and identified the exact edge structure. Zigzag nanoribbons are also semiconducting and present spin polarized edges. Their 2D structure, high electrical and thermal conductivity, and low noise also make GNRs a possible alternative to copper for integrated circuit interconnects. Some research is also being done to create quantum dots by changing the width of GNRs at select points along the ribbon, creating quantum confinement.
The first measurements of their bandgaps were made by the groups of Phillip Kim and Phaedon Avouris.
Graphene nanoribbons possess semiconductive properties and may be a technological alternative to silicon semiconductors and may be capable of sustaining microprocessor clock speeds in the vicinity of 1 THz.