Graphene ribbons

WHAT ARE GRAPHENE RIBBONS?

  

Graphene ribbons, are strips of graphene with ultra-thin width. Graphene ribbons were introduced originally as a theoretical model by Mitsutaka Fujita and co-authors to examine the effect of the edge and nanoscale size in graphene.

Production

Large quantities of width controlled graphene ribbons can be produced via graphite nanotomy process, where the application of sharp knife diamond in graphite produces nanobloques of graphite, which are exfoliated to produce graphene ribbons. Also it can be produced by cutting or unzip nanotubes. Another technique by Dai group graphene ribbons were produced by plasma etching of nanotubes partly embedded in a polymer film. More recently, graphene ribbons have been grown onto silicon carbide substrates using ion implantation followed by vacuum or laser annealing. 

Electronic structure

The electronic states of GNRs largely depend on the edge structures. Zigzag edges provide the edge localized state with non-bonding molecular orbitals near the Fermi energy. They are anticipated to have large changes in optical and electronic properties from quantization. Calculations based on tight binding predict that zigzag graphene ribbons are always metallic while armchairs can be either metallic or semiconducting, depending on their width. However, DFT calculations show that armchair ribbons are semiconducting with an energy gap scaling with the inverse of the graphene ribbon width. 

Indeed, experimental results show that the energy gaps do rise with decreasing graphene ribbon width. Graphene ribbons with controlled edge orientation have been fabricated by scanning tunneling microscope lithography. Opening of energy gaps up to 0.5 eV in a 2.5 nm wide armchair ribbon was reported. 

The 2D structure, high electrical and thermal conductivity, and low noise make graphene ribbons a possible substitute to copper for integrated circuit interconnects. Some research is being done to create quantum dots by changing the width of graphene ribbons at select points along the ribbon, creating quantum confinement.

Graphene ribbons possess semiconductive properties and may be a technological alternative to silicon semiconductors.

Polyremic composites

Graphene ribbons and their oxidized counterparts called graphene oxide ribbons have been investigated as nano-fillers to progress the mechanical properties of polymeric composites. Raifee, Koratkar, and Tour et al. report increases in the mechanical properties of epoxy composites on loading of graphene ribbons. 

In a recent study, Lalwani, Sitharaman and co-workers report an increase in the mechanical properties of biodegradable polymeric composites of poly (propylene fumarate) at low weight loading of oxidized graphene ribbons, fabricated for bone tissue engineering applications.

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