Graphene nanoribbons

Graphene nanoribbons (also called nano-graphene ribbons), often abbreviated GNRs, are thin strips of graphene or unrolled single-walled carbon nanotubes. Graphene ribbons were originally introduced as a theoretical model by Mitsutaka Fujita and co-authors to examine the edge and nanoscale size effect in graphene.^[1][2][3]

Their electronic states largely depend on the edge structures (armchair or zigzag, the first being the upper side of the picture on the left, and the later being the right side). 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. ^[4] Indeed, experimental results show that the energy gaps do increase with decreasing GNR width. ^[5] Graphene nanoribbons with controlled edge orientation have been fabricated by Scanning Tunneling Microscope (STM) lithography. ^[6] Opening of energy gaps up to 0.5 eV in a 2.5 nm wide armchair ribbon was reported. Zigzag nanoribbons are also semiconducting and present spin polarized edges. Their gap opens thanks to an unusual antiferromagnetic coupling between the magnetic moments at opposite edge carbon atoms. This gap size is inversely proportional to the ribbon width^[7][8] and its behavior can be traced back to the spatial distribution properties of edge-state wave functions, and the mostly local character of the exchange interaction that originates the spin polarization.

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.^[9]

The first measurements of their bandgaps were made by the groups of Philip Kim and Phaedon Avouris.

Graphene nanoribbons possess semiconductive properties and may be a technological alternative to silicon semiconductors.^[10] and may be capable of sustaining microprocessor clock speeds in the vicinity of 1 THz^[11] Field-effect transistors less than 10nm wide have been created with GNR - "GNRFETs" - with an I_on / I_off ratio > 10⁶ at room temperature. ^[12][13]

• 

  GNR band structure for arm-chair type. Tight binding calculations show that armchair type can be semiconducting or metallic depending on width (chirality).

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  GNR band structure for zig-zag type. Tight binding calculations show that zigzag type is always metallic.

See also

• Graphene
• Graphite
• Graphene oxide paper
• Carbon nanotube
• Mitsutaka Fujita
• Katsunori Wakabayashi

References

1. ^ Fujita M., Wakabayashi K., Nakada K. and Kusakabe K. "Peculiar Localized State at Zigzag Graphite Edge" J. Phys. Soc. Jpn. 65, 1920 (1996)
2. ^ Nakada K., Fujita M., Dresselhaus G. and Dresselhaus M.S. "Edge state in graphene ribbons: Nanometer size effect and edge shape dependence" Phys. Rev. B 54, 17954 (1996)
3. ^ Wakabayashi K., Fujita M., Ajiki H. and Sigrist M. "Electronic and magnetic properties of nanographite ribbons" Phys. Rev. B 59, 8271 (1999)
4. ^ Barone, V., Hod, O., and Scuseria, G. E. "Electronic Structure and Stability of Semiconducting Graphene Nanoribbons" Nano Lett. 6, 2748 (2006)
5. ^ Han., M.Y., Özyilmaz, B., Zhang, Y., and Kim, P. "Energy Band-Gap Engineering of Graphene Nanoribbons" Phys. Rev. Lett. 98, 206805 (2007)
6. ^ L. Tapaszto, G. Dobrik, P. Lambin, L.P. Biro "Tailoring the atomic structure of graphene nanoribbons by scanning tunneling microscope lithography" Nature Nanotechnology 3 , 397 (2008)
7. ^ Son Y.-W., Cohen M. L., and Louie S. G., "Energy Gaps in Graphene Nanoribbons" Phys. Rev. Lett. 97, 216803 (2006)
8. ^ Jung. J., Pereg-Barnea T., MacDonald A. H. "Theory of Interedge Superexchange in Zigzag Edge Magnetism" Phys. Rev. Lett. 102, 227205 (2009)
9. ^ Wang, Z. F., Shi, Q. W., Li, Q., Wang, X., Hou, J. G., Zheng, H., et al. "Z-shaped graphene nanoribbon quantum dot device" Applied Physics Letters, 91(5), 053109 (2007)
10. ^ Bullis, Kevin (2008-01-28). "Graphene Transistors". Technology Review (Cambridge: MIT Technology Review, Inc). http://www.technologyreview.com/Nanotech/20119/. Retrieved 2008-02-18. 
11. ^ Bullis, Kevin (2008-02-25). "TR10: Graphene Transistors". Technology Review (Cambridge: MIT Technology Review, Inc). http://www.technologyreview.com/read_article.aspx?id=20242. Retrieved 2008-02-27. 
12. ^ Wang, X.; Ouyang, Y.; Li, X.; Wang, H.; Guo, J.; Dai, H. (2008). "Room-Temperature All-Semiconducting Sub-10-nm Graphene Nanoribbon Field-Effect Transistors". Physical Review Letters 100 (20). doi:10.1103/PhysRevLett.100.206803.  edit
13. ^ http://news.stanford.edu/news/2008/may28/ribbon-052808.html

External links

• Graphene nanoribbons on arxiv.org