Graphene Nanoribbon

Introduction to Graphene Nanoribbon

Hatef Sadeghi

Graphene, a honeycomb sheet of carbon atoms in benzene ring structure [1-3] is likely to be replace by silicon base devices, not only because silicon based technology approaches its performance limitation in atomic sizes [4] but also because of its interesting and remarkable electronic, optical and thermal properties [5]. From the discovery of monolayer graphene (GNR) in 2004 [6] different aspects of the electronics properties of mono- bi- and tri- layer graphene leads Scientists to future investigations to find out differences between them. Further investigation shows that single atomic layer of carbon (GNR), has linear dispersion as reported in [7, 8]. Conduction and valance band meet each other in k Brillion zone of E-k relation plot in GNRs [9]. So GNRs with zigzag shaped edge are metallic and GNRs with armchair shaped edges depending on their widths can be either metallic or semiconducting [10]. One of the remarkable properties of BGN is the tunable energy band gap along applied perpendicular electric fields [5]. Past studies show that conduction and valance bands in BGNs can be tuned by external electric field. On the other hand, the BGNs could be employed in digital electronics because band can be varied by means of an external perpendicular field and induced significant band gap between the valence and conduction bands from a zero-gap semiconductor to an insulator [5, 11-13]. Different behavior may also be expected for BGNs due to the presence of a gap in the energy spectrum of the latter material [14]. However, high speed moving of charge carriers and losing relatively little energy to scattering, or colliding in graphene should lead to build ultrahigh frequency devices so-called ballistic transistors.

Andre Geim's Graphene introduction and research update lecture

[1]    G. Fiori and G. Iannaccone, "Performance analysis of Graphene Bilayer Transistors through tight-binding simulations," Iwce-13: 2009 13th International Workshop on Computational Electronics, pp. 301-304, 2009.
[2]    M. Zarenia, et al., "Electrostatically Confined Quantum Rings in Bilayer Graphene," Nano Letters, vol. 9, pp. 4088-4092, 2009.
[3]    Y. L. Mao, et al., "First-principles study of the doping effects in bilayer graphene," New Journal of Physics, vol. 12, p. 033046, 2010.
[4]    K. S. Novoselov, et al., "Electric Field Effect in Atomically Thin Carbon Films," Science, vol. 306, p. 666, 2004.
[5]    V. P. Wenjuan Zhu, Marcus Freitag and Phaedon Avouris, "Carrier scattering, mobilities, and electrostatic potential in monolayer, bilayer, and trilayer graphene," Physical Review B, vol. 80, p. 235402, 2009.
[6]    A. K. Geim and K. S. Novoselov, "The rise of graphene," Nature Materials, vol. 6, pp. 183-191, 2007.
[7]    C. Berger, et al., "Electronic confinement and coherence in patterned epitaxial graphene," Science, vol. 312, pp. 1191-1196, 2006.
[8]    T. Seyller, et al., "Epitaxial graphene: a new material," Physica Status Solidi B-Basic Solid State Physics, vol. 245, pp. 1436-1446, 2008.
[9]    J. B. Oostinga, et al., "Gate-induced insulating state in bilayer graphene devices," Nature Materials, vol. 7, pp. 151-157, 2008.
[10]    N. Xu and J. W. Ding, "Conductance growth in metallic bilayer graphene nanoribbons with disorder and contact scattering," Journal of Physics-Condensed Matter, vol. 20, p. 485213, 2008.
[11]    H. Y. Xu, et al., "Edge disorder and localization regimes in bilayer graphene nanoribbons," Physical Review B, vol. 80, p. 045308, 2009.
[12]    G. M. Rutter, et al., "Structural and electronic properties of bilayer epitaxial graphene," Journal of Vacuum Science & Technology A, vol. 26, pp. 938-943, 2008.
[13]    S. Russo, et al., "Double-gated graphene-based devices," New Journal of Physics, vol. 11, p. 095018, 2009.
[14]    Y. Ujiie, et al., "Regular conductance fluctuations indicative of quasi-ballistic transport in bilayer graphene," Journal of Physics-Condensed Matter, vol. 21, p. 382202, 2009.

Groups working on Graphene

General knowledge in Graphene Nanoribbon from Wikipedia

Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer carbon foils in 1962. Graphene is most easily visualized as an atomic-scale chicken wire made of carbon atoms and their bonds. The crystalline or "flake" form of graphite consists of many graphene sheets stacked together.
The carbon-carbon bond length in graphene is about 0.142 nanometers. Graphene sheets stack to form graphite with an interplanar spacing of 0.335 nm,[citation needed] which means that a stack of 3 million sheets would be only one millimeter thick. Graphene is the basic structural element of some carbon allotropes including graphite, charcoal, carbon nanotubes and fullerenes. It can also be considered as an indefinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons. The Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene".
Read more from original website

Recent News in Graphene

  • Charged impurities proven to be the source of low electron mobility in graphene Researchers from Vanderbilt say they now understand for certain why graphene is so sensitive to its electrical environment. Solving this issue will allow to have better electron mobility in graphene at room-temperature, and come close to graphene's theoretical (but not practical) high electron mobility.The problem is charged impurities on the surface of graphene. This was suspected before, but is now confirmed. Now the challenge will be to make graphene without those charged impurities.More info:
    Posted Mar 15, 2012, 6:03 AM by Hatef Sadeghi
  • Graphene membranes sealed everything but water, can be used to distill alcohol A team of researchers led by Professor Sir Andre Geim demonstrated a graphene-Oxide based membrane that is impermeable to all gases and liquids (i.e. it's vacuum-tight) - but water can evaporate though it as if there's no membrane at all.The researchers explain: "Graphene oxide sheets arrange in such a way that between them there is room for exactly one layer of water molecules. They arrange themselves in one molecule thick sheets of ice which slide along the graphene surface with practically no friction. If another atom or molecule tries the same trick, it finds that graphene capillaries either shrink in low humidity or get clogged with water molecules."This membrane can be used to remove ...
    Posted Jan 27, 2012, 5:57 AM by Hatef Sadeghi
  • Researchers discover new graphene nanomaterials With tunable functionality in electronics Researchers from the Rensselaer Polytechnic Institute have discovered new graphene based materials that can be customized to produce specific band gap and magnetic properties (i.e. have tunable functionality in electronics). The materials may be used to enable new nanoelectronics, optics, and spintronics devices.The researchers found out that graphitic nanoribbons can be segmented into several different surface structures called nanowiggles. Each of these structures produces highly different magnetic and conductive properties. This means that you can basically create a new graphene nanostructure that is customized for a specific task or device.More info:
    Posted Jan 8, 2012, 5:10 AM by Hatef Sadeghi
  • Carbon Nanotube-Enabled Flexible Backplanes Promise Smart Device Ubiquity Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a material that uses carbon nanotubes to create a flexible backplane for an artificial electronic skin (e-skin).Curiously the researchers bemoan the general problem that has existed in this are of flexible electronics of not being able to attain a pure single-walled carbon nanotube (SWNT) solution to create your flexible electronic devices. I say curious because Zhenan Bao—the same researcher at Stanford who developed the artificial skin—also developed in cooperation with researchers from the University of California Davis a method by which to come up with the exact mix of SWNTs you want.In the Berkeley Lab press ...
    Posted Dec 20, 2011, 8:26 AM by Hatef Sadeghi
  • IBM produced RF ICs on an 8" graphene wafer IBM has managed to produce RF integrated circuits on an 8" graphene wafer. IBM says that this demonstration is a "major step in transitioning this promising material from a scientific curiosity into a real technology". The graphene was grown on copper foil from high-temperature vapor and later coated with the polymer PMMA.These are RF devices - as it's still difficult to create logic using graphene (it has no natural bandgap), although some researchers are working towards methods to fix this issue.More info:
    Posted Dec 11, 2011, 6:48 PM by Hatef Sadeghi
  • Graphene-based transistor array that can record electrical signals generated by biological cells Researchers from the Juelich Research Center and the Technische Universitaet Muenchen developed a graphene-based transistor array that can record electrical signals generated by biological cells.The team demonstrated an array of 16 graphene solution-gated field-effect transistors (G-SGFETs) - produced over a copper foil using standard photolithographic and etching and chemical vapor deposition processes. A biological cell layer analogous to the heart muscle was deposited directly over this array. The transistor array detected and recorded single cells' action potentials at high resolution.More info:
    Posted Dec 11, 2011, 6:46 PM by Hatef Sadeghi
  • Graphene oxide spun into several meters long fibers Researchers from China's Zhejiang University in Hangzhou demonstrated meter long graphene fibers - made from nano-sized flakes of graphene oxide. These fibers are strong and flexible and can be tied in knots or woven into conductive "mats".The researchers use web spinning to turn a graphene oxide solution into long (tens of meters!) fibers. They then treated those fibers with chemical reduction to turn them back in strings of graphene. The next stage for their research is to improve the fiber's strength - which currently cannot compete with carbon fibers.More info:
    Posted Dec 11, 2011, 6:44 PM by Hatef Sadeghi
  • Graphene used as a transparent conducting layer for UV LEDs Researchers from Korea and the USA developed a Ultraviolet nitride (UV) LED that uses a few layers of graphene as a transparent conducting layer. They say that Graphene may prove better than the currently-used ITO as it performs better in terms of cost, transparency, and, heat and current spreading. Graphene also sports improved transmission in the ultraviolet.Graphene however suffers from reliability and degradation issues that must be further investigated.More info:
    Posted Nov 10, 2011, 8:57 AM by Hatef Sadeghi
  • Dramatic optical limiting effect in graphene demonstrated Researchers from Singapore and the UK demonstrated a dramatic optical limiting effect in graphene using dispersed sub-oxidized graphene. While transparency in graphene is useful, having non-transparent (or light limiting) graphene also has its applications.The optical-limiting effect achieved using suspensions of carbon nanotubes or carbon black occurs through a 'damage' mechanism involving the development of microbubbles or microplasmas at high light fluence, which increases light scattering and breaks the optical transparency.More info:
    Posted Nov 8, 2011, 2:36 AM by Hatef Sadeghi
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