Graphene nanoribbons
Encyclopedia
Graphene nanoribbons 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.
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. Indeed, experimental results show that the energy gaps do increase with decreasing GNR width. Graphene nanoribbons with controlled edge orientation have been fabricated by Scanning Tunneling Microscope (STM) lithography. 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
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.
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. and may be capable of sustaining microprocessor
clock speeds
in the vicinity of 1 THz Field-effect transistors less than 10nm wide have been created with GNR - "GNRFETs" - with an
ratio 
at room temperature.
Graphene
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...
or unrolled single-walled carbon nanotubes. Graphene ribbons were originally introduced as a theoretical model by Mitsutaka Fujita
Mitsutaka Fujita
was a Japanese physicist. He proposed the edge state that is unique in thegraphene zigzag edges. Also, he theoretically pointed out the importance andpeculiarity of nanoscale and edge shape effects in nanographene. The...
and co-authors to examine the edge and nanoscale size effect in graphene.
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. Indeed, experimental results show that the energy gaps do increase with decreasing GNR width. Graphene nanoribbons with controlled edge orientation have been fabricated by Scanning Tunneling Microscope (STM) lithography. 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
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.
The first measurements of their bandgaps were made by the groups of Philip Kim
Philip Kim
Philip Kim is a condensed matter physicist known for study of quantum transport in carbon nanotubes and graphene, including observations of quantum Hall effects in graphene.-Academic career:...
and Phaedon Avouris.
Graphene nanoribbons possess semiconductive properties and may be a technological alternative to silicon semiconductors. and may be capable of sustaining microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
clock speeds
Clock rate
The clock rate typically refers to the frequency that a CPU is running at.For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wave...
in the vicinity of 1 THz Field-effect transistors less than 10nm wide have been created with GNR - "GNRFETs" - with an
ratio at room temperature. See also
- GrapheneGrapheneGraphene 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...
- GraphiteGraphiteThe mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
- Graphene oxide paperGraphene Oxide PaperGraphene oxide paper or graphite oxide paper is a composite material fabricated from graphite oxide.The material has exceptional stiffness and strength, due to the intrinsic strength of the two-dimensional graphene backbone and to its interwoven layer structure which distributes loads.The starting...
- Carbon nanotubeCarbon nanotubeCarbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
- Mitsutaka FujitaMitsutaka Fujitawas a Japanese physicist. He proposed the edge state that is unique in thegraphene zigzag edges. Also, he theoretically pointed out the importance andpeculiarity of nanoscale and edge shape effects in nanographene. The...
- Katsunori WakabayashiKatsunori Wakabayashiis a physicist at the International Center for Materials Nanoarchitectonics , National Institute for Materials Science , Japan. He is an authority and leading researcher in nanotechnology in the area of energy states of single wall carbon nanotubes .-Principal research area:His research is notable...