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Graphene nanoribbons (GNRs, also called nano-graphene ribbons or nano-graphite ribbons) are strips of
graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...
with width less than 100 nm. Graphene ribbons were introduced as a theoretical model by
Mitsutaka Fujita was a Japanese physicist. He proposed the edge state that is unique to graphene zigzag edges. Also, he theoretically pointed out the importance and peculiarity of nanoscale and edge shape effects in nanographene. The theoretical concept of gr ...
and coauthors to examine the edge and nanoscale size effect in graphene. Some earlier studies of graphitic ribbons within the area of conductive polymers in the field of synthetic metals include works by Kazuyoshi Tanaka, Tokio Yamabe and co-authors, Steven Kivelson and Douglas J. Klein. While Tanaka, Yamabe and Kivelson studied so-called zigzag and armchair edges of graphite, Klein introduced a different edge geometry that is frequently referred to as a bearded edge.


Production


Nanotomy

Large quantities of width-controlled GNRs can be produced via
graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...
nanotomy, where applying a sharp diamond knife on graphite produces graphite nanoblocks, which can then be exfoliated to produce GNRs as shown by Vikas Berry. GNRs can also be produced by "unzipping" or axially cutting nanotubes. In one such method multi-walled carbon nanotubes were unzipped in solution by action of
potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, which dissolves in water as K+ and ions to give an intensely pink to purple solution. Potassium permanganate is widely us ...
and
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
. In another method GNRs were produced by
plasma etching Plasma etching is a form of plasma processing used to fabricate integrated circuits. It involves a high-speed stream of glow discharge (Plasma (physics), plasma) of an appropriate gas mixture being shot (in pulses) at a sample. The plasma source, ...
of nanotubes partly embedded in a
polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
film. More recently, graphene nanoribbons were grown onto
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...
(SiC) substrates using
ion implantation Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the target's physical, chemical, or electrical properties. Ion implantation is used in semiconductor device fabrica ...
followed by vacuum or laser annealing. The latter technique allows any pattern to be written on SiC substrates with 5 nm precision.


Epitaxy

GNRs were grown on the edges of three-dimensional structures etched into
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...
wafers. When the wafers are heated to approximately , silicon is preferentially driven off along the edges, forming nanoribbons whose structure is determined by the pattern of the three-dimensional surface. The ribbons had perfectly smooth edges, annealed by the fabrication process. Electron mobility measurements surpassing one million correspond to a
sheet resistance Sheet resistance is the resistance of a square piece of a thin material with contacts made to two opposite sides of the square. It is usually a measurement of electrical resistance of thin films that are uniform in thickness. It is commonly used ...
of one ohm per square — two orders of magnitude lower than in two-dimensional graphene.


Chemical vapor deposition

Nanoribbons narrower than 10 nm grown on a
germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...
wafer act like semiconductors, exhibiting a
band gap In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...
. Inside a reaction chamber, using
chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (electro ...
, methane is used to deposit hydrocarbons on the wafer surface, where they react with each other to produce long, smooth-edged ribbons. The ribbons were used to create prototype
transistors A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
. At a very slow growth rate, the graphene crystals naturally grow into long nanoribbons on a specific
germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...
crystal facet. By controlling the growth rate and growth time, the researchers achieved control over the nanoribbon width. Recently, researchers from SIMIT (Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences) reported on a strategy to grow graphene nanoribbons with controlled widths and smooth edges directly onto dielectric
hexagonal boron nitride Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula B N. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexago ...
(h-BN) substrates. The team use nickel nanoparticles to etch monolayer-deep, nanometre-wide trenches into h-BN, and subsequently fill them with graphene using
chemical vapour deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (subst ...
. Modifying the etching parameters allows the width of the trench to be tuned to less than 10 nm, and the resulting sub-10-nm ribbons display bandgaps of almost 0.5 eV. Integrating these nanoribbons into
field effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the current through a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET (MOSFET). FETs have three termi ...
devices reveals on–off ratios of greater than 104 at room temperature, as well as high carrier mobilities of ~750 cm2 V−1 s−1.


Multistep nanoribbon synthesis

A bottom-up approach was investigated. In 2017 dry contact transfer was used to press a fiberglass applicator coated with a powder of atomically precise graphene nanoribbons on a hydrogen-passivated Si(100) surface under
vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...
. 80 of 115 GNRs visibly obscured the substrate lattice with an average apparent height of 0.30 nm. The GNRs do not align to the Si lattice, indicating a weak coupling. The average bandgap over 21 GNRs was 2.85 eV with a standard deviation of 0.13 eV. The method unintentionally overlapped some nanoribbons, allowing the study of multilayer GNRs. Such overlaps could be formed deliberately by manipulation with a
scanning tunneling microscope A scanning tunneling microscope (STM) is a type of scanning probe microscope used for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, then at IBM Zürich, the Nobel Prize in ...
. Hydrogen depassivation left no band-gap. Covalent bonds between the Si surface and the GNR leads to metallic behavior. The Si surface atoms move outward, and the GNR changes from flat to distorted, with some C atoms moving in toward the Si surface.


Electronic structure

The electronic states of GNRs largely depend on the edge structures (armchair or zigzag). In zigzag edges each successive edge segment is at the opposite angle to the previous. In armchair edges, each pair of segments is a 120/-120 degree rotation of the prior pair. The animation below provides a visualization explanation of both. 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 theory predict that zigzag GNRs are always metallic while armchairs can be either metallic or semiconducting, depending on their width. However,
density functional theory Density functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body ...
(DFT) calculations show that armchair nanoribbons are semiconducting with an energy gap scaling with the inverse of the GNR width. Experiments verified that energy gaps increase with decreasing GNR width. Graphene nanoribbons with controlled edge orientation have been fabricated by
scanning tunneling microscope A scanning tunneling microscope (STM) is a type of scanning probe microscope used for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, then at IBM Zürich, the Nobel Prize in ...
(STM) lithography. Energy gaps up to 0.5 eV in a 2.5 nm wide armchair ribbon were reported. Armchair nanoribbons are metallic or semiconducting and present spin polarized edges. Their gap opens thanks to an unusual antiferromagnetic coupling between the
magnetic moment In electromagnetism, the magnetic moment or magnetic dipole moment is the combination of strength and orientation of a magnet or other object or system that exerts a magnetic field. The magnetic dipole moment of an object determines the magnitude ...
s 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. Therefore, the quantum confinement, inter-edge superexchange, and intra-edge direct exchange interactions in zigzag GNR are important for its magnetism and band gap. The edge magnetic moment and band gap of zigzag GNR are reversely proportional to the electron/hole concentration and they can be controlled by alkaline
adatom An adatom is an atom that lies on a crystal surface, and can be thought of as the opposite of a surface vacancy. This term is used in surface chemistry and epitaxy, when describing single atoms lying on surfaces and surface roughness. The word ...
s. Their 2D structure, high electrical and
thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...
and low noise also make GNRs a possible alternative to copper for integrated circuit interconnects. Research is exploring the creation of quantum dots by changing the width of GNRs at select points along the ribbon, creating
quantum confinement A potential well is the region surrounding a local minimum of potential energy. Energy captured in a potential well is unable to convert to another type of energy (kinetic energy in the case of a gravitational potential well) because it is captu ...
. Heterojunctions inside single graphene nanoribbons have been realized, among which structures that have been shown to function as tunnel barriers. Graphene nanoribbons possess semiconductive properties and may be a technological alternative to silicon semiconductors capable of sustaining
microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...
clock speeds in the vicinity of 1 THz
field-effect transistors The field-effect transistor (FET) is a type of transistor that uses an electric field to control the Electric current, current through a semiconductor. It comes in two types: JFET, junction FET (JFET) and MOSFET, metal-oxide-semiconductor FET (M ...
less than 10 nm wide have been created with GNR – "GNRFETs" – with an Ion/Ioff ratio >106 at room temperature. File:cnt_gnrarm_v3.gif, GNR band structure for armchair type. Tight binding calculations show that armchair type can be semiconducting or metallic depending on width (chirality). File:cnt_zz_v3.gif, GNR band structure for zigzag type. Tight binding calculations predict that zigzag type is always metallic. File:Graphene_Nanoribbons_of_controlled_width.jpg, TEM micrographs of GNRs of (a) w=15, (b) w=30, (c) w=40 (exfoliating), and (d) w=60 nm deposited on 400 mesh lacey carbon grids and (e) FESEM micrograph of 600 nm ribbon. (f) Electron microscope images of a 120-nm graphene ribbons (FESEM), (g) 50 nm square GQDs (FESEM), (h,i) 25×100 nm2 rectangular GQDs (FESEM), and (j) 8°-angled tapered GNR (or triangular GQD) (FESEM)). The large densities of square and rectangular GQDs (g) showed extensive folding (white arrows). Bar sizes=(a) 250 nm, (b,g,i) 50 nm, (c,d) 500 nm, and (h) 1 μm.


Electronic structure in external fields

The electronic properties in external field such as static electric or magnetic field have been extensively studied. The various levels of the tight-binding model as well as first principles calculations have been employed for such studies. For for zigzag nanoribbons the most interesting effect under an external electric field is inducing of half-metallicity. In a simple tight-binding model the effect of the external in-plane field applied across the ribbon width is the band gap opening between the edge states. However, the first principles spin-polarized calculations demonstrate that the spin up and down species behave differently. One spin projection closes the band gap whereas another increases. As a result, at some critical value of field, the ribbon turns into a metallic for one spin projection (up or down) and an insulating for another spin (down or up). In this way, half-metallicity that may be useful for spintronics applications is induced. Armchair ribbons behave differently from their zigzag siblings. They usually feature a band gap that closes under an external in-plane electric field. At some critical value of the field the gap fully closes forming a Dirac cone linear crossing, see Fig. 9d in Ref. This intriguing result have been corroborated by the density functional theory calculations and explained in a simplified tight-binding model. It does not depend on the chemical composition of the ribbon edges, for example both fluorine and chorine atoms can be used for the ribbon edge passivation instead of a usual hydrogen. Also this effect can be induced by chemical co-doping, i.e. by placing nitrogen and boron atoms atop the ribbon at its opposite sides. Modelwise the effect can be explained by a pair of cis-polyacetylene chains placed at a distance corresponding to the ribbon width and subjected to the different gate potentials. Bearded ribbons with Klen-type edges behave in the tight-binding model approximation similar to zigzag ribbons. Namely, the band gap opens between the edge states. Due to chemical instability of this type of the edge configuration, such ribbons are normally excluded from the publications. Whether they can at least hypothetically exhibit half-metallicity in external in-plane fields similar to zigzag nanoribbons is not yet clear. A vast family of cousins of the above ribbons with both similar edges is the class of ribbons combining non-equivalent edge geometries in a single ribbon. One of the simplest examples can be a half-bearded nanoribbon. Such ribbons, in principle, could be more stable than nanoribbons with two bearded edges because they could be realized via asymmetric hydrogenation of zigzag ribbons. In the nearest neighbor tight-binding model and in non-spin-polarized density functional theory calculations such ribbons exhibit chiral anomaly structure. The fully flat band of a pristine half-bearded nanoribbon subjected to the in-plane external electric field demonstrates unidirectional linear dispersions with group velocities of opposite directions around each of the two Dirac points. At high fields, the linear bands around the Dirac points transform into a wiggly cubic-like dispersions. This nontrivial behavior is favorable for the field-tunable dissipationless transport. The drastic transformation from fully flat to linear and then cubic-like band allows for a continuum \vec\cdot\vec model description based on the Dirac equation. The Dirac equation supplemented with the suitable boundary conditions breaking the inversion/mirror symmetry and a single field strength parameter admits an analytic solution in terms of Airy-like special functions.


Mechanical properties

While it is difficult to prepare graphene nanoribbons with precise geometry to conduct the real
tensile test Tensile testing, also known as tension testing, is a fundamental materials science and engineering test in which a sample is subjected to a controlled tension until failure. Properties that are directly measured via a tensile test are ultimate ...
due to the limiting resolution in nanometer scale, the mechanical properties of the two most common graphene nanoribbons (zigzag and armchair) were investigated by computational modeling using
density functional theory Density functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body ...
,
molecular dynamics Molecular dynamics (MD) is a computer simulation method for analyzing the Motion (physics), physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamics ( ...
, and
finite element method Finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat tran ...
. Since the two-dimensional
graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...
sheet with strong bonding is known to be one of the stiffest materials, graphene nanoribbons
Young's modulus Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...
also has a value of over 1 TPa. The Young's modulus,
shear modulus In materials science, shear modulus or modulus of rigidity, denoted by ''G'', or sometimes ''S'' or ''μ'', is a measure of the Elasticity (physics), elastic shear stiffness of a material and is defined as the ratio of shear stress to the shear s ...
and
Poisson's ratio In materials science and solid mechanics, Poisson's ratio (symbol: ( nu)) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value ...
of graphene nanoribbons are different with varying sizes (with different length and width) and shapes. These mechanical properties are anisotropic and would usually be discussed in two in-plane directions, parallel and perpendicular to the one-dimensional periodic direction. Mechanical properties here will be a little bit different from the two-dimensional graphene sheets because of the distinct geometry, bond length, and bond strength particularly at the edge of graphene nanoribbons. It is possible to tune these nanomechanical properties with further chemical doping to change the bonding environment at the edge of graphene nanoribbons. While increasing the width of graphene nanoribbons, the mechanical properties will converge to the value measured on the graphene sheets. One analysis predicted the high Young's modulus for armchair graphene nanoribbons to be around 1.24 TPa by the molecular dynamics method. They also showed the nonlinear elastic behaviors with higher-order terms in the stress-strain curve. In the higher strain region, it would need even higher-order (>3) to fully describe the nonlinear behavior. Other scientists also reported the nonlinear elasticity by the finite element method, and found that Young's modulus,
tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
, and
ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...
of armchair graphene nanoribbons are all greater than those of zigzag graphene nanoribbons. Another report predicted the linear elasticity for the strain between -0.02 and 0.02 on the zigzag graphene nanoribbons by the density functional theory model. Within the linear region, the electronic properties would be relatively stable under the slightly changing geometry. The energy gaps increase from -0.02 eV to 0.02 eV for the strain between -0.02 and 0.02, which provides the feasibilities for future engineering applications. The
tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
of the armchair graphene nanoribbons is 175 GPa with the great ductility of 30.26%
fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
strain, which shows the greater mechanical properties comparing to the value of 130 GPa and 25% experimentally measured on monolayer graphene. As expected, graphene nanoribbons with smaller width would completely break down faster, since the ratio of the weaker edged bonds increased. While the tensile strain on graphene nanoribbons reached its maximum, C-C bonds would start to break and then formed much bigger rings to make materials weaker until fracture.


Optical properties

The earliest numerical results on the optical properties of graphene nanoribbons were obtained by Lin and Shyu in 2000. The different
selection rules In physics and chemistry, a selection rule, or transition rule, formally constrains the possible transitions of a system from one quantum state to another. Selection rules have been derived for electromagnetic transitions in molecules, in atoms, in ...
for optical transitions in graphene nanoribbons with armchair and zigzag edges were reported. These results were supplemented by a comparative study of zigzag nanoribbons with single wall armchair
carbon nanotubes A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''SWC ...
by Hsu and Reichl in 2007. It was demonstrated that selection rules in zigzag ribbons are different from those in carbon nanotube and the eigenstates in zigzag ribbons can be classified as either symmetric or antisymmetric. Also, it was predicted that edge states should play an important role in the optical absorption of zigzag nanoribbons. Optical transitions between the edge and bulk states should enrich the low-energy region (<3 eV) of the absorption spectrum by strong absorption peaks. Analytical derivation of the numerically obtained selection rules was presented in 2011. The selection rule for the incident light polarized parallel (longitudinally) to the zigzag ribbon axis is that \Delta J = J_2 - J_1 is odd, where J_ and J_ enumerate the energy bands, while for the perpendicular polarization \Delta J is even. Intraband (intersubband) transitions between the conduction or valence sub-bands are also allowed in parallel polarization if \Delta J is even. For perpendicular polarization the intraband transitions between the conduction or valence sub-bands are allowed when \Delta J is odd. For graphene nanoribbons with armchair edges the selection rules are \Delta J is odd for the perpendicular and \Delta J = 0 for the parallel polarization of the incident light. Similar to carbon tubes the intersubband transitions in parallel polarization are forbidden for armchair graphene nanoribbons though they are allowed for the perpendicular polarization and \Delta J being odd. Since energy bands in armchair nanoribbons and zigzag carbon nanotubes can be aligned, when N_t = 2 N_r + 4, where N_t and N_r are the numbers of atoms in the unit cell of the tube and ribbon, respectively, the selection rules for parallel polarization give rise to an exact correlation between optical absorption peaks of these two types of nanostructures. Despite different selection rules in single wall armchair carbon nanotubes and zigzag graphene nanoribbons a hidden correlation of the absorption peaks originating from the bulk states is predicted. The correlation of the absorption peaks in armchair tubes and zigzag ribbons takes place when the matching condition N_t = 2 N_r + 4 holds even though the energy bands of such a tube and ribbon do not align precisely. A similar correlation between bulk absorption peaks can be obtained for armchair nanotubes and nanoribbons with bearded edges, but in this case the matching conditions alters to N_t = 2 N_r + 2. These results obtained within the nearest-neighbor approximation of the tight-binding model have been corroborated with first principles density functional theory calculations for zigzag nanoribbons and armchair tubes taking into account exchange and correlation effects. First-principle calculations with quasiparticle corrections and many-body effects explored the electronic and optical properties of graphene-based materials. With GW calculation, the properties of graphene-based materials are accurately investigated, including graphene nanoribbons, edge and surface functionalized armchair graphene nanoribbons and scaling properties in armchair graphene nanoribbons.


Analyses

Graphene nanoribbons can be analyzed by scanning tunneling microscope, Raman spectroscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy. For example, out-of-plane bending vibration of one C-H on one benzene ring, called SOLO, which is similar to zigzag edge, on zigzag GNRs has been reported to appear at 899 cm−1, whereas that of two C-H on one benzene ring, called DUO, which is similar to armchair edge, on armchair GNRs has been reported to appear at 814 cm−1 as results of calculated IR spectra. However, analyses of graphene nanoribbon on substrates are difficult using infrared spectroscopy even with a Reflection Absorption Spectrometry method. Thus, a large quantity of graphene nanoribbon is necessary for infrared spectroscopy analyses.


Reactivity

Zigzag edges are known to be more reactive than armchair edges, as observed in the dehydrogenation reactivities between the compound with zigzag edges (tetracene) and armchair edges (chrysene). Also, zigzag edges tends to be more oxidized than armchair edges without gasification. The zigzag edges with longer length can be more reactive as it can be seen from the dependence of the length of acenes on the reactivity.


Applications


Polymeric nanocomposites

Graphene nanoribbons and their oxidized counterparts called graphene oxide nanoribbons have been investigated as nano-fillers to improve the mechanical properties of polymeric nanocomposites. Increases in the mechanical properties of epoxy composites on loading of graphene nanoribbons were observed. An increase in the mechanical properties of biodegradable polymeric nanocomposites of poly(propylene fumarate) at low weight percentage was achieved by loading of oxidized graphene nanoribbons, fabricated for bone tissue engineering applications.


Contrast agent for bioimaging

Hybrid imaging modalities, such as photoacoustic (PA) tomography (PAT) and thermoacoustic (TA) tomography (TAT) have been developed for bioimaging applications. PAT/TAT combines advantages of pure
ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...
and pure optical imaging/
radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...
(RF), providing good spatial resolution, great penetration depth and high soft-tissue contrast. GNR synthesized by unzipping single- and multi-walled
carbon nanotubes A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''SWC ...
have been reported as
contrast agent A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
s for photoacoustic and thermoacoustic imaging and
tomography Tomography is imaging by sections or sectioning that uses any kind of penetrating wave. The method is used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, cosmochemistry, ast ...
.


Catalysis

In catalysis, GNRs offer several advantageous features that make them attractive as catalysts or catalyst supports. Firstly, their high surface-to-volume ratio provides abundant active sites for catalytic reactions. This enhanced surface area enables efficient interaction with reactant molecules, leading to improved catalytic performance. Secondly, the edge structure of GNRs plays a crucial role in catalysis. The zigzag and armchair edges of GNRs possess distinctive electronic properties, making them suitable for specific reactions. For instance, the presence of unsaturated carbon atoms at the edges can serve as active sites for adsorption and reaction of various molecules. Moreover, GNRs can be functionalized or doped with heteroatoms to tailor their catalytic properties further. Functionalization with specific groups or doping with elements like silicon, nitrogen, boron, or transition metals can introduce additional active sites or modify the electronic structure, allowing for selective catalytic transformations.


See also

*
Graphene oxide paper Graphene oxide paper or graphite oxide paper is a material fabricated from graphite oxide. Micrometer thick films of graphene oxide paper are also named as graphite oxide membranes (in the 1960s) or (more recently) graphene oxide membranes. The me ...
* Katsunori Wakabayashi *
Silicene Silicene is a two-dimensional allotrope of silicon, with a hexagonal honeycomb structure similar to that of graphene. Contrary to graphene, silicene is not flat, but has a periodically buckled topology; the coupling between layers in silicene is ...
, which can also form nanoribbons * Graphene electronics * Graphene helix


References

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External links


WOLFRAM Demonstrations Project: Electronic Band Structure of Armchair and Zigzag Graphene Nanoribbons

Graphene nanoribbons on arxiv.org
Graphene