Graphene nanoribbons (GNRs, also called nano-graphene ribbons or nano-graphite ribbons) are strips of graphene with width less than 50 nm. Graphene ribbons were introduced as a theoretical model by Mitsutaka Fujita and coauthors to examine the edge and nanoscale size effect in graphene.
Large quantities of width-controlled GNRs can be produced via graphite nanotomy, where applying a sharp diamond knife on graphite produces graphite nanoblocks, which can then be exfoliated to produce GNRs. 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 and sulfuric acid. In another method GNRs were produced by plasma etching of nanotubes partly embedded in a polymer film. More recently, graphene nanoribbons were grown onto silicon carbide (SiC) substrates using ion implantation followed by vacuum or laser annealing. The latter technique allows any pattern to be written on SiC substrates with 5 nm precision.
GNRs were grown on the edges of three-dimensional structures etched into silicon carbide wafers. When the wafers are heated to approximately 1,000 °C (1,270 K; 1,830 °F), 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 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 wafer act like semiconductors, exhibiting a band gap. Inside a reaction chamber, using chemical vapor deposition, 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. At a very slow growth rate, the graphene crystals naturally grow into long nanoribbons on a specific germanium 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 (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. 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 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. 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. 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.
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. 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[contradictory] while armchairs can be either metallic or semiconducting, depending on their width. However, density functional theory (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. Claims that graphene nanoribbons with controlled edge orientation have been fabricated by scanning tunneling microscope (STM) lithography are highly controversial and some of the data might have been fabricated, as one of the authors has been recognized guilty of scientific misconduct by an official commission of the Max Planck Gesellschaft. Energy gaps up to 0.5 eV in a 2.5 nm wide armchair ribbon were reported.
Zigzag nanoribbons are semiconducting[contradictory] 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. 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 adatoms.
Their 2D structure, high electrical and thermal conductivity 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. 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 clock speeds in the vicinity of 1 THz field-effect transistors less than 10 nm wide have been created with GNR – "GNRFETs" – with an Ion/Ioff ratio >106 at room temperature.
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.
The earliest numerical results on the optical properties of graphene nanoribbons were obtained by Lin and Shyu in 2000. The different selection rules for optical transitions in graphene nanoribobns with armchair and zigzag edges were reported. These results were supplemented by a comparative study of zigzag nanoribbons with single wall armchair carbon nanotubes 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 ( 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 longitudinally to the zigzag ribbon axis is that is odd, where and number the energy bands, while for the perpendicular polarization is even. Intraband (intersubband) transitions between the conduction (valence) subbands are also allowed if is even.
For graphene nanoribbons with armchair edges the selection rule is . Similar to tubes transitions intersubband transitions are forbidden for armchair graphene nanoribbons. Despite different selection rules in single wall armchair carbon nanotubes and zigzag graphene nanoribbons a hidden correlation of the absorption peaks is predicted. The correlation of the absorption peaks in tubes and ribbons should take place when the number of atoms in the tube unit cell is related to the number of atoms in the zigzag ribbon unit cell as follows: , which is so-called matching condition for the periodic and hard wall boundary conditions. The aforementioned results were obtained within the nearest-neighbor approximation of the tight-binding model neglecting the excitonic 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.
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 and pure optical imaging/radio frequency (RF), providing good spatial resolution, great penetration depth and high soft-tissue contrast. GNR synthesized by unzipping single- and multi-walled carbon nanotubes have been reported as contrast agents for photoacoustic and thermoacoustic imaging and tomography.
- Kawai, Shigeki; Saito, Shohei; Osumi, Shinichiro; Yamaguchi, Shigehiro; Foster, Adam S.; Spijker, Peter; Meyer, Ernst (2015). "Atomically controlled substitutional boron-doping of graphene nanoribbons". Nature Communications. 6: 8098. Bibcode:2015NatCo...6E8098K. doi:10.1038/ncomms9098. PMC . PMID 26302943.
- Fujita M.; Wakabayashi K.; Nakada K.; Kusakabe K. (1996). "Peculiar Localized State at Zigzag Graphite Edge". Journal of the Physics Society Japan. 65 (7): 1920. Bibcode:1996JPSJ...65.1920F. doi:10.1143/JPSJ.65.1920.
- Nakada K.; Fujita M.; Dresselhaus G.; Dresselhaus M.S. (1996). "Edge state in graphene ribbons: Nanometer size effect and edge shape dependence". Physical Review B. 54 (24): 17954. Bibcode:1996PhRvB..5417954N. doi:10.1103/PhysRevB.54.17954.
- Wakabayashi K.; Fujita M.; Ajiki H.; Sigrist M. (1999). "Electronic and magnetic properties of nanographite ribbons". Physical Review B. 59 (12): 8271. arXiv: . Bibcode:1999PhRvB..59.8271W. doi:10.1103/PhysRevB.59.8271.
- Mohanty, Nihar; Moore, David; Xu, Zhiping; Sreeprasad, T.S.; Nagaraja, Ashvin; Rodriguez, Alfredo Alexander; Berry, Vikas (2012). "Nanotomy Based Production of Transferrable and Dispersible Graphene-Nanostructures of Controlled Shape and Size". Nature Communications. 3 (5): 844. Bibcode:2012NatCo...3E.844M. doi:10.1038/ncomms1834.
- Brumfiel, G. (2009). "Nanotubes cut to ribbons New techniques open up carbon tubes to create ribbons". Nature. doi:10.1038/news.2009.367.
- Kosynkin, Dmitry V.; Higginbotham, Amanda L.; Sinitskii, Alexander; Lomeda, Jay R.; Dimiev, Ayrat; Price, B. Katherine; Tour, James M. (2009). "Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons". Nature. 458 (7240): 872–6. Bibcode:2009Natur.458..872K. doi:10.1038/nature07872. PMID 19370030.
- Liying Jiao; Li Zhang; Xinran Wang; Georgi Diankov; Hongjie Dai (2009). "Narrow graphene nanoribbons from carbon nanotubes". Nature. 458 (7240): 877–80. Bibcode:2009Natur.458..877J. doi:10.1038/nature07919. PMID 19370031.
- "Writing Graphene Circuitry With Ion 'Pens'". ScienceDaily. March 27, 2012. Retrieved 29 August 2012.
- "AIP's Physics News Highlights March 27, 2012". American Institute of Physics (AIP). 2012-03-28. Retrieved 29 August 2012.
- Tongay, S.; Lemaitre, M.; Fridmann, J.; Hebard, A. F.; Gila, B. P.; Appleton, B. R. (2012). "Drawing graphene nanoribbons on SiC by ion implantation". Appl. Phys. Lett. 100 (73501): 073501. Bibcode:2012ApPhL.100g3501T. doi:10.1063/1.3682479.
- "Writing graphene circuitry with ion 'pens'". American Institute of Physics. Nanowerk News. March 27, 2012. Retrieved 29 August 2012.
- "New form of graphene allows electrons to behave like photons". kurzweilai.net. February 6, 2014. Retrieved October 11, 2015.
- Orcutt, Mike (August 13, 2015). "New Technique Gives Graphene Transistors a Needed Edge | MIT Technology Review". MIT Technology Review. Retrieved 2015-10-11.
- "'Armchair nanoribbon' design makes graphene a wafer-scalable semiconductor | KurzweilAI". www.kurzweilai.net. August 19, 2015. Retrieved 2015-10-13.
- Chen, Lingxiu; He, Li; Wang, Huishan (2017). "Oriented graphene nanoribbons embedded in hexagonal boron nitride trenches". Nature Communications: 14703. arXiv: . Bibcode:2017NatCo...814703C. doi:10.1038/ncomms14703.
- Yang, X.; Dou, X.; Rouhanipour, A.; Zhi, L.; Räder, H. J.; Müllen, K. (2008). "Two-Dimensional Graphene Nanoribbons". Journal of the American Chemical Society. 130 (13): 4216–4217. doi:10.1021/ja710234t. PMID 18324813.
- Dössel, L.; Gherghel, L.; Feng, X.; Müllen, K. (2011). "Graphene Nanoribbons by Chemists: Nanometer-Sized, Soluble, and Defect-Free". Angewandte Chemie International Edition. 50 (11): 2540. doi:10.1002/anie.201006593. PMID 21370333.
- "the Foresight Institute » Blog » Cleanly placing atomically precise graphene nanoribbons". www.foresight.org. Retrieved 2017-02-15.
- Barone, V.; Hod, O.; Scuseria, G. E. (2006). "Electronic Structure and Stability of Semiconducting Graphene Nanoribbons". Nano Letters. 6 (12): 2748–54. Bibcode:2006NanoL...6.2748B. doi:10.1021/nl0617033. PMID 17163699.
- Han., M.Y.; Özyilmaz, B.; Zhang, Y.; Kim, P. (2007). "Energy Band-Gap Engineering of Graphene Nanoribbons". Physical Review Letters. 98 (20): 206805. arXiv: . Bibcode:2007PhRvL..98t6805H. doi:10.1103/PhysRevLett.98.206805. PMID 17677729.
- Tapasztó, Levente; Dobrik, Gergely; Lambin, Philippe; Biró, László P. (2008). "Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography". Nature Nanotechnology. 3 (7): 397–401. doi:10.1038/nnano.2008.149. PMID 18654562.
- Son Y.-W.; Cohen M. L.; Louie S. G. (2006). "Energy Gaps in Graphene Nanoribbons". Physical Review Letters. 97 (21): 216803. arXiv: . Bibcode:2006PhRvL..97u6803S. doi:10.1103/PhysRevLett.97.216803. PMID 17155765.
- Jung. J.; Pereg-Barnea T.; MacDonald A. H. (2009). "Theory of Interedge Superexchange in Zigzag Edge Magnetism". Physical Review Letters. 102 (22): 227205. arXiv: . Bibcode:2009PhRvL.102v7205J. doi:10.1103/PhysRevLett.102.227205. PMID 19658901.
- Huang, Liang Feng; Zhang, Guo Ren; Zheng, Xiao Hong; Gong, Peng Lai; Cao, Teng Fei; Zeng, Zhi (2013). "Understanding and tuning the quantum-confinement effect and edge magnetism in zigzag graphene nanoribbon". J. Phys.: Condens. Matter. 25 (5): 055304. Bibcode:2013JPCM...25e5304H. doi:10.1088/0953-8984/25/5/055304.
- Wang, Z. F.; Shi, Q. W.; Li, Q.; Wang, X.; Hou, J. G.; Zheng, H.; Yao, Y.; Chen, J. (2007). "Z-shaped graphene nanoribbon quantum dot device". Applied Physics Letters. 91 (5): 053109. arXiv: . Bibcode:2007ApPhL..91e3109W. doi:10.1063/1.2761266.
- Bullis, Kevin (2008-01-28). "Graphene Transistors". Technology Review. Cambridge: MIT Technology Review, Inc. Retrieved 2008-02-18.
- Bullis, Kevin (2008-02-25). "TR10: Graphene Transistors". Technology Review. Cambridge: MIT Technology Review, Inc. Retrieved 2008-02-27.
- Wang, Xinran; Ouyang, Yijian; Li, Xiaolin; Wang, Hailiang; Guo, Jing; Dai, Hongjie (2008). "Room-Temperature All-Semiconducting Sub-10-nm Graphene Nanoribbon Field-Effect Transistors". Physical Review Letters. 100 (20): 206803. arXiv: . Bibcode:2008PhRvL.100t6803W. doi:10.1103/PhysRevLett.100.206803. PMID 18518566.
- Ballon, M. S. (2008-05-28). Carbon nanoribbons hold out possibility of smaller, speedier computer chips. Stanford Report
- Lin, Ming-Fa; Shyu, Feng-Lin (2000). "Optical Properties of Nanographite Ribbons". J. Phys. Soc. Jpn. 69 (11): 3529. Bibcode:2000JPSJ...69.3529L. doi:10.1143/JPSJ.69.3529.
- Hsu, Han; Reichl, L. E. (2007). "Selection rule for the optical absorption of graphene nanoribbons". Phys. Rev. B. 76 (4): 045418. Bibcode:2007PhRvB..76d5418H. doi:10.1103/PhysRevB.76.045418.
- Chung, H. C.; Lee, M. H.; Chang, C. P.; Lin, M. F. (2011). "Exploration of edge-dependent optical selection rules for graphene nanoribbons". Optics Express. 19 (23): 23350. Bibcode:2011OExpr..1923350C. doi:10.1364/OE.19.023350.
- Sasaki, K.-I.; Kato, K.; Tokura, Y.; Oguri, K.; Sogawa, T. (2011). "Theory of optical transitions in graphene nanoribbons". Phys. Rev. B. 84 (8): 085458. arXiv: . doi:10.1103/PhysRevB.84.085458.
- Saroka, V. A.; Shuba, M. V.; Portnoi, M. E. (2017). "Optical selection rules of zigzag graphene nanoribbons". Phys. Rev. B. 95 (15): 155438. arXiv: . Bibcode:2017PhRvB..95o5438S. doi:10.1103/PhysRevB.95.155438.
- Onida, Giovanni; Rubio, Angel (2002). "Electronic excitations: Density-functional versus many-body Green's-function approaches". Rev. Mod. Phys. 74 (2): 601. Bibcode:2002RvMP...74..601O. doi:10.1103/RevModPhys.74.601.
- Prezzi, Deborah; Varsano, Daniele; Ruini, Alice; Marini, Andrea; Molinari, Elisa (2008). "Optical properties of graphene nanoribbons: The role of many-body effects". Physical Review B. 77 (4): 041404. arXiv: . Bibcode:2008PhRvB..77d1404P. doi:10.1103/PhysRevB.77.041404.
Yang, Li; Cohen, Marvin L.; Louie, Steven G. (2007). "Excitonic Effects in the Optical Spectra of Graphene Nanoribbons". Nano Lett. 7 (10): 3112–5. arXiv: . Bibcode:2007NanoL...7.3112Y. doi:10.1021/nl0716404. PMID 17824720.
Yang, Li; Cohen, Marvin L.; Louie, Steven G. (2008). "Magnetic Edge-State Excitons in Zigzag Graphene Nanoribbons". Physical Review Letters. 101 (18): 186401. Bibcode:2008PhRvL.101r6401Y. doi:10.1103/PhysRevLett.101.186401. PMID 18999843.
- Zhu, Xi; Su, Haibin (2010). "Excitons of Edge and Surface Functionalized Graphene Nanoribbons". J. Phys. Chem. C. 114 (41): 17257. doi:10.1021/jp102341b.
- Zhu, Xi; Su, Haibin (2011). "Scaling of Excitons in Graphene Nanoribbons with Armchair Shaped Edges". Journal of Physical Chemistry A. 115 (43): 11998–12003. Bibcode:2011JPCA..11511998Z. doi:10.1021/jp202787h.
- Raifee, Mohammad; Wei Lu; Abhay V. Thomas; Ardavan Zandiatashbar; Javad Rafiee; James M. Tour (16 November 2010). "Graphene nanoribbon composites". ACS Nano. 4 (12): 7415–7420. doi:10.1021/nn102529n. PMID 21080652.
- Lalwani, Gaurav; Allan M. Henslee; Behzad Farshid; Liangjun Lin; F. Kurtis Kasper; Yi-Xian Qin; Antonios G. Mikos; Balaji Sitharaman (2013). "Two-Dimensional Nanostructure-Reinforced Biodegradable Polymeric Nanocomposites for Bone Tissue Engineering". Biomacromolecules. 14 (3): 900–9. doi:10.1021/bm301995s. PMC . PMID 23405887.
- Lalwani, Gaurav; Xin Cai; Liming Nie; Lihong V. Wang; Balaji Sitharaman (December 2013). "Graphene-based contrast agents for photoacoustic and thermoacoustic tomography". Photoacoustics. 1 (3–4): 62–67. doi:10.1016/j.pacs.2013.10.001. PMC . PMID 24490141.Full Text PDF.