Graphene nanoribbons (also called nano-graphene ribbons or nano-graphite ribbons), often abbreviated GNRs, are strips of graphene with ultra-thin width (<50 nm). 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.
Large quantities of width controlled GNRs can be produced via graphite nanotomy  shown by Berry group, where sharp diamond knife application on graphite produces graphite nanoblocks, which are exfoliated to produce GNRs. GNRs can also be produced by unzipping or cutting open nanotubes. In one such method by Tour group multi-walled carbon nanotubes were unzipped in solution by action of potassium permanganate and sulfuric acid. In another method by Dai group GNRs were produced by plasma etching of nanotubes partly embedded in a polymer film. More recently, graphene nanoribbons have been grown onto silicon carbide (SiC) substrates using ion implantation followed by vacuum or laser annealing. The latter technique allows one to write any pattern onto SiC substrates with 5 nm precision.
The electronic states of GNRs largely depend on the edge structures (armchair or zigzag). 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, 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. 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 also can be memorably controlled by alkaline adatoms.
Tight-binding numerical simulation  obtained by means of the open-source code NanoTCAD ViDES have demonstrated that field effect transistors exploiting GNR as channel material can comply with ITRS requirements for next-generation devices.
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.
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 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.
First-principle calculations with quasiparticle corrections and many-body effects are performed to study 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. Raifee, Koratkar, and Tour et al. report increases in the mechanical properties of epoxy composites on loading of graphene nanoribbons. In a recent study, Lalwani, Sitharaman and co-workers report an increase in the mechanical properties of biodegradable polymeric nanocomposites of poly(propylene fumarate) at low weight% 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.
- Fujita M., Wakabayashi K., Nakada K. and 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. and 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. and Sigrist M. (1999). "Electronic and magnetic properties of nanographite ribbons". Physical Review B 59 (12): 8271. arXiv:cond-mat/9809260. Bibcode:1999PhRvB..59.8271W. doi:10.1103/PhysRevB.59.8271.
- Nihar Mohanty, David Moore, Zhiping Xu, T. S. Sreeprasad, Ashvin Nagaraja, Alfredo A. Rodriguez and Vikas Berry (2012). "Nanotomy Based Production of Transferrable and Dispersible Graphene-Nanostructures of Controlled Shape and Size". Nature Communications 3: 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. Mar 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.
- S. Tongay, M. Lemaitre, J. Fridmann, A. F. Hebard, B. P. Gila, and B. R. Appleton (2012). "Drawing graphene nanoribbons on SiC by ion implantation". Appl. Phys. Lett. 100 (073501). Retrieved 29 August 2012.
- "Writing graphene circuitry with ion 'pens'". American Institute of Physics. Nanowerk News. Mar 27, 2012. Retrieved 29 August 2012.
- Barone, V., Hod, O., and 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., and Kim, P. (2007). "Energy Band-Gap Engineering of Graphene Nanoribbons". Physical Review Letters 98 (20). arXiv:cond-mat/0702511. Bibcode:2007PhRvL..98t6805H. doi:10.1103/PhysRevLett.98.206805.
- 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., and Louie S. G. (2006). "Energy Gaps in Graphene Nanoribbons". Physical Review Letters 97 (21). arXiv:cond-mat/0611602. Bibcode:2006PhRvL..97u6803S. doi:10.1103/PhysRevLett.97.216803.
- Jung. J., Pereg-Barnea T., MacDonald A. H. (2009). "Theory of Interedge Superexchange in Zigzag Edge Magnetism". Physical Review Letters 102 (22). arXiv:0812.1047. Bibcode:2009PhRvL.102v7205J. doi:10.1103/PhysRevLett.102.227205.
- L. F. Huang, G. R. Zhang, X. H. Zheng, P. L. Gong, T. F. Cao, and Z. Zeng (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.
- Fiori G., Iannaccone G. (2007). "Simulation of Graphene Nanoribbon Field-Effect Transistors". IEEE Electron Device Letters 28 (8): 760. arXiv:0704.1875. Bibcode:2007IEDL...28..760F. doi:10.1109/LED.2007.901680.
- 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:0705.0023. 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). arXiv:0803.3464. Bibcode:2008PhRvL.100t6803W. doi:10.1103/PhysRevLett.100.206803.
- Ballon, M. S. (2008-05-28). Carbon nanoribbons hold out possibility of smaller, speedier computer chips. Stanford Report
- 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:0706.0916. 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:0707.2983. 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. 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.
- Lalwani, Gaurav; Allan M. Henslee, Behzad Farshid, Liangjun Lin, F. Kurtis Kasper, Yi-Xian Qin, Antonios G. Mikos, and Balaji Sitharaman (February 13, 2013). "Two-Dimensional Nanostructure-Reinforced Biodegradable Polymeric Nanocomposites for Bone Tissue Engineering". Biomacromolecules. doi:10.1021/bm301995s. 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. doi:10.1016/j.pacs.2013.10.001. PMID 24490141.