Several methods to open a band gap in graphene have been developed, including doping, hydrogenation, and fabrication of nanoribbons, nanomeshes and nanorings. Size exclusion chromatography sec shows a bimodal distribution of linear polymers m n 26,000 g mol 1 and cyclic oligomers m n 3,000 g mol 1 characteristic for a stepgrowth polymerization mechanism. Such control requires the development of fabrication tools capable of precisely controlling width and edge geometry of gnrs at the atomic scale. By micromachining the graphene into graphene nanoribbons gnrs, an energy gap can be observed by measuring the nonlinear conductance at room temperature, which is created by the lateral. Roomtemperature magnetism and tunable energy gaps in edge. Ultranarrow metallic armchair graphene nanoribbons nature.
Gap prediction in hybrid graphenehexagonal boron nitride. The sizes of these energy gaps are investigated by measuring the conductance in the nonlinear response regime at low temperatures. The energy gap in graphene is crucial for many applications. The carboncarbon bond length in graphene is about 0. Chapter 4 electrical properties of graphene wrinkles and.
Twodimensional graphene nanoribbons journal of the. Engineering techniques that use finite size effect to introduce tunable edge magnetism and energy gap are by far the most promising ways for enabling graphene 1 to be used in electronics and. Energy and transport gaps in etched graphene nanoribbons f molitor, c stampfer, j guttinger, a jacobsen, t ihn and k ensslin. Energy gap opening by crossing drop cast singlelayer. September, 2008 graphite is a known material to human kind for centuries as the lead of a pencil. This differs from the results of simple tightbinding calculations or solutions of the. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene. Energy band gap engineering of graphene nanoribbons melinda y. Fterminated armchair graphene nanoribbons have lower band gaps than those of hterminated ones when they have the same band width. Dynamics of mechanical waves in periodic graphene nanoribbon. The gnrs considered have either armchair or zigzag shaped edges on both sides with hydrogen passivation.
Based on a firstprinciples approach, we present scaling rules for the band gaps of graphene nanoribbons gnrs as a function of their widths. Here, we report the fabrication of atomically precise gqds consisting of lowbandgap n 14 armchair graphene nanoribbon agnr segments that are achieved through edge fusion of n 7 agnrs. Energy gaps in graphene nanoribbons youngwoo son,1,2 marvin l. The band structures of strained graphene nanoribbons gnrs are examined using a tightbinding hamiltonian that is directly related to the type and magnitude of strain. Regular graphene has no band gap its unusually rippled valence and conduction bands actually meet in places, making it more like a metal. Suppression of electronvibron coupling in graphene. The nanoribbons are characterized by ms, uvvis, and scanning tunneling microscopy stm. The energy gap difference between highest occupied molecular orbital homo and lowest unoccupied molecular orbital lumo dependence for finite width and length is computed for both armchair and zigzag. This decrease in conductivity at high applied electric eld is described by carrier velocity saturation due to optical phonon emission. One of the obstacles to the use of graphene is its lack of band gap, meaning it is difficult to use in digital electronics that need large current onoff ratios. Pdf energy gap in graphene nanoribbons with structured. Louie1,2 1department of physics, university of california at berkeley, california 94720, usa 2materials sciences division, lawrence berkeley national laboratory, berkeley, california 94720, usa 3department of physics, konkuk university, seoul 143701, korea. Low temperature and temperaturedependent measurements reveal a length and orientationindependent transport gap whose size is inversely proportional to gnr width.
Energy bandgap engineering of graphene nanoribbons. For gnrs with zigzag shaped edges, gaps appear because of a staggered sublattice. Twodimensional graphene does not have a band gap, and the band gap remains close to zero even if a strain as large as 20% is applied. It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. Narrow graphene nanoribbons gnrs can exhibit a semiconducting behavior with a band gap due to quantum confinement, 5, 6 thus overcoming the lack of usage of graphene in digital logic circuits. Solutionsynthesized chevron graphene nanoribbons exfoliated. Graphene nanoribbons with controlled edge orientation have been fabricated by scanning tunneling microscope stm lithography. Computer simulations zhao with coworkers 19 performed simulations of deformation behaviors exhibited by graphene nanoribbons with various sizes under uniaxial tensile load. Electronic states at energies in the gap are localized, and charge transport exhibits a tran. Quasiparticle energies and band gaps in graphene nanoribbons li yang,1,2 cheolhwan park,1,2 youngwoo son,3 marvin l. Graphene ribbons were introduced as a theoretical model by mitsutaka fujita and coauthors to examine the edge and nanoscale size effect in graphene. Graphene nanoribbons have been largely studied theoretically, experimentally and with the perspective of electronic applications. The sizes of these energy gaps are investigated by. By adding modified, singleatomthick graphene nanoribbons to thermoplastic polyurethane, researchers at rice university have developed an enhanced polymer material that is far more impermeable to pressurized gas and far lighter than the current metal used in gas tanks.
Graphene nanoribbons are among the recently discovered carbon nanostructures, with unique characteristics for novel applications. Electronic structure of graphene nanoribbons huseyin. Highlights the electronic properties of graphene nanoribbons are studied for the fterminated instead of the hterminated by using the firstprinciples. This differs from the results of simple tightbinding calculations or solutions of the dirac. Jun 17, 2011 we simulate the natural frequencies and the acoustic wave propagation characteristics of graphene nanoribbons gnrs of the type 8,0 and 0,8 using an equivalent atomisticcontinuum fe model previously developed by some of the authors, where the cc bonds thickness and average equilibrium lengths during the dynamic loading are identified through the minimisation of the system hamiltonian. Competing gap opening mechanisms of monolayer graphene. Rationalizing and reconciling energy gaps and quantum confinement in narrow atomically precise armchair graphene nanoribbons. Using the diracfermion approach, we calculate the energy spectrum of an infinitely long nanoribbon of finite width w, terminated by dirichlet boundary conditions in the transverse direction. Aug 28, 2011 graphene nanoribbons with perfect edges are predicted to exhibit interesting electronic and spintronic properties1,2,3,4, notably quantumconfined bandgaps and magnetic edge states.
Energy gap in graphene nanoribbons with structured. Widthdependent band gap in armchair graphene nanoribbons. Graphene nanoribbons show promise for healing spinal injuries. Experiments verified that energy gaps increase with decreasing gnr width. Compared to a twodimensional graphene whose band gap remains close to zero even if a large strain is applied, the band gap of a graphene nanoribbon gnr is sensitive to both. Here we show that correlation effects not included in previous density functional simulations play a key role in these systems. Technology exploration for graphene nanoribbon fets. Introduction graphene, which is a monolayer of carbon atoms packed into a twodimensional honeycomb lattice, has emerged as a promising candidate material for beyondcmos nanoelectronics. Ihn 1solid state physics laboratory, eth zurich, 8093 zurich, switzerland 2physics department, ben gurion university, beer sheva 84105, israel we investigate the density and temperaturedependent conductance of graphene nanoribbons with. Sep 20, 2016 the combination of graphene nanoribbons made with a process developed at rice university and a common polymer could someday be of critical importance to healing damaged spinal cords in people. Graphene nanoribbons gnrs, also called nano graphene ribbons or nanographite ribbons are strips of graphene with width less than 50 nm. Color online band gap e g as a function of structural parameters of gnms. Graphene is widely regarded as a promising material for electronic applications because the exceptionally high mobilities of its charge carriers enable extremely fast transistors 1 1. Graphene nanoribbons 18 display unique electronic properties based on truly twodimensional 2d graphene 9 with potential applications in nanoelectronics 10,11.
We show that a structured external potential that acts within the edge regions of. Extraction of e g for the high quality gnr devices using negf simulation. Graphene based devices offer high mobility for ballistic transport, high carrier. Abstract we investigate electronic transport in lithographically patterned graphene ribbon structures. Graphene nanoribbons improve compressed gas storage. Its fascinating electrical, optical, and mechanical properties ignited enormous interdisciplinary interest from the physics, chemistry, and materials science fields. Energy band gap engineering of graphene nanoribbons. The ability to control the width, edge structure, and dopant level with atomic precision has created a large class of accessible electronic landscapes for use in logic applications. There has been tremendous progress in designing and synthesizing graphene nanoribbons gnrs. Introduction graphene nanoribbons gnrs have onedimensional structures with hexagonal two.
Band gap of strained graphene nanoribbons springerlink. Both varieties of ribbons are shown to have band gaps. Finally, graphene nanoribbons that have been treated with a diaminopropane. Surface synthesis of atomically precise graphene nanoribbons. Graphene nanoribbons with smooth edges as quantum wires xinran wang, yijian ouyang, liying jiao, hailiang wang, liming xie, justin wu, jing guo, and hongjie dai supplementary information. Tuning the band gap of graphene nanoribbons synthesized. Graphene as a two dimensional material, is the single layer of graphite. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene nanostructures by. Dielsalder polymerization of acetal protected cyclopentadienone 3 yields the polyphenylene precursor 4. Mar 22, 2016 the demand for smaller and smaller electronic devices has led to great strides towards the use of novel materials like graphene. Sep 08, 2014 doped graphene nanoribbons with potential. Here we report a technique for modifying gnr band gaps via covalent selfassembly of a new species of molecular precursors. The electronic properties of graphene nanoflakes gnfs with embedded hexagonal boron nitride hbn domains are investigated by combined ab initio density functional theory calculations and machinelearning techniques. Energy and transport gaps in etched graphene nanoribbons article pdf available in semiconductor science and technology 2525.
Energy gap modulation of graphene nanoribbons by f. The synthesis of chocgnrs is depicted in figure 1a. The finite size effects on the electronic structure of graphene ribbons are studied using first principles density functional techniques. Energy gaps in zerodimensional graphene nanoribbons. Narrow graphene nanoribbons gnrs can exhibit a semiconducting behavior with a band gap due to quantum con. We report the energy level alignment evolution of valence and conduction bands of armchairoriented graphene nanoribbons agnr as their band gap shrinks with increasing width. Doping of graphene and graphene nanoribbons is relevant because, depending on the location of the dopants and their concentration, their physicochemical properties could be tuned and controlled. Graphene nanoribbons with smooth edges as quantum wires. Various microscopic studies of these novel structures showed a high tendency to selfassemble. Gaps tunable by electrostatic gates in strained graphene. Nonetheless, scientists have tried to tease them apart. Louie1,2, 1department of physics, university of california at berkeley, berkeley, california 94720, usa 2materials sciences division, lawrence berkeley national laboratory, berkeley, california 94720, usa received 29 june 2006. Ihn solid state physics laboratory, eth zurich, 8093 zurich, switzerland received 5 november 2008. A band gap can be created by patterning the 2d graphene into a nanometerwide graphene nanoribbon gnr.
Pdf energy gaps, magnetism, and electric field effects. Its realization remains a challenging problem, as the transformation of. A prerequisite for future graphene nanoribbon gnr applications is the ability to finetune the electronic band gap of gnrs. Graphene band gap heralds new electronics research. To extend the real applications, an energy gap is n eeded, which. Finite graphene nanoribbon gnr heterostructures host intriguing topological in gap states rizzo, d.
Energy gaps in graphene nanoribbons youngwoo son, 1,2marvin l. Quantum dots in graphene nanoribbons nano letters acs. Apr 18, 2016 graphene nanoribbons gnr also called nanographite ribbons carbon based material onedimensional structures with hexagonal two dimensional carbon lattices a derivative of graphene graphene ribbons were introduced as a theoretical model by mitsutaka fujita 9 10. Ihn solid state ph ysics l abor atory, eth zurich, 8093 zurich, switzerland. Energy gaps in zerodimensional graphene nanoribbons article in applied physics letters 914. By fabricating graphene in odd shapes, such as ribbons, band gaps up to 100 mev have been realised, but these are considered too small for electronics.
These states may be localized either at the bulk edges or at the ends of the structure. One of the most important features of graphene nanoribbons, from both basic science and application points of view, is their electrical band gap 1. Experimental observation of strong exciton effects in. One of the most recent advancements is the development of graphene nanoribbons gnrs layers of graphene with ultrathin width of less than 50 nm. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene nanostructures by lithographic processes. Quasi1d graphene nanoribbons are of interest due to the presence of an effective energy gap, overcoming the gap less band structure of graphene and leading to overall. It can also be considered as an indefinitely large aromatic molecule, the ultimate case of the family of. However, the lack of an energy band gap in graphene limits its use in logic applications.
Recent progress in fabrication techniques of graphene. Graphene nanostructures, where quantum confinement opens an energy gap in the band structure, hold promise for future electronic devices. Tunable halfmetallicity and edge magnetism of hsaturated. Cf bond is an ionic bond, while, cc bond displays a typical nonpolar covalent bonding feature. Reticular growth of graphene nanoribbon 2d covalent. Graphene devices operated at high sourcedrain bias show a saturating iv characteristic. Correlated topological states in graphene nanoribbon. Illustration of a pn junction in a heterostructure made of pristine. Graphene is a oneatomiclayer thick twodimensional material made of carbon atoms arranged in a honeycomb structure.
Graphene nanoribbons with smooth edges behave as quantum. Sep 16, 2014 the successful fabrication of single layered graphene has generated a great deal of interest and research into graphene in recent years. The one atom thin carbon film is ultralight, extremely flexible and highly conductive. Quasiparticle energies and band gaps in graphene nanoribbons. The energy gap difference between highest occupied molecular orbital homo and lowest unoccupied molecular orbital lumo dependence for finite width and length is computed for both armchair and zigzag ribbons and compared to their onedimensional. Simulation of energy band gap opening of graphene nano ribbons. The existence of curious materials called half metals is predicted.
Pdf energy and transport gaps in etched graphene nanoribbons. Graphene is the basic structural element of some carbon allotropes including graphite charcoal carbon nanotubes fullerence chemical structures. Jul 25, 2007 the finite size effects on the electronic structure of graphene ribbons are studied using first principles density functional techniques. Our study suggests the existence of three classes of energy gaps in multilayer armchair nanoribbons, and strong dependence of magnetic properties on the edge.
Geometric, electronic, and magnetic properties erjun kan, zhenyu li and jinlong yang university of science and technology of china, china 1. Charge transport mechanism in networks of armchair. Solid state physics laboratory, eth zurich, 8093 zurich, switzerland email. A new synthetic strategy toward novel linear twodimensional graphene nanoribbons up to 12 nm has been established. High resolution aberrationcorrected tem image of a high quality gnr. The energy gaps of the quasi0d graphene based systems, defined as the differences between lumo and homo energies, depend not only on the sizes of the hbn domains. The electronic properties of graphene zigzag nanoribbons with electrostatic potentials along the edges are investigated. Mar 24, 2016 graphene, the material with a number of miraculous properties, is considered a possible replacement. The temperature dependent conductance measurements show larger energy gaps opening for narrower ribbons. For bp, the environmental instability limits its application in nanoscale electronic and magnetic devices 15. Graphene quantum dots gqds hold great promise for applications in electronics, optoelectronics, and bioelectronics, but the fabrication of widely tunable gqds has remained elusive.
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