A prerequisite for future graphene nanoribbon gnr applications is the ability to finetune the electronic band gap of gnrs. Twodimensional graphene nanoribbons journal of the. Graphene nanoribbons are among the recently discovered carbon nanostructures, with unique characteristics for novel applications. It can also be considered as an indefinitely large aromatic molecule, the ultimate case of the family of. Reticular growth of graphene nanoribbon 2d covalent. 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. This differs from the results of simple tightbinding calculations or solutions of the dirac. Its realization remains a challenging problem, as the transformation of. Energy gaps in graphene nanoribbons youngwoo son, 1,2marvin l. 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. 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. Graphene nanoribbons with controlled edge orientation have been fabricated by scanning tunneling microscope stm lithography. The sizes of these energy gaps are investigated by. Graphene nanoribbons gnrs, also called nano graphene ribbons or nanographite ribbons are strips of graphene with width less than 50 nm.
Ihn solid state physics laboratory, eth zurich, 8093 zurich, switzerland received 5 november 2008. Gap prediction in hybrid graphenehexagonal boron nitride. High resolution aberrationcorrected tem image of a high quality gnr. Correlated topological states in graphene nanoribbon. Electronic structure of graphene nanoribbons huseyin.
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. Based on a firstprinciples approach, we present scaling rules for the band gaps of graphene nanoribbons gnrs as a function of their widths. Graphene is the basic structural element of some carbon allotropes including graphite charcoal carbon nanotubes fullerence chemical structures. 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. 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. The energy gap in graphene is crucial for many applications.
The finite size effects on the electronic structure of graphene ribbons are studied using first principles density functional techniques. Graphene nanoribbons show promise for healing spinal injuries. Various microscopic studies of these novel structures showed a high tendency to selfassemble. Graphene as a two dimensional material, is the single layer of graphite. Energy gaps in zerodimensional graphene nanoribbons article in applied physics letters 914. Energy and transport gaps in etched graphene nanoribbons article pdf available in semiconductor science and technology 2525. One of the most recent advancements is the development of graphene nanoribbons gnrs layers of graphene with ultrathin width of less than 50 nm. This decrease in conductivity at high applied electric eld is described by carrier velocity saturation due to optical phonon emission. Graphene is a oneatomiclayer thick twodimensional material made of carbon atoms arranged in a honeycomb structure. 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 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. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene.
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. Highlights the electronic properties of graphene nanoribbons are studied for the fterminated instead of the hterminated by using the firstprinciples. Energy gap in graphene nanoribbons with structured. The existence of curious materials called half metals is predicted. To extend the real applications, an energy gap is n eeded, which. Energy and transport gaps in etched graphene nanoribbons f molitor, c stampfer, j guttinger, a jacobsen, t ihn and k ensslin. Competing gap opening mechanisms of monolayer graphene. Charge transport mechanism in networks of armchair.
Finally, graphene nanoribbons that have been treated with a diaminopropane. 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. Dielsalder polymerization of acetal protected cyclopentadienone 3 yields the polyphenylene precursor 4. Energy band gap engineering of graphene nanoribbons. Narrow graphene nanoribbons gnrs can exhibit a semiconducting behavior with a band gap due to quantum con. Such control requires the development of fabrication tools capable of precisely controlling width and edge geometry of gnrs at the atomic scale. Here we show that correlation effects not included in previous density functional simulations play a key role in these systems. Fterminated armchair graphene nanoribbons have lower band gaps than those of hterminated ones when they have the same band width. Color online band gap e g as a function of structural parameters of gnms. One of the most important features of graphene nanoribbons, from both basic science and application points of view, is their electrical band gap 1. Graphene nanoribbons with smooth edges as quantum wires. 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.
Experimental observation of strong exciton effects in. 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. We show that a structured external potential that acts within the edge regions of. Rationalizing and reconciling energy gaps and quantum confinement in narrow atomically precise armchair 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. For gnrs with zigzag shaped edges, gaps appear because of a staggered sublattice. Solutionsynthesized chevron graphene nanoribbons exfoliated.
The nanoribbons are characterized by ms, uvvis, and scanning tunneling microscopy stm. 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. 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. Technology exploration for graphene nanoribbon fets. Graphene nanoribbons improve compressed gas storage. Gaps tunable by electrostatic gates in strained graphene. Its fascinating electrical, optical, and mechanical properties ignited enormous interdisciplinary interest from the physics, chemistry, and materials science fields. The synthesis of chocgnrs is depicted in figure 1a. These states may be localized either at the bulk edges or at the ends of the structure. Quantum dots in graphene nanoribbons nano letters acs. Mar 24, 2016 graphene, the material with a number of miraculous properties, is considered a possible replacement.
Tunable halfmetallicity and edge magnetism of hsaturated. Computer simulations zhao with coworkers 19 performed simulations of deformation behaviors exhibited by graphene nanoribbons with various sizes under uniaxial tensile load. There has been tremendous progress in designing and synthesizing graphene nanoribbons gnrs. Diagram showing the transition from a direct band gap black to an indirect gap white in a graphene nanoribbon depending on the voltage applied to the left v l. 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. Energy gaps in graphene nanoribbons youngwoo son,1,2 marvin l. Sep 08, 2014 doped graphene nanoribbons with potential.
Energy bandgap engineering of graphene nanoribbons. However, the lack of an energy band gap in graphene limits its use in logic applications. Energy bandgap engineering of graphene nanoribbons nasaads. The temperature dependent conductance measurements show larger energy gaps opening for narrower ribbons. Graphene band gap heralds new electronics research. A band gap can be created by patterning the 2d graphene into a nanometerwide graphene nanoribbon gnr. Nonetheless, scientists have tried to tease them apart. 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. Here we report a technique for modifying gnr band gaps via covalent selfassembly of a new species of molecular precursors. Electronic states at energies in the gap are localized, and charge transport exhibits a tran. Dynamics of mechanical waves in periodic graphene nanoribbon. Graphene based devices offer high mobility for ballistic transport, high carrier.
The one atom thin carbon film is ultralight, extremely flexible and highly conductive. The gnrs considered have either armchair or zigzag shaped edges on both sides with hydrogen passivation. Regular graphene has no band gap its unusually rippled valence and conduction bands actually meet in places, making it more like a metal. The electronic properties of graphene zigzag nanoribbons with electrostatic potentials along the edges are investigated. Ihn solid state ph ysics l abor atory, eth zurich, 8093 zurich, switzerland. Mar 22, 2016 the demand for smaller and smaller electronic devices has led to great strides towards the use of novel materials like graphene. Suppression of electronvibron coupling in graphene.
Several methods to open a band gap in graphene have been developed, including doping, hydrogenation, and fabrication of nanoribbons, nanomeshes and nanorings. For bp, the environmental instability limits its application in nanoscale electronic and magnetic devices 15. Band gap of strained graphene nanoribbons springerlink. Geometric, electronic, and magnetic properties erjun kan, zhenyu li and jinlong yang university of science and technology of china, china 1. Energy gaps in zerodimensional graphene nanoribbons. 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. Finite graphene nanoribbon gnr heterostructures host intriguing topological in gap states rizzo, d. Extraction of e g for the high quality gnr devices using negf simulation.
Jul 25, 2007 the finite size effects on the electronic structure of graphene ribbons are studied using first principles density functional techniques. 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. Graphene nanostructures, where quantum confinement opens an energy gap in the band structure, hold promise for future electronic devices. Pdf energy and transport gaps in etched graphene nanoribbons. Abstract we investigate electronic transport in lithographically patterned graphene ribbon structures. Graphene nanoribbons 18 display unique electronic properties based on truly twodimensional 2d graphene 9 with potential applications in nanoelectronics 10,11. 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. Both varieties of ribbons are shown to have band gaps.
Low temperature and temperaturedependent measurements reveal a length and orientationindependent transport gap whose size is inversely proportional to gnr width. Pdf energy gap in graphene nanoribbons with structured. Energy gap modulation of graphene nanoribbons by f. Graphene nanoribbons with smooth edges behave as quantum. Surface synthesis of atomically precise graphene nanoribbons. 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. This differs from the results of simple tightbinding calculations or solutions of the. Widthdependent band gap in armchair graphene nanoribbons. Recent progress in fabrication techniques of graphene. 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. Quasiparticle energies and band gaps in graphene nanoribbons li yang,1,2 cheolhwan park,1,2 youngwoo son,3 marvin l. Energy band gap engineering of graphene nanoribbons melinda y. Graphene ribbons were introduced as a theoretical model by mitsutaka fujita and coauthors to examine the edge and nanoscale size effect in graphene.
Solid state physics laboratory, eth zurich, 8093 zurich, switzerland email. 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. Pdf energy gaps, magnetism, and electric field effects. It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. Experiments verified that energy gaps increase with decreasing gnr width. 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. Cf bond is an ionic bond, while, cc bond displays a typical nonpolar covalent bonding feature. 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. 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. September, 2008 graphite is a known material to human kind for centuries as the lead of a pencil. A new synthetic strategy toward novel linear twodimensional graphene nanoribbons up to 12 nm has been established.
Illustration of a pn junction in a heterostructure made of pristine. Simulation of energy band gap opening of graphene nano ribbons. Chapter 4 electrical properties of graphene wrinkles and. 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. Tuning the band gap of graphene nanoribbons synthesized. Introduction graphene nanoribbons gnrs have onedimensional structures with hexagonal two. 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. 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. 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. 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. Graphene quantum dots gqds hold great promise for applications in electronics, optoelectronics, and bioelectronics, but the fabrication of widely tunable gqds has remained elusive. Dec 14, 2015 graphene nanoribbons gnrs are a new class of materials that have promising applications in nextgeneration nanoelectronic and optoelectronic devices 1,2,3. The sizes of these energy gaps are investigated by measuring the conductance in the nonlinear response regime at low temperatures. Quasiparticle energies and band gaps in graphene nanoribbons.
Our study suggests the existence of three classes of energy gaps in multilayer armchair nanoribbons, and strong dependence of magnetic properties on the edge. 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. The carboncarbon bond length in graphene is about 0. Energy gap opening by crossing drop cast singlelayer. Ultranarrow metallic armchair graphene nanoribbons nature. 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.
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