Electronic and Magnetic Properties of Zigzag Graphene Nanoribbons on the (111) Surface of Cu, Ag, and Au

Li, Yan; Zhang, Wei; Morgenstern, Markus; Mazzarello, Riccardo

doi:10.1103/physrevlett.110.216804

Cited by 69 publications

(79 citation statements)

References 44 publications

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“…In the case of infinite zigzag ribbons, binding between unhydrogenated edge carbon atoms and Au(111) has been predicted. 36 This causes curving of the ribbon and quenches the edge magnetization.…”

Section: Different Edge Hydrogenation Patternsmentioning

confidence: 99%

Electronic states in finite graphene nanoribbons: Effect of charging and defects

et al. 2013

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Ijäs, M.; Ervasti, M.; Uppstu, Christer; Liljeroth, Peter; van der Lit, J.; Swart, I.; Harju, A. We study the electronic structure of finite armchair graphene nanoribbons using density-functional theory and the Hubbard model, concentrating on the states localized at the zigzag termini. We show that the energy gaps between end-localized states are sensitive to doping, and that in doped systems, the gap between the end-localized states decreases exponentially as a function of the ribbon length. Doping also quenches the antiferromagnetic coupling between the end-localized states leading to a spin-split gap in neutral ribbons. By comparing dI/dV maps calculated using the many-body Hubbard model, its mean-field approximation and density-functional theory, we show that the use of a single-particle description is justified for graphene π states in case spin properties are not the main interest. Furthermore, we study the effect of structural defects in the ribbons on their electronic structure. Defects at one ribbon terminus do not significantly modify the electronic states localized at the intact end. This provides further evidence for the interpretation of a multipeak structure in a recent scanning tunneling spectroscopy (STS) experiment resulting from inelastic tunneling processes [van der Lit et al., Nat. Commun. 4, 2023]. Finally, we show that the hydrogen termination at the flake edges leaves identifiable fingerprints on the positive bias side of STS measurements, thus possibly aiding the experimental identification of graphene structures. Electronic states in finite graphene nanoribbons: Effect of charging and defects

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Section: Different Edge Hydrogenation Patternsmentioning

confidence: 99%

Electronic states in finite graphene nanoribbons: Effect of charging and defects

et al. 2013

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“…However, the random orientation of the edges and the influence of a possible strong edge-substrate hybridization 21 did not allow full access to the nature of edge-magnetism in graphene. Though the 4 magnetic order is expected to persist to some extent on zigzag segments of randomly oriented graphene edges, the mixing of different edge types are expected to substantially weaken the effect 19,22 .…”

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confidence: 99%

“…The direct cutting of graphene is done by the beam- Using the STM nanolithographic technique, we have defined nanoribbons into chemical vapor deposition grown graphene sheets on gold substrates with large Au (111) terraces. Au (111) was predicted to be one of the few substrates preserving edge magnetism in supported graphene ribbons 21 . Nanoribbons with pre-defined armchair or zigzag edge orientation and widths ranging down to 3 nm have been defined (Fig.1).…”

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confidence: 99%

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Magda

Jin

Hagymási

et al. 2014

Nature

698

627

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Magnetic order emerging in otherwise non-magnetic materials as carbon is a paradigmatic example of a novel type of s-p electron magnetism predicted to be of exceptional hightemperature stability 1 . It has been demonstrated that atomic scale structural defects of graphene can host unpaired spins 2,3 . However, it is still unclear under which conditions longrange magnetic order can emerge from such defect-bound magnetic moments. Here we propose that in contrast to random defect distributions, atomic scale engineering of graphene edges with specific crystallographic orientation -comprising edge atoms only from one sublattice of the bipartite graphene lattice -can give rise to a robust magnetic order. We employ a nanofabrication technique 4 based on Scanning Tunneling Microscopy to define graphene nanoribbons with nanometer precision and well-defined crystallographic edge orientations.While armchair ribbons display quantum confinement gap, zigzag ribbons narrower than 7 nm reveal a bandgap of about 0.2 -0.3 eV, which can be identified as a signature of 2 interaction induced spin ordering along their edges. Moreover, a semiconductor to metal transition is revealed upon increasing the ribbon width, indicating the switching of the magnetic coupling between opposite ribbon edges from antiferromagnetic to ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hope for graphene-based spintronic devices operating under ambient conditions.The intrinsic magnetism of graphite has a long and controversial history 1 . The origin of the measured magnetic signal is generally attributed to atomic scale structural defects locally breaking the sub-lattice balance of the bipartite hexagonal lattice 5,6 . However, the unambiguous identification of the structural sources of the measured magnetic signal has proven challenging as they are buried inside the bulk of the material. The isolation of single graphene layers 7 opens new prospects in this direction 8,9 as their atomic structure is fully accessible for imaging and controlled modification. In particular, graphene edges of specific (zigzag) crystallographic orientation comprising carbon atoms from only one sub-lattice of the bipartite hexagonal lattice are predicted to host magnetic order 10 , in striking contrast to armchair edges incorporating an equal number of carbon atoms from both sublattices.The strong influence of edge orientation on the electronic structure of graphene nanoribbons had However, the random orientation of the edges and the influence of a possible strong edge-substrate hybridization 21 did not allow full access to the nature of edge-magnetism in graphene. Though the 4 magnetic order is expected to persist to some extent on zigzag segments of randomly oriented graphene edges, the mixing of different edge types are expected to substantially weaken the effect 19,22 . Therefore, the lack of experimental control over the edge orientation seems one of the main ...

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“…They play an important role in the electronic transport and in the magnetic properties of lowdimensional materials [1][2][3][4]. Their existence has long been related to the microscopic details of the edge of the crystal [5][6][7].…”

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Orbital Edge States in a Photonic Honeycomb Lattice

et al. 2017

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We experimentally reveal the emergence of edge states in a photonic lattice with orbital bands. We use a two-dimensional honeycomb lattice of coupled micropillars whose bulk spectrum shows four gapless bands arising from the coupling of p-like photonic orbitals. We observe zero-energy edge states whose topological origin is similar to that of conventional edge states in graphene. Additionally, we report novel dispersive edge states that emerge not only in zigzag and bearded terminations, but also in armchair edges. The observations are reproduced by tight-binding and analytical calculations. Our work shows the potentiality of coupled micropillars in elucidating some of the electronic properties of emergent 2D materials with orbital bands.Boundary modes are a fundamental property of finitesize crystals. They play an important role in the electronic transport and in the magnetic properties of lowdimensional materials [1][2][3][4]. Their existence has long been related to the microscopic details of the edge of the crystal [5][6][7]. Recent advances in the study of topological physics have revealed that, for topologically nontrivial materials, the existence of surface states is directly related to the properties of the bulk [8][9][10]. This is the case of conduction electrons in graphene [11][12][13], in which the nearest neighbor coupling of the cylindrically symmetric p z orbitals of the carbon atoms gives rise to two bands (here labeled s-bands) crossing in an ungapped spectrum (Dirac cones). The localized edge modes in this system exist for any type of terminations except for armchair [14,15]. They are topologically protected by the chiral symmetry of the honeycomb lattice, and their existence can be predicted by calculating the winding number of the bulk wavefunctions [11][12][13].In 2007, Wu and co-workers proposed an orbital version of graphene by considering a honeycomb lattice with p x,y orbitals in each lattice site [16,17]. The strong spatial anisotropy of the orbitals results in four ungapped bands with distinct features: two bands showing Dirac crossings and two flat bands, which were first reported experimentally in a polariton-based photonic simulator [18]. The interest in this kind of orbital Hamiltonians has taken a new thrust due to the rapid emergence of 2D materials [19], such as black phosphorus [20][21][22] and 2D transition metal dichalcogenides [23], whose bands originate from spatially anisotropic atomic orbitals. Edge states in MoS 2 flakes have been observed [24], and recent works aim at quantifying their impact in the transport properties [25]. Edge states in orbital modes have also been studied theoretically in connection to d-wave superconductivity [11,26] and spin-orbit coupling in superlattices of nanocrystals [27], systems very hard to realize experimentally with tuneable parameters. A photonic simulator of orbital bands, would open the door to the study of the microscopic properties of orbital edge states [28] and the connection to the topological properties of orbital bulk bands. I...

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Electronic and Magnetic Properties of Zigzag Graphene Nanoribbons on the (111) Surface of Cu, Ag, and Au

Cited by 69 publications

References 44 publications

Electronic states in finite graphene nanoribbons: Effect of charging and defects

Electronic states in finite graphene nanoribbons: Effect of charging and defects

Room-temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Orbital Edge States in a Photonic Honeycomb Lattice

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