Enhanced Half-Metallicity in Edge-Oxidized Zigzag Graphene Nanoribbons (original) (raw)
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Spin Dependent Electronic Transport in Edge Oxidized Zigzag Graphene Nanoribbon
Materials Today: Proceedings, 2018
In this work, we calculated spin dependent electronic transport properties of edge oxidized zigzag graphene nanoribbon (ZGNR). Three types of O-ZGNR structures were considered. In one, the edge states of the graphene nanoribbon were fully oxidized while the partial oxidation of the edge states was considered in the others. Simulation results, using density functional theory (DFT), revealed that the first configuration had no significant spin polarization effect. To the contrary, the other configurations had effect of spin polarization on the transport properties in both parallel and anti-parallel configurations. Total energy for non-magnetic, ferromagnetic and antiferromagnetic state is calculated to predict the ground state of the corresponding configuration. Spin polarization is estimated to assess the application of the considered structures in spintronics.
Edge reconstructions induce magnetic and metallic behavior in zigzag graphene nanoribbons
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The edge reconstructions of zigzag graphene nanoribbons with one and two lines of alternating fused five and seven membered rings along one edge with hydrogen passivation are studied using first principles density functional theory. Reconstructions on one edge stabilize the systems in a metallic ground state with finite magnetic moment. The reconstructed edge suppresses the local spin density of atoms and contributes a finite density of states at the Fermi energy. Our study shows the possibilities of fabricating the metallic electrodes for semiconducting graphene devices with full control over their magnetic behavior without any lattice mismatch between leads and the channel.
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In this study, we investigate the electronic and magnetic properties of graphane nanoribbons. We find that zigzag and armchair graphane nanoribbons with H-passivated edges are nonmagnetic semiconductors. While bare armchair nanoribbons are also nonmagnetic, adjacent dangling bonds of bare zigzag nanoribbons have antiferromagnetic ordering at the same edge. Band gaps of the Hpassivated zigzag and armchair nanoribbons exponentially depend on their width. Detailed analysis of adsorption of C, O, Si, Ti, V, Fe, Ge and Pt atoms on the graphane ribbon surface reveal that functionalization of graphane nanoribbons is possible via these adatoms. It is found that C, O, V and Pt atoms have tendency to replace H atoms of graphane. We showed that significant spin polarizations in graphane can be achieved through creation of domains of H-vacancies and CH-divacancies.
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The electronic and magnetic properties of varying width, oxygen functionalized armchair graphene nanoribbons (AGNRs) are investigated using first-principles density functional theory (DFT). Our study shows that O-passivation results in a rich geometrical environment which in turn determines the electronic and magnetic properties of the AGNR. For planar systems a degenerate magnetic ground state, arising from emptying of O lone-pair electrons, is reported. DFT predicts ribbons with ferromagnetic coupling to be metallic whereas antiferromagnetically coupled ribbons present three band gap families: one metallic and two semiconducting. Unlike hydrogen functionalized AGNRs, the oxygen functionalized ribbons can attain a lower energy configuration by adopting a non-planar geometry. The non-planar structures are non-magnetic and show three semiconducting families of band gap behavior. Quasiparticle corrections to the DFT results predict a widening of the band gaps for all planar and non-planar, semiconducting systems. This suggests that oxygen functionalization could be used to manipulate the electronic structures of AGNRs.
Physical Review B, 2013
We report the results of first-principles calculations for the atomic, electronic, and magnetic properties of the Co atoms embedded in divacancy defects in graphene nanoribbons with zigzag-shaped edges. We find that the edges play an important role in the stabilization of a Co-divacancy complex near the edge, where the edge C atoms undergo large relaxations, resulting in a tilted-edge structure. When Co is positioned in the middle of the ribbon, the edge C atoms generally remain on the sheet, forming a flat-edge structure due to the small edge effect. The spin polarization of the edges is determined by two bipartite lattices separated by the Co atom. When a Co-divacancy pair is formed near the same edge, the edge structure is significantly modified. The magnetic interaction between the Co atoms is either ferromagnetic or antiferromagnetic, depending on the relative positions of the Co atoms, and its magnetic ordering can be described by the combined effect of the bipartite lattices formed around individual Co atoms.
Intrinsic Half-Metallicity in Modified Graphene Nanoribbons
Physical Review Letters, 2009
We perform first-principles calculations based on density functional theory to study quasi one-dimensional edge-passivated (with hydrogen) zigzag graphene nanoribbons (ZGNRs) of various widths with chemical dopants, boron and nitrogen, keeping the whole system isoelectronic. Gradual increase in doping concentration takes the system finally to zigzag boron nitride nanoribbons (ZBNNRs). Our study reveals that, for all doping concentrations the systems stabilize in anti-ferromagnetic ground states. Doping concentrations and dopant positions regulate the electronic structure of the nanoribbons, exhibiting both semiconducting and half-metallic behaviors as a response to the external electric field. Interestingly, our results show that ZBNNRs with terminating polyacene unit exhibit half-metallicity irrespective of the ribbon width as well as applied electric field, opening a huge possibility in spintronics device applications.
Ferromagnetism in Graphene Nanoribbons: Split versus Oxidative Unzipped Ribbons
Nano Letters, 2012
Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons (GNRs), and (b) oxidative unzipped and chemically converted graphene nanoribbons (CCGNRs) were investigated for their magnetic properties using the combination of static magnetization and electron spin resonance measurements. The two types of ribbons possess remarkably different magnetic properties. While the low temperature ferromagnet-like feature is observed in both types of ribbons, such room temperature feature persists only in potassium-split ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a 'positive exchange bias'. Electron spin resonance measurements infer that the carbon related defects may responsible for the observed magnetic behaviour in both types of ribbons. Furthermore, proton hyperfine coupling strength has been obtained from hyperfine sublevel correlation experiments performed on the GNRs. Electron spin resonance provides no indications for the presence of potassium (cluster) related signals, emphasizing the intrinsic magnetic nature of the ribbons. Our combined experimental results may infer the coexistence of ferromagnetic clusters with anti-ferromagnetic regions leading to disordered magnetic phase. We discuss the origin of the observed contrast in the magnetic behaviours of these two types of ribbons.
Half-metallicity in graphene nanoribbons with topological defects at edge
The Journal of Chemical Physics, 2012
First-principles calculations have been performed to investigate the electronic properties of graphene nanoribbons with topological line defects composed of octagons and fused pentagons. We find that the edge-passivated zigzag graphene nanoribbons (ZGNRs) with the line defects along the edge show half-metallicity as the line defect is close to one edge. The electronic properties of the ZGNRs with line defects can be tuned by changing the ribbon width and the position of the line defect. When the position of the line defect changes, there are transitions from an antiferromagnetic semiconductor to an antiferromagnetic half-metal, and then to a ferromagnetic metal, suggesting the potential applications of the system in spintronic devices.
Edge-functionalized and substitutionally doped graphene nanoribbons: Electronic and spin properties
Physical Review B, 2008
Graphene nanoribbons are the counterpart of carbon nanotubes in graphene-based nanoelectronics. We investigate the electronic properties of chemically modified ribbons by means of density functional theory. We observe that chemical modifications of zigzag ribbons can break the spin degeneracy. This promotes the onset of a semiconducting-metal transition, or of a half-semiconducting state, with the two spin channels having a different band gap, or of a spin-polarized half-semiconducting state, where the spins in the valence and conduction bands are oppositely polarized. Edge functionalization of armchair ribbons gives electronic states a few eV away from the Fermi level and does not significantly affect their band gap. N and B produce different effects, depending on the position of the substitutional site. In particular, edge substitutions at low density do not significantly alter the band gap, while bulk substitution promotes the onset of semiconducting-metal transitions. Pyridinelike defects induce a semiconducting-metal transition.