Electronic and magnetic properties of graphane nanoribbons (original) (raw)

Graphane Nanoribbons: A Theoretical Study

Arxiv preprint arXiv:1001.4407, 2010

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.

Electronic and magnetic structure of graphene nanoribbons

This review covers some of the basic theoretical aspects of the electronic and magnetic structure of graphene nanoribbons, starting from the simplest tight-binding models to the more sophisticated ones where the electron-electron interactions are considered at various levels of approximation. Nanoribbons can be classified into two basic categories, armchair and zigzag, according to their edge termination, which determines profoundly their electronic structure. Magnetism, as a result of the interactions, appears in perfect zigzag ribbons as well as in armchair ribbons with vacancies and defects of different types.

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.

On-surface synthesis of graphene nanoribbons with zigzag edge topology

Nature, 2016

Graphene-based nanostructures exhibit a vast range of exciting electronic properties that are absent in extended graphene. For example, quantum confinement in carbon nanotubes and armchair graphene nanoribbons (AGNRs) leads to the opening of substantial electronic band gaps that are directly linked to their structural boundary conditions 1,2. Even more intriguing are nanostructures with zigzag edges, which are expected to host spin-polarized electronic edge states and can thus serve as key elements for graphene-based spintronics 3. The most prominent example is zigzag graphene nanoribbons (ZGNRs) for which the edge states are predicted to couple ferromagnetically along the edge and antiferromagnetically between them 4. So far, a direct observation of the spin-polarized edge states for specifically designed and controlled zigzag edge topologies has not been achieved. This is mainly due to the limited precision of current top-down approaches 5-10 , which results in poorly defined edge structures. Bottom-up fabrication approaches, on the other hand, were so far only

Role of Vacancies in Zigzag Graphene Nanoribbons: An Ab Initio Study

Journal of Nano Research, 2014

We have studied the effects of vacancies on the structural, electronic and magnetic properties of zigzag-edged graphene nanoribbons (ZGNRs). Our calculations were carried out using an abinitio density functional pseudopotential computational method combined with the generalized gradient approximation for the exchange-correlation functional. The equilibrium geometries, electronic charge spin density distributions, electronic band structures, and magnetic moments were examined in the presence of single vacancy and double vacancies. Structural optimization showed that vacancies induce substantial structural changes in ZGNRs. We found that introducing vacancies into ZGNR changes the spatial distribution of neighbor atoms, particularly those located around the vacancies. Our calculations showed that the vacancies have significant effect on the magnetization of ZGNR. The calculations showed that the changes in the structural geometry, the electronic structure and the magnetization of ZGNR...

Graphene nanoribbons with mixed cove-cape-zigzag edge structure

Carbon, 2021

A recently developed bottom-up synthesis strategy enables the fabrication of graphene nanoribbons with well-defined width and non-trivial edge structures from dedicated molecular precursors. Here we discuss the synthesis and properties of zigzag nanoribbons (ZGNRs) modified with periodic cove-capecove units along their edges. Contrary to pristine ZGNRs, which show antiferromagnetic correlation of their edge states, the edge-modified ZGNRs exhibit a finite single particle band gap without localized edge states. We report the on-surface synthesis of such edge-modified ZGNRs and discuss tunneling conductance dI/dV spectra and dI/dV spatial maps that reveal a noticeable localization of electronic states at the cape units and the opening of a band gap without presence of edge states of magnetic origin. A thorough ab initio investigation of the electronic structure identifies the conditions under which antiferromagnetically coupled, edge-localized states reappear in the electronic structure. Further modifications of the ribbon structure are proposed that lead to an enhancement of such features, which could find application in nanoelectronics and spintronics.

Spin-transport selectivity upon Co adsorption on antiferromagnetic graphene nanoribbons

The Journal of Chemical Physics, 2010

We investigate from first principles the electronic and transport properties of zigzag graphene nanoribbons in the presence of Co adatoms. Comparing different adsorption sites across the width, we find that the Co-C coupling is rather sensitive to the local environment. While a net spin polarization appears in all cases, the spin filtering effect is significantly enhanced when the Co adatom is at the edge, where the adsorption energy is maximized and a partial suppression of edge-associated transport channels occurs. We also probe the magnetic interaction in the nonbonding regime, for Co-graphene nanoribbon ͑GNR͒ distances ranging from adsorption totypical configurations. Our results indicate that Co-GNR coupling is still appreciable in an intermediate range, whereas it becomes vanishingly small in the limit ofdistances.

Spin-asymmetric graphene nanoribbons in graphane on silicon dioxide

Physical Review B, 2011

Hydrogenated graphene, graphane, is studied on oxygen-terminated silicon dioxide substrate using ab initio calculations. A structure with hydrogenation only on one side of the graphene layer is found stable and its hydrogen configurations are presented. Additionally, we form zigzag graphene nanoribbons by selectively removing hydrogens from the epitaxial graphane layer. In these ribbons, the spin degeneracy of the freestanding antiferromagnetic zigzag ribbons is broken, and band gaps of different magnitude emerge for the opposite spin species. This degeneracy breaking is due to a charge imbalance in the substrate below the ribbon, introduced through the asymmetric alignment of the substrate atoms with respect to the edges of the graphene ribbon.

Enhanced Half-Metallicity in Edge-Oxidized Zigzag Graphene Nanoribbons

Nano Letters, 2007

We present a novel comprehensive first-principles theoretical study of the electronic properties and relative stabilities of edge-oxidized zigzag graphene nanoribbons. The oxidation schemes considered include hydroxyl, carboxyl, ether, and ketone groups. Using screened exchange density functional theory, we show that these oxidized ribbons are more stable than hydrogen-terminated nanoribbons except for the case of the etheric groups. The stable oxidized configurations maintain a spin-polarized ground state with antiferromagnetic ordering localized at the edges, similar to the fully hydrogenated counterparts. More important, edge oxidation is found to lower the onset electric field required to induce half-metallic behavior and extend the overall field range at which the systems remain half-metallic. Once the half-metallic state is reached, further increase of the external electric field intensity produces a rapid decrease in the spin magnetization up to a point where the magnetization is quenched completely. Finally, we find that oxygen containing edge groups have a minor effect on the energy difference between the antiferromagnetic ground state and the above-lying ferromagnetic state.