Effect of electron localization on the edge-state spins in a disordered network of nanographene sheets

Joly, Vincent; Takahara, Katsunori; Takai, Kazuyuki; Sugihara, Kō; Enoki, Toshiaki; Koshino, Mikito; Tanaka, Hidekazu

doi:10.1103/physrevb.81.115408

Cited by 49 publications

(43 citation statements)

References 37 publications

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“…Sharper peaks appear in all samples, with linewidth close to that for sigma dangling bond spins observed in nanoporous carbon materials (B0.1 mT) 41 . On the other hand, the broader peak, which is only observed in ba-GO, has a linewidth similar to that of localized spins originating from the edge of nanographene (B1 mT) 42,43 . The p-electron radical at the edges of graphene is delocalized along the edges to some extent, and exhibits fast spin-lattice relaxation through interaction with the adjacent p-electron system, giving rise to a broad linewidth in ESR.…”

Section: Figure 3 | Characterization Of Go and Ba-go Powder (A) Thermentioning

confidence: 91%

Probing the catalytic activity of porous graphene oxide and the origin of this behaviour

et al. 2012

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Graphene oxide, a two-dimensional aromatic scaffold decorated by oxygen-containing functional groups, possesses rich chemical properties and may present a green alternative to precious metal catalysts. Graphene oxide-based carbocatalysis has recently been demonstrated for aerobic oxidative reactions. However, its widespread application is hindered by the need for high catalyst loadings. Here we report a simple chemical treatment that can create and enlarge the defects in graphene oxide and impart on it enhanced catalytic activities for the oxidative coupling of amines to imines (up to 98% yield at 5 wt% catalyst loading, under solvent-free, open-air conditions). This study examines the origin of the enhanced catalytic activity, which can be linked to the synergistic effect of carboxylic acid groups and unpaired electrons at the edge defects. The discovery of a simple chemical processing step to synthesize highly active graphene oxide allows the premise of industrial-scale carbocatalysis to be explored.

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Section: Figure 3 | Characterization Of Go and Ba-go Powder (A) Thermentioning

confidence: 91%

Probing the catalytic activity of porous graphene oxide and the origin of this behaviour

et al. 2012

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“…Defects were present in all samples as deduced from the ESR signals, but their origin and type remains unknown. ESR has also been applied to different nanographitic structures with rather uncontrolled thickness distributions, where signals are interpreted in terms of vacancies, edge states and itinerant electrons [23,29,30,33,[44][45][46][47][48][49][50][51][52][53][54][55], but again the origin and type of the defects was unknown. Recently the first electrically detected ESR study on heavily doped graphene on SiC has been published [56] revealing a contrast in conductivity ∆σ/σ of about 0.5 % for the conduction electrons, which was used to pinpoint the strength of valley splitting in graphene on SiC.…”

Section: Introductionmentioning

confidence: 99%

Preferential antiferromagnetic coupling of vacancies in graphene onSiO2: Electron spin resonance and scanning tunneling spectroscopy

et al. 2014

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Monolayer graphene grown by chemical vapor deposition and transferred to SiO2 is used to introduce vacancies by Ar + ion bombardment at a kinetic energy of 50 eV. The density of defects visible in scanning tunneling microscopy (STM) is considerably lower than the ion fluence implying that most of the defects are single vacancies as expected from the low ion energy. The vacancies are characterized by scanning tunneling spectroscopy (STS) on graphene and HOPG. A peak close to the Dirac point is found within the local density of states of the vacancies similar the the peak found previously for vacancies on HOPG. The peak persists after air exposure up to 180 min, such that electron spin resonance (ESR) at 9.6 GHz can probe the vacancies exhibiting such a peak. After an ion flux of 10/nm 2 , we find an ESR signal corresponding to a g-factor of 2.001-2.003 and a spin density of 1-2 spins/nm 2 . The peak width is as small as 0.17 mT indicating exchange narrowing. Consistently, the temperature dependent measurements reveal antiferromagnetic correlations with a Curie-Weiss temperature of -10 K. Thus, the vacancies preferentially couple antiferromagnetically ruling out a ferromagnetic graphene monolayer at ion induced spin densities of 1 − 2/nm 2 .

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“…In our previous works concerning activated carbon fibers [2,3] and active carbon materials [15] EPR signals were almost the same as observed for RGO, with similar g values and temperature evolution. Three signals were ascribed to the three different paramagnetic centers: -line (1) from "pure" carbon (not in contact with adsorbed molecules), -line (2) from carbon interacting with molecules adsorbed at adsorption sites where adsorbed molecules get strongly immobilized at the surface, -line (3) from carbon at adsorption sites where adsorbed molecules show more "freedom" of rotational movements.…”

Section: Resultsmentioning

confidence: 93%

“…Especially interesting is the fact that the pure graphene layer shows ballistic conduction [1], while introduction of defects causes the strong electron localization, which can even lead to the magnetism of graphene-based materials [2]. The main source of defects is obviously the edge of a layer, with the zig-zag conformation generating the localized states [3,4]. Other atoms can attach to the graphene layer only at the defects, because the in-plane C-C bonds (σ bonds) are very strong and chemically inert.…”

Section: Introductionmentioning

confidence: 99%

EPR and Impedance Measurements of Graphene Oxide and Reduced Graphene Oxide

et al. 2017

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We report the observations of electron paramagnetic resonance and impedance measurements of graphene oxide and reduced graphene oxide performed in the wide temperature range in order to get insight into the electronic properties of graphene-based materials and the role of oxygen functionalities in the charge carrier transport phenomena. In such systems the strong spin localization, hopping charge carrier transport as well as the formation of adsorption layers are observed, all the phenomena changing significantly after the heavily oxidized graphene is reduced.

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Effect of electron localization on the edge-state spins in a disordered network of nanographene sheets

Cited by 49 publications

References 37 publications

Probing the catalytic activity of porous graphene oxide and the origin of this behaviour

Probing the catalytic activity of porous graphene oxide and the origin of this behaviour

Preferential antiferromagnetic coupling of vacancies in graphene onSiO2: Electron spin resonance and scanning tunneling spectroscopy

EPR and Impedance Measurements of Graphene Oxide and Reduced Graphene Oxide

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