Room-temperature ferromagnetism of graphene.
TL;DR: The experimental results on the ferromagnetism of graphene-based materials at room temperature are reported and it is believed that the observed room-temperature ferromagnetic properties are believed to come from the defects on graphene.
Abstract: Aiming at molecular-based magnets, ferromagnetism of pure carbon-based materials is fundamentally and technologically extremely important for many applications. While it is still not fully understood, many recent theoretical works have suggested that one-atom-thick two-dimensional graphene materials may show ferromagnetism due to the existence of various defects or topological structures as the spin units and the possible long-range ordered coupling among them. Here, we report the experimental results on the ferromagnetism of graphene-based materials at room temperature. The observed room-temperature ferromagnetism is believed to come from the defects on graphene.
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TL;DR: The status of graphene research is presented, which includes aspects related to synthesis, characterization, structure, and properties.
Abstract: Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.
3,513 citations
TL;DR: In this article, the present knowledge about point and line defects in graphene are reviewed and particular emphasis is put on the unique ability of graphene to reconstruct its lattice around intrinsic defects, leading to interesting effects and potential applications.
Abstract: Graphene is one of the most promising materials in nanotechnology. The electronic and mechanical properties of graphene samples with high perfection of the atomic lattice are outstanding, but structural defects, which may appear during growth or processing, deteriorate the performance of graphene-based devices. However, deviations from perfection can be useful in some applications, as they make it possible to tailor the local properties of graphene and to achieve new functionalities. In this article, the present knowledge about point and line defects in graphene are reviewed. Particular emphasis is put on the unique ability of graphene to reconstruct its lattice around intrinsic defects, leading to interesting effects and potential applications. Extrinsic defects such as foreign atoms which are of equally high importance for designing graphene-based devices with dedicated properties are also discussed.
2,828 citations
Cites background from "Room-temperature ferromagnetism of ..."
...In addition to polymerized fullerenes,(120) nanotubes,(121) graphite,(122) and nanodiamonds,(123) magnetism was recently reported for graphene produced from graphene oxide.(124) On the basis of calculations, the observed magnetic behavior in all these systems was explained in terms of defects in the graphitic network (either native or produced by ion irradiation) such as under-coordinated carbon atoms, for example, vacancies,(125) interstitials,(126) carbon adatoms,(47) and atoms at the edges of graphitic nanofragments with dangling bonds either passivated with hydrogen atoms or free....
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TL;DR: In this article, the density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides with hydrazine or heat treatment.
Abstract: The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...
1,033 citations
TL;DR: In this paper, a review of magnetic properties of spintronic devices based on carbon nanofragments and graphite is presented, with the help of computational examples based on simple model Hamiltonians.
Abstract: Magnetic materials and nanostructures based on carbon offer unique opportunities for future technological applications such as spintronics. This paper reviews graphene-derived systems in which magnetic correlations emerge as a result of reduced dimensions, disorder and other possible scenarios. In particular, zero-dimensional graphene nanofragments, one-dimensional graphene nanoribbons and defect-induced magnetism in graphene and graphite are covered. Possible physical mechanisms of the emergence of magnetism in these systems are illustrated with the help of computational examples based on simple model Hamiltonians. In addition, this review covers spin-transport properties, proposed designs of graphene-based spintronic devices, magnetic ordering at finite temperatures as well as the most recent experimental achievements.
981 citations
Cites background from "Room-temperature ferromagnetism of ..."
...The value of this approach has already been demonstrated by the proposal of reconfigurable spintronic logic gates exploiting the strong antiferromagnetic couplings in the bowtie-shaped graphene fragments (Wang et al., 2009a)....
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...Room-temperature magnetic hysteresis has also been reported for graphene samples produced in bulk quantities from graphite using the chemical approaches (Matte et al., 2009; Wang et al., 2009b)....
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...The zeroenergy states are spatially segregated in the two triangular parts of the molecule (Wang et al., 2009a)....
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TL;DR: Li et al. as discussed by the authors reported that highly disordered graphene nanosheets can find promising applications in high-capacity Li ion batteries because of their exceptionally high reversible capacities and good cyclic stability.
Abstract: Graphene has aroused intensive interest because of its unique structure, superior properties, and various promising applications. Graphene nanostructures with significant disorder and defects have been considered to be poor materials because disorder and defects lower their electrical conductivity. In this paper, we report that highly disordered graphene nanosheets can find promising applications in high-capacity Li ion batteries because of their exceptionally high reversible capacities (794−1054 mA h/g) and good cyclic stability. To understand the Li storage mechanism of graphene nanosheets, we have prepared graphene nanosheets with structural parameters tunable via different reduction methods including hydrazine reduction, low-temperature pyrolysis, and electron beam irradiation. The effects of these parameters on Li storage properties were investigated systematically. A key structural parameter, Raman intensity ratio of D bands to G bands, has been identified to evaluate the reversible capacity. The gr...
944 citations
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TL;DR: Monocrystalline graphitic films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands and they exhibit a strong ambipolar electric field effect.
Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.
55,532 citations
26,456 citations
TL;DR: This study reports an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation and reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions.
Abstract: Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.
18,958 citations
TL;DR: In this paper, a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high surface area carbon material which consists of thin graphene-based sheets.
12,756 citations
TL;DR: It is reported that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization, making it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.
Abstract: Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.
8,534 citations