Optical Spectroscopy Investigation of the Structural and Electrical Evolution of Controllably Oxidized Graphene by a Solution Method
04 May 2012-Journal of Physical Chemistry C (American Chemical Society)-Vol. 116, Iss: 19, pp 10702-10707
TL;DR: In this paper, a precisely controlled chemical modification of exfoliated graphene on a substrate was achieved by solution-phase oxidation, which exhibited an energy band gap of 2 eV.
Abstract: A precisely controlled chemical modification of exfoliated graphene on a substrate was achieved by solution-phase oxidation. The structural and electrical evolution of graphene induced by oxygen-related defects was investigated using micro-Raman and photoluminescence spectroscopy. The sp2-hybrid carbon network in monolayer graphene was found to gradually decrease with increasing degree of oxidation. The size of the graphene quantum dots was finally reduced to about 1 nm, which exhibited an energy band gap of 2 eV. The double-layer graphene showed a symmetry breaking induced by the defects. The process of solution modification may provide a facile method to tailor the electrical properties of graphene on a chip for constructing carbon-based nanoelectronics.
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6 citations
TL;DR: In this article, an X-ray photoelectron spectroscopy (XPS) study of two graphene-based devices that were analyzed by imposing a significant current under +3 V bias was conducted.
Abstract: We report on an X-ray photoelectron spectroscopy (XPS) study of two graphene based devices that were analyzed by imposing a significant current under +3 V bias. The devices were fabricated as graphene layers(s) on hexagonal SiC substrates, either on the C- or Si-terminated faces. Position dependent potential distributions (IR-drop), as measured by variations in the binding energy of a C1s peak are observed to be sporadic for the C-face graphene sample, but very smooth for the Si-face one, although the latter is less conductive. We attribute these sporadic variations in the C-face device to the incomplete electrical decoupling between the graphene layer(s) with the underlying buffer and/or substrate layers. Variations in the Si2p and O1s peaks of the underlayer(s) shed further light into the electrical interaction between graphene and other layers. Since the potential variations are amplified only under applied bias (voltage-contrast), our methodology gives unique, chemically specific electrical information that is difficult to obtain by other techniques.
6 citations
Dissertation•
16 Oct 2019
TL;DR: In this article, a technique based on microscopie optique optique sur substrats antireflets (BALM) is proposed, based on the utilisation originale de couches antiresflets tres minces (2-5 nm) and fortement absorbantes (metalliques) and evaluated les merites of this technique for l'etude des materiaux 2D and de leur reactivite chimique.
Abstract: La microscopie optique sur substrats antireflets est un outil de caracterisation simple et puissant qui a notamment permis l'isolation du graphene en 2004. Depuis, le domaine d'etude des materiaux bidimensionnels (2D) s'est rapidement developpe, tant au niveau fondamental qu'applique. Ces materiaux ultraminces presentent des inhomogeneites (bords, joints de grains, multicouches, etc.) qui impactent fortement leurs proprietes physiques et chimiques. Ainsi leur caracterisation a l'echelle locale est primordiale. Cette these s'interesse a une technique recente de microscopie optique a fort contraste, nommee BALM, basee sur l'utilisation originale de couches antireflets tres minces (2-5 nm) et fortement absorbantes (metalliques). Elle a notamment pour but d'evaluer les merites de cette technique pour l'etude des materiaux 2D et de leur reactivite chimique. Ainsi, les differents leviers permettant d'ameliorer les conditions d'observation des materiaux 2D ont tout d'abord ete etudies et optimises pour deux materiaux modeles : l'oxyde de graphene et les monocouches de MoS₂. L'etude de la dynamique de depot de couches moleculaires a notamment permis de montrer a la fois l'extreme sensibilite de BALM pour ce type de mesures et l'apport significatif des multicouches antireflets pour l'augmentation du contraste lors de l'observation des materiaux 2D. L'un des atouts principaux de BALM venant de sa combinaison a d'autres techniques, nous nous sommes particulierement interesses au couplage de mesures optiques et electrochimiques pour lesquelles le revetement antireflet sert d'electrode de travail. Nous avons ainsi pu etudier optiquement la dynamique de reduction electrochimique de l'oxyde de graphene (GO), l'electro-greffage de couches minces organiques par reduction de sels de diazonium sur le GO et sa forme reduite (r-GO), ainsi que l'intercalation d'ions metalliques entre feuillets de GO. En combinant versatilite et fort-contraste, BALM est ainsi etabli comme un outil prometteur pour l'etude des materiaux 2D et en particulier pour la caracterisation locale et in situ de leur reactivite chimique et electrochimique.
6 citations
01 Jan 2014
TL;DR: In this article, post synthesis thermal treatments up to 400°C of graphene oxide (GrO) prepared from commercial graphite and of GrO-silica nanocomposites prepared by a solution of commercial Fumed silica nanoparticles (average diameter 7 nm or 40 nm) and the GrO.
Abstract: In the present study we investigate post synthesis thermal treatments up to 400°C of graphene oxide (GrO) prepared from commercial graphite and of GrO-silica nanocomposites prepared by a solution of commercial Fumed silica nanoparticles (average diameter 7 nm or 40 nm) and the GrO. The thermal treatments were carried out in air, vacuum or He atmosphere to highlight tunable changes. Two GrO batches with small differences in the D (~1350 cm -1 ) and G (~1580 cm -1 ) Raman bands have been employed to evaluate effects depending on preparation. Thermal effects have been monitored through the Raman spectroscopy focussing on D, G and 2D (2500-3500 cm -1 ) bands spectral ranges. The experiments evidenced that the I(D)/I(G) amplitude ratio and the 2D region profile change during thermal treatments in the range below 180°C with maximum rate at ~120°C. At higher temperature, with maximum efficiency at about 200°C, only the D and G bands show modifications with a tendency to decrease I(D)/I(G) and reduce the G band width. The comparison among GrO batches and nanocomposite evidences that the thermal history during preparation and defective structures of GrO are key factors for the final material.
5 citations
Cites background or methods from "Optical Spectroscopy Investigation ..."
...In details, a change of the I(D)/I(G) amplitude ratio has been observed during the GrO reduction [11-14]....
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...Furthermore, the 2D region is composed of sub-band more sensitive to oxidation changes; this region features also relevant modifications associated to morphological properties of the graphene as surface roughness and number of layers [8, 10, 12, 13]....
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01 Jan 2021
TL;DR: In this article, the real and imaginary parts of the refractive index of graphene are defined, and the electric field modes between 300 nm and 600 nm are obtained by parameterized scanning calculation of the incident wavelength λ.
Abstract: Based on COMSOL Multiphysics software, the geometric model of graphene structure is set on the two-dimensional plane, and the thickness of graphene layer is set at 400 nm. The real and imaginary parts of the refractive index of graphene are defined. Then, the Ag and Au films are coated on both sides of graphene to form the Ag/G/Ag and Au/G/Au sandwich structures, respectively. In addition, the electric field modes between 300 nm and 600 nm are obtained by parameterized scanning calculation of the incident wavelength λ. At the same time, adsorption, scattering and extinction spectra are plotted. Results indicated that the maximum field strength of both the Ag/G/Ag and Au/G/Au sandwich structures are nearly doubled as compared to the intrinsic graphene. Finally, the adsorption, scattering and extinction properties are discussed. It is concluded that the resonance absorption peaks can be adjusted and improved by Ag/Au modification. The strongest plasma resonance mode shifts towards high energy. Moreover, Ag/G/Ag has stronger surface plasmon resonance effect than that of Au/G/Au structure.
3 citations
References
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TL;DR: Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena can now be mimicked and tested in table-top experiments.
Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.
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26,456 citations
TL;DR: This work shows that graphene's electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers, and allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
Abstract: Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality We show that its electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers The D peak second order changes in shape, width, and position for an increasing number of layers, reflecting the change in the electron bands via a double resonant Raman process The G peak slightly down-shifts This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area
13,474 citations
TL;DR: In this paper, a model and theoretical understanding of the Raman spectra in disordered and amorphous carbon is given, and the nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of \ensuremath{\pi} states and the long-range polarizability of the long range bonding.
Abstract: The model and theoretical understanding of the Raman spectra in disordered and amorphous carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of \ensuremath{\pi} states and the long-range polarizability of \ensuremath{\pi} bonding. Visible Raman data on disordered, amorphous, and diamondlike carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the ${\mathrm{sp}}^{2}$ sites in ${\mathrm{sp}}^{2}$-bonded clusters. In cases where the ${\mathrm{sp}}^{2}$ clustering is controlled by the ${\mathrm{sp}}^{3}$ fraction, such as in as-deposited tetrahedral amorphous carbon (ta-C) or hydrogenated amorphous carbon (a-C:H) films, the visible Raman parameters can be used to derive the ${\mathrm{sp}}^{3}$ fraction.
12,593 citations
TL;DR: An improved method for the preparation of graphene oxide (GO) is described, finding that excluding the NaNO(3), increasing the amount of KMnO(4), and performing the reaction in a 9:1 mixture of H(2)SO(4)/H(3)PO(4) improves the efficiency of the oxidation process.
Abstract: An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers’ method (KMnO4, NaNO3, H2SO4) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO3, increasing the amount of KMnO4, and performing the reaction in a 9:1 mixture of H2SO4/H3PO4 improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers’ method or Hummers’ method with additional KMnO4. Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers’ method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers’ method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the ...
9,812 citations