Showing papers on "Graphene published in 2003"
TL;DR: By applying a full spin-polarized description to the system, it is demonstrated that adatom defects have a magnetic moment of about 0.5micro(B) and its role in diffusion over the surface is calculated.
Abstract: We use ab initio methods to calculate the properties of adatom defects on a graphite surface. By applying a full spin-polarized description to the system we demonstrate that these defects have a magnetic moment of about $0.5{\ensuremath{\mu}}_{B}$ and also calculate its role in diffusion over the surface. The magnetic nature of these intrinsic carbon defects suggests that it is important to understand their role in the recently observed magnetism in pure carbon systems.
405 citations
TL;DR: In this paper, the binding of molecular oxygen to a graphene sheet and to a (8,0) single walled carbon nanotube, by means of spin-unrestricted density-functional calculations, was studied.
Abstract: We study the binding of molecular oxygen to a graphene sheet and to a (8,0) single walled carbon nanotube, by means of spin-unrestricted density-functional calculations. We find that triplet oxygen retains its spin-polarized state when interacting with graphene or the nanotube. This leads to the formation of a weak bond with essentially no charge transfer between the molecule and the sheet or tube, as one would expect for a physisorptive bond. This result is independent on the approximation used for the exchange-correlation functional. The binding strength, however, depends strongly on the functional, reflecting the inability of current approximation functionals to deal correctly with dispersion forces. Gradient-corrected functionals yield very weak binding at distances around 4 A, whereas local density functional results yield substantially stronger binding for both graphene and the nanotube at distances of less than 3 A. The picture of oxygen physisorption is not substantially altered by the presence of topological defects such as 5–7 Stone–Wales pairs.
259 citations
TL;DR: The quasipercolation model, a percolation-like model, was created based on X-ray diffraction analysis of monolithic carbonized medium-density fiberboard (c-MDF) as discussed by the authors.
255 citations
TL;DR: In this article, the position of the G peak and the appearance of transverse optic phonon peaks of carbon onions have been identified in terms of the Raman spectrum from carbon onions, and the curvature of the graphene planes is invoked to explain the relaxation of Raman selection rules and appearance of the new peaks.
248 citations
TL;DR: In this article, a model was developed to predict the chemical reactivity of carbon nanotubes (CNTs) quantitatively from their initial structures, which can be applied to the controlled functionalization of CNTs.
Abstract: We have developed a model to predict the chemical reactivity of carbon nanotubes (CNTs) quantitatively from their initial structures. The parameters, universal for each reaction, of the model can be obtained from a graphene sheet analysis. The chemical reactivity of hydrogenation, hydroxylation, and fluorination were predicted within 0.1-0.3 eV errors, compared with first principle simulation results. The model also predicted the enhanced chemical reactivity of mechanically bent CNTs. The predictions can be applied to the controlled functionalization of CNTs.
189 citations
Book Chapter•
30 Mar 2003
TL;DR: In this article, the authors use the term nanotube to describe carbon filaments with tubular graphene walls parallel to the axis and use the terms nanofiber for carbon filament with graphene layers at other angles.
Abstract: Carbon nanotubes and nanofibers are graphitic filaments/whiskers with diameters ranging from 0.4 to 500 nm and lengths in the range of several micrometers to millimeters. Carbon nanofibers and nanotubes are grown by the diffusion of carbon (via catalytic decomposition of carbon containing gases or vaporized carbon from arc discharge or laser ablation) through a metal catalyst and its subsequent precipitation as graphitic filaments [1–6]. Three distinct structural types of filaments have been identified based on the angle of the graphene layers with respect to the filament axis [5, 7], namely stacked, herringbone (or cup-stacked [8]), and nanotubular [9] as shown in Figure 1. It can be seen that the graphite platelets are perpendicular to the fiber axis in the stacked form, the graphene platelets are at an angle to the fiber axis in the herringbone form, and tubular graphene walls are parallel to the fiber axis in the nanotube. In the literature today, the common practice is to classify the stacked and herringbone forms of graphitic filaments under the general nomenclature of “nanofibers” whereas “nanotube” is used to describe the case where tubular graphene walls are parallel to the filament axis. Other definitions used today are that highly crystallized tubular structures are nanotubes whereas defective ones are nanofibers, or tubular structures ∼20 nm or below in diameter are nanotubes but larger diameter filaments are fibers. In this work, we prefer to use the term nanotube to describe carbon filaments with tubular graphene walls parallel to the axis and use the term nanofiber for carbon filaments with graphene layers at other angles. This is because special physical properties arise from the “nanotube” structure which distinguish it from the “nanofiber” structure, which itself has other advantageous properties, as will be described later. Carbon nanofibers and nanotubes have been synthesized since the 1960s, but why has one particular form (i.e. the nanotube) received so much attention recently? In 1991, Iijima reported that highly graphitized carbon nanotubes, formed from the arc discharge of graphite electrodes, contained several coaxial tubes and a hollow core [9]. This important discovery led to the realization that with graphene tubes parallel to the filament axis, these highly crystallized tubular carbon structures would inherit several important properties of “intraplane” graphite. In particular, a nanotube exhibits high electrical conductivity, thermal conductivity, and mechanical strength along its axis. As there are very few open edges and dangling bonds in the structure, nanotubes are also very inert and species tend
169 citations
TL;DR: Shioyama et al. as discussed by the authors showed that the van der Waals interaction between the faced sides of the graphene sheet can be observed in the interlayer of K-GIC and polymerized progressively.
155 citations
TL;DR: The bundle-of-capillaries model was used to characterize the hydrodynamics of this monolith, and its permeability was found to agree well with the theoretical one.
Abstract: The preparation of a novel carbon monolithic column for high performance liquid chromatography is described. A phenolic resin rod with embedded 10-μm silica beads was prepared by acid-catalyzed polymerization of a resorcinol/iron(III) complex and formaldehyde. This rod was carbonized and graphitized under inert atmosphere with a programmed temperature cycle from room temperature to 1250 °C. Subsequently, the silica beads along with iron catalysts were removed, leaving a porous carbon rod. Imaging of this monolithic rod by scanning and transmission electron microscopies revealed a highly interconnected bimodal porous structure. The porosity and pore size distribution of the mesopores were characterized by N2 absorption/desorption. Graphene sheets were found in the TEM images of the carbon rod, and the graphite index was characterized by Raman spectrum and X-ray diffraction. A monolithic column prepared with the aforementioned carbon rod was evaluated using a mixture of alkylbenzenes. It exhibited an excell...
150 citations
TL;DR: In this paper, the results of Raman analysis indicated that no free PC molecules are present in the concentrated solution, which suggested that the ion/solvent interactions would be an important factor that determines the ability of stable surface film formation in PC-based solutions.
Abstract: Electrochemical lithium intercalation within graphite was investigated in propylene carbonate (PC) containing different concentrations, 0.82 and 2.72 mol dm - 3 , of bis(perfluoroethylsulfonyl)imide, LiN(SO 2 C 2 F 5 ) 2 . Lithium ion was reversibly intercalated into and deintercalated from graphite in the latter concentrated solution in spite of the use of pure PC as a solvent, whereas ceaseless solvent decomposition and intensive exfoliation of graphene layers occurred in the former solution. X-ray diffraction analysis revealed that a stage I graphite intercalation compound was formed alter being fully charged in the 2.72 mol dm - 3 solution. The results of Raman analysis indicated that no free PC molecules are present in the concentrated solution, which suggested that the ion/solvent interactions would be an important factor that determines the ability of stable surface film formation in PC-based solutions.
147 citations
TL;DR: In this paper, the potential energy surfaces for dissociative adsorption of H2 on highly symmetric sites on graphene were investigated and discussed, and it was shown that reconstructions of the carbon atoms play an important role in the H2 -graphene interactions.
Abstract: We investigate and discuss the interaction of H2 with graphene based on density functional (DFT) theory. We calculate the potential energy surfaces for the dissociative adsorption of H2 on highly symmetric sites on graphene. Our calculation results show that reconstructions of the carbon atoms play an important role in the H2 -graphene interactions. Activation barrier for H2 dissociation on an unrelaxed graphene is considerably high, ∼4.3 eV for a T–H–T geometry and ∼4.7 eV for a T–B–T geometry. The T–H–T(T–B–T) geometry means that the center of mass position of H2 is at the hollow(bridge) site, and the two H atoms are directed towards the top sites on the graphene. On the other hand, when the carbon atoms are allowed to relax, the activation barrier decreases, and becoming 3.3 eV for the T–H–T geometry and 3.9 eV for the T–B–T geometry. In this case, the two carbon atoms near the hydrogen atoms move 0.33 A towards the gas phase for the T–H–T geometry and 0.26 A for the T–B–T geometry.
143 citations
TL;DR: In this article, the authors show that narrow nanotubes with optimized diameters between about 0.34 and 0.5 nm can be either semiconducting or metallic, but with electron structures near the Fermi level that often cannot be understood starting from the graphene sheet model, successful in the study of larger diameter tubes.
Abstract: We report local-density-functional results that show that narrow nanotubes with optimized diameters between about 0.34 and 0.5 nm can be either semiconducting or metallic, but with electron structures near the Fermi level that often cannot be understood starting from the graphene sheet model, successful in the study of larger diameter tubes. Our total-energy calculations indicate that narrow nanotubes recently observed either as the central shell of a multiwalled tube or encased in a porous zeolite, if isolated, should be stable against complete unzipping along the nanotube axis.
TL;DR: In this paper, a density functional theory (DFT) calculation of the interactions between selected semiconducting and metallic single-walled carbon nanotubes (SWCNTs) and single oxygen molecules is carried out in order to provide a rationale for the recent experimental observations of UV-light accelerated oxidation of carbon Nanotubes and the accompanying changes in the thermoelectric power.
TL;DR: In this paper, elemental boron and two phosphorus compounds were doped into an activated carbon cloth and a carbon felt to improve oxidation inhibition, and the results for B-doped samples are consistent with previous studies in which B was found to exhibit both a catalytic and an inhibiting effect on carbon oxidation.
TL;DR: In this paper, the authors studied the chemisorption of NO 2 on carbon nanotubes by modeling the interaction between NO 2 and N 2 O 4 with an infinitely long (8,0) single-walled carbon Nanotube, using planewave/pseudopotential-based density functional theory.
Abstract: The chemisorption of NO 2 on carbon nanotubes is studied by modeling the interaction between NO 2 and N 2 O 4 with an infinitely long (8,0) single-walled carbon nanotube, using planewave/pseudopotential-based density functional theory (DFT). In sharp contrast to the case of graphite, for which NO 2 adsorption is physical, a NO 2 radical could readily adsorb on the exterior of an (8,0) tube by addition, similar to the reaction between NO 2 and alkenes. The process is slightly endothermic and reversible with a low energy barrier, with the NO 2 group in either the nitro or nitrite configuration. Adsorption of a second NO 2 is considerably exothermic, and desorption of NO 2 from such a configuration is much more difficult. The chemisorption of NO 2 also increases the conductivity of the (8,0) tube. On the other hand, N 2 O 4 only plays a minor role in the equilibrium between desorption and adsorption processes. These results indicate that the (8,0) tube is more reactive toward NO 2 than graphite, due to the curvature on the rolled graphene sheet.
TL;DR: In this article, the phonon dispersions and atomic displacements for single-wall carbon nanotubes of arbitrary chirality are calculated based on the force constants of graphene, with symmetry imposed modifications providing the twisting acoustic mode exactly.
Abstract: The phonon dispersions and atomic displacements for single-wall carbon nanotubes of arbitrary chirality are calculated. The full symmetry is implemented. The approach is based on the force constants of graphene, with the symmetry imposed modifications providing the twisting acoustic mode exactly. The functional dependence of frequencies of the Raman and infrared active modes on the wrapping angle and on the diameter are presented. The armchair tubes are found to be infrared inactive under the light linearly polarized along the tube axis. Also the overbending absolute value and the wave vector dependence on the tube geometry are found and the chirality selective method for the sample characterization is proposed. Finally, the specific heat calculations are carried out.
TL;DR: In this article, a model for the process of the growth of carbon nanotubes obtained by chemical vapour deposition in the presence of transition metal nanoparticles (Me-NPs) which act as a catalyst is presented.
Abstract: We present a model for the process of the growth of carbon nanotubes (CNTs) obtained by chemical vapour deposition in the presence of transition metal nanoparticles (Me-NPs) which act as a catalyst. We have deduced that the growth of a CNT occurs in the presence of two forces: (i) a viscous force, due to the surrounding hot gas, which opposes and slows down the growth of the CNT, and (ii) an extrusive force that causes the growth and that in the steady-state stage of the growth is completely balanced by the viscous force. We believe that it is the great decrease in free energy in the assembling reaction that occurs at the interface of the Me-NP catalyst that causes the extrusive force for the growth of a CNT. Moreover, the process of chemisorption of a C2 fragment, through the interaction of the C2?? ?system with the 3d metal orbitals, has been considered as well as the coordination action of the Fe, Ni and Co metal surfaces. The structural properties of the Fe, Co and Ni surfaces show that the (1, ? 1, 0) planes of Fe and the (1, 1, 1) planes of Co and Ni exhibit the symmetry and distances required to overlap with the lattice of a graphene sheet. This gives us information about the coordination mechanism responsible for assembling the CNTs. In fact, we show that it is possible to cleave an Me-NP in such a way as to match the correct symmetry and dimension of the armchair structure of a single-walled nanotube. The mechanism of C2 addition at the edge of the growing CNT has also been considered in relation to the highest occupied molecular orbital?lowest unoccupied molecular orbital (HOMO?LUMO) symmetry. We demonstrate that the action of d orbitals of the metal atoms forming the Me-NP makes possible the thermally forbidden reaction, which involves the C2?? system.
TL;DR: In this paper, the electronic structure of carbon nanotubes was studied theoretically by first-principles techniques and the local density approximation (LDA) was optimized with the local-density approximation in density functional theory, and many-body effects between electrons were taken into account within the LDA.
Abstract: We study the electronic structure of carbon nanotubes theoretically by first-principles techniques. Geometry is optimized with the local-density approximation (LDA) in density functional theory, and many-body effects between electrons are taken into account within the $\mathrm{GW}$ approximation. We find that the (5,0) tube is metallic even at the $\mathrm{GW}$ level, being different from the tight-binding result. The (6,0) tube is also confirmed to be metallic. The $\mathrm{GW}$ correction to LDA is found to be small in metallic tubes. The (7,0) tube is semiconducting, in which the $\mathrm{GW}$ correction considerably increases the gap. On the other hand, the $\mathrm{GW}$ correction is small in graphene, suggesting that the density functional theory gives a reasonable description of large nanotubes.
TL;DR: In this paper, the authors performed ab initio calculations of charged graphene and single-wall carbon nanotubes (CNTs) and obtained a wealth of electromechanical behaviors.
Abstract: We perform ab initio calculations of charged graphene and single-wall carbon nanotubes (CNTs). A wealth of electromechanical behaviors is obtained. (1) Both nanotubes and graphene expand upon electron injection. (2) Upon hole injection, metallic nanotubes and graphene display a nonmonotonic behavior. Upon increasing hole densities, the lattice constant initially contracts, reaches a minimum, and then starts to expand. The hole densities at minimum lattice constants are 0.3 $|e|/\mathrm{atom}$ for graphene and between 0.1 and $0.3|e|/\mathrm{atom}$ for the metallic nanotubes studied. (3) Semiconducting CNT's with small diameters $(d\ensuremath{\lesssim}20\mathrm{\AA{}})$ always expand upon hole injection. (4) Semiconducting CNT's with large diameters $(d\ensuremath{\gtrsim}20\mathrm{\AA{}})$ display a behavior intermediate between those of metallic and large-gap CNT's. (5) The strain versus extra charge displays a linear plus power-law behavior, with characteristic exponents for graphene, metallic, and semiconducting CNT's. All these features are physically understood within a simple tight-binding total-energy model.
TL;DR: In this article, double-walled carbon nanotubes (DWNTs) have been produced by catalytic decomposition of benzene over Fe−Mo/Al2O3 catalyst at 900 °C.
Abstract: High-quality double-walled carbon nanotubes (DWNTs) have been produced by catalytic decomposition of benzene over Fe−Mo/Al2O3 catalyst at 900 °C. The produced carbon materials are DWNT bundles free of amorphous carbon covering on the surface. DWNTs have inner tube diameters in the range of 0.69−2.53 nm and outer tube diameters in the range of 1.44−3.30 nm. The interlayer spacing between graphene layers ranges from 0.35 to 0.38 nm. Transmission electron microscopy and Raman analysis show that produced carbon materials have a low defect level in the atomic carbon structure, indicating the synthesis of high-quality DWNTs. Our results demonstrate that benzene is an ideal carbon feedstock to synthesize high-purity DWNTs over Fe−Mo/Al2O3 catalyst.
TL;DR: In this paper, the results of an experimental study on metal-catalyzed synthesis of carbon tubular nanostructures in opposed flow flame are reported, which reveal the presence of highly organized carbonaceous structures with the configurations showing strong dependence on the flame location.
TL;DR: In this article, the conditions for the formation of nested carbon nanotubes are discussed and a comparison of the values of chiral angles with those of the corresponding interwall spacings, both obtained from the ED patterns, leads to the conclusion that these MWCNTs have a scroll structure, very probably consisting of one single rolled-up graphene sheet.
TL;DR: In this paper, the performance of graphites with and without high amounts of rhombohedral phase in the structure has been investigated, and it was shown that the differences in surface structure and morphology have the highest impact in a propylene carbonate/ethylene sulfite-based electrolyte.
TL;DR: In this paper, the surface structure of natural graphite is changed and a fresh dense layer of oxides is formed, which inhibit electrolyte decomposition, block intercalation of solvated lithium ions and prevent graphene planes from moving along the a-axis direction.
TL;DR: Raman spectra were measured of highly fluorinated graphite samples prepared at room temperature, 380 and 515°C, and showed that graphite fluorides, (CF)n and (C2F)n are formed via fluorine-intercalated phase with planar graphene layers.
TL;DR: In this article, an in situ electrochemical atomic force microscopy (AFM) observation of a composite graphite electrode surface was performed in 1 ǫ−3 LiClO4 dissolved in a mixture of ethylene carbonate (EC)+diethyl carbonate, and propylene carbonates (PC) to show the applicability of scanning probe microscopy to studies using composite graphites electrodes.
TL;DR: In this article, the binding energy for further adsorption changes sign and becomes favorable after several chemisorbed atoms, since a puckered sp 3 hybridized site heavily distorts the surrounding sp 2 framework.
Abstract: A graphene sheet is well known to be highly stable against chemisorption of a single hydrogen atom, since a puckered sp 3 hybridized site heavily distorts the surrounding sp 2 framework. However, successive adjacent chemisorbed hydrogen atoms can engage in a collective stabilization mediated by cooperative alternate puckering in the underlying carbon sheet. After several chemisorbed atoms, the binding energy for further adsorption changes sign and becomes favorable. This process requires access to both sides of the graphene sheet. Therefore it is suppressed on a graphite surface, but may be accessible in carbon nanotubes, if the initial kinetic barrier to creating the nucleation island can be overcome.
TL;DR: In this article, a novel nanoporous carbon−silica composite with medium hydrophilicity is synthesized by a series of methods consisting of preexpansion of the interlayer of graphite oxide (GO) by surfactant intercalation, the inter calcation of tetraethoxylsilane (TEOS) and its hydrolysis in the inter layer, followed by post carbonization to form a robust bridged/pillared network.
Abstract: A novel nanoporous carbon−silica composite with medium hydrophilicity is synthesized by a series of methods consisting of preexpansion of the interlayer of graphite oxide (GO) by surfactant intercalation, the intercalation of tetraethoxylsilane (TEOS) and its hydrolysis in the interlayer, followed by post carbonization to form a robust bridged/pillared network. High-resolution N2 adsorption results show that carbonization at 823 K gives a composite having the highest specific surface area of more than 1000 m2/g with both microporosity and mesoporosity. Varieties of analytical results using DRIFT, NMR, XPS, and RAMAN spectra indicate that this composite contains small graphene sheets in its structure and its silicon components are silica particles with +4 valence. Morphology observation, thermal desorption, and other properties suggest the important roles of dispersion of GO in aqueous solution, preexpansion of GO interlayer, interlayer hydrolysis of TEOS molecules, and the carbonization condition in the f...
TL;DR: In this article, the authors investigated the interaction of a hydrogen atom (H) with graphene based on the density functional theory and showed that reconstructions of carbon atoms play an important role in the H adsorption on graphene.
Abstract: We investigate and discuss the interaction of a hydrogen atom (H) with graphene based on the density functional theory (DFT). Our calculation results show that reconstructions of carbon atoms play an important role in the H adsorption on graphene. When constituent carbon atoms are held rigid, endothermic H adsorption is about 0.2 eV, and the activation barrier is 0.3 eV for H adsorption, due to the strong π-bonding network of the hexagonal carbon. On the other hand, when carbon atoms are allowed to relax, the carbon atom directly below the H atom moves 0.33 A upward towards the gas phase, and an s p 3 -like geometry is formed between the H and carbon atoms of graphene. This relaxation stabilizes the hydrogen–carbon interaction, and the exothermic hydrogen adsorption on the graphene has a binding energy of 0.67 eV. We also show that the effective pathway for H adsorption on graphene, which gives an activation barrier for the H adsorption on graphene of 0.18 eV.
TL;DR: In this paper, the formation mechanism of the microstructure in wood carbonized by the flash heating process seems to originate from fragmented and oxygen-containing pyrolysis compounds in contrast to conventional heating.
TL;DR: In this article, a spongy carbon is characterized by interconnected thin layers forming a spathy structure with meso-and macroporosity, which is produced by a pulsed microplasma cluster source in the presence of a metal-organic catalyst.