Showing papers on "Graphite published in 1996"
TL;DR: In this article, it was shown that carbon onion cores can be transformed to diamond by electron irradiation of graphitic carbon materials, and that the carbon onions act as nanoscopic pressure cells for diamond formation.
Abstract: SPHERICAL particles of carbon consisting of concentric graphite-like shells ('carbon onions') can be formed by electron irradiation of graphitic carbon materials1,2. Here we report that, when such particles are heated to ∼700 °C and irradiated with electrons, their cores can be transformed to diamond. Under these conditions the spacing between layers in the carbon onions decreases from 0.31 in the outer shells (slightly less than the 0.34-nm layer spacing of graphite) to about 0.22 nm in the core, indicating considerable compression towards the particle centres. We find that this compression allows diamond to nucleate—in effect the carbon onions act as nanoscopic pressure cells for diamond formation.
620 citations
TL;DR: In recent years, important advances in the understanding of the pressure-temperature phase and transformation diagram for carbon have occurred as a result of developments in both experimental and theoretical techniques as discussed by the authors.
580 citations
TL;DR: Nanotube cavities should be less chemically reactive than graphite and may serve as nanosize test tubes, and have been illustrated by monitoring the decomposition of silver nitrate within nanotubes in situ in an electron microscope, which produced chains of silver nanobeads separated by high-pressure gas pockets.
Abstract: Open carbon nanotubes were filled with molten silver nitrate by capillary forces. Only those tubes with inner diameters of 4 nanometers or more were filled, suggesting a capillarity size dependence as a result of the lowering of the nanotube-salt interface energy with increasing curvature of the nanotube walls. Nanotube cavities should also be less chemically reactive than graphite and may serve as nanosize test tubes. This property has been illustrated by monitoring the decomposition of silver nitrate within nanotubes in situ in an electron microscope, which produced chains of silver nanobeads separated by high-pressure gas pockets.
494 citations
TL;DR: In this article, the authors report the fabrication and characterization of magnetic thin films, consisting of cobalt nanocrystals encapsulated in graphite-like carbon cages, that meet these structural requirements.
Abstract: A VARIETY of crystalline materials have now been encapsulated in nanometre-scale graphitic cages1–8 and tubules9–11. For magnetic materials, encapsulation should serve the dual role of protecting air-sensitive particles against degradation and reducing the magnetic coupling between individual particles, thus potentially opening the way for applications of these composite materials as ultra-high-density magnetic recording media12,13. But to realize this potential, the materials must be available in the form of thin, smooth films, with precise control of the size of the individual magnetic crystallites. Here we report the fabrication and characterization of magnetic thin films, consisting of cobalt nanocrystals encapsulated in graphite-like carbon cages, that meet these structural requirements.
407 citations
TL;DR: In this paper, the authors review the present understanding of diamond-like carbon growth mechanisms and discuss the correlation between the deposition parameters (e.g., species energy, substrate temperature, substrate material, angle of incidence, deposition rate and environment) and the film properties (density, surface morphology, sp 3 /sp 2 ratio) studied using a host of experimental methods.
284 citations
TL;DR: The conventionally used Tersoff potential is improved to realistically describe interlayer forces in graphite and high-energy processes in carbon, and three defect structures are identified which correspond to experimentally observed hillocks on graphite surfaces.
Abstract: We use molecular dynamics simulations and ab initio calculations to study the structures and formation probabilities of isolated surface defects produced by ion irradiation of (1000) graphite. We improve the conventionally used Tersoff potential [J. Tersoff, Phys. Rev. Lett. 61, 2879 (1988)] to realistically describe interlayer forces in graphite and high-energy processes in carbon. We identify three defect structures which correspond to experimentally observed hillocks on graphite surfaces, and examine their formation at different implantation energies.
274 citations
TL;DR: In this paper, the synthesis of carbon nanotubes and boron doped (1 to 5 at.% B) was achieved by an electric arc-discharge between an anode made of homogeneous BC 4 N and a cathode making of graphite.
272 citations
TL;DR: In this paper, structural transformations in the sliding friction of hydrogen-free diamond-like carbon (DLC) films prepared by pulsed laser deposition are investigated, and the low friction is related to a friction induced transformation of the surface into a graphite-like phase and the formation of an adherent transfer film of this material on the counterface.
248 citations
TL;DR: A pure-carbon planar structure composed of pentagons and heptagons that is metallic with a density of states at the Fermi level of 0.1 state per eV per atom is proposed.
Abstract: Carbon is well-known as an insulator, a semimetal, a molecular solid, and a one-dimensional semiconductor or low-density-of-states metal. We propose a pure-carbon planar structure composed of pentagons and heptagons that is metallic with a density of states at the Fermi level of \ensuremath{\sim}0.1 state per eV per atom. This structure, planar carbon pentaheptite, is metastable with a total energy per carbon atom comparable to that of ${\mathrm{C}}_{60}$. The structure can be rolled into tubes in a manner similar to graphite. Possible synthetic pathways are discussed.
234 citations
TL;DR: In this paper, a potentiostatic pulse method was employed to electrochemically deposit silver nanocrystallites on the atomically smooth graphite basal plane surface, where the current increased in approximate proportion to (time)1/2 as expected for an instantaneous nucleation and three-dimensional growth mode of deposition.
Abstract: A potentiostatic pulse method has been employed to electrochemically deposit silver nanocrystallites on the atomically smooth graphite basal plane surface. Voltage pulses having amplitudes of 100, 250, and 500 mV vs Ag0 and durations of 10 or 50 ms were applied to graphite surfaces immersed in dilute (≈1.0 mM) aqueous silver nitrate. During the deposition pulse, the current increased in approximate proportion to (time)1/2 as expected for an instantaneous nucleation and three-dimensional growth mode of deposition. Consistent with this growth mode, noncontact atomic force microscopy (NC-AFM) examination of graphite surfaces following silver deposition revealed the existence of silver particles at a coverage of near 1010 cm-2 which were well-separated from one another on atomically smooth regions of the graphite basal plane surface. These particles were disk-shaped having a height of 15−50 A and an apparent diameter which varied from 200 to 600 A; particle dimensions increased smoothly with the coulometric l...
215 citations
TL;DR: In this article, two graphite-like materials of composition BC0.8-1.0H0.9H 0.4-0.7 and BC3.0-3.2-2 have been described, which are described as BCN(H) and BCNB(H), respectively, by the interaction of acetonitrile with boron trichloride in a hydrogen and nitrogen atmosphere.
Abstract: New graphite-like materials of composition BC0.9-1.3N0.8-0.9H0.4-0.7 and BC3.0-3.2N0.8-1.0H0.2-2, which are described as BCN(H) and BC3N(H), have been prepared by the interaction of acetonitrile with boron trichloride in a hydrogen and nitrogen atmosphere and acrylonitrile with boron trichloride, respectively. X-ray and electron diffraction analyses indicate that these materials have hexagonal structures similar to that of graphite. ESCA spectra and the possible chemical bonds suggest that the ideal structure of BCN is made of the unit structure of BC2N + BN, while BC3N is composed of BC3N + BNC3. A BCN(H) plate has a basal-plane conductivity of 1.28 (Ω cm)-1 at room temperature, while a BC3N(H) plate has that of 88.5 (Ω cm)-1. Thermoelectric measurements indicate that both materials behave as p-type semiconductors and a BCN(H) plate has a high Seebeck coefficient of 300 μV/°K at room temperature in air.
TL;DR: In this article, the effects of mechanical grinding on morphology and electrochemical performance of graphite and soft carbon powders with respect to lithium insertion were studied, and a direct correlation between the irreversible capacity of the milled samples and their specific surface area was observed, consistent with catalytically induced reduction of the electrolyte.
Abstract: The effects of mechanical grinding on morphology and electrochemical performance of graphite and soft carbon powders with respect to lithium insertion were studied The morphology of the milled graphitic powders was found to depend strongly upon the nature of the interactions (eg, impact or shear) generated by the two kinds of mixer mills used For the same milling time, crystallite size was smallest and the density of defects highest for graphitic powders that were ball-milled using impact interactions The specific surface area of the milled samples does not increase indefinitely with increased milling time, but there is a critical milling time (m{sub c}) beyond which the specific surface area goes through a maximum (graphite) or levels off for cokes By controlling milling conditions, graphite and soft carbon powders with well-defined morphology, d-spacings, surface area, and crystallite size can be made The reversible (reversible amount of inserted Li) vs irreversible capacity (irreversible lithium loss between the first discharge and charge) was measured for various C/Li cells using various tailor-made graphite and soft carbon powders A direct correlation between the irreversible capacity of the milled samples and their specific surface area was observed, consistent with catalytically induced reduction of the electrolyte Formore » milling times greater than m{sub c}, the irreversible capacity remains constant or even decreases while the reversible capacity still increases With mechanical grinding, both graphite and coke samples having irreversible capacity of 328 mAh/g for a reversible capacity of 708 mAh/g ({approximately}Li{sub 2}C{sub 6}) were obtained« less
TL;DR: In this article, the bonding states of BC2N thin films prepared by chemical vapor deposition, one of the new layered BCN compounds, were investigated by using x-ray photoelectron spectroscopy to measure chemical shifts of 1s electrons, being compared with those in graphite and hexagonal (h) BN.
Abstract: We have studied the bonding states of BC2N thin films prepared by chemical vapor deposition, one of the new layered BCN compounds. The chemical bonding states of boron, carbon, and nitrogen atoms in the BC2N thin films were investigated by using x‐ray photoelectron spectroscopy to measure chemical shifts of 1s electrons, being compared with those in graphite and hexagonal (h‐) BN. The results exhibited that the thin films had significant B–C and C–N bonds and were clearly different from graphite and h‐BN, indicating that an atomic‐level hybrid of the three elements was synthesized.
TL;DR: In this paper, near-edge x-ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type.
Abstract: Near‐edge x‐ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type. Diamond, chemical vapor deposited (CVD) diamond films of varying quality. Diamond‐like carbon (DLC) films, and graphite were examined with this technique and these measurements were compared with Raman spectroscopy results and scanning electron microscopy images of carbon film morphology. For the mixed sp2 and sp3 bonded DLC materials, NEXAFS does not suffer from the large Raman cross‐section difference between sp2 and sp3 type bonds, thus allowing unambiguous characterization of carbon thin films with a broader range of sp2/sp3 bonding ratios than possible with Raman spectroscopy alone. This capability was used to determine the transition point where the sequential‐CVD carbon film growth technique produces predominately sp3 or sp2 bonded material.
TL;DR: In this paper, topographical changes of the basal plane of highly oriented pyrolytic graphite (HOPG) in 1 M LiClO4/ethylene carbonate−diethyl carbonate (1:1 by volume) were observed under polarization by electrochemical scanning tunneling microscopy.
Abstract: In order to elucidate surface reactions on graphite negative electrodes of secondary lithium ion batteries, topographical changes of the basal plane of a highly oriented pyrolytic graphite (HOPG) in 1 M LiClO4/ethylene carbonate−diethyl carbonate (1:1 by volume) were observed under polarization by electrochemical scanning tunneling microscopy. A step edge on the basal plane of HOPG was treated as a model of the edge plane of HOPG. When the sample potential was stepped to 1.1 V vs Li/Li+, two kinds of hill-like structure of ca. 10 A height appeared on the HOPG surface. The first hill was formed far apart from a step edge and was almost unchanged with time. The second hill was formed in the vicinity of the step and was spread out with time. The formation of the second hill caused the exfoliation of graphite layers. The observed height of the hills was comparable to the values of the increment of the interlayer spacing for ternary graphite intercalation compounds of alkali metal with solvent molecules prepar...
TL;DR: In this article, the effect of particle size on the catalytic activity for oxygen reduction reaction at platinum/recast ionomer interface was investigated, porous electrodes of well-defined geometry and very well calibrated Pt particles on graphite were used.
TL;DR: The reactivity of fluorine with graphite depends strongly on reaction temperature and purity of the fluorine atmosphere as mentioned in this paper, and the presence of fluoride impurities accelerates the reaction even at room temperature.
TL;DR: In this article, the authors proposed a charged carbon nuclei cluster model for the formation of diamond from graphitic soot and diamond on the iron and the silicon substrates, respectively.
TL;DR: In this paper, a single-fiber carbon microelectrode (3.5 {micro}m radius, 1 cm length) is used to determine the activity coefficient of the lithium intercalate and associated hot sites; the use of the chemicalpotential gradient as the driving force for transport phenomena is shown to yield constant physicochemical properties that are independent of the degree of intercalation.
Abstract: To clarify the electrochemical processes governing the performance of lithiated carbon electrodes and obtain appropriate physicochemical properties, experiments conducted with a single-fiber carbon microelectrode (3.5 {micro}m radius, 1 cm length) are mathematically simulated. Equilibrium-potential data are used to determine the activity coefficient of the lithium intercalate and associated hot sites. Transport within the carbon fiber is influenced significantly by activity-coefficient variations; the use of the guest chemical-potential gradient as the driving force for transport phenomena is shown to yield constant physicochemical properties that are independent of the degree of intercalation. The theoretical calculations display good agreement with several different experimental data sets. The diffusion coefficient of lithium in partially graphitic carbon is obtained along with rate constants (i.e., the exchange current density) associated with the electrochemical reaction that takes place on the fiber surface.
TL;DR: In this article, the tribological properties of graphite, non-graphitic carbon, carbon-carbon composite, and carbon-amorphous carbon in nitrogen and air were investigated.
TL;DR: In this paper, twenty elements were codeposited with carbon in an arc discharge between graphite electrodes, and the majority of them were evaporated from composite anodes that contained the elements or their oxides stuffed into central bores in the graphite rods.
Abstract: Twenty elements were codeposited with carbon in an arc discharge between graphite electrodes. The majority of them were evaporated from composite anodes that contained the elements or their oxides stuffed into central bores in the graphite rods. The deposits, found in the soot at the reactor walls or as slag at the cathode, were characterized using scanning and transmission electron microscopy, electron energy loss spectroscopy, and x‐ray diffraction. The products fall into four categories: (1) elements that can be encapsulated in the form of their carbides (B, V, Cr, Mn, Y, Zr, Nb, Mo); (2) elements that are not encapsulated but tolerate the formation of graphitic carbon cages (Cu, Zn, Pd, Ag, Pt); (3) elements that form stable carbides, competing with and pre‐empting the carbon supply for the graphitic cage formation (Al, Si, Ti, W); and (4) the iron‐group metals (Fe, Co, Ni) that stimulate the formation of single‐walled tubes and strings of nanobeads in the conventional arc discharge condition, and produce the nanometer‐size carbon‐coated ferromagnetic particles in a modified arc discharge in which metals are in molten form in graphite crucible anodes exposed to a helium jet stream. The criterion determining the formation according to one of the four categories is discussed on the basis of this extended study. It is apparent that the physical properties such as vapor pressure, melting and boiling points, the completeness of the electronic shells of the elements, or their heat of carbide formation are not sufficient to explain the selectivity of the encapsulation without exceptions. A hypothesis is advanced that emphasizes the existence of the carbide, interfacial compatibility with the graphitic network, as well as the transport and supply parameters in the reaction space.
TL;DR: In this article, the conductivity of graphite platelets with diameter-to-thickness ratios of the order of 100 was characterized by X-ray diffraction and electron microscopy: orientation of filler and porosity of the polymer matrix were observed.
TL;DR: Nanocrystalline graphite with a crystallite size of about 2 nm is formed after 8 h of ball milling as mentioned in this paper. But this graphite is relatively stable against heating when compared with some nanocrystine metals.
Cray1
TL;DR: In this paper, the results of first-principles molecular dynamics simulations of a surface-induced diamond-to-graphite transition are presented, which provide a microscopic model for the early stages of the graphitization process.
Abstract: GRAPHITIZATION of diamond at ambient pressure was first observed in the 1920s1,2, but the mechanisms responsible for this transformation and, in particular, those underlying the nucleation and growth of graphite in diamond, remain controversial3–5. In addition to their fundamental interest, these processes have technological relevance—for example, for the growth by chemical vapour deposition6 of diamond-like films, which sometimes include graphitic islands7. Here we report the results of first-principles molecular dynamics simulations of a surface-induced diamond-to-graphite transition, which provide a microscopic model for the early stages of the graphitization process. We find that a well defined diamond/graphite interface forms during the transition; the electronic properties of the atoms at this interface suggest that they are highly chemically active sites. In addition to its relevance to graphite inclusion in diamond films, our model should yield insight into the process of selective etching in vapour-deposited carbon films, and possibly also into diamond nucleation.
TL;DR: In this paper, the sublimation kinetics of 2-30 nm thick ice layers deposited in ultra high vacuum at 100 K, on different surfaces; Pt(111) and graphite (0001) surfaces with and without various pre-adsorbed monolayers.
TL;DR: In this article, carbon deposition on a catalyst surface during decomposition of different carbon-containing compounds can be used for the synthesis of carbon nanotubes of graphitic structure, and different supported transition metal oxides were found to be active in the production of these materials.
TL;DR: In this paper, the early stages of film growth via deposition of size-selected silver clusters on graphite, as a function of incident cluster size, were investigated, and it was shown that the deposited clusters are mobile and coalesce into three-dimensional particles with a "universal" diameter of ≊14 nm.
Abstract: We have investigated the early stages of film growth via deposition of size‐selected silver clusters on graphite, as a function of incident cluster size. For all sizes from 50 to 250 atoms per cluster, the deposited clusters are mobile and coalesce into three‐dimensional particles with a ‘‘universal’’ diameter of ≊14 nm, possibly a consequence of lattice strain between the silver and graphite. The 14 nm particles are found mainly in small aggregates, indicating that they themselves are to some degree mobile. We have also found evidence that the particle mobility is influenced by the cluster impact angle.
TL;DR: In this paper, the effectiveness of several preparation protocols was investigated: mechanical polishing with successively finer grades of alumina, Ar+ sputtering, chemical polishing, and chemical plating followed by Tl underpotential deposition.
Abstract: The quantity and chemical nature of carbonaceous impurities remaining on polycrystalline Ag surfaces after preparation depend on the protocol used for cleaning. The effectiveness of several preparation protocols was investigated in this study: mechanical polishing with successively finer grades of alumina, Ar+ sputtering, chemical polishing, and chemical polishing followed by Tl underpotential deposition. The impurities detected on polycrystalline Ag surfaces subjected to these preparation procedures are carbon, oxygen, and aluminum, and these are qualitatively and quantitatively identified with X-ray photoelectron spectroscopy. With Raman spectroscopy, these carbonaceous impurities are qualitatively identified as graphite, hydrocarbon, and cyanide species, the last of these being present only on the chemically polished surfaces.
Journal Article•
TL;DR: In this paper, the use of Raman spectroscopy as a principal tool to investigate the vibrational dynamics of carbon materials and to provide indirect structural characterization of their short-, medium and long-range order.
Abstract: Use of carbon materials is no longer limited to diamond jewelry or graphite pencils and lubricants. The last decade has witnessed an explosion of technological applications driven by the development of fabrication methods and the discovery of several new classes of pure carbon. Structural diversity exhibited by the carbon atoms, from local chemical order to long-range crystalline order, is key to understanding their physical and chemical properties and in future materials development. This article summarizes the use of Raman spectroscopy as a principal tool to investigate the vibrational dynamics of carbon materials and to provide indirect structural characterization of their short-, mediumand long-range order.
TL;DR: In this article, the authors analyzed the low pressure synthesis of diamond with the activity and the chemical potential of carbon, which are the criteria for the transfer of carbon from one phase to another.