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Showing papers on "Fullerene published in 1994"


Journal ArticleDOI
25 Mar 1994-Science
TL;DR: The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements and indicate that they are highly defective and have a local structure similar to turbostratic graphite.
Abstract: Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a "Russian doll" structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the c axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of "MC 8 ." These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a "paper-mache" of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite.

429 citations


Journal ArticleDOI
18 Nov 1994-Science
TL;DR: A detailed mechanism that features the high electric field at (and field-emission from) open nanotube tips exposed to the arc plasma, and consequent positive feedback effects from the neutral gas and plasma, is proposed for tube growth in such arcs.
Abstract: Carbon nanotubes produced in arcs have been found to have the form of multiwalled fullerenes, at least over short lengths. Sintering of the tubes to each other is the predominant source of defects that limit the utility of these otherwise perfect fullerene structures. The use of a water-cooled copper cathode minimized such defects, permitting nanotubes longer than 40 micrometers to be attached to macroscopic electrodes and extracted from the bulk deposit. A detailed mechanism that features the high electric field at (and field-emission from) open nanotube tips exposed to the arc plasma, and consequent positive feedback effects from the neutral gas and plasma, is proposed for tube growth in such arcs.

313 citations


Journal ArticleDOI
01 Jan 1994-Nature
TL;DR: In this paper, the 3He NMR spectra of the endohedral compounds 3He@C60 and 3he@C70 were analyzed and it was shown that the 3he nuclei encapsulated in C6o and C70 are shielded by 6 and 29 parts per million respectively, relative to free 3He.
Abstract: FULLERENES have internal cavities large enough to encapsulate atoms1,2. Recently, noble-gas atoms were introduced into about one in a million fullerene molecules3. It is now possible to achieve far greater yields of these noble-gas endohedral compounds4. Because 3He has a spin of 1/2 and is an excellent NMR nucleus5,6, it can be used as a probe for the magnetic shielding environment inside the fullerene cavity. This environment should reflect possible ring currents and hence the aromaticity in fullerenes7–15, an issue that measurements of magnetic susceptibility16,17 have not completely resolved. Here we present 3He NMR spectra of the endohedral compounds 3He@C60 and 3He@C70 (the @ symbol denotes a compound that is endohedral). We find that the 3He nuclei encapsulated in C6o and C70 are shielded by 6 and 29 parts per million respectively, relative to free 3He. These shieldings are unexpectedly large, indicating significant diamagnetic ring currents in C60 and very large ones in C70. Our results also show that, because of its small size and inertness, helium can serve as a useful probe of magnetic molecular properties. In addition, our work represents the first 3He NMR spectra of stable helium compounds.

300 citations


Patent
08 Dec 1994
TL;DR: In this paper, the authors introduce methods of introducing functional groups onto the surface of such fibrils, which are then used to attach functional groups to the surfaces of such structures.
Abstract: Graphitic nanotubes, which includes tubular fullerenes (commonly called “buckytubes”) and fibrils, which are functionalized by chemical substitution or by adsorption of functional moieties. More specifically the invention relates to graphitic nanotubes which are uniformly or non-uniformly substituted with chemical moieties or upon which certain cyclic compounds are adsorbed and to complex structures comprised of such functionalized fibrils linked to one another. The invention also relates to methods of introducing functional groups onto the surface of such fibrils.

225 citations


Journal ArticleDOI
TL;DR: The gram-order of fullerene (C60) with 99.8 wt% purity was isolated from carbon soot by fractional precipitation with 5,11,17,23,29,35,41,47-octa-tert-butylcalix[8]arene-49,50,51,52,53,54,55,56-octol as mentioned in this paper.
Abstract: The gram-order of fullerene (C60) with 99.8 wt% purity was isolated from carbon soot by fractional precipitation with 5,11,17,23,29,35,41,47-octa-tert-butylcalix[8]arene-49,50,51,52,53,54,55,56-octol. This is a very convenient and efficient C60 purification method without any precious apparatus.

204 citations


Book ChapterDOI
TL;DR: The triplet states are also formed efficiently by energy transfer from triplet sensitizers with energies above 35 kcal/mol as discussed by the authors, which makes them excellent photosensitizers.
Abstract: On irradiation with visible and UV light, fullerenes C60 and C70 give high yields of their triplet states. Fluorescence is very weak from both, and phosphorescence has been observed only from C70. The triplet states are also formed efficiently by energy transfer from triplet sensitizers with energies above 35 kcal/mol. Triplet fullerenes transfer energy efficiently to oxygen, giving singlet molecular oxygen, but they react and quench singlet oxygen very inefficiently, making them excellent photosensitizers. The fullerenes C60 and C70 are easily reduced but very difficult to oxidize. Electron transfer to triplet C60 and C70 occurs readily from electron donors to produce the radical anions. C60 can also be oxidized by excited high-potential photosensitizers to the radical cation. Some dihydrofullerenes also give high yields of the triplet state and singlet oxygen on irradiation. Photoreaction of C60 with electron-rich compounds appears to be an efficient route to difunctionalized adducts.

200 citations


Journal ArticleDOI

188 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed mechanism is proposed to account for conversion of the polycyclic polyyne rings into fullerenes, and a fullerene fragment is prepared by a Bergman enediyne cyclization followed by a radical-induced ring closure and a retro [2 + 2] process.
Abstract: We describe studies of the annealing and dissociation of even-numbered carbon cluster ions containing 50-70 atoms. The polycyclic polyyne ring isomers for cluster ions in this size regime can be annealed almost entirely into the fullerene geometry, with a small fraction being converted into an isomer which appears to be a large monocyclic ring. Surprisingly, we find that C[sub 60][sup +] behaves essentially the same as other similarly-sized clusters (such as C[sub 58][sup +]). This has important implications for understanding the mechanism of these structural transformations, as well as the overall scheme for fullerene synthesis. The activation energies for conversion of the polycyclic rings to fullerenes are low and relatively independent of cluster size, though the efficiency of forming a fullerene (rather than a large monocyclic ring) increases with cluster size. Based on our experimental results, a detailed mechanism is proposed to account for conversion of the polycyclic polyyne rings into fullerenes. According to this mechanism, a fullerene fragment is prepared by a Bergman enediyne cyclization followed by a radical-induced ring closure and a retro [2 + 2] process. The polyyne chains are then configured to spiral around the fullerene fragment and zip up to form a spheroidal fullerene. Wemore » also consider how these processes fit into an overall scheme for fullerene synthesis from small carbon fragments and describe a scheme that is consistent with the experimental results presented here. 36 refs., 14 figs., 1 tab.« less

173 citations


Journal ArticleDOI
TL;DR: In this article, the soot produced as a byproduct of fullerene synthesis by arc-evaporation consists of a microporous carbon with a surface area, after activation with carbon dioxide, of ca. 700 m2 g-1.
Abstract: The soot produced as a byproduct of fullerene synthesis by arc-evaporation consists of a microporous carbon with a surface area, after activation with carbon dioxide, of ca. 700 m2 g–1. Here, we investigate the structure of this material, and its appearance after electron irradiation and high-temperature heat treatment, using high-resolution electron microscopy. We show that the heat treatment transforms the new carbon into a structure containing large, tube-like pores, rather than into polycrystalline graphite. This suggests that the arc-evaporated carbon may have a novel, fullerene-related microstructure, and that it may be the precursor for nanotube formation.

130 citations


Journal ArticleDOI
01 Jul 1994-Science
TL;DR: Nanotubes represent the cylindrical form of carbon, intermediate between graphite and fullerite, and are found to have significantly larger orientation-averaged susceptibility, on a per carbon basis, than any other form of elemental carbon.
Abstract: Elemental carbon can be synthesized in a variety of geometrical forms, from three-dimensional extended structures (diamond) to finite molecules (C(60) fullerite). Results are presented here on the magnetic susceptibility of the least well-understood members of this family, nanotubes and C(60) fullerite. (i) Nanotubes represent the cylindrical form of carbon, intermediate between graphite and fullerite. They are found to have significantly larger orientation-averaged susceptibility, on a per carbon basis, than any other form of elemental carbon. This susceptibility implies an average band structure among nanotubes similar to that of graphite. (ii) High-resolution magnetic susceptibility data on C(60) fullerite near the molecular orientational-ordering transition at 259 K show a sharp jump corresponding to 2.5 centimeter-gram-second parts per million per mole of C(60). This jump directly demonstrates the effect of an intermolecular cooperative transition on an intramolecular electronic property, where the susceptibility jump may be ascribed to a change in the shape of the molecule due to lattice forces.

128 citations


Journal ArticleDOI
11 Feb 1994-Science
TL;DR: A method is proposed that could increase the efficiency of the process of noble gas insertion into C60 and provide a more general means to create endohedral fullerene compounds.
Abstract: On the basis of semiempirical and high-level ab initio calculations, theoretical evidence is presented of a "window" mechanism operable on the surface of C60 and other fullerenes. Through this mechanism, large holes may be formed in fullerenes excited to their triplet state, openings through which atoms and small molecules can pass. This work provides a theoretical foundation for experiments that have prepared endohedral noble gas compounds of C60 under thermal excitation. A method is proposed that could increase the efficiency of the process of noble gas insertion into C60 and provide a more general means to create endohedral fullerene compounds.

Journal ArticleDOI
TL;DR: In this article, the first and second-order lines in the Raman scattering spectra of arc-derived carbons are observed only when Co metal is present in the core of the anode.



Journal ArticleDOI
TL;DR: In this article, single-layer carbon nanotubes were synthesized by co-vaporizing cobalt with carbon in an arc fullerene generator and the diameter distribution of the tubes and their morphologies were studied using transmission electron microscopy.
Abstract: We have synthesized single-layer carbon nanotubes by co-vaporizing cobalt with carbon in an arc fullerene generator and have identified conditions that lead to high yields. The diameter distribution of the tubes and their morphologies are studied using transmission electron microscopy. For nanotubes produced using cobalt and carbon, the tube diameters range from 1 to 2 nm with distribution peaks at 1.3 and 1.5 nm. When sulfur is added to the carbon and cobalt, production of single-layer nanotubes is enhanced and the tubes have a wider range of diameters (from 1 to 6 nm). The diameter distribution for these nanotubes shows prominent peaks at 1.3 and 1.5 nm and additional maxima at 2.7 and 3.6 nm. Cobalt-containing crystallites, some encapsulated in graphitic polyhedra, are produced with the nanotubes and are found in the soot away from the cathode.

Journal ArticleDOI
01 Nov 1994-Nature
TL;DR: In this paper, the structure and reactivity of gas-phase fullerenes doped with niobium (NbCn+ with n = 28-50) were investigated.
Abstract: SINCE the discovery of fullerenes1, efforts have been made to trap metal atoms inside fullerene cages2, and both endohedral3,4 and exohedral5,6 metallofullerenes have been synthesized. There is, however, a third possibility: a 'networked' metallofullerene, where the metal atom is incorporated into the carbon cage. Here we report the results of experiments to study the structure and reactivity of gas-phase fullerenes doped with niobium (NbCn+ with n = 28–50). These experiments, which use injected-ion drift-tube tech-niques, indicate that for fullerenes containing an even number of carbon atoms the metal is endohedral, but for fullerenes with an odd number of carbon atoms, the niobium metal is bound as a part of the carbon cage. Thus, networked metallofullerenes appear to be a stable class of metallofullerene. We suggest that such metallo-fullerenes can form if the metal atom retains sufficient electron density to form several strong covalent metal–carbon bonds.

Journal ArticleDOI
TL;DR: In this article, modified fullerene was evaluated with respect to the ability to form monolayers and an ether moities was attached to the C{sub 60} molecule and the product was characterized.
Abstract: The authors seek to develop modified fullerenes that form self-assembled monolayers. An ether moities was attached to the C{sub 60} molecule and the product was characterized. The modified fullerene was evaluated with respect to the ability to form monolayers.

Journal ArticleDOI
TL;DR: The ESR-active lanthanofullerene La C[sub 82] has been isolated from various hollow fullerenes by an efficient single-stage chromatographic separation process as mentioned in this paper.
Abstract: The ESR-active lanthanofullerene La C[sub 82] has been isolated from various hollow fullerenes by an efficient single-stage chromatographic separation process. Pyrenylethyl-silica was used as a stationary phase with toluene as an eluent. Lanthanum-containing fullerenes were prepared by the arc heating of metal-impregnated graphite rods in a He atmosphere. Fast atom bombardment mass analysis of the isolated sample confirmed the isolation of La C[sub 82]. ESR absorption spectra of the present sample prove the separation of a La C[sub 82] isomer with a 1.15-G hyperfine splitting. The UV-vis-near-IR absorption spectra of the sample reveal near-IR absorption peaks which are characteristic of the fullerene radical anions. 40 refs., 4 figs.

Journal ArticleDOI
TL;DR: In this paper, a simple model for the qualitative evaluation of the local curvature of fullerene surfaces is presented and used for the prediction of addition sites in higher fullerenes.
Abstract: HPLC Separation of higher fullerenes was compared on two different stationary phases, and the preparative isolation of pure C76 is described. Higher-fullerene derivatives 1 and 2 were prepared by Diels-Alder reaction of C70 and C76 with an ortho-quinodimethane intermediate generated in situ. Three out of four possible isomeric C70 monoadducts, i.e.1a–c, and, for the first time, one isomeric C76 monoadduct, i.e.2c, could be isolated in pure form and characterized by 1H-NMR, 13C-NMR, UV/VIS, and mass spectrometry. Five other C76 isomers i.e., 2a,b,d–f were obtained in partially separated product fractions. Coalescence temperatures and energy barriers were determined for the cyclohexene-ring inversion in two of the isomeric C70 derivatives. The structure of the C70 adducts could be deduced unambiguously from symmetry considerations based on high- and low-temperature 1H-NMR spectroscopy. A simple model for the qualitative evaluation of the local curvature of fullerene surfaces is presented and used for the prediction of addition sites in higher fullerenes. These predictions are compared to the experimental results mentioned above as well as to predictions resulting from π-bond-order considerations and from calculated pyramidalization angles.

Journal ArticleDOI
TL;DR: A model in which the ultraviolet dielectric tensor of planar graphite is transported to the spherical geometry of a nanoscale multishell fullerene with a central cavity is developed, finding that the effect of clustering is important and reduces but does not remove completely the quantitative difficulties of the graphitic mult ishell model.
Abstract: We develop a model in which the ultraviolet dielectric tensor of planar graphite is transported to the spherical geometry of a nanoscale multishell fullerene with a central cavity. This is accomplished by assigning to every point of the multishell fullerene a local dielectric tensor identical to that of graphite with its c axis aligned along the local radial direction. The dynamic, multipolar polarizabilities of the model fullerene are obtained from the exact solutions of the nonretarded Maxwell equations. The ultraviolet absorption spectrum of the hollow fullerene is calculated as a function of the ratio of the inner and outer radii. Comparisons of the theoretical absorption spectra with the 2175-\AA{} interstellar extinction hump and with recent absorption measurements for synthetic multishell fullerenes indicate that the dielectric properties of graphite are qualitatively adequate for understanding the optical data. However, difficulties persist with both the astrophysical and laboratory absorption peaks which lead us to consider the possible role of multishell fullerene aggregation into small or large clusters. It is found that the effect of clustering is important and reduces but does not remove completely the quantitative difficulties of the graphitic multishell model. Finally theoretical electron-energy-loss spectra (EELS) of these structures with an empty or filled cavity are calculated from the multipolar polarizabilities of the model. The results indicate that spatially resolved EELS measurements should be ideally suited to study the dielectric properties of individual multishell fullerenes and to ascertain to what extent they differ from those of planar graphite.

Journal ArticleDOI
TL;DR: In this article, the morphology of multiple-shell fullerenes is investigated by ab initio calculations using Yang's O(N) method, and it is found that for large single-shell femtoseconds, the spherical morphology has lower energy than that of polyhedrons.
Abstract: The morphology of multiple-shell fullerenes is investigated by ab initio calculations using Yang's O(N) method. It is found that for large single-shell fullerenes with ${\mathit{I}}_{\mathit{h}}$ symmetry, the spherical morphology has lower energy than that of polyhedrons. The formation energy per atom follows a simple scaling law. Including an estimate of intershell van de Waals interactions leads to the conclusion that spherical multiple-shell fullerenes are likely the most stable structure of large carbon clusters. These results are in good agreement with recent experiments.

Journal ArticleDOI
21 Jul 1994-Nature
TL;DR: In this article, the authors reported the preparation of pure crystalline Sc_2@C_(84) and analyses of its structure by electron diffraction and high-resolution transmission electron microscopy.
Abstract: IT was first proposed in 1985 that fullerenes can confine atoms in their interior because of their closed-cage structure. Attempts to verify this conjecture following the mass production of fullerenes have yielded metallofullerenes in bulk, and there is now good evidence that these compounds are endohedral—that is, that the metal atoms are inside. But direct confirmation in the form of structural data has been lacking, in part because of the difficulty of separating different metallofullerenes and obtaining pure crystals. Here we report the preparation of pure crystalline Sc_2@C_(84) and analyses of its structure by electron diffraction and high-resolution transmission electron microscopy. At room temperature the Sc_2@C_(84) molecules pack in a hexagonal-close-packed structure with a ratio of lattice constants c/ɑ = 1.63, the value expected for ideal-sphere packing. The molecular spacing of 11.2 A is the same as that found earlier in crystalline C_(84) (refs 5, 6). The match between our microscopic images and simulations is markedly better for endohedral models than for those in which the metal atoms reside in the lattice outside the C_(84) cages. We believe that this combination of observations points inevitably to the conclusion that the metal atoms are inside the fullerenes.

Journal ArticleDOI
TL;DR: In this article, the authors measured energy losses by carbon clusters C p (p ≤ 8) and fullerene ions C 60 in thin carbon foils in the energy range from 0.3 to 5.65 MeV/atom.
Abstract: Energy losses by carbon clusters C p ( p ≤ 8) and fullerene ions C 60 in thin carbon foils have been measured in the energy range from 0.3 to 5.65 MeV/atom. A small enhancement in energy loss is obtained for carbon atoms in the clusters relative to single carbon ions at the same velocity. Very large pulse height defects have been observed in the energy response of a silicon detector bombarded by C 60 ions with energies ranging from 6 to 30 MeV.


Journal ArticleDOI
TL;DR: In this paper, the synthesis of a series of new C60 derivatives of interest for their potential in the study of LB properties of fullerenes is reported, including perfluorinated fulleropyrrolidine 4d.

Patent
11 Mar 1994
TL;DR: In this paper, a method of forming synthetic hydrogen defect free diamond or diamond like films on a substrate was proposed, which involves providing vapor containing fullerene molecules with or without an inert gas.
Abstract: A method of forming synthetic hydrogen defect free diamond or diamond like films on a substrate. The method involves providing vapor containing fullerene molecules with or without an inert gas, providing a device to impart energy to the fullerene molecules, fragmenting at least in part some of the fullerene molecules in the vapor or energizing the molecules to incipient fragmentation, ionizing the fullerene molecules, impinging ionized fullerene molecules on the substrate to assist in causing fullerene fermentation to obtain a thickness of diamond on the substrate.

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a novel form of metallofullerenes, namely, those with radioactive atoms encapsulated in the C[sub 82]cage.
Abstract: We demonstrate a novel form of metallofullerenes, namely, those with radioactive atoms encapsulated in the C[sub 82]cage. The metal atoms were made radioactive by a neutron capture reaction or through a nuclear decay process. The most important and intriguing finding of the present study is that the endohedral form of metallofullerenes is not affected by the recoil energy of the metal atom resulting from emission of electrons in the [beta] decay. Such a stability of the cage against the recoil energy of the encapsulated atom was confirmed by the elution behavior of the metallofullerene in liquid chromatography. Successful encapsulation of radioactive atoms inside the fullerene cage will greatly widen the potential use of endohedral metallofullerenes not only in basic science and technology but also in other areas, such as medicine. 14 refs., 3 figs.

Journal ArticleDOI
TL;DR: The analytical potential of C[sub 60] fullerenes as sorbent materials for preconcentration of metal traces by formation of neutral chelates was studied for the first time in this paper.
Abstract: The analytical potential of C[sub 60] fullerenes as sorbent materials for preconcentration of metal traces by formation of neutral chelates was studied for the first time in this work. The model system used for this purpose was the determination of lead traces in waters by using ammonium pyrrolidinedithiocarbamate as ligand. The chelate is formed in a continuous-flow system, sorbed on a C[sub 60] fullerene minicolumn, and subsequently eluted for transfer to an atomic absorption spectrometer. Two other simultaneous batches of experiments were performed in parallel by using C[sub 18] bonded silica and activated carbon as sorbents in order to study the features of the new sorbent material and its advantages. The primary assets of C[sub 60] fullerenes in this respect are a high sensitivity arising from efficient adsorption and also high selectivity derived from the special features of this new type of sorbent material. 27 refs., 3 figs., 2 tabs.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the smallest fullerene, the dodecahedron C$20$, has the lowest energy, while the monocyclic ring is the most stable 20-atom carbon species.
Abstract: Contrary to recent experimental evidence suggesting that the monocyclic ring is the most stable 20-atom carbon species, highly accurate calculations convincingly predict that the smallest fullerene, the dodecahedron C$_{20}$, has the lowest energy. A related corannulene-like bowl is nearly degenerate in energy to the fullerene. Thermodynamic considerations suggest that at formation temperatures of around 700 K the bowl should be the dominant species. The recent application of gradient corrections to LDA which supported the ring structure is qualitatively in error. (RK-94-02)