Showing papers on "Fullerene published in 1990"

Solid C60: a new form of carbon

Abstract: A new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules. Infrared spectra and X-ray diffraction studies of the molecular packing confirm that the molecules have the anticipated 'fullerene' structure. Mass spectroscopy shows that the C70 molecule is present at levels of a few per cent. The solid-state and molecular properties of C60 and its possible role in interstellar space can now be studied in detail.

Isolation, separation and characterisation of the fullerenes C60 and C70: the third form of carbon

Abstract: Pure samples of the species C60(Buckminsterfullerene) and C70(fullerene-70) have been prepared, and their structures characterised by their mass and 13C NMR spectra; the results indicate the existence of a family of stable fullerenes, thus confirming that carbon possesses a third form in addition to diamond and graphite.

Scanning tunnelling microscopy of solid C 60 /C 70

Abstract: THE detection of a strong peak in mass spectra of carbon vapour corresponding to a cluster of 60 carbon atoms1 led to the proposal that these clusters corresponded to highly symmetric C60. molecules in the shape of truncated icosahedra1,2. Recently macroscopic quantities of C60 and the related species C70 (thought to have an elongated cage structure) have been prepared3,4 and purified in a solid form, called fullerite5. The availability of a solid form has made possible studies using infrared and ultraviolet-visible absorption spectroscopy, X-ray and electron diffraction5, NMR and Raman spectroscopy, all of which provide evidence that supports the proposed 'soccer ball' structure of C60. Here we report the direct imaging of C60 molecules in sub-micrometre-sized particles of fullerite, using scanning tunnelling microscopy. The images reveal spherical molecules, spaced about 1 nm apart, stacked in close-packed arrays. Our results give a direct demonstration of the highly symmetric structure of these clusters.

Laser deposition of carbon clusters on surfaces - a new approach to the study of fullerenes

Abstract: We have accumulated large pure carbon clusters (Fullerenes) on a surface. These clusters were produced by laser vaporization of graphite in a static rare‐gas atmosphere. Their presence on the surface was confirmed by an isotope scrambling experiment using a laser‐desorption/laser‐ionization mass spectrometric detection scheme.

Carbon ARC Generation of C60

Abstract: Generation of C60 at a rate of more than 10 grams per day has been accomplished by operation of a carbon arc in an atmosphere of helium. Optimum yield of 15% was found to occur near 100‐200 torr, but yields greater than 3% were found throughout the range between 50 and 760 torr. A model is proposed to explain the observed behavior based on competition between annealing of graphitic sheets to curve so that they minimize dangling bonds, and further rapid growth of these sheets in the gas phase to form giant fullerenes. In agreement with predictions of this model, laser vaporization of graphite targets was found to produce macroscopic quantities of C60 only when performed in an oven above 1000 C.

Formation of high mass carbon cluster ions from laser ablation of polymers and thin carbon films

Abstract: Three materials were studied by laser ablation/Fourier transform mass spectrometry, using 266 nm laser radiation: a copolymer of ethylene and tetrafluoroethylene (ETFE), polyphenylene sulfide (PPS), and a diamond‐like carbon film (DLC). In each case, positive ion mass spectra exhibit primarily even‐numbered, high mass carbon clusters (‘‘fullerenes’’) of the type previously reported for graphite ablation. In the case of ETFE, a large C+60 peak (‘‘buckminsterfullerene’’) was observed. The polymer spectra showed a strong dependence on the number of laser pulses on one spot and the laser power density. For ETFE, the fullerene ion relative intensity first increases and then decreases as a function of the number of laser pulses. For the DLC film, fullerenes are observed with a single laser pulse on a fresh spot of the sample. The results are interpreted in terms of a gas phase growth model for the fullerene ion formation.

C 60 , fullerenes, giant fullerenes and soot

Abstract: During a series of experiments in which the nucleation of carbon vapour was studied in order to explore carbon chain and particle formation in stars the highly stable c60 molecule was detected. The properties of this molecule are in almost perfect accord with the proposal that the molecule has the closed cage buckminsterfullerene structure in which all 60 atoms are equivalent and lie at the corners of a truncated icosahedron, a shape familiar to many today in the form of the modern foot- or soccerball. This molecule is expected to be stabilised by geodesic and aromatic factors. The most important aspect of this discovery lies in the fact that such a symmetric object can form spontaneously from a chaotic, hot, carbon plasma. This novel conjecture is consistent with a wide range of observations on carbonaceous materials. The emphasis in this article is on those aspects of the c60 saga which pertain to non-planar organic chemistry both on earth and in space.

Materials with diamond-like properties and method and means for manufacturing them

Abstract: Diamonds or diamond like substances are formed by breaking covalent bonds of fullerene and/or azite particles in the presence of carbon containing gases to form tetrahedral diamond like structures.

Fullerene cage clusters. The key to the structure of solid carbon

Abstract: The recent plethora of carbon cluster studies has yielded results which indicate that several different types of intermediate participate in the formation of carbon microparticles in the gas phase. Cumulene and/or poly-yne chains, either open-ended or in the form of monocyclic rings occur. It has been proposed that some of the more stable clusters are closed-cage fullerenes (C60buckminsterfullerene being archetypal) and other which are highly reactive have curved and closing shells. These may be the embryos which accrete carbon rapidly, ultimately resulting in carbon microparticles. The nucleation mechanism developed to explain the spontaneous formation of C60 predicts that such microparticles should have icospiral concentric shell internal structures, a result which can be shown to be quantitatively consistent with observation. This analysis and the relationships between the various carbon clusters are surveyed here. There are several important aspects of this new nucleation scenario that suggest that it applies to soot formation as well.

Solid C60 — How We Found It

Abstract: In May of 1990, crystals of a new form of carbon were observed crystallizing from a solution of the newly-produced macroscopic quantities of fullerene molecules This discovery followed many years of work we had done in producing and measuring the optical properties of small particles of graphitic carbon, a work which was aimed, in part, at a better understanding of the various spectral features of interstellar material Among three distinctly different types of carbon particulates, distinguished by their differing ultraviolet and Raman spectra, was one that later proved to contain macroscopic quantities of C 60 and C 70 Evidence for fullerenes came from mass spectra, infrared spectra, and X-ray and electron diffraction More, recent experiments with our collaborators have included scanning tunneling microscopy and gas phase emission spectroscopy in the infrared At the moment, there is no obvious connection with interstellar spectral features

Laser deposition, vibrational spectroscopy, nmr spectroscopy and stm imaging of c60 and c70

Abstract: We recently demonstrated that C60 and C70, as well as other fullerenes, can be deposited and accumulated on surfaces using laser ablation of graphite In an Inert gas atmosphere. After learning of the work of Kratschmer et al. Indicating the presence of C60 In carbon soot, we showed that samples consisting almost exclusively of C60 and C70 can be sublimed from such soot. Vibrational Raman spectra of C60 and C70 were obtained from these samples. The C60 spectrum Is consistent with the calculated spectrum of Buckmlnsterfullerene, and ?he strongest three lines can be assigned on the basis of frequency and polarization. The NMR spectrum of dissolved C60 was then obtained, and found to consist of a single resonance, establishing the Icosahedral symmetry of this molecule. STM images of the C60 molecules on a Au(111) crystal face show that these clusters form hexagonal arrays with an Intercluster spacing of 11.0 A and are mobile at ambient temperature. Distinctly taller species evident In the arrays are believed to be C70 clusters. Vibrational Raman and infrared spectra have also been obtained for separated C60 and C7 0. Five years have passed since Kroto, Heath, O'Brien, Curl and Smalley, inspired by the work of R. Buckminster Fuller, realized that there was a most elegant solution to the problem of explaining the extraordinary inertness and stability observed for 60 atom pure-carbon clusters 1 . The solution proposed was the beautifully symmetric arrangement familiar as the soccerball pattern - a truncated icosahedron consisting of 12 pentagons and 20 hexagons. As Kroto would write: "This structure necessitated the throwing of all caution to the wind ... and it was proposed immediately; after all, it was surely too perfect a solution to be wrong." 2 The experimental evidence required to substantiate this intuitive leap proved difficult to obtain, however. While many ingenious experiments indirectly supported the picture that not only C60 but all of the observed carbon clusters with an even number of atoms (n > 24) can exist in the form of 2-d closed nets of 12 pentagons and ( n/2 - 10 ) hexagons 3 , doubts persisted, and some investigators suggested alternative structures for these clusters 4 , 5. Over the last few months the gap between intuition and experiment has been closing rapidly. With the discovery that macroscopic samples of fullerenes can be produced and accumulated 6-8 it has become possible to rapidly obtain a wealth of new information about them 6, 7, 9-13. In this paper we describe the course of our work on carbon cluster deposition, vibrational spectroscopy, NMR spectroscopy, and scanning tunnelling microscopy during this period of time. Early this year, we began an effort to develop a new approach to studying carbon clusters by trying to deposit them on surfaces using laser ablation of graphite under a static inert gas atmosphere 8. A highly sensitive surface analytical mass spectrometer 14 was used to analyze the deposited material. The observed mass spectrum, shown in Figure 1, showed a broad range of fullerenes, with C60 and C70 particularly prominent.

Production, Characterization, and Deposition of Carbon Clusters

Abstract: We have developed a new cluster ion source that can generate intense beams of metal and semiconductor clusters of a very wide-size range. With the source, we have observed intense beams of carbon clusters with mean cluster sizes of up to 4000 atoms/clusters. However, we have found that for generating small fullerenes, such as C60 and C70, the recently discovered technique by Kraetschmer et al. is much more efficient. By improving the technique, we have generated gram quantities of C60 and C70 and systematically investigated their thermal desorption properties. During the heating process, we have discovered that at high temperatures the bulk fullerenes, fullerite, transformed to another form of carbon, which still evaporates at temperatures above 700 C, but does not dissolve in benzene.

STM Topographical Images of C60

Abstract: STM topographical images of C 60 are reported. The images are consistent with a molecule approximately 9 A in diameter possessing the now-famous soccer ball structure. With the molecule deposited on gold, its atomic structure is not resolved. On graphite the structure of the within the borders of the C 60 molecule is dominated by that of the graphite forming a moire-like pattern. Some evidence of atomic structure is seen in multilayers of C 60 where some five- and six-membered rings are visible. These may, however, be features of fragments of the fullerene rather than whole molecules.