Cluster structure of fullerene-containing soot and C60 fullerene powder

Electron microscopy and electron diffraction methods were employed in a study of the structure of a fullerene-containing soot produced in gas discharge and of a C₆₀ fullerene powder. The data obtained were analyzed with the use of fractal geometry concepts. It has been shown that, in the structure of the objects studied, several spatial scales can be identified. The effective radius of the structure’s “elementary particles” calculated using scaling relationships is equal to 6 Å for the soot and 4.5 Å for the C₆₀ fullerene. The “elementary particles” combine into associates. The number of particles in an associate in both the soot and the C₆₀ powder is not large (about 10). The associates form fractal nanoclusters 30–80 nm in size having a fractal dimension of 1.60±0.05 in the soot and of 1.8±0.05 in the C₆₀ fullerene. The structure of the soot nanocluster is unstable and can be significantly modified by externally applied factors (e.g., as a result of treatment with toluene). The nanoclusters combine into aggregates having the form of branching cross-linked filaments. Eventually, these aggregates combine to form macroparticles of soot.     

ELECTRON SPIN RESONANCE CHARACTERISTICS OF NITROGEN-DOPED FULLERENE

The nitrogen-doped fullerene has been obtained by arc discharge between two high-purity graphite rods in the atmosphere of N₂ and He, The electron spin resonance(ESR) characteristics of N-doped fullerene have been investigated. The results show that the ESR spectra of N-doped fallerene axe composed of two parts, a paramagnetic signal of N-center and a paramagnetic signal of C-center, For comparing with N-doped fullerene, we have also studied ESR spectra of C₆₀ powder, C₆₀ sublimed film and H-doped C₆₀ film. For C₆₀ powder and H-doped C₆₀ film, their in situ ESR. measurements are carried out at various temperatures, and reasonable explanations are proposed.     

Fullerene C60 formation in partially ionized carbon vapor

The assembling rate of a fullerene C₆₀ molecule has been theoretically studied as a function of electron concentration and temperature in partially ionized carbon vapor. For C⁶⁰ formation via one or two intermediate stages of cluster collisions, it has been shown that there is a region of plasma parameters (the temperature and electron concentration) in which fullerene C₆₀ is formed more efficiently. The C₆₀ formation rate versus temperature and electron concentration relationships have been found to correlate with the trends in the collision cross-section of carbon clusters as functions of these parameters.     

On the encapsulation of azafullerenes inside the single-walled carbon nanotubes: Density-functional theory based treatments

We theoretically studied the encapsulation of azafullerene (C₅₉N) inside the single-walled carbon nanotubes (SWCNTs) from the first-principles. Adsorption energy is calculated, and the azafullerene affinities for the typical semiconducting and metallic nanotubes are investigated and compared with those of pure C₆₀ fullerene. It has been found that the azafullerene as well as the fullerene affinity for the semiconducting nanotubes is stronger than that for the metallic ones, and the energy values and binding distances are typical for the physisorption. Our first-principles results indicate that the interaction between SWCNTs and azafullerenes is comparable with the nanotubes-C₆₀ system. The charge analysis shows, however, that the charges have been transferred from the cage to the tube in the azafullerene peapods, while in the fullerene peapods the charges were found to be transferred from the tube to the fullerene nanocage. Furthermore, it was found that the interaction between the considered fullerenes and host nanotubes strongly depends on the tube diameters.     

Vibrational spectra of lanthanide endofullerenes with different symmetries of molecular structure

Quantum-chemical calculations of the geometric structure and vibrational spectra of lanthanide endofullerenes have been carried out. The vibrational frequencies of lanthanide atoms depend substantially on the symmetry of the molecular structure of the endofullerene and on the distance between the metal atom and the carbon cage. The infrared spectra of the endofullerenes M@C₆₀ contain vibrations that are forbidden by symmetry for the empty fullerene C₆₀. A change in the vibrational spectra due to the encapsulation of a metal atom in fullerenes with a C₆₀ cage is considerably more pronounced than that of the higher fullerenes. In the vibrational spectra, there are lines not characteristic of C₆₀, which indicates the presence of M@C₆₀ endofullerenes in a mixture with C₆₀ fullerenes.     

Quasi-one-dimensional fullerene-nanotube composites: Structure, formation energetics, and electronic properties

Carbon nanotubes coated with close-packed C₆₀ (or C₇₀) fullerenes, which are “attached” to the nanotubes by van der Waals forces, are considered and classified as a new class of nanocomposites. Semiempirical and molecular-dynamics calculations reveal the most energetically stable systems and show that a topological (Stone-Wales) defect on a nanotube can promote a more favorable “attachment” of fullerene to the nanotube. It has been shown that the molecular interaction of the fullerene coating with the nanotube leads to a significant change in its electronic spectrum, namely, to the formation of minibands including a large number of branches associated with the lift of the degeneracy of levels of C₆₀ and to the consolidation of branches of the carbon nanotube into the Brillouin zone smaller than that in the carbon nanotube. This fact should strongly change the interaction of light with such a nanocomposite as compared to carbon nanotubes and fullerenes, which provides prospect of its application in photovoltaics.     

Interaction between B-Doped C60 Fullerene and Glycine Amino Acid from First-Principles Simulation

The possibility of formation of complexes between glycine and boron doped C60 （C59B） fullerene is investigated and compared with that of C60 fullerene by using the density functional theory calculations. It has been found that the binding of glycine to C59B generated the most stable complexes via its carbonyl oxygen active site, with a binding energy of-37.89 kcal/mol, while the glycine molecule prefers to bind to the pure C60 cage via its amino nitrogen active site, consistent with the recent experimental and theoretical studies. We have also tested the stability of the most stable Gly-C59B complex with ab initio molecular dynamics simulation, carried out at room temperature. These indicate that the B-doped C60 fullerenes seem to be more suitable materials for bindings to proteins than pure C60 fullerenes.     

Processing of C<Subscript>60</Subscript> thin films by Matrix-Assisted Pulsed Laser Evaporation (MAPLE)

Thin films of fullerenes (C₆₀) were deposited onto silicon using matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out from a frozen homogeneous dilute solution of C₆₀ in anisole (0.67 wt%), and over a broad range of laser fluences, from 0.15 J/cm² up to 3.9 J/cm². MAPLE has been applied for deposition of fullerenes for the first time and we have studied the growth of thin films of solid C₆₀. The fragmentation of C₆₀ fullerene molecules induced by ns ablation in vacuum of a frozen anisole target with C₆₀ was investigated by matrix-assisted laser desorption/ionization (MALDI). Our findings show that intact fullerene films can be produced with laser fluences ranging from 0.15 J/cm² up to 1.5 J/cm².     

Influence of defects in the carbon network on the static polarizability of fullerenes

The static polarizability of the C₆₀, C₇₀, C₈₀, and C₁₈₆ fullerenes has been calculated within the semiempirical MNDO approximation implemented in the MOPAC quantum-chemical program package. It is demonstrated that the results obtained are comparable with experimental data and the results of the ab initio B3LYP method using the 6–31G(d, p) basis set. The influence of topological defects (five-, seven-, and eight-membered rings), vacancies produced by removing pentagons, and nitrogen and boron atoms on the geometric parameters and the polarizability of the C₆₀, C₂₄₀, and C₅₄₀ fullerenes has been investigated by the MNDO method. It is revealed that the polarizability of the fullerene with topological defects is higher than the polarizability of the perfect icosahedral fullerene. The formation of vacancies in the carbon cage leads to a linear decrease in the polarizability of the fullerene and an increase in the specific polarizability. The polarizability of the heterofullerene with nitrogen or boron atoms spaced apart in the carbon cage is higher than that of the fullerene with heteroatoms located adjacent to each other.     

Intercalation of C60 fullerene crystals with alkali and alkaline-earth metals through self-propagating high-temperature synthesis

A method for rapidly intercalating C₆₀ fullerene crystals has been implemented using self-propagating high-temperature synthesis. The method has been used to intercalate C₆₀ fullerene crystals with alkali (K, Rb) and alkaline-earth (Ca, Ba) metals. The superconducting transition temperatures of the prepared compounds have been measured. The C₆₀ fullerene crystals intercalated with calcium have been investigated using X-ray diffraction.     

Phase transition in C60-2-thioxo-l, 3dithiole cycloadduct

Quadratic electrooptic coefficient (QEOC) measurements have been made for fullerene C₆₀) and its derivative C₆₀-2-thioxo-l,3-dithiole. An anomaly in C_p has been revealed at about — 60°C that corresponds to the appearance of a structural phase transition. Correlation with a temperature anomaly in the QEOC is revealed. This leads to the conclusion that the QEOC for fullerene depends mainly on vibrational and rotational contributions. The contribution arising from charge distribution asymmetry is most important in the fullerene derivative. The observed temperature anomalies of the QEOC result in the possibility of using the QEOC as a sensitive tool for observing low-temperature phase transitions in the fullerene derivatives.     

X-ray diffraction analysis of C<Subscript>60</Subscript> fullerene powder and fullerene soot

C₆₀ fullerene powder and fullerene soot are examined by the method of small-angle X-ray diffraction. Small-angle diffraction patterns constructed in the Guinier coordinates make it possible to find the radii of inertia of scattering elements. The small-angle diffraction scattering findings agree well with large-angle X-ray diffraction data.     

Effect of a buffer layer, composition and annealing on the performance of a bulk heterojunction polythiophene/fullerene composite photovoltaic device

Post-annealing of P3HT/C₆₀-based plastic solar cells, composite ratio and, incorporation of a buffer layers at the ITO–polymer/fullerene composite interface and the polymer/fullerene composite–Al interface have shown significant improvement in the performance of the photovoltaic device, both in terms of open-circuit voltage and short-circuit current. The annealing temperature, time duration and P3HT/C₆₀ composite ratios have been optimized for the best performance of typical ITO/PEDOT:PSS/P3HT:C₆₀/LiF/Al solar cell. The C₆₀ content is very crucial because it improves the photocurrent in the beginning but after a certain value it leads to decrease in absorption, thereby decreasing the photocurrent.     

Investigation of the possibility of functionalization of C20 fullerene by benzene via Diels–Alder reaction

C₂₀ fullerene, this novel species with all its pentagonal faces has displayed some unique operations in making fast pericyclic reactions. As an example, the high dienophile character of the C₂₀ fullerene and the ability of this species in making an ultra-fast Diels–Alder reaction with 1,3-butadiene, has been recently reported. Moreover, new experimental reports claim that the C₆₀ fullerene, one of the fullerene family, could make a Diels–Alder reaction with the central ring of anthracene and make the ring non-aromatic. These reports may encourage researchers to do more studies on the properties of this small carbon cage.To address this question, the present research has discussed all the reaction channels of the Diels–Alder cycloaddition of benzene molecule as a 1,3-diene with the C₂₀ fullerene in order to answer this question: “Is C₂₀ fullerene able to make a Diels–Alder reaction with this molecule?”.     

Synthesis of fullerenes

We present a review of the methods most frequently used for the synthesis of fullerenes and the changes that these methods have experienced since 1985 when Kroto and co‐workers discovered C₆₀. We also analyze the most important models that explain the mechanism of the formation of fullerenes in carbon soot, as well as the new methodologies that lead to the rational chemical synthesis of fullerenes and of fullerene fragments as precursors. Copyright © 2013 John Wiley & Sons, Ltd.     

On the possibility of considering the fullerene shell C60 as a conducting sphere

The dynamical and static dipole polarizabilities of the C₆₀ molecule have been calculated on the basis of the experimental data on the cross section of the fullerene photoabsorption. It has been shown that the fullerene shell in the static electric field behaves most likely as a set of separate carbon atoms rather than as a conducting sphere.     

Rise of the fullerene yield in an arc discharge under the action of gas flow in a hollow electrode

When a turbulent gas flow and a hollow electrode are combined in a discharge chamber, a synergetic effect is observed: the weight of the deposit decreases by five to six times and fullerene-containing soot dissolves completely (without precipitation) in benzene. The mass spectra of the synthesis products contain the lines of C₆₀, C₇₀, and C_{74 + 2n} (n = 0–40) fullerenes. This indicates a 100% yield of the fullerene mixture. As a result, the output of the fullerene synthesis process increases by a factor of more than 10.     

Formation of metallofullerenes by laser ablation of externally doped fullerenes C60Mx (M=Sm, Pt and Ni)

Photofragmentation of metal fullerides C₆₀M_x (M=Sm, Pt and Ni) has been studied by excimer laser ablation–TOF mass spectrometry. Metallofullerenes of the type C_nM (n<60) have been observed in both the positive and negative ionic modes, with C₅₉M being the most prominent species. It is supposed that the metal atom is incorporated into the network of the fullerene cage to replace one carbon atom of the cage, forming substitutional metallofullerene. The occurrence of the C₅₉M, C₅₈M, C₅₇M clusters in the mass spectra is confirmed by the coincidence of the intensity distribution of the mass peaks with the isotopic abundance pattern calculated from the natural abundance of isotopes of C and M. Odd-numbered high-carbon clusters are observed in our laser ablation study of all the metal fullerides in the negative ion channel. The evolution of the mass spectra of these samples with laser irradiation shots indicates that the transformation process from an externally doped fullerene to the substitutionally doped fullerene involves the loss of metal carbide, MC. The structures of metallofullerenes C_2n+1M and C_2nM with even and odd total numbers of atoms respectively are discussed. Formation mechanisms with the participation of odd-numbered all-carbon fullerene clusters as intermediates are supposed. Received: 18 June 2001 / Accepted: 28 September 2001 / Published online: 2 May 2002     

Thermal imidization of polyamic acid–fullerene composites: 'in situ' X-ray diffraction study

'In situ' wide angle (WAXS) and small angle X-ray scattering (SAXS) studies were carried out to characterize the structural changes occurring during the conversion of a polyamic acid into the polyimide in the presence of fullerene, C₆₀. The variations in crystallinity, long period, and the SAXS invariant of the samples are discussed in the light of the various temperature ranges studied. The conversion of the polyamic acid into the polyimide is analyzed according to the different structural steps. Results reveal that C₆₀ affects the degree of order of the composite in the molecular direction, giving rise to slightly smaller crystals than those found in pure polyamic acid. The difference in the SAXS data between the pure PAA and the composite are discussed through the interaction of C₆₀ molecules with the polyamic acid, which seems to hinder the imidization reaction up to 185°C.     

Specific features of the evaporation of C60 films

The evaporation of pure C₆₀ films is investigated. The rates of evaporation of the fullerene are experimentally measured, and the saturated vapor pressures are determined in the temperature range 250–290°C. The influence of atmospheric oxygen and ultraviolet irradiation on the rate of evaporation of the fullerene is studied. It is shown that the evaporation parameters of pure C₆₀ films differ substantially from the reference values.