Core electron level structure in C<Subscript>60</Subscript>F<Subscript>18</Subscript> and C<Subscript>60</Subscript>F<Subscript>36</Subscript> fluorinated fullerenes

The structure of C1s and F1s core electron levels in C₆₀F₁₈ and C₆₀F₃₆ fluorinated fullerenes has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. It is established that C1s levels of carbon atoms not bound to fluorine in these compounds are shifted down by 1.0 and 1.6 eV relative to the C1s level in the usual C₆₀ fullerene, so that the binding energies of the core electron levels in C₆₀F₁₈ and C₆₀F₃₆ amount to E _b (C1s, C-C) = 285.7 and 286.3 eV, respectively. These values are characteristic and can be used for the identification of both homogeneous fluorinated fullerenes and combined materials comprising a mixture of various fluorinated fullerenes with each other and with different carbon-containing based materials.     

C60,C180,C60@C180富勒烯分子的压缩力学特性与电子结构

采用分子动力学方法模拟了C60,C180,C60@C180富勒烯分子的压缩过程,用PM3半经验量子力学方法计算了压缩C60,C180,C60@C180分子的电子结构,讨论了C60,C180,C60@C180分子压缩力学特性的差异,以及电子结构在压缩过程中的变化．结果表明,由于分子几何构形上的差异,C60分子的承载与吸收能量能力显著高于C180和C60@C180分子,而CC60@C180分子略高于C180分子;C60分子具有最高的化学稳定性,而C60@C180分子的稳定性最低;C60和C60@C180分子的压缩变形越大,越容易失去电子,稳定性越低;C180分子在加载点处发生压缩“塌陷”时,化学活性明显增加．     

Theoretical investigation of the C<Subscript>60</Subscript>/copper phthalocyanine organic photovoltaic heterojunction

Molecular heterojunctions, such as the one based on copper phthalocyanine (CuPc) and carbon fullerene (C₆₀) molecules, are commonly employed in organic photovoltaic cells as electron donor-acceptor pairs. We have investigated the different atomic structures and electronic and optical properties of the C₆₀/CuPc heterojunction through first-principles calculations based on density functional theory (DFT) and time-dependent DFT. In general, configurations with the CuPc molecule “lying down” on C₆₀ are energetically more favorable than configurations with the CuPc molecule “standing up”. The lying-down configurations also facilitate charge transfer between the two molecules, due to the stronger interaction and the larger overlap between electronic wavefunctions at the interface. The energetically preferred structure consists of CuPc placed so that the Cu atom is above a bridge site of C₆₀, with one N-Cu-N bond of CuPc being parallel to a C-C bond of C₆₀. We also considered the structure of a periodic CuPc monolayer deposited on the (001) surface of a face-centered cubic (fcc) crystal of C₆₀ molecules with the lying-down orientation and on the (111) surface with the standing-up configuration. We find that the first arrangement can lead to larger open circuit voltage due to an enhanced electronic interaction between CuPc and C₆₀ molecules.      

Extraction equilibria in a fullerene-containing C<Subscript>60</Subscript>-C<Subscript>70</Subscript>-<Emphasis Type="Italic">o</Emphasis>-Xylene-<Emphasis Type="Italic">i</Emphasis>-butylamine-water system

Extraction equilibria of the liquid(I)-liquid(II) type have been studied for the first time in a system containing light fullerenes C₆₀ and C₇₀. The experiments were performed with a five-component mixture of fullerene C₆₀, fullerene C₇₀, o-xylene, ibutylamine, and water at 25°C. Isothermal diagrams describing the distribution of fullerene components between separating liquid phases have been obtained. The distribution coefficients of fullerenes (C₆₀ and C₇₀ concentrations in the xylene phase relative to those in the amine phase) are found to be almost constant and approximately equal to ～16.1 for both C₆₀ and C₇₀.     

Doped C<Subscript>60</Subscript> Study from First Principles Simulation

We have performed first principles density functional theory method simulations on electronic structures of B, N, Co, P, and Bi doped C₆₀ solids. Our electronic structure simulations show that boron, phosphorous, and cobalt doped face-centered cubic (FCC) C₆₀ solids have the electronic structures of n-type semiconductors. Nitrogen doped FCC C₆₀ solid has an electronic structure similar to those of a p-type semiconductor. P doped C₆₀ is a potential good candidate in thermoelectric application. For Bi doped C₆₀, a transformation from n-type to p-type semiconductor and gradually to metal, which corresponding to the Bi:C₆₀ dopant ratio at 1:60, 2:60, and 3:60, respectively, can be seen from our electronic density of states (DOS) analysis. There are volume contraction and charge transfer increasing in the 2:60 of Bi doped C₆₀ results compared with those of 1:60 Bi doped C₆₀ case. The charge transfer at a tetrahedral site is as three times larger as that of octahedral site. For the concentration of Bi doped C₆₀ higher than 3:60, the system is expected to be a superconductor.     

Fullerene-containing C<Subscript>60</Subscript>-CdTe(CdSe) composite nanostructures

We have developed a technology for obtaining homogeneous films based on fullerene-containing C₆₀-CdTe and C₆₀-CdSe composites. The surface morphology of the initial films is characterized by an average lateral roughness size of about 150 nm. Annealing in a vacuum of 10^?5 Torr for 3 h showed that C₆₀-CdSe films are stable at temperatures up to T=180°C, while the same treatment of films of the (C₆₀)_1?x(CdTe)_x system with x<0.5 leads to the appearance of surface clusters of the semiconductor component with an average size of about 500 nm. The cluster density and size increase with the content of CdTe in the initial composite powder. The photoluminescence spectrum of a (C₆₀)_1?x(CdTe)_x film with x=0.5 upon annealing displays a dominating peak at 730 nm, which is indicative of a significant modification of the film structure as a result of this post-growth treatment. It is demonstrated that fullerene-containing composite network nanostructures with a lateral resolution up to 250 nm can be created by direct electron-beam lithography.     

NMR Evidence for C<Subscript>60</Subscript> Configurational Fluctuations Around Na Sites in Na<Subscript>2</Subscript>CsC<Subscript>60</Subscript>

The ²³Na nuclear magnetic resonance (NMR) spectrum, spin-lattice and spin–spin relaxation, as well as spin echo double resonance (SEDOR) are investigated in the ternary alkali fulleride compound Na₂CsC₆₀ in the temperature range of 10–300 K. The NMR line associated with the tetrahedral sodium site is split below 170 K (T and T′ lines) similarly to Rb₃C₆₀ although the crystal structures of these two materials are different. SEDOR measurements prove that the T and T′ sites are microscopically close. The merger of the two lines at about 170 K is attributed to motional narrowing resulting from a site exchange due to angular reorientations of the C₆₀ molecules. The exchange dynamics inferred from the spectra, spin–spin relaxation, and spin-lattice relaxation are all consistent and agree with inelastic neutron scattering, supporting our proposal that the observed T-T′ splitting originates from different local fullerene configurations around the tetrahedral alkaline sites.     

The photoluminescence of amorphous carbon in a-C:C<Subscript>60</Subscript> films obtained by fullerene C<Subscript>60</Subscript> deposition

The results of experimental investigations of the carbon deposits obtained in the course of fullerene C₆₀ sublimation are presented. It is shown that the films formed at a high deposition rate possess a composite structure representing a mixture of fullerenes and an amorphous carbon phase with a graphitelike short-range order. The films containing amorphous nonhydrogenated carbon possess photoluminescent properties analogous to those of hydrogenated amorphous carbon films with a high hydrogen content. The possible mechanism of photoluminescence of the composite carbon films is discussed.     

Equation of State for <Emphasis Type="Italic">C</Emphasis><Subscript>60</Subscript> Fullerene Aqueous Solutions

In the present work PVT data of the C₆₀ fullerene aqueous solution (C₆₀ FAS) were measured as a function of the concentration of C₆₀ molecules using the variable cell method with metal bellows in the temperature range from 295 to 360 K at pressures from 0.1 to 103.2 MPa. On the liquid–vapor equilibrium line the density (ρ) of the C₆₀ FAS was measured using the pycnometer method. As a result, numerical values for the isothermal modulus of elasticity (K_T), isobaric expansivity (α_P), isothermal deviation of entropy factor (TΔS), enthalpy (ΔH), and internal energy (ΔU) have been determined. Finally, an equation of state for the C₆₀FAS was obtained for the first time.     

C<Subscript>60</Subscript> end-functionalized four-armed polymers: synthesis and optical limiting properties

A series of bromo-terminated four-armed homopolymers [polystyrene (PSt) and poly(methyl methacrylate) (PMMA)], prepared by atom transfer radical polymerization (ATRP), were subsequently functionalized with fullerene C₆₀ by atom transfer radical addition (ATRA) reaction using CuBr/2,2′-bipyridine (bipy) as the catalyst system. The C₆₀ end-capped four-armed polymer derivatives were then characterized by gel permeation chromatography (GPC), UV–vis, FT-IR, thermal gravimetric analyses (TGA) and differential scanning calorimeter (DSC). Another technique of synthesizing C₆₀-functionalized four-armed polymers from azide functional polymers was also applied for comparison. The optical limiting behavior of C₆₀ end-capped four-armed polymers prepared via ATRA reaction were measured in THF solution at 532 nm. Both groups of fullerene-functionalized polymers (C₆₀-PSts and C₆₀-PMMAs) are provided with optical limiting properties.     

Fullerene C<Subscript>60</Subscript> diffusion in thin layers of amorphous polymers: Polystyrene and poly(α-methylstyrene)

The outdiffusion of fullerene C₆₀ from submicron films of polymer-fullerene blends has been studied by thermodesorption mass spectrometry (TDMS). The energy parameters of C₆₀ diffusion in polystyrene and poly(α-methylstyrene) were determined and compared to the parameters of desorption of C₆₀ molecules from a multilayer film of pure fullerene deposited onto a substrate from toluene solution.     

Permittivity of low-concentration C<Subscript>60</Subscript> fullerene solutions in <Emphasis Type="Italic">p</Emphasis>-xylene

The frequency dependence of the permittivity of C₆₀ fullerene solutions in p-xylene has been determined at various small concentrations of fullerene molecules. The results are discussed using notions of the solution structure.     

Intercalation of C<Subscript>60</Subscript> fullerene crystals with calcium and barium via self-propagating high-temperature synthesis

We report a process for rapid intercalation of C₆₀ fullerene crystals using self-propagating high-temperature synthesis. The process has been used to intercalate C₆₀ fullerene crystals with calcium and barium. The superconducting transition temperatures of the intercalated fullerites have been measured, and the calcium-intercalated C₆₀ fullerene crystals have been characterized by X-ray diffraction.     

Formation of Gaseous Negative Ions of Fluoro and Trifluoromethyl Derivatives of C<Subscript>60</Subscript> Fullerene Studied by Knudsen-Cell Mass Spectrometry

Experimental procedures are described for producing negative ions of fluoro and trifluoromethyl derivatives of C₆₀ in the vapor phase and characterizing them by Knudsen-cell mass spectrometry. Some common aspects of the formation of such ions are established, and the associated ion-molecule equilibria are investigated. Electron affinity data are presented for C₆₀(CF₃)_2n molecules. It is shown that, upon ionization, the fluorofullerenes tend to loose one or several fluorine atoms.     

Nanostructure of laser pyrolysis carbon blacks: observation of multiwall fullerenes

A study of the nanostructure of both as-produced and thermally treated laser pyrolysis carbon blacks which comprise unusual types of nanoparticles and fullerenes is reported. It has been shown that those blacks are characterized by two-level nanostructure, i.e. they consist of amorphous nanoparticles 30–40 nm in size and C₆₀ clusters. Heat treatment at 3000°C causes restructurization with appearance of fullerene-like multishell nanoparticles of ∼20 nm size, higher fullerenes and multishell (cage-inside-cage) fullerenes. Transmission electron microscopy observation showed the occurrence of three different cage-inside-cage clusters: two-shell 1.4 nm size (C₆₀@C₂₄₀), two-shell 2.0 nm size (C₂₄₀@C₅₆₀) and three-shell 2.0 nm size (C₈₀@C₂₄₀@C₅₆₀).     

Depth profile XPS analysis of polymeric materials by C<Subscript>60</Subscript><Superscript>+</Superscript> ion sputtering

When the depth profile of chemical composition is studied with X-ray photoelectron spectroscopy (XPS), the Ar⁺ ion sputtering method is generally adopted. However, in the case of polymers, chemical composition is destroyed, and so it is impossible to obtain accurate depth profile on polymers. In this research, the depth profile XPS analysis of aliphatic polymers, aromatic polymers, fluorine containing polymers, and natural polymers were conducted with the sputtering source being C₆₀ ⁺ ion, and the degree of damage was examined while comparing the results with the case of conventional Ar⁺ ion. It was found that Ar⁺ ion induces significant carbonization in all the polymers above-mentioned. Meanwhile, it turned out that C₆₀ ⁺ ion causes little damage to most polymers. However, in the case of the non-aromatic polymers containing halogen, hydroxyl, carboxyl, and ether groups in their backbones, the following three damage modes were found: (1) the functional group ratio changes by over ±10%; (2) new functional groups are formed; (3) the above (1) and (2) phenomena occur simultaneously.     

Diamond synthesis from C<Subscript>60</Subscript> fullerite using boron and titanium diboride

Boron-doped diamond has been synthesized from C₆₀ fullerite at 7 GPa and 2000–2050 K using unconventional solvents for carbon: boron and titanium diboride.     

Concentration-dependent variations in the density of C<Subscript>60</Subscript> fullerene solutions in aromatic solvents

The densities of C₆₀ fullerene solutions in benzene, toluene, and p-xylene have been determined by pyknometry and studied as a function of the fullerene concentration in solution. All dependences exhibit a non-monotonic character, whereby the density initially decreases, passes through a minimum, and then grows with increasing fullerene concentration. The position of the minimum shifts toward greater C₆₀ concentrations on the passage from benzene to toluene and p-xylene.     

Disordering and the electronic transport behaviors of NbC–Al<Subscript>4</Subscript>C<Subscript>3</Subscript>–C composite

A composite nanomaterial composed of NbC nanocrystals, Al₄C₃ nanorods and carbon nanofibers as well as amorphous carbon was fabricated by arc-discharging a Nb₃Al block as an anode in CH₄ gas. The growth process of the NbC–Al₄C₃–C composite was deduced according to the microstructures of its components and the experimental conditions. NbC nanocrystals with non-stoichiometric chemical composition were in a cubic shape. As the decomposition product of the precursor of CH₄ gas, carbon nanofibers were thought to be as templates, reacting with Al atoms, to form Al₄C₃ nanorods with a diameter of 15–40 nm. A thin layer of aluminum carbide oxide covered the surface of Al₄C₃ nanorods. The temperature dependence of the resistivity for the NbC–Al₄C₃–C composite was described by the variable-range-hopping (VRH) model between about 100 K and 300 K because of the strong localization of electrons by disorder in the carbon matrix. Below 100 K, the transport behaviors of the pellet deviated from the VRH model due to the conduction competition between the semi-conducting carbon matrix and metallic NbC nanocrystals.     

Thermodynamic properties of fullerite C<Subscript>70</Subscript>

A new expression for the isochoric heat capacity and the equation of state of fullerite C₇₀ are obtained in the framework of a quantum-statistical method. Analogs of the Debye law and Dulong–Petit law for this fullerite are formulated. Fullerene C₇₀ molecules are modeled by isotropic quantum oscillators under the assumption that their nonsphericity weakly influences the thermodynamic properties of the condensed phase. The intramolecular oscillations of carbon atoms are described using the Debye theory and the cold contribution to the free energy of fullerite is calculated using the Lennard-Jones pair potential for fullerene molecules. A comparison of the proposed theory to experiment shows good agreement.