Reflection electron energy-loss spectra of the fullerenes C60 and C70

High purity polycrystalline samples of C₆₀ and C₇₀ were obtained and studied by the electron energy-loss spectroscopy in the reflection mode. The spectra were used for determination of the loss functions of fullerenes. Loss functions of the fullerenes were compared with those of graphite. It was established that the relative intensities of the peaks corresponding to (+)- and -plasmons depended on the primary electron energy, while the (+)-plasmon energies did not depend on the primary electron energy and were equal to 25.0 eV for C₆₀ and 24.8 eV for C₇₀. The conclusion on the space localization for plasma occilations in fullerenes was made on the base of the study of the energy dependent loss functions.     

A comparative study of ion-induced damages in C60 and C70 fullerenes

The stability of fullerenes (C₆₀ and C₇₀) under swift heavy ion irradiation is investigated. C₆₀ and C₇₀ thin films were irradiated with 120 MeV Ag ions at fluences from 1×10¹² to 3×10¹³ ions/cm². The damage cross-section and radius of damaged cylindrical zone were found to be higher for C₆₀ than C₇₀ as evaluated by Raman spectroscopy, which shows that the C₇₀ molecule is more stable under energetic ion impact. The higher damage cross-section of the C₆₀ molecule compared with that of the C₇₀ molecule is explained on the basis of thermal conductivity in the framework of the thermal spike model. The surface morphology of pristine C₆₀ and C₇₀ films is studied by atomic force microscopy. UV-visible absorption studies revealed that band gap for C₆₀ and C₇₀ fullerenes thin films decreases with increasing ion fluence. Resistivity of C₆₀ and C₇₀ thin films decreases with increasing ion fluence but the decrease is faster for C₆₀ than C₇₀, indicating higher damage in C₆₀. Irradiation at a fluence of 3×10¹³ ions/cm² results in complete damage of fullerenes (C₆₀ and C₇₀) into amorphous carbon.     

Longitudinal field repolarization studies of reorientational dynamics in the fullerenes C60 and C70

LFμSR studies on the pure fullerenes C₆₀ and C₇₀ show temperature dependent features associated with the reorientational behaviour of the fullerenyl radicals MuC₆₀ and MuC₇₀ in the crystalline host substrate. If not excluded from the experimental setup, molecular oxygen undergoes spin exchange reactions with the radicals. The data for C₆₀ correspond to a situation effectively static at 150 K and fully averaged to isotropy at 300 K, while for C₇₀ the data conspicuously do not conform to the predictions of the pseudostatic model employed in ALC‐μSR studies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dielectric relaxation,ac and dc conductivities in the fullerenes C60 and C70

The complex conductivity in polycrystalline C₆₀ and C₇₀ has been investigated for frequencies 20 Hz≤ν≤10⁶ Hz and temperatures 10 K≤T≤750 K. The high-frequency dielectric constants ε_α= 2.6±0.1(C₆₀) and ε_∞= 4.6±0.1 (C₇₀) were deduced from these experiments. The observed low temperature relaxation process in C₆₀ fits well into the relaxation dynamics of the C₆₀ molecules as determined by many other experimental techniques operating on very different time scales. In addition to the study of the dipolar relaxation process, the dc and ac conductivities were determined. From the temperature dependence of the dc conductivities energy barriers of E_G=1.75±0.1 eV (C₆₀) and E_G=1.7±0.1 eV (C₇₀) were estimated. In C₇₀ we found indications for small polaron tunneling.     

Dielectric relaxation,ac and dc conductivities in the fullerenes C60 and C70

The complex conductivity in polycrystalline C₆₀ and C₇₀ has been investigated for frequencies 20 Hz≤ν≤10⁶ Hz and temperatures 10 K≤T≤750 K. The high-frequency dielectric constants ε_α= 2.6±0.1(C₆₀) and ε_∞= 4.6±0.1 (C₇₀) were deduced from these experiments. The observed low temperature relaxation process in C₆₀ fits well into the relaxation dynamics of the C₆₀ molecules as determined by many other experimental techniques operating on very different time scales. In addition to the study of the dipolar relaxation process, the dc and ac conductivities were determined. From the temperature dependence of the dc conductivities energy barriers of E_G=1.75±0.1 eV (C₆₀) and E_G=1.7±0.1 eV (C₇₀) were estimated. In C₇₀ we found indications for small polaron tunneling.     

Atomic force microscopy of C60/C70 single-crystal fullerenes under ethanol

C₆₀/C₇₀ crystal surfaces were imaged by atomic force microscopy under ethanol with resolution of single molecules. Spherical and elongated elliptical fullerenes can be distinguished corresponding most likely with C₆₀, respectively C₇₀. Determination of the maximum diameter for a large number of molecules confirms the presence of two species of fullerenes, one with 9.4 Å, the other with 11.2 Å. The measured ratio C₆₀:C₇₀ is 81:19 which resembles the spectroscopical data. The molecules are arranged either in hexagonal (hcp) or cubic (fcc) packing, in some areas the two arrangements alternate within a few nm. Elongated fullerenes apparently prefer the hexagonal packing.     

Effect of fullerenes C60and C70 on the absorption spectrum of 2-cyclooctylamino-5-nitropyridine

The influence of fullerenes C₆₀ and C₇₀ on the absorption spectrum of 2-cyclooctylamino-5-nitropyridine (COANP) is studied. A substantial shift of the absorption band edge of COANP-C₇₀ to the IR region was observed. This effect was compared with the data obtained for COANP-C₆₀. The experimental results were explained using the model that takes into account the interaction between electronic subsystems of COANP and fullerene.     

Some features of analysis of solutions of fullerenes C60 and C70 by their absorption spectra

The absorption spectra of a series of solutions of C₆₀ and C₇₀ and of their mixture in o-xylene are studied. The deviation from the Bouguer-Lambert-Beer law was observed in the UV absorption band of the solutions. The possible reasons for this effect were analyzed. It is shown that to calculate reliably the composition and concentrations of fullerene mixtures, it is necessary to determine preliminarily the linearity region for the 335-nm absorption band.     

Studies of third-order nonlinear optical properties of C60 by the optical Kerr effect

60 at 1.064 μm is determined by the optical Kerr effect in toluene solution. Values of -6.5×10^-33 esu and 2.0×10^-32 esu for the real and imaginary parts of γ, respectively, are obtained. Based on the experimental results and symmetry constraint, it is concluded that a three-level model is not adequate to describe the third-order nonlinearity of C₆₀. It is also inferred that the non-resonant γ of C₆₀ should be positive in sign, which is in agreement with reported off-resonant measurements of γ of C₆₀ by third-harmonic generation. Received: 3 September 1997/Revised version: 1 December 1997     

C60、C240、C60@C240富勒烯分子压缩特性的分子动力学研究

采用Tersoff-Brenner势的分子动力学方法,研究了双石墨层作用下C60、C240及C60@C240富勒烯分子的压缩力学特性.根据计算结果,讨论了三种分子压缩过程中几何构形、能量、压缩载荷等的变化及其差异.研究表明,压缩过程中,仅C240分子出现了“塌陷“现象,塌陷时,该分子的能量及外载一度下降;相同压缩应变下,C240的体积压缩率以及C60@C240的能量吸收率最大,而C60的体积压缩率及能量吸收率均最小; C60@C240分子的最大承载能力及C240的最大承受变形能力最大,而C60分子的最大承载和最大承受变形能力均最小;在C60@C240分子的压缩中,当应变小于20%时,内笼C60的体积及其能量变化很小;C60与C240之间的范德华尔能在整个压缩C60@C240分子的能量变化中仅仅占有非常小的份额.     

Site occupancy and molecular complex formation of 19F ions in fullerenes C60 and C70 studied by TDPAD

TDPAD spectroscopy measurements have been performed on two fullerene samples, C₆₀ and C₇₀, with recoil implanted ¹⁹F ions as probe nuclei. Quadrupole coupling frequencies of ν_Q= 54(1) MHz for C₆₀ and ν_Q= 57(1) MHz for C₇₀ were observed. These frequencies are associated with a C–F molecular complex formation. The C₇₀ sample was also examined for possible effects due to variation of temperature. No significant changes were observed. An additional frequency of ν_Q= 13(1) MHz registered for both samples has to be attributed to the formation of H–F complexes. Finally, both samples were analysed for proton dose dependent effects, due to the (p,p'γ) implantation process but no effects have shown up. Specifically, computational studies based on quantum chemical methods were performed to assist in the interpretation of the experimental results, using the code MOPAC. This revised version was published online in August 2006 with corrections to the Cover Date.     

Negative ions of hydrogenated and deuterated C60 fullerenes

This paper reports on the results of mass spectrometric and theoretical investigations of hydrogenated and deuterated fullerene derivatives C₆₀H(D)_x. The formation and decay (through electron autodetachment) of negative molecular ions of the C₆₀H₁₈ and C₆₀D₁₈ hydrofullerenes are discussed. A comparative analysis of these processes is performed for different fullerene derivatives.