Oscillation of nested fullerenes (carbon onions) in carbon nanotubes

Nested spherical fullerenes, which are sometimes referred to as carbon onions, of I _h symmetries which have N(n) carbon atoms in the nth shell given by N(n) = 60n ² are studied in this paper. The continuum approximation together with the Lennard-Jones potential is utilized to determine the resultant potential energy. High frequency nanoscale oscillators or gigahertz oscillators created from fullerenes and both single- and multi-walled carbon nanotubes have attracted much attention for a number of proposed applications, such as ultra-fast optical filters and ultra-sensitive nano-antennae that might impact on the development of computing and signalling nano-devices. Further, it is only at the nanoscale where such gigahertz frequencies can be achieved. This paper focuses on the interaction of nested fullerenes and the mechanics of such molecules oscillating in carbon nanotubes. Here we investigate such issues as the acceptance condition for nested fullerenes into carbon nanotubes, the total force and energy of the nested fullerenes, and the velocity and gigahertz frequency of the oscillating molecule. In particular, optimum nanotube radii are determined for which nested fullerenes oscillate at maximum velocity and frequency, which will be of considerable benefit for the design of future nano-oscillating devices.     

Polyhydroxy fullerenes

Characterization of C₆₀ polyhydroxyfullerenes (PHF) prepared in alkaline media, preparation facilitated by phase-transfer catalyst, presents challenges in determining the chemical structure resulting from the possibility of multiple isomers or analogs with greater or fewer hydroxyl groups from a single reaction mixture. This paper presents the utilization of analytical methods employed in tandem, especially X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy for semi-quantitative analysis on the number of hydroxyl groups present in PHF. Capillary Electrophoresis was used for purity estimation of the material. Multiple spectra and electropherograms were analyzed using a new simultaneous curve fitting method. The most accurate estimate of hydroxyl groups for C₆₀ polyhydroxy fullerenes obtained is between 16 and 18 allylic hydroxyl groups by combining analytical methods’ results with 5 % accuracy. High precision (reproducibility) of the experiments is observed. Purity of 98 % is estimated by capillary electrophoresis. The size of PHF nanoparticles or aggregates has been determined by atomic force microscopy to be 7.4–14.2 nm. According to the elemental analysis the average probable empirical formula for the most pure PHF at pH 7.1 is C₆₀O₁₇H₁₂Na₅(NaHCO₃)₃(H₂O)₁₃ and the average formula weight is 1,605.9 g/mol. This is the first thorough characterization of PHF in terms of purity.     

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.     

Molecular fusion of fullerenes

New experimental data is reported for the absolute cross sections for the fusion reaction channel in single gas-phase collisions between fullerenes. The experimental data is compared with the results of quantum mechanical and classical molecular dynamics simulations as well as with simple models. Quantum molecular dynamics simulations are in very good quantitative agreement with the experimental data. The overall dynamical behaviour can be well-described qualitatively in the framework of simple models. Received 2 October 2000     

Pressure-induced ferromagnetism of fullerenes

Ferromagnetic behavior of polymerized fullerenes appears quite close to the boundary where the fullerene molecules are destroyed. However, when the presence of a disordered or graphitic phase is detectable by the standard characterisation methods, the ferromagnetic features quickly disappear.     

Characterization of fullerenes using positrons

Positron distributions and lifetimes in the K_xC₆₀ crystals for x=0, 3, 4, 6 have been calculated using the superposed-atom model and the numerical relaxation technique. It is revealed that positrons are distributed predominantly at the octahedral interstices in the fcc lattice of pure C₆₀. The distributions and lifetimes of positrons are significantly changed by potassium doping. In the fcc K₃C₆₀, the positron density shows its maxima in the interstitial region between the octahedral and tetrahedral interstices and has some amplitude in the inner space of the C₆₀ molecules. In contrast to this, positrons are distributed one-dimensionally along the [001] direction in the bct K₄C₆₀ while positrons are nearly localized into the C₆₀ molecules in the bcc K₆C₆₀.     

Defect-induced ferromagnetism in fullerenes

Based on the ab initio electronic structure calculations the picture of ferromagnetism in polimerized C₆₀ is proposed which seems to explain the whole set of controversial experimental data. We have demonstrated that, in contrast with cubic fullerene, in rhombohedral C₆₀ the segregation of iron atoms is energetically unfavorable which is a strong argument in favor of intrinsic character of carbon ferromagnetism which can be caused by vacancies with unpaired magnetic electrons. It is shown that: (i) energy formation of the vacancies in the rhombohedral phase of C₆₀ is essentially smaller than in the cubic phase, (ii) there is a strong ferromagnetic exchange interactions between carbon cages containing the vacancies, (iii) presence of iron impurities can diminish essentially the formation energy of intrinsic defects, and (iv) the fusion of the magnetic single vacancies into nonmagnetic bivacancies is energetically favorable. The latter can explain a fragility of the ferromagnetism.     

Inorganic nanotubes and fullerenes

The possibility of stable non-carbon fullerenes is discussed for the case of phosphorus fullerene-like cage structures. On the basis of Density Functional Tight Binding calculations it is shown that many such cages correspond to metastable structures, but with increasing nuclearity become less stable with respect to separate molecular P₄ units. Stability rules, known for carbon fullerenes, such as the “isolated pentagon rule”, do not reflect the different electronic and steric requirements of the phosphorus atom. The computational results tend to rule out phosphorus fullerenes.     

Diffuse scattering from fullerenes

Fullerene solids exhibit textbook examples of orientational freezing transitions, i.e. structural transitions from a high temperature phase, where the molecules undergo rapid reorientation, to a low temperature phase where the molecules are locked-in into discrete orientations. In general, even low temperature phases are not completely ordered because of frozen-in orientational disorder, partly also because of a high density of stacking faults. Diffuse scattering has been used extensively to characterize both dynamic and static disorder in fullerene solids. A review is given on the experimental results as well as on the various techniques employed to analyze the data.     

Gas-phase aggregation of fullerenes by laser ablation of fullerenes in reactive and nonreactive matrices

60 molecules, whereas little or no coalescence was found in the nonreactive mixture. In the negative ion TOF channel the maximum peak of twice C₆₀ coalescence by laser desorption was always located at masses greater than 120 carbon mass units, which is different from all previous reports. We suggest that the formation mechanism was due to strong interactions between the C₆₀ molecules and silica particles or surface species such as the H or OH group existing in the matrix. Received: 6 May 1996/Revised version: 22 July 1996     

Aspects of organic chemistry of fullerenes

Successive additions to [60]fullerene show a remarkable degree of regioselectivity. Two characteristic examples of additions, namely nucleophilic cyclopropanations of 6-6 double bonds as well as formations of 5–6 bridged open azafulleroids, have been systematically investigated by analytical, spectroscopic as well as by computational methods. Regioselective additions to activated positions within the carbon framework of fullerene derivatives are the key steps for both controlled ring opening of the fullerene core and the synthesis of heterofullerenes.     

Possible scheme of synthesis-assembling of fullerenes

A new scheme of fullerene formation is proposed on the basis of the similarity between the experimentally detected carbon structures. According to experimental data, the microclusters of C₂ and C₁₀ are synthesized first and then either an intermediate nucleus cluster or an obtainable lower fullerene is assembled from them. A high-symmetry fullerene can be assembled with a high probability from a nucleus cluster with a “good” symmetry. The atomic and electronic structures of molecules such as C₃₆, C₆₀, C₇₀, and C₇₆ are analyzed. For C₃₆, the NMR spectra are calculated and compared with the experimental data.     

Metal atom catalyzed enlargement of fullerenes

A metal catalyzed enlargement of fullerenes has been demonstrated by in situ high-resolution transmission electron microscopy. It was found that carbon atoms and clusters can be continuously incorporated into a closed fullerene cage at a high temperature, leading to an increase in the diameter and consequently the formation of giant fullerene with the assist of adsorbed metal atoms. Density functional theoretical simulations indeed suggest that the activation energy for the carbon incorporation and the associated Stone-Wales transformation can be substantially reduced due to the presence of metal atoms, which should be of key importance for the fullerene growth.     

富勒烯分子的光学双稳性

本文采用非线性法布里-珀罗腔的全光光学方法,在C_(60)/C_(70)薄膜中首次观测到双稳开关现象,其开关时间为10ns.