Fullerene Tubules Research Articles

Catalytic production and purification of nanotubules having fullerene-scale diameters

Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene in the presence of various supported transition metal catalysts. The influence of different parameters such as the nature of the support, the size of active metal particles and the reaction conditions on the formation of nanotubules was studied. The process was optimized towards the production of nanotubules having the same diameters as the fullerene tubules obtained from the arc-discharge method. The separation of tubules from the substrate, their purification and opening were also investigated.

Catalytic production and purification of nanotubules having fullerene-scale diameters

Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene in the presence of various supported transition metal catalysts. The influence of different parameters such as the nature of the support, the size of active metal particles and the reaction conditions on the formation of nanotubules was studied. The process was optimized towards the production of nanotubules having the same diameters as the fullerene tubules obtained from the arc-discharge method. The separation of tubules from the substrate, their purification and opening were also investigated.

Physical interaction between tip and molecules in scanning force microscopy imaging of adsorbed C60 and fullerene tubules

After the discovery of C60, a large family of fullerene molecules was also identified. Among them, elongated fullerenes are formed by the tubular assembly of carbon atoms. The van der Waals bonds between fullerene molecules are due to the correlations between fluctuating charge densities inside the molecules. The interaction is then dominated by collective excitations which are sensitive to the shape of the molecules. Therefore, van der Waals attraction is expected to be modified when considering successively spherical C60, C70 and more elongated fullerenes (tubules). This paper presents self-consistent computations of the van der Waals interaction between a (111) diamond probe tip and various fullerene molecules adsorbed on a gold surface. Relative to spherical C60, the dependence law of the force experienced by the probe tip as a function of the tip-sample distance decreased when approaching fullerene tubules. Simulations of scanning force microscope scans of carbon tubules next to C60 molecules show that the shape of the molecules affects the interpretation of scanning force microscopy imaging. Particularly, information about the height of the various molecules deposited on the surface must be considered with some care since carbon tubules with the same radius as C60 interact more strongly with the probe tip.

Density-functional calculations of electronic and structural properties of small fullerene tubules

Results of first-principles density-functional calculations of electronic properties of structure-optimized isolated fullerene tubules are reported. Special emphasis is put on structural properties of the smallest tubules one can think of, and on whether they are metallic or semiconducting. We find that the smallest tubules have markedly different structural and electronic properties from those of a folded graphite sheet, a fact that distinguishes them from the larger, more graphite-like tubules. As compared to a folded sheet of graphite, the smallest tubules have large structural relaxations which become progressively smaller as the diameter of the tubule increases. The electronic structures of the smallest tubules are modifed by significant interaction across the interior of the tubule. This leads to an overall broadening of 2–3 eV of the electronic density of states compared with the larger tubules. For the smallest, the (1, 0) tubule, the structural relaxations lead to a semiconducting behaviour with a band gap of around 1 eV.

Fullerene molecules and tubules polarizabilities, vibrational modes and nanocapillarity

Recent algorithmic and computational advances for density-functional-based investigations of clusters now allow for the calculation of a multitude of low-energy phenomena in complex clusters and molecules. Here we discuss methods for the first-principles calculation of linear and non-linear electronic polarizabilities and for vibrational modes. Results from recent calculations on the C 60 molecule show that the local-density-approximation (LDA) is capable of a very accurate quantitative description of such phenomena. As an example of how the high polarizability of caged carbon compounds might be beneficially exploited for new technological applications, we review recent simulations which predicted that fullerene tubules behave as molecular straws.

High yield synthesis and HREM study of fullerene tubules and fullerene onions

The fullerene tubules and fullerene onions are synthesized in macroscopic quantity with high yield by modified Kratschmer et. al. method. Besides ordinary concentric fullerene tubules, also are observed abnormal nonconcentric multilayer glaphitic tubules with varying layer spacings. The curved graphitic tubules are observed, showing the tendency to form torus. Under appropriate helium pressure, about half of the synthesized product is the multi-shell fullerene onions, polyhedral in shape in accord with the theoretical calculation. [11]

First-Principles Determination of the Polarizabilities of Carbon Tubules as a Function of Length

ABSTRACTWe use the local-density-approximation to the density-functional theory to determine the axial polarizabilities of fullerene tubules as a function of length and winding topologies. Specifically, we present linear polarizabilities for tubules of composition C12H24, C36H24, C40H20 and C60H24. The size-dependent variation in the dipole-coupled gaps between pairs of occupied and unoccupied levels leads to enhancements in the polarizability per valence electron as the length of the tubule increases. The results are compared to recent densityfunctional based calculations of the linear and nonlinear polarizabilities for fullerene and benzene molecules.

Fullerene/Tubule Based Hollow Carbon Nano-Gears

ABSTRACTWe report the design of several symmetric star-shaped closed carbon cages using ball and stick models. Despite the presence of seven- and eight-membered rings, these hollow carbon sprockets—containing less than 500 carbon atoms—are predicted to be more energetically stable than C60. Also, we show that these sprockets can be connected to capped fullerene tubules to form a nanostructure similar to a mechanical gear and shaft. In addition, using molecular dynamics and a reactive hydrocarbon potential, we show that these gears can be turned against each other at high angular velocities without large deformations. These nanogears illustrate some of the possible complex small structures that can be formed by inserting 5-, 7-, and 8-membered rings in an otherwise graphitic network. These nanogears also show surprisingly robust mechanical properties.

Tubulanes: carbon phases based on cross-linked fullerene tubules

Structure and properties are calculated for five predicted carbon phases, called tubulanes, which are shown to be possible reaction products of single-layer and multiple-layer carbon tubules. Each carbon atom is equivalent and in a modified sp 3 state in these phases which contain column structures that are directly related to those in either armchair or zig-zag carbon tubules. One such phase has a predicted bulk modulus which is within 6% of that of diamond, and a predicted heat of formation which is much lower than for either the C 60 fullerene or other previously characterized no-diamond-like phases containing only sp 3 carbons.

Electronic structure of a stepped graphite surface.

A first-principles band calculation and theoretical simulation of scanning tunneling microscopy and spectroscopy (STM and STS) are performed on a stepped surface of graphite. The calculated band structure and the density of states are similar to those of fullerene tubules. Unlike in fullerene tubules, however, a localized state on the step appears at the Fermi level due to the existence of an edge in the graphite sheet. The calculated STM image shows a triangular lattice structure similar to that of the bulk graphite. However, the positions of the peaks of the tunneling current do not coincide with the atomic sites and shift gradually as they diverge from the step. The calculated STS spectra at a location near the step show a strong peak reflecting the localized state.

Dimerization structures of metallic and semiconducting fullerene tubules

Possible dimerization patterns and electronic structures in fullerene tubules as the one-dimensional pi-conjugated systems are studied with the extended Su-Schrieffer-Heeger model. We assume various lattice geometries, including helical and nonhelical tubules. The model is solved for the half-filling case of $\pi$-electrons. (1) When the undimerized systems do not have a gap, the Kekule structures prone to occur. The energy gap is of the order of the room temperatures at most and metallic properties would be expected. (2) If the undimerized systems have a large gap (about 1eV), the most stable structures are the chain-like distortions where the direction of the arranged trans-polyacetylene chains is along almost the tubular axis. The electronic structures are ofsemiconductors due to the large gap.

Dimerization and energy-level structures in fullerene tubules investigated with an electron-phonon model

Possible dimerization patterns and electronic structures in fullerene tubules as the π-conjugated systems are studied with the extended Su-Schrieffer-Heeger model. We assume various lattice geometries, including helical and nonhelical tubules, and tubules with end caps. The model is solved for the half-filling case of π-electrons. (1) When the undimerized systems do not have a gap, the Kekul e ́ structures tend to occur. These structures are commensurate with the boundary condition in the direction perpendicular to the tubular axis. The energy gap is of the order of the room temperatures at most. Thus, the nearly metallic properties would be expected. (2) If the undimerized systems have a large gap (∼ 1eV), the most stable structures are the chain-like distortions where the direction of the arranged trans-polyacetylene chains is along almost the tubular axis. When we try to obtain the Kekulé structures, the mismatch of the boundary condition occurs and they are energetically unfavorable. The electronic structures are of semiconductors due to the large gap.

Simulated Fullerene Tubules Act as Straws

Simulated Fullerene Tubules Act as Straws

Nanocapillarity in fullerene tubules.

Fullerene tubules are shown to be highly polarizable ``molecular straws'' capable of ingesting dipolar molecules. Local-density-functional calculations on HF molecules within a finite-length tubule, of size 144 atoms, demonstrate this effect. The energy of incarceration is several times the thermal ambient at room temperature. These calculations, now feasible on desktop workstations, open the way to the study of nanoscale capillarity and to, perhaps, precise control over shielding of specific ``guest'' compounds from external electric and magnetic fields.

Formation of general fullerenes by their projection on a honeycomb lattice

We propose the use of a projection method based on a honeycomb lattice to enhance the geometrical understanding of general fullerenes. An arbitrary fullerene consisting of pentagonal and hexagonal arrangements of carbon atoms is completely specified by the distribution of twelve pentagonal defects on an otherwise hexagonal honeycomb lattice. Utilizing this projection method, we demonstrate the geometric specification of icosahedral hyperfullerenes and general chiral fullerene tubules suitably capped on each end.

Are fullerene tubules metallic?

We have calculated the electronic structure of a fullerene tubule using a first-principles, self-consistent, all-electron Gaussian-orbital based local-density-functional approach. Extending these results to a model containing an electron-lattice interaction, we estimate that the mean-field transition temperature from a Peierls-distorted regime to a high-temperature metallic regime should be well below room temperature. Such fullerene tubules should have the advantages (compared to the other conjugated carbon systems) of a carrier density similar to that of metals and zero band gap at room temperature.