Fullerene Coalescence in Nanopeapods:  A Path to Novel Tubular Carbon

Abstract

A fascinating structural transformation occurring inside single-walled carbon nanotubes (SWNTs) is the fullerene coalescence, which is responsible for forming stable zeppelinlike carbon molecules. We report in situ transmission electron microscope (TEM) observations revealing sequences of fullerene coalescence induced by electron irradiation on pristine nanotube peapods, together with extensive theoretical investigations of the microscopic mechanism underlying this process. TEM images indicate that the merging of fullerenes results in stable but corrugated tubules (5 to 7 Å in diameter) confined within SWNTs. These observations have been confirmed using a combination of theoretical approaches based on molecular dynamics, empirical potentials, tight-binding methods, Monte Carlo techniques, and first principles calculations. We have fully elucidated the coalescence mechanism of fullerenes inside SWNTs under electron irradiation and thermal annealing. The process occurs via the polymerization of C 60 molecules followed by surface reconstruction, which can be triggered either by the formation of vacancies (created under electron irradiation) or by surface-energy minimization activated by thermal annealing. These novel tubular forms of carbon contain hexagons, pentagons, heptagons, and octagons. The stability, electronic properties, and electron conductance of the novel tubules are strongly affected by the final geometry of the coalesced fullerene complex. The possibility of forming highly conducting and semiconducting tubular structures suggests new avenues in designing carbon nanowires with specific electronic characteristics.

Characteristics of bamboo defects in peapod-grown double-walled carbon nanotubes

“…9͒. For comparison, previous calculations in the literature with this method on peapods have shown that the method can describe the coalescence of C 60 fullerenes, 26 albeit the method predicts a much higher temperature for the coalescence than the experiments: the simulation predicts that coalescence begins at around 2500 K while the experiments take place at around 900 K. Nevertheless, since our calculations show that the bamboo junction is stable at temperatures much higher than the C 60 coalescence temperature predicted by the same method, we can safely conclude that the bamboo junctions are stable in the temperature range of the annealing, and therefore they should persist during the formation of the inner shells.…”

Ion and electron irradiation-induced effects in nanostructured materials

“…355,356 The resulting structures consisted of corrugated tubules nested inside the original SWNT. These carbon nanostructures exhibited pentagonal, hexagonal, heptagonal, and octagonal rings and resembled the theoretically proposed Haeckelite structures.…”

Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of –sp2 carbon

“…However, under the same conditions, most of the SWCNT networks are transformed either to MWCNT arrays ranging from 15 to 30 nm in diameters with several incomplete sp 2 outer tube walls ( Fig. 1f; which give rise to either dangling bonds and structural imperfections that may enhance the coalescence of CNTs) 14,20,25,[34][35][36][37] or to well-defined MWCNTs with hollow cores and completely formed tube-wall (as straight lattice fringes in Fig. 1g,h).…”