Stone–Wales defect

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A Stone–Wales defect is a crystallographic defect that occurs on carbon nanotubes and graphene and is thought to have important implications for the mechanical properties of carbon nanotubes. The defect is named after Anthony Stone and David Wales of Cambridge University, who described it in a 1986 paper[1] on the isomerization of fullerenes. However, a rather similar defect was described much earlier by Peter Thrower in a paper on defects in graphite.[2] For this reason the term Stone–Thrower–Wales defect is sometimes used. The defect is thought to be responsible for nanoscale plasticity and the brittle–ductile transitions in carbon nanotubes.

The Stone–Wales crystallographic defect transformation (pyracylene transformation) is the rotation of two carbon atoms by 90° with respect to the midpoint of the bond. The Stone–Wales transformation is also used to describe the structural changes of sp²-bonded carbon nanosystems. For example, it has been proposed that the coalescence process of fullerenes or carbon nanotubes may occur through a sequence of such a rearrangements. By the Stone–Wales transformation, four hexagons are changed into two pentagons and two heptagons.

A Stone–Wales defect is the rearrangement of the six-membered rings of graphene into pentagons and heptagons.[citation needed] This rearrangement is a result of π/2 (90°) rotation of a C–C bond. The density of Stone–Wales defects is usually small due to the high activation barrier of several eV for the bond rotation. However, the defects has been imaged using scanning tunneling microscopy as well as resonant–vibrational spectroscopy techniques[clarify].[citation needed] A number of theoretical studies have shown that the absorption energies and charge transfer energies for single-walled carbon nanotubes are larger than the corresponding values on pristine carbon nanotubes.[citation needed] The diminished resonance and higher strain energy of this defect increased the probability of nucleophilic attack which provides a possible explanation for the enhanced reactivity. Research has also shown the incorporation of defects along a carbon-nanotube network can program a carbon-nanotube circuit to enhance the conductance along a specific path. These defects lead to a charge delocalization which redirects and incoming electron down a given trajectory.[citation needed]

References[edit]

  1. ^ Stone, A. J.; Wales, D. J. (1986). "Theoretical studies of icosahedral C60 and some related structures". Chemical Physics Letters 128 (5-6): 501–503. doi:10.1016/0009-2614(86)80661-3. 
  2. ^ Thrower, P.A. (1969). "The study of defects in graphite by transmission electron microscopy". Chemistry and Physics of Carbon 5: 217–320.