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Honolulu, HI, United States, 2006/09/19 - With a better understanding of how fullerenes form, scientists and material engineers would be in a better position to provide conditions more favorable for the formation of a particular fullerene..
With a better understanding of how fullerenes and nanotubes form, scientists and material engineers would be in a better position to provide conditions more favorable for the formation of a particular fullerene or a particular chirality and length nanotube. Researchers have used a number of computational and theoretical tools to explain the experimental observations and develop a picture of the dynamics for fullerene growth, yet no universally agreed model exists for the fullerene growth. To understand the phenomenon of fullerene growth during its synthesis, researchers modeled a minimum energy growth route using a semi-empirical quantum mechanics code. C2 addition leading to C60 was modeled and three main routes, i.e. cyclic ring growth, pentagon and fullerene road, were studied.
Since the discovery of fullerenes by Kroto and Smalley in 1985, four basic fullerene growth mechanisms have been established:
1) graphene-to-fullerene transformation where sputtered or vaporized graphene sheet transforms into a closed-cage fullerene by ejecting a number of smaller carbon clusters;
2) the pentagon road or Limacon model, where an open-cage structure like corannulene grows by the addition of carbon atoms or molecules at its edges, and eventually the cage is closed;
3) ring-stacking, where carbon rings fuse together to form closed-cage fullerenes; and
4) the fullerene road, where a smaller closed-cage fullerene grows into a larger one by C1, C2 or C3 insertion into the cage.
Sabih D. Khan from the Carbon-based Nanotechnology Laboratory in Islamabad, Pakistan, explained his group's recent simulations to Nanowerk: "C60 growth can be modeled by the sequential addition of C1, C2, C3 or larger carbon molecules, but experimental observations from emission spectra of regenerative sooting discharge indicate C2 to be an important constituent of carbonaceous plasma, which may lead to the formation of fullerenes. The scientific core of our finding is based on the addition of the C2s leading to the whole range of C clusters including the linear chains, rings, sheets and curved structures. We have also seen that open as well as closed structures can be formed by this route. The efficacy and applicability to closed cages has an edge over other C species' addition like C1s, C3s etc."
Read the full article on the Nanowerk website.
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By Michael Berger, Copyright 2006 Nanowerk LLC