XXI. General Studies of Carbon Nanostructures
The growth of single-walled carbon nanotubes (SWNTs) from Fe38 clusters has been simulated using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, in conjunction with non-equilibrium molecular dynamics. Growth of the nanotube sidewall was induced by the supply of gas-phase atomic carbon at two different rates to randomly chosen sites in the Fe-C boundary region of both (5,5)-SWNT-Fe38 and (8,0)-SWNT-Fe38.1,2 The dependence of SWNT growth dynamics on both the chiral angle of the SWNT (θ) and the rate of carbon supply were therefore elucidated. SWNTs grown in this manner exhibited a large number of defects. In addition, SWNT healing was driven by the relative rates of defect removal and addition in the nanotube sidewall near the SWNT-Fe38 boundary.3 The mechanisms by which adatom, vacancy and 5-77-5 type defects were removed from the SWNT generally took place over timescales of 1-25 ps. These mechanisms were therefore enhanced using lower rates of carbon supply. Using a rapid supply of carbon, an inverse relationship between θ and the SWNT growth rate was established during the early stages of growth. In particular, (8,0)-SWNTs exhibited a mean growth rate ca. 20-30% greater than that of (5,5)-SWNTs during the first 40 ps of growth. A recently proposed 'steady-state' model of SWNT growth4 suggests that the converse is the case when growth is induced by the diffusion of carbon over the catalyst surface to the SWNT-catalyst boundary. However, average SWNT growth and ring-addition rates of (5,5)- and (8,0)-SWNTs can be explained in terms of the direction in which incident carbon extends the sp2-hybridized network with respect to the SWNT axis. It is concluded therefore that the energetic and kinetic properties of SWNT growth mechanisms, and therefore SWNT growth rates, depend on the manner in which carbon density is supplied to the nanotube itself (i.e. direct addition at the SWNT-catalyst interface, as opposed to addition following diffusion over the catalyst surface). It is also postulated that a dependence of SWNT growth rate on the form of carbon feedstock supplied to the SWNT (i.e. C, as opposed to Cn) would be observed.This abstract was created on: 2009/4/9 22:8:54 (EST).
1. Y. Ohta, Y. Okamoto, S. Irle, K. Morokuma, J. Phys. Chem. C, 113,159, (2009).
2. Y. Ohta, Y. Okamoto, S. Irle, K. Morokuma, K. Phys. Rev. B, (Submitted).
3. A. J. Page, Y. Ohta, S. Irle, Y. Okamoto, K. Morokuma, J. Phys. Chem. C, (Submitted).
4. F. Ding, A. R. Harutyunyan, B. I. Yakobson, PNAS, 106, 2506, (2009).
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