Growth Process of Single-Walled Carbon Nanotubes from Metal Cluster:
Density Functional Tight-Binding Molecular Dynamics Simulation |
Yasuhito Ohta,1 Yoshiko Okamoto,1 Stephan Irle2, and Keiji Morokuma1
1Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto 606-8103, Japan
2Institute for Advanced Research and Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan |
The authors previously performed quantum chemical molecular dynamics (QM/MD) simulations based on the density functional tight binding (DFTB) method and proposed the “shrinking hot giant fullerene” mechanism for formation of fullerenes from small carbon clusters [1]. This method enabled us to study nonequilibrium processes involving bond breaking and formation of many-body molecular systems. They also performed QM/MD study on the mechanism of carbon nanotube growth from the SiC surface [2]. Synthetic techniques of the mass production of single walled carbon nanotubes (SWNTs) have been making significant progress since their discovery in 1993. Transition metals such as Fe, Co, Ni, Mo, Y play an essential role as catalysts for SWNT synthesis. However, the mechanism for the growth process of SWNTs still remains unclear. In the present study [3], we investigated the growth process of SWNTs using the DFTB molecular dynamics method. An open-ended nanotube was attached to the transition metal clusters, which are composed of Fe atoms, and carbon atoms were continuously bombarded around the boundary between the nanotube and metal atoms. We observed an efficient growth of the attached nanotube. Introduction of the electronic temperature to take into account the multiple degeneracy of transition metal d orbitals was a key to the success. We explore the essential steps of the growth process by changing the size of the metal clusters, density of feedstock molecules, and temperature.
[1] S. Irle, G. Zheng, Z. Wang, and K. Morokuma, J. Phys. Chem. B, 2006, 110, 14531-14545.
[2] Z. Wang, S. Irle, G. Zheng, M. Kusunoki, and K. Morokuma, J. Phys. Chem. C, 2007, 111, 12960-12972.
[3] Y. Ohta, Y. Okamoto, S. Irle, and K. Morokuma, ACS Nano, in press. |
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