科研之友
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摘要
We present the first-principles calculations for vacancy aggregates in carbon nanotubes which clarify relations unrecognized in the past between vacancy generation and nanomorphology. We find that the most stable form of the vacancy aggregates in single-walled carbon nanotubes (SWCNTs) is the local thinning. It is clarified that the linear vacancy in which vacant sites are topologically arranged to be parallel to the tube axis is healed in SWCNT, rendering the thinning of the vacancy area energetically favorable. In double-walled CNTs (DWCNTs), we find that the interwall interaction, which has been overlooked in the past, is decisive to determine the morphology of the vacancy aggregates. It has been clarified that wall-wall repulsive interaction suppresses the thinning due to the healing of the linear-shaped vacancy aggregates, causes limitation of the thinning, and alternatively produces the round-shaped vacancy in the outer tube. In the resultant slimmed DWCNTs, it is found that both conduction-band bottom and the valence-band top states are solely distributed on the inner tube, in contrast with normal spacing DWCNTs. This peculiar distribution in space is caused by reduction in hybridization between pi orbitals and the nearly free-electron state.
- 出版日期2010-5-15
