Multiwalled carbon nanotubes have been deposited on graphite cathodes by the arc discharge technique in a He atmosphere. A micro-Raman mapping, performed after scanning electron microscopy, reveals, in some regions of the sample, strong bands in the $1780–1860{\mathrm{cm}}^{-1}$ range due to linear carbon chains inside the nanotubes. A temperature-dependent Raman study, up to about $1000\mathrm{K}$, shows a strong but reversible decrease in their intensity. This phase transition behavior is explained as a temperature-driven reduction of the Peierls distortion of the linear carbon chain.

• Received 8 February 2007

DOI:https://doi.org/10.1103/PhysRevB.75.121405