High-temperature evolution of linear carbon chains inside multiwalled nanotubes

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 cm(-1) range due to linear carbon chains inside the nanotubes. A temperature-dependent Raman study, up to about 1000 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.