Pressure dependence of the Raman modes in iodine-doped single-walled carbon nanotube bundles

Abstract

Raman spectra of iodine-doped single-walled carbon nanotube (I-SWNT) bundles excited with 514.5 nm were studied at room temperature and elevated pressure up to 7 GPa. The low frequency modes in I-SWNT exhibit very small pressure-induced frequency shifts, in contrast to the pressure shift of \ensuremath{\sim}7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/GPa (or larger) reported for the radial modes in undoped SWNT samples. This weak pressure dependence and the resonance with 514.5 nm excitation, corroborate the previous assignment of the Raman bands at \ensuremath{\sim}110 and 175 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in I-SWNT to polyiodide chains. Furthermore, based on a comparison between the pressure behavior of the I-SWNT and undoped SWNT samples, we suggest that the ${\mathrm{I}}_{n}^{\ensuremath{-}}$ molecules might reside both in the interstitial channels and inside the pores of the tubes in SWNT bundles.