Reinterpretation of Single-Wall Carbon Nanotubes by\nRaman Spectroscopy

Abstract

Raman spectra of\nsingle-wall carbon nanotubes (SWNTs) exhibit a\nunique radial breathing mode (RBM) band (∼100–300 cm^–1) and a G^– peak (∼1570 cm^–1), along with a D band (∼1350 cm^–1). We show that the typical Raman signals for SWNTs are the signature\nof their helical structure determined using density functional theory\nsimulation and structural analysis for hydrogenated and dehydrogenated\nSWNT samples. We demonstrate that the G^– mode at\n∼1570 cm^–1 is unique to opened tubular graphene\nstructures of ∼2 nm diameter. We also demonstrate that the\nD mode of ∼1350 cm^–1 is originated from edge\ndefects of opened SWNTs, revealing strong eigenvectors, which is absent\nin concentric tubes. We also report a radial–tangential mode\n(RTM) for concentric and opened SWNTs, which appears following RBM.\nWe also interpret the low-energy Raman signal, reported as an RBM\nband, to be convolution of “localized RBM” (∼170\ncm^–1) and RTM (∼190 cm^–1) for helical SWNTs. We also show that the analysis of the Raman\nspectra of SWNTs is consistent with general understanding on Raman\nanalysis of carbon materials.