Reinterpretation of Single-Wall Carbon Nanotubes by Raman Spectroscopy

Abstract

Raman spectra of single-wall carbon nanotubes (SWNTs) exhibit a unique radial breathing mode (RBM) band (similar to 100-300 cm(-1)) and a G(-) peak (similar to 1570 cm(-1)), along with a D band (similar to 1350 cm(-1)). We show that the typical Raman signals for SWNTs are the signature of their helical structure determined using density functional theory simulation and structural analysis for hydrogenated and dehydrogenated SWNT samples. We demonstrate that the G(-) mode at similar to 1570 cm(-1) is unique to opened tubular graphene structures of similar to 2 nm diameter. We also demonstrate that the D mode of similar to 1350 cm(-1) is originated from edge defects of opened SWNTs, revealing strong eigenvectors, which is absent in concentric tubes. We also report a radial-tangential mode (RTM) for concentric and opened SWNTs, which appears following RBM. We also interpret the low-energy Raman signal, reported as an RBM band, to be convolution of "localized RBM" (similar to 170 cm(-1)) and RTM (similar to 190 cm(-1)) for helical SWNTs. We also show that the analysis of the Raman spectra of SWNTs is consistent with general understanding on Raman analysis of carbon materials.