Low frequency Raman studies of multi-wall carbon nanotubes: experiments and theory

TL;DR

This study combines experimental low frequency Raman spectroscopy and theoretical modeling to analyze the radial breathing modes of multi-wall carbon nanotubes, demonstrating the technique's effectiveness for structural characterization.

Contribution

It introduces a model describing radial breathing vibrations in MWNTs and validates it with experimental data, enhancing understanding of their vibrational properties.

Findings

Excellent agreement between simulated and experimental spectra

Raman spectroscopy effectively characterizes MWNT structure

Radial breathing modes originate from coupled wall vibrations

Abstract

In this paper, we investigate the low frequency Raman spectra of multi-wall carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency Raman modes are unambiguously identified on purified samples thanks to the small internal diameter of the MWNT. We propose a model to describe these modes. They originate from the radial breathing vibrations of the individual walls coupled through the Van der Waals interaction between adjacent concentric walls. The intensity of the modes is described in the framework of bond polarization theory. Using this model and the structural characteristics of the nanotubes obtained from transmission electron microscopy allows to simulate the experimental low frequency Raman spectra with an excellent agreement. It suggests that Raman spectroscopy can be as useful regarding the characterization of MWNT as it is in the case of single-wall nanotubes.