Raman spectra for characterization of defective CVD multi‐walled carbon nanotubes

TLDR

Curved graphene fragments, whose size reflects structural disorder, are considered building blocks of carbon nanotubes and are proposed to form a mosaic structure of nanotube walls. The study compares Raman spectra of CVD multi‑walled carbon nanotubes and graphene flakes deposited on them, focusing on D, G, and 2D band behavior to characterize the nanotubes. Raman spectroscopy, complemented by HRTEM imaging, was used to analyze D, G, and 2D band behavior in the samples. The I₂D/I_D intensity ratio shows a nearly linear dependence on MWCNT diameter, with each catalyst type yielding a distinct slope, and also varies with the amount of graphene flakes deposited during ethylene decomposition.

Abstract

Curved graphene fragments can be considered as building blocks of carbon nanotubes. Thus, the size of graphene fragments may be considered as one of the most important characteristics of their structural disorder. In this paper, we have performed a comparative Raman study of CVD multi‐walled carbon nanotubes (MWCNTs) and graphene flakes deposited on MWCNTs. Raman data have been considered in combination with HRTEM characterization of nanotubes. The basic attention has been paid to the behavior of D (disorder‐induced), G (tangential mode), and 2D (two‐phonon scattering) bands in Raman spectra in order to use them for MWCNT characterization. A ratio of intensities of 2D and D bands ( I 2D / I D ) demonstrates almost a linear dependence on the mean diameter of MWCNTs produced with two different types of catalysts (see abstract figure). It should be mentioned that each type of catalyst provides the linear dependence with its own specific slope. The graphene fragments have been proposed to form a mosaic structure of nanotube walls. I 2D / I D ratio depends on the amount of graphene flakes deposited on nanotube surface via ethylene decomposition. A dependence of intensity ratio I 2D / I D on the diameter of nanotubes produced with different types of catalysts.