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Fig. 32 Raman spectra of pristine and oxidized SWCNTs
Nevertheless, although unambiguous characterization of CNTs is not achievable
with just a single technique, the synergy of different methodologies can supply
relevant information on their structure, purity, and defects, before and after chemical
manipulation.
Hence, we will report here the most common techniques helping in the charac-
terization of CNTs.
5.1 Spectroscopies
The most common spectroscopic techniques used in the CNT field are
UV-vis-NIR, IR, and Raman.
These techniques are very useful as they help to elucidate the helicity, the
diameter, and the presence of structural defects.
5.1.1 Raman Spectroscopy
Raman spectroscopy has emerged as a very useful diagnostic tool to probe purity,
structure, and degree of functionalization of carbon nanotubes [
137
].
Carbon nanotubes present a rich Raman spectrum (Fig.
32
). Major features are
the G band (G-graphite), the D band (D-diamond or disorder), and the RBM
(radial breathing modes).
The G band, localized in the spectrum between 1,500 and 1,600 cm
1
, represents
the high frequency tangential mode (Fig.
33
) and results from a multi-peak combi-
nation. The two most relevant G peaks observed are the G
+
and G
, referring
