Topics in Current Chemistry (2020) 378:15
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nanotube sample. Also, measurements are highly dependent on sample preparation and specific protocol details, and most of the times a reference is needed
[117]. As stated previously, this article does not pretend to be an extensive review
on the characterization techniques used to study nanotubes, but we just would like
to give a brief overview of the main techniques used for characterization of CNTs
with biomedical applications. For a more detailed review, interested readers could
go to Refs. [117–119].
3.1 Raman Spectroscopy
Raman spectroscopy is one of the most powerful and used techniques for carbon
nanotube characterization [120]. It is fast, does not need sample preparation, and
is non-destructive. For SWCNTs, Raman spectroscopy provides qualitative and
quantitative information about diameter, purity, crystallinity, and electronic structure, allowing to distinguish between metallic and semiconducting CNTs [121]. Furthermore, it supports studying and bundle CNTs [122, 123]. The most characteristic bands of nanotubes in Raman spectra are: (1) A 1g or “breathing mode”, related
to the diameter of the tube, (2) D-line, assigned to residual ill-organized graphite,
and (3) G-band, related to highly ordered CNT sidewalls. The ratio between D- and
G-bands can provide quantitative information about sidewall damage and changes
produced by functionalization [124].
3.2 Electron Microscopy (EM)
EM includes transmission electron microscopy (TEM) and scanning electron
microscopy (SEM). These are essential tools for studying directly the local structure of CNT at the nanometer level. TEM allows determining lengths and outer and
inner diameters (Fig. 4) [88]. It also gives a qualitative estimation of the metallic
and carbonaceous impurities, which appear as dark dots in the images [104]. The
main disadvantages of EM techniques include possible damage to the sample due to
the high energy of the electronic beam, and the large impact of sample preparation
and drying in the results.
3.3 Scanning Probe Microscopy
Among the different techniques encompassed within the scanning techniques, the
two most commonly used to characterize functionalized CNT are atomic force
microscopy (AFM) and scanning tunneling microscopy (STM) [46, 125]. AFM can
be used to evaluate the stiffness and strength of individual MWCNT as well to measure their size distribution [126]. STM can reveal the atomic structure and the electronic properties of individual SWCNT [127], and is also able to image functional
groups attached to the nanotube [125].
190
Reprinted from the journal
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nanotube sample. Also, measurements are highly dependent on sample preparation and specific protocol details, and most of the times a reference is needed
[117]. As stated previously, this article does not pretend to be an extensive review
on the characterization techniques used to study nanotubes, but we just would like
to give a brief overview of the main techniques used for characterization of CNTs
with biomedical applications. For a more detailed review, interested readers could
go to Refs. [117–119].
3.1 Raman Spectroscopy
Raman spectroscopy is one of the most powerful and used techniques for carbon
nanotube characterization [120]. It is fast, does not need sample preparation, and
is non-destructive. For SWCNTs, Raman spectroscopy provides qualitative and
quantitative information about diameter, purity, crystallinity, and electronic structure, allowing to distinguish between metallic and semiconducting CNTs [121]. Furthermore, it supports studying and bundle CNTs [122, 123]. The most characteristic bands of nanotubes in Raman spectra are: (1) A 1g or “breathing mode”, related
to the diameter of the tube, (2) D-line, assigned to residual ill-organized graphite,
and (3) G-band, related to highly ordered CNT sidewalls. The ratio between D- and
G-bands can provide quantitative information about sidewall damage and changes
produced by functionalization [124].
3.2 Electron Microscopy (EM)
EM includes transmission electron microscopy (TEM) and scanning electron
microscopy (SEM). These are essential tools for studying directly the local structure of CNT at the nanometer level. TEM allows determining lengths and outer and
inner diameters (Fig. 4) [88]. It also gives a qualitative estimation of the metallic
and carbonaceous impurities, which appear as dark dots in the images [104]. The
main disadvantages of EM techniques include possible damage to the sample due to
the high energy of the electronic beam, and the large impact of sample preparation
and drying in the results.
3.3 Scanning Probe Microscopy
Among the different techniques encompassed within the scanning techniques, the
two most commonly used to characterize functionalized CNT are atomic force
microscopy (AFM) and scanning tunneling microscopy (STM) [46, 125]. AFM can
be used to evaluate the stiffness and strength of individual MWCNT as well to measure their size distribution [126]. STM can reveal the atomic structure and the electronic properties of individual SWCNT [127], and is also able to image functional
groups attached to the nanotube [125].
190
Reprinted from the journal