the effects of oxidizers on the diameters of the carbon nanotubes ...

semiconductor behavior (Dresselhaus, et al. 2002). In semiconducting tube bundles <strong>the</strong>
frequency <strong>of</strong> G + line is determined by bundle size. For semiconducting SWNT in
bundles, <strong>the</strong> linewidths are determined by <strong>the</strong> intertube interactions and <strong>the</strong> diameter
distribution. In metallic tubes, <strong>the</strong> G - line feature is broadened. This broadening is
related to <strong>the</strong> presence <strong>of</strong> free electrons in nanotubes with metallic character.
The ratio <strong>of</strong> <strong>the</strong> D-band to G-band intensity, ID/IG, is used as a measure <strong>of</strong> <strong>the</strong>
defect density <strong>of</strong> a particular CNT and can provide information on <strong>the</strong> crystalline
quality <strong>of</strong> <strong>the</strong> CNTs. A small ID/IG ratio suggests reasonable crystalline quality and a
perfect graphite structure. In o<strong>the</strong>r words, if <strong>the</strong>re is a high ratio between <strong>the</strong> G band and
D band peak intensities, it shows that <strong>the</strong> CNTs are <strong>of</strong> high purity
(Dresselhaus, et al. 2002).
In <strong>the</strong> lower frequency region, <strong>the</strong> spectrum is dominated by <strong>the</strong> in-phase mode
known as <strong>the</strong> radial breathing mode (RBM) appearing between 120 cm -1 and 250 cm -1
for SWNT. The RBM also provides information on chirality and thus <strong>the</strong> electronic
properties <strong>of</strong> CNTs (Thess, et al. 1996). The RBM frequency is associated with <strong>the</strong>
symmetric movement <strong>of</strong> carbon atoms in <strong>the</strong> radial direction (Figure 4.6). The RBM
frequency is inversely proportional to <strong>the</strong> reciprocal diameter <strong>of</strong> <strong>the</strong> SWNT with <strong>the</strong>
relationship below (Jorio, et al. 2003).
W(cm -1 )=224(cm -1 )/dt(nm) (4.1)
Figure 4.5. Raman spectra showing <strong>the</strong> main peaks <strong>of</strong> SWNTs
(Source: Dresselhaus, et al. 2002)
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