Electrochemical sensors based on carbon nanotubes - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 483

(a) RBM (b) G band

FIGURE 15.18 Schematic picture showing the atomic vibrations for (a) the RBM and (b) the G band
modes. (Reprinted with permission from [128]. Copyright (2003) IOP Publishing Ltd.)

1582

HOPG

1582

MWNT

1592
G

1570
G

SWNT
semicond.

metallic
SWNT

1587
G

G
1550

1450 1550 1650

Frequency (cm 1 )

FIGURE 15.19 G band for highly ordered pyrolytic graphite (HOPG), MWNT bundles, one isolated
semiconducting SWNT and one isolated metallic SWNT. (Reprinted with permission from [128]. Copyright
(2003) IOP Publishing Ltd.)

The D band, the disorder induced mode, normally appears between 1250 and
1450 cm 1 . This band is activated in the fi rst-order scattering process of sp 2 carbons
by the presence of in-plane substitutional hetero-atoms, vacancies, grain boundaries or
other defects and by fi nite-size effects [134]. The G band is the second-order overtone

of the D band.