Biomedical Engineering Reference
In-Depth Information
Figure 9.4 shows a transmission electron microscope (TEM)
image showing the nanostructure of a MWCNT where various layers
of graphitic carbon and a hollow core are clearly evident. MWCNTs
are essentially concentric single-walled tubes, where each individual
tube can have a different chirality. These concentric tubes are held
together by van der Waals weak bonding. High-resolution electron
micrographs of typical needles show (002) lattice images of the
graphite structure along the needle axes. The appearance of the same
number of lattice fringes from both sides of a needle suggests that
it has a seamless and tubular structure. The smallest tube observed
was 2.2 nm in diameter and was the innermost tube in one of the
needles (Fig. 4c). CNTs grown at ENEA laboratories and analyzed are
also shown in Fig. 9.4d.
(a)
(b)
(c)
(d)
d)
Figure 9.4
TEM micrograph showing the layered structure of a MWCNT
produced by arc discharge. Electron micrograph of graphitic
carbon tubules. Parallel dark lines correspond to (002) lattice
images of graphite. A cross-section of each tubule is illustrated:
(a) Tube consisting of five graphitic sheets with a diameter of
6.7 nm. (b) Two-sheet tube with a diameter of 5.5 nm. (c) Seven-
sheet tube with a diameter of 6.5 nm, which has the smallest
hollow diameter of 2.2 nm. Reprinted by with permission
from Ref. [23]. (d) CNTs grown by RF-PECVD, including TEM
analysis, at ENEA laboratories.
Generally, SWCNTs are most desired for fundamental investi-
gations of the structure-property relationships in CNTs, since the
