Biomedical Engineering Reference
In-Depth Information
FIGURE 18.5
Electrostatic deflection of a CNT induced by a constant field of (A) 0 V and (B) 60 V across the electrodes
[35]
.
measure the mass of particles as small as 22
6 fg (1 fg
10
15
g). This nanobalance worked by
attaching the mass to be measured to the tip of a nanotube. The change in the resonance frequency of
the altered nanotube enabled the mass of the particle to be calculated
[35]
. The conductance of CNTs
is of great interest, partly due to the possibility of using CNTs as interconnects for molecular devices
without heat dissipation. AFM studies have shown that conductance effects are related to defects in
the CNT which is in turn related to the production method used to make the CNTs. Wang et al.
[35]
utilized their
in situ
TEM setup to repeat this experiment by measuring the conductance of a CNT in
contact with liquid mercury.
Nanotube alignment is important, because in addition to mechanical properties, functional proper-
ties, such as electrical, magnetic, and optical properties, of polymer/CNT nanocomposites are linked
directly to the alignment of CNTs in the matrix. Jose et al.
[39]
successfully synthesized surface-
modified multiwalled carbon nanotubes (MWNTs) via electrospinning, using a rotating mandrel.
They used TEM to successfully verify high nanotube alignment.
18.2.2
Focused Ion Beam
Focused ion beams (FIBs) have become a popular tool for surface modification of materials and func-
tional structure prototyping at the micro- and nanoscale. Modern FIBs have spot sizes of less than
5 nm and are produced by using electrostatic lenses to focus the image of a point source, often gal-
lium liquid metal ion source, onto the substrate and to deflect it in a precise fashion. For a compre-
hensive review of developments in FIB implantation and sputtering, FIB gas-assisted etching, and
FIB-induced deposition, the reader is referred to Stanishevsky
[40-43]
.
18.2.2.1 FIB Case Studies
Moghadam et al.
[44]
have recently reported on the use of FIB for analysis of pharmaceutical micro-
spheres, which had been prepared by a double-emulsion, solvent-evaporation technique (
Figure 18.6
).
Normally, cross-sectioning is required to examine such microspheres. However, in this case it was
possible to remove the outer surfaces of the microspheres, layer by layer. Despite having nonporous
