Biomedical Engineering Reference
In-Depth Information
14.7
HRTEM images of a formed nodular CNT and an untreated CNT in
the insert (a) and schematic diagram of the formation of nodular CNTs
(b) (Zhang
et al.
, 2004).
Hydrogenation of CNT films through H 2 RF plasma processes improved
the CNT field emission properties via creation of defects along the CNT
structure (Yu et al., 2004; Feng et al., 2007). The enhancement of emission
properties was attributed to apparition of nodular CNTs due to bending of
graphene sheets along the CNT wall (Fig. 14.7 (a)) (Zhang et al., 2004).
During the H 2 RF plasma treatment, it was suggested that hydrogen ions
bombarding the tube sidewall remove carbon atoms from the CNT surface
under -CH x radical forms. Meanwhile, a small fraction of -CH x redeposited
on the remaining CNT surface induces the formation of nanoscale particles
with an onion-like structure distributed along the tubes (Fig. 14.7 (b)). The
improvement of the emission characteristics was attributed to the change in
the electronic (formation of sp 3 defects in sp 2 graphite network) and/or
geometrical CNT structure (Zhang et al., 2004).
Vertically aligned CNTs were hydrogenated in a H 2 +Ar pulsed DC
plasma, and correlations between the plasma characteristics and the CNT
surface chemistry were discussed (Jones et al., 2008). Actually, scanning
electron microscope (SEM) morphological analysis of CNTs treated in this
way showed the etching of the tangled nanotubes and the 'welding' of
nanoparticles. The extent of the etching effect was correlated with the
quantity of plasma-excited hydrogen H* interacting with CNTs.
￿ ￿ ￿ ￿ ￿ ￿
Plasma polymerization
The plasma polymerization process has been used to coat CNTs with
plasma polymer films. Several examples are reported in the literature. A
plasma polymerization method spraying a mixture of aniline and CNTs was
developed to deposit plasma polyaniline onto CNTs leading to the
formation of composite films with improved electrical properties
in
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