Biomedical Engineering Reference
In-Depth Information
14.6
HRTEM images of MWNTs (a) before and (b) after Ar microwave
plasma treatment for 3 minutes (Qin and Hu, 2008).
surface can also be tailored. This is an important characteristic of this type
of surface treatment since having saturation of these groups on the surface
can alter the electronic conductivity of nanotube materials.
To facilitate the discussion, we will classify the plasma treatment of CNTs
into: (1) CNT surface etching, which is generally carried out via an argon
(Ar) plasma treatment; (2) coating of CNTs through plasma polymerization;
and (3) plasma functionalization, which allows the grafting of reactive
functional groups on to CNT surfaces and opens the way to a wide variety
of subsequent chemical reactions.
Carbon nanotube surface etching
The plasma surface modification of CNTs is a non-reactive treatment when
Ar gas is used. The effects of argon RF plasma treatment on the surface of
vertically grown CNTs have been investigated. The inert Ar plasma
produces an efficient etching and cleaning process of CNT films, causing
structural changes in the CNTs and leading to an increase in their field
emission ability (Ahn et al., 2003). An observed improvement in gas
ionization in comparison with that of untreated aligned CNTs was also
observed after Ar RF plasma treatment (Yan et al., 2005). The Ar plasma
was also used to activate the CNT surface, allowing the subsequent grafting
of maleic anhydride (Tseng et al., 2007) or 1-vinylimidazole (Yan et al.,
2007).
Nevertheless, the destruction of carbon nanotube sidewalls was observed
after treatment with an Ar non-reactive
-wave plasma (Qin and Hu, 2008).
Figure 14.6 shows high resolution transmission electronic microscopy
(HRTEM) images of multi-wall CNTs recorded before and after Ar
μ
-wave
plasma treatment. We can observe that ion bombardment and irradiation in
Ar plasma deform the graphite walls and destroy the CNT layered structure;
a reduction in the power supplied to the plasma or in the treatment duration
can reduce the destruction of sidewalls.
μ
