Biomedical Engineering Reference
In-Depth Information
Plank
. [55] have studied by XPS the thiolation of the SWCNTs
and their self-assembly. They provide XPS evidence of the existence
of sulphur attached to carbon atoms on the nanotube walls. The
thiolated CNTs are shown to self-assemble onto gold electrodes.
Furthermore, Droppa
et al
. [56] have studied by XPS technique the
incorporation of nitrogen into CNTs. The N1s and C1s peaks have
been investigated. Compared to non-nitrogenated samples, the C1s
peak exhibits both a shift and an asymmetric broadening to higher
binding energies. The tip shift of this peak, due to the polar character
of the carbon-nitrogen bond, is a clear evidence of the incorporation
of nitrogen into the carbon nanotube structure, as claimed by the
authors. Datsyuk
et al
. [57] employed XPS technique to confirm
the different functionalities produced for each oxidation agent
onto graphitic surface of the MWCNTs submitted to a purification
protocol. XPS analysis gives useful information on the nature of the
functional groups and also on the presence of structural defects on
the nanotube surface. The XPS C1s and O1s peaks of the as-received
CNTs and after treatment with HCl are investigated. Deconvolution
of the C1s peak of the as-received MWCNTs showed a main peak
at 284.1 eV, attributed to the graphitic structure in agreement
with the photoemission studies on MWCNTs. Moreover, a peak at
285.5 eV was attributed to defects on the nanotube structure,
whereas the peaks at 286.7, 288.3, and 290 eV, correspond to carbon
atoms attached to different oxygen-containing moieties.
Nuclear magnetic resonance (NMR) analysis has been applied to
study the electronic properties in the SWCNTs [58]. Two types of
et al
13
C
nuclear spins were identified with different spin-lattice relaxation
rates. The fast-relaxing component was assigned to metallic tubes;
whereas the slow-relaxing component was found with a significantly
lower density of states at the Fermi level. Exposure to oxygen has a
substantial effect on relaxation rates of both components.
Another important property of the CNTs which favors their use
in gas sensing is their high specific surface area. In fact, the CNTs
exhibit a very high surface-to-volume ratio with the advantage of high
capacity of gas adsorption by providing high gas sensitivity toward
adsorbed molecules. Brunauer-Emmett-Teller (BET) experiments
are currently performed to measure the surface area of the
nanomaterials. Solid state gas detection results from the adsorption
(interaction of gas molecules with surface) of the gas molecules on
a material surface. Due to the high specific surface area of the CNTs,
