Biomedical Engineering Reference
In-Depth Information
of an HOPG wafer by heating at similar to 640°C. Underpotential
deposition of approximately similar to 80 mV caused polypyrrole
to form only on the step and pit edges of HOPG at and not on the
basal plane. The size of these nanostructures could be controlled by
limiting the pyrrole polymerization time at anodic potentials.
In addition, traditional top-down nanofabrication methods
such as focused ion beam (FIB), can be used to fabricate nanopore
array electrodes [225]. FIB milling thus represents a simple and
convenient method for fabrication of prototype nanopore electrode
arrays. These electrode nano-arrays can be used in electrochemical
nanofabrication for applications in sensing and fundamental
electrochemical studies.
1.14 NANOSCALE ELECTROCHEMISTRY
Individual carbon nanotubes have been modified selectively on one
end with metal using a bipolar electrochemical technique [226].
A stable suspension of nanotube was introduced in a capillary
containing 10 mM HAuCl
4
aqueous electrolyte, and a high electric
field is applied to orientate and polarize the individual tubes. During
their transport through the capillary under sufficient polarization
(30 kV), each nanotube is the site of water oxidation on one end and
the site of metal ion reduction on the other end with the size of the
formed metal cluster being proportional to the potential drop along
the nanotube.
Bipolar electrochemistry occurs when an external electrical
field polarizes an object that is not physically connected to the
electrodes and thus generates an anodic and a cathodic area on
the same object. The substrate can be any kind of material, but its
conductivity must be higher than that of the surrounding medium.
The induced potential difference between the two extremities of the
object, and therefore the kinetics of the associated redox reactions,
is directly proportional to the particle's effective length [227].
When the capillary is exposed to a high electric field (10-30 kV), an
electroosmotic flow is generated inside the capillary, transporting
the CNT/AuCl
4
suspension from the anodic capillary inlet toward
the cathodic compartment. A 1 mm long carbon fiber was inserted
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