Biomedical Engineering Reference
In-Depth Information
The precipitation method involves electrochemical generation
of a precursor to one of the constituent elements, in a solution
containing precursors to the other elements [54-57]. The reaction
is essentially homogeneous, but as one reactant is formed at
the electrode surface, most of the product precipitates on the
surface. This method resembles passive oxide film formation on
reactive metals, where metal ions react with the solvent, oxygen
or hydroxide. The film thickness is controlled by the amount of
electrogenerated precursor. However, as the method resembles
precipitation, the quality of the resulting deposit is questionable,
and the process is difficult to control. Film thickness is necessarily
limited by the need for precursor transport through the deposit. A
classic example is the formation of CdS
by oxidizing a Cd electrode
in a sulphide solution [54,58-62]. Two stage methods are where
thin films of the compound element, or an alloy, are first deposited,
at least one by electrodeposition [63]. A second stage, annealing,
then results in interdiffusion and reaction of the elements to form
the compound. The deposits are annealed in air, an inert gas, or a
gaseous precursor to one of the compound's component elements.
For instance, electrodeposited CuIn alloys have been annealed in H
S
2
to form CuInS
[64]. Given the need for annealing, this methodology
has limitations for the formation of more involved device structures.
In general, annealing has been used to either form or improve the
structures of compound films formed by the electrodeposition
methods described above. The primary tool for understanding
compound electrodeposition and for improving control over the
process has been the methodology of EC-ALE [65,66].
2
1.3 ELECTROCHEMICAL DEPOSITION METHODS FOR
METALLIC NANOSTRUCTURES
Inorganicnanoparticlescanbefabricatedbymanydifferenttechniques.
Electrochemical and wet-chemical methods are demonstrated
to be effective approaches to make metal nanostructures under
control without addition of a reducing agent or protecting agent.
An
electrochemical reduction method for fabricating metal
nanoparticles on carbon substrates simultaneously assembling
into ordered functional nanostructures was developed [67]. Silver
in situ
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