Biomedical Engineering Reference
In-Depth Information
) was adsorbed on a highly oriented pyrolytic graphite
surface modified by 4-aminophenyl monolayer with coordination
interaction, and then homogeneously dispersed Ag nanoparticles
could be obtained through pulsed potentiostatic reduction.
Multilayered metal nanostructures on glassy carbon electrodes have
been obtained by extending this method [68,69]. Room temperature
ionic liquids are molten salts at room temperature. The larger
electrochemical window of ionic liquids in comparison with aqueous
electrolytes enables the broader investigation of electrodeposition
of metal and semiconductor elements and compounds in nanoscale.
Nanoscale electrocrystallization of metals such as nickel (Ni) and
cobalt (Co) and the electrodeposition of semiconductors (Ge) on
Au (111) and Si (111):H have been studied in the underpotential
and overpotential range from ionic liquids [70]. For example, 3D
growth in Co electrodeposition on Au (111) from ionic liquids based
on imidazolium cations starts at potentials below -0.17 V vs. Co/
Co(II). 3D and 2D structures of Co and Ni deposition in the nanoscale
were also illustrated. In addition, nanocrystalline aluminum can
be obtained by electrodeposition from ionic liquids containing
imidazolium cations without additives [71]. The crystal refinement
is due to a cathodic decomposition of the imidazolium ions to a
certain extent giving rise to nanocrystalline aluminum.
Metal nanowires can be obtained using solution phase reduction
[72], template synthesis [73-76] and physical vapor deposition
(PVD) [77] onto carbon nanotubes. Metal wires with widths down to
20 nm and lengths of millimeters can be prepared on silicon surface
using electron beam lithography [78] or by PVD [79]. However,
none of these methods is useful to prepare free-standing metal
nanowires that are longer than 20 μm. Penner et al. [80] have used
the step edge defects on single crystal surfaces as templates to form
metal nanowires by electrochemical step edge decoration. Metallic
molybdenum (Mo) wires with diameters ranging from 15 nm to
1 μm and lengths of up to 500 μm were prepared in a two-step
procedure on freshly cleaved graphite surfaces [81]. Such nanowires
can be obtained size selectively because the mean wire diameter
was directly proportional to the square root of the electrolysis time.
Parallel arrays of long (>500 μm), dimensionally uniform nanowires
composed of Mo, copper (Cu), Ni, Au, and palladium (Pd) can also be
cation (Ag
+
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