Biomedical Engineering Reference
In-Depth Information
1.11 COLLOIDAL POLYSTYRENE (PS) LATEX TEMPLATES
In nanoelectrodeposition, the aim is to place only a single layer or
more of coverage on a surface in a very controlled way. Colloidal
crystal such as polystyrene (PS) latex templates have been widely
used to synthesize highly ordered macroporous ceramics [198],
metals [199], and polymers [200,201] where a particular interest
has been in the optical, magnetic and photonic bandgap properties
of the resultant structures. PS latex nanospheres can be self-
assembled on hydrophobic surfaces such as unoxidized silicon or
gold and used as templates [202,203]. Two- or three-dimensional
highly ordered macroporous cobalt, iron, nickel, gold, platinum, and
palladium films containing close packed arrays of spherical holes of
uniform size (an inverse opal structure) can be prepared by such
simple and versatile template technique [202-204]. The films were
prepared by electrochemical reduction of metal cations (e.g., gold
ions) dissolved in aqueous solution within the interstitial spaces
of preassembled colloidal templates assembled on gold surfaces.
Following the electrochemical deposition of the metal films, the
polystyrene templates were removed by dissolution in toluene. The
resulting films will show well-formed two- or three-dimensional
porous structures consisting of interconnected hexagonal close
packed arrays of spherical voids. The diameter of the spherical voids
within the structures can be varied by changing the diameter of the
PS latex spheres used to form the template. The thickness of the
films is controlled by varying the charge passed in their deposition.
Electrochemical deposition is ideal for the production of thin
supported layers for applications such as photonic mirrors, because
the surface of the electrochemically deposited film can be very
uniform. Electrochemical deposition occurs from the electrode
surface out through the overlying template, the first layer of
templated material, deposited out to a thickness comparable with
the diameter of the template spheres used, has a different structure
from subsequent layers. The subsequent growth of the film by
electrodeposition out through the template leads to a modulation
of the surface topography of the film in a regular manner that will
depend on the precise choice of deposition bath and deposition
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