Biomedical Engineering Reference
In-Depth Information
the ultrasensitive, real-time, and parallel detection of analytes
in solutions.
1.9 TEMPLATE METHODS
The growth of thin films displaying special features like aligned
pores perpendicularly to the substrate surface and nanoporous
structures has attracted the attention of many research groups. A lot
of bottom-up techniques, particularly those in which, self-assembly
processes play a relevant role in the growth mechanisms of that
nanostructures have been reported. Among them, electrochemical
techniques constitute one of the most used to fabricate highly ordered
nanostructures for replicating other nanostructured materials and
for growing functionalized material arrays. Such electrochemical
nanofabrication is mainly based on ordered and nanoporous anodic
aluminum oxide membranes (AAO), anodic titania membranes,
colloidal polystyrene (PS) latex spheres, self-assembled monolayers
(SAMs) and self-assembled block copolymers and even carbon
nanotubes. Template methods offer very important strategies for
complicated nanostructures.
1.9.1 Anodized Aluminum Oxide (AAO) Membranes
A simple and completely nonlithographic preparation technique for
free-standing nanostructured films with a close-packed hexagonal
array of nanoembossments has been developed by porous anodic
aluminum oxide (AAO) membrane templates with different pore
diameters. They have been largely used to construct different free-
standing inorganic and organic nanowires [125-127], nanotubes
[128] and ordered arrays of nanoparticles [129] since invented.
Aluminum anodization provides a simple and inexpensive way
to obtain nanoporous templates with uniform and controllable pore
diameters and periods over a wide range. The usual electrochemical
method for producing the AAO film is the anodization of high-
purity Al plates at constant voltage (e.g., anodized at 22 V from an
Al foil and detached by the reverse-bias method) [130]. Membranes
with several different pore sizes can be made, for example, in the
following electrolytes: Aqueous solutions of H
SO
4
at 10-20 V for
2
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