Biomedical Engineering Reference
In-Depth Information
pores ~10-25 nm, H
C
O
4
at 40-80 V for pores ~40-100 nm, and
2
2
H
at 100-140 V for pores ~100-170 nm. The pore diameter
is linearly related to the anodizing voltage (1.2 nm/V). A voltage
reduction was done to the thin barrier layer that inhibits anodic
current during electrodeposition [131]. Other attempts have been
made to create nanoporous symmetries other than hexagonal
packing [132]. Recently, a novel AAO membrane with a six-
membered ring symmetry coexisting with the usual hexagonal
structure has been fabricated by constant current anodization [133].
The pore sizes of this structure can be tailored by changing the
processing conditions. Ordered arrays of nanodots with novel
structure have been fabricated by such AAO template. In the final
stage, the porous alumina substrate can be removed by etching
in KOH. Moreover, one of the interesting possibilities afforded
by the anodization process is that the anodization can take place
on arbitrary surfaces, such as curved surfaces. Unique features
including cessation, bending, and branching of pore channels are
observed when fabricating AAO templates on curved surfaces
[134]. The new structures may open new opportunities in optical,
electronic, and electrochemical applications.
Many strategies have been ingeniously implemented to fabricate
complicated nanostructures based on the AAO templates. For
example, hexagonally ordered Ni nanocones have been fabricated
using an a porous AAO template where the pores are of a cone
shape [135]. The conical AAO film was found to exhibit hexagonal
order with a period of 100 nm. The Ni nanocones and the surface
morphology of the nanoconical film exhibit the same periodic
structure of the template as shown in Fig. 1. 11.
The hexagonally ordered Ni nanocones and nanoconical film
were produced using anodization and metal plating techniques. The
conical AAO template was produced using a process of repeated
applications of the anodization and pore-widening steps, applying
the two steps alternately. The Ni nanocones were produced by
electroless Ni deposition onto the conical AAO template, with the
pores filled with Ni particles. The resulting Ni nanocones exhibit
the same ordered structure. The Ni nanoconical film was produced
by detaching the deposited Ni layer, with the surface morphology
also a hexagonally ordered array with a period of 100 nm. These
PO
3
4
 
Search WWH ::




Custom Search