Biomedical Engineering Reference
In-Depth Information
with high fidelity in pattern transfer as well as with a good degree
of flexibility in materials [137]. The growth of metal nanowires
using AAO membranes as hard templates has been reviewed [138].
These kinds of metal nanowires can be applied to superconductivity,
optical spectroscopy, sensing, and catalytic conversion, and energy
harvesting. The AAO template method provides access to arrays of
single-crystal metal nanowires and to quasi-one-dimensional metal
nanostructures with controlled compositional variation along their
length. Semiconductors such as ZnO and TiO
with nanostructures
can also be manufactured with such template or by related
anodization techniques.
2
1.9.2 Zinc Oxide (ZnO)
ZnO exhibits many unusual properties including uniaxial
piezoelectric response and n-type semiconductor characteristics.
Such properties can be used in applications such as field-emission
materials [139], light-emitting diodes (LEDs) [140], solar cells [141],
and gas sensors [142]. Electrodeposition of ZnO films has been reported
by several groups and used in fabrication of oriented nanowire
and nanorod arrays [143-148]. ZnO films can be electrodeposited
cathodically in aqueous chloride solutions using dissolved oxygen
as a precursor. The deposition reaction in the electrolyte is:
Zn
+
1
2
+ 2e
-
�ZnO. The deposition mechanism was analyzed
in termhemical induced surface precipitation due to an increase of
local pH resulting from the oxygen reduction reaction. A dramatic
effect of temperature on the formation of ZnO was observed. When
the temperature increases (
2+
O
2
˚
C), a transition between
amorphous insulating zinc oxyhydroxide (ZnO
x
T
≈ 50
transition
) to well-
crystallized and conducting ZnO happens [149]. The dimensions
and the deposition rate of electrodeposited ZnO nanowire arrays
can be controlled by changing the chemical nature of the anions in
solution. A significant variation of the diameter (65 to 110 nm) and
length (1.0 to 3.4 μm) of the nanowires can be obtained by changing
only the nature of the anions in solution [150]. Recently, large-scale,
single-crystalline ZnO nanotube arrays were directly fabricated onto
F-doped SnO
(OH)
y
(FTO) glass substrate via an electrochemical deposition
2
Search WWH ::
Custom Search