ELECTROCHEMICAL NANOFABRICATIONS: A GENERAL REVIEW - Electrochemical Nanofabrication: Principles and Applications - page 22

the local polypyrrole electrosynthesis with short voltage pulses.
A polypyrrole ring with needle-like feature can be selectively
nanofabricated, which was grown with 1 μs pulses in 0.2 M
H
2

/0.2M Pyrrole. To obtain the ring structure, a 50 μm diameter
flattened cylindrical Pt wire tool was brought to a distance of 1 μm
from the workpiece substrate before applying the pulses. The small
distance between tool and the substrate strongly hinders the supply
of monomer at the reaction site. The consequent relatively low
supersaturation leads to a low density of nuclei, which grow and
form isolated polypyrrole fibers. With the increase of the distance, a
more compact ring-like structure can be obtained.

SO
4

1.8 TEMPLATE-FREE METHODS FOR CONDUCTING
POLYMER NANO-ARCHITECTURE

The assembly of large arrays of oriented nanowires containing
molecularly aligned conducting polymers without using a porous
membrane template to support the polymer was reported
[120]. The uniform oriented nanowires were prepared through
controlled nucleation and growth during a stepwise electrochemical
galvanostatic deposition process, in which a large number of nuclei
were first deposited on the substrate using a large current density.
After the initial nucleation, the current density was reduced stepwise
in order to grow the oriented nanowires from the nucleation sites
created in the first step. The usefulness of these new polymer
structures is demonstrated with a chemical sensor device for H
2

,
the detection of which is widely investigated for biosensors. It offers
a general approach to control nucleation and has potential for
growing oriented nanostructures of other materials.
Figure 1. 10 demonstrates the steps to electrochemically fabricate
arrays of oriented conducting polyaniline (PANI) nanowires by well
controlled nucleation and growth without templates. After initiating
the nucleation of the conducting polymer at high current densities
the current density is reduced to avoid formation of further nuclei.
The existing nuclei grew preferentially vertically to the surface. A
typical procedure involves electrochemical deposition in an aniline-
containing electrolyte solution, by using the substrate as the working
electrode. This process involves 0.08 mAcm

O
2

-2

for 0.5 h, followed