ELECTROCHEMICAL NANOFABRICATIONS: A GENERAL REVIEW - Electrochemical Nanofabrication: Principles and Applications - page 12

The application of conducting AFM probe anodization to
nanolithography was also used in the fabrication and patterning of
materials in a similar manner as STM probes. AFM-tip-induced and
current-induced local oxidation of silicon and metals was reported,
and this novel local oxidation process can be used to generate thin
oxide tunneling barriers of 10-50 nm [87]. The direct modification
of silicon and other semiconductor and metal surfaces by the
process of anodization using the electric field from an SPM is one
promising method of accomplishing direct-writing lithography for
the electronic device fabrication [85]. This technique involves the
application of an electrical bias to both the conducting probe and
the sample substrate to locally oxidize selected regions of a sample
surface. Nanostructures down to a few tens of nanometers in size
have been also fabricated with Langmuir-Blodgett (LB) films
and self-assembled monolayers (SAMs) using AFM lithography
[102]. AFM anodization was successfully carried out with SAMs
on the silicon substrate. Applied voltage between the AFM tip
and sample, the scanning speed, surface group, and the relative
humidity in air are very important factors for nanometer-scale
lithography of the ultrathin films. The high structural order and
perfect thickness of ultrathin organic molecular assemblies are
the major advantages of nanoscale lithography. Soft matter such
as conducting polymers can also be patterned in the nanoscale
by such lithographic method using AFM. Cai et al. described the
first observation of localized electropolymerization of pyrrole and
aniline on highly oriented pyrolytic graphite (HOPG) substrates
under AFM tip-sample interactions [88]. A scanning or oscillating
AFM tip, providing the horizontal scratching force and the vertical
tapping force, is essential as the driving force for the surface
modification with the conducting polymer. It was shown that under
the AFM tip interaction, electropolymerization can be blocked
on the bare HOPG substrate or enhanced on the as-polymerized
film. The localized electropolymerization in selected surface
areas enables the nanomodification of lines, square platforms or
hollows of polypyrrole and polyaniline on the substrates. Nano-
writing of intrinsically conducting polymer can be also achieved
via a novel electrochemical nanolithographic technique using
electrochemical

AFM. Conducting polymer (polythiophene