Biomedical Engineering Reference
In-Depth Information
patterned metal structures [83-86], semiconductors [86,87] and soft
matter such as conducting polymers [88,89]. The electrochemical
processing of material surfaces at the nanoscale both laterally
and vertically can be conducted by scanning probe anodization/
cathodization, which uses the tip-sample junction of a scanning probe
microscope connected with an adsorbed water column as a minute
electrochemical cell. Reviews on SPM nanolithography examined
its various applications in modification, deposition, removal and
manipulation of materials for nanoscale fabrication [90].
STM has tremendous potential in metal deposition studies. The
initial stages of metal deposition and the Ag adlayer on Au (111)
have been studied by Kolb et al. [91].The inherent nature of the
deposition process which is strongly influenced by the defect
structure of the substrate, providing nucleation centers, requires
imaging in real space for a detailed picture of the initial stage. With
STM, the atomic resolution helps understand these processes on a
truly atomistic level. Underpotentially deposited Ag revealed a series
of ordered adlayer structures with an increasing density of adatoms
when the applied potentials were decreased. Nanostructuring can
be also achieved by involving electrochemical processes into the
overall procedures. For example, Li et al. [92,93] deposited Ag and
Pt clusters on a graphite surface by applying positive voltage pulses
to the STM tip in a solution containing the respective metal cations.
This effect was attributed to nucleation within holes that were
created on the graphite substrate surface by the voltage pulses. Kolb
et al. [94], on the other hand, were able to detach Cu clusters from
a tip, where they had been previously deposited electrochemically,
onto a Au substrate by mechanical contact. However, all of these
techniques suffer from restrictions, which could be largely avoided
if controlled nanostructuring could be achieved by a direct local
electrochemical reaction on the substrate, with the geometry
being determined by the location of the tip that acts as a local
counterelectrode. By applying ultrashort voltage pulses (≤100 ns),
holes of about 5 nm in diameter and 0.3 to 1 nm depth on an Au
substrate can be created by local anodic dissolution, while cathodic
polarization leads to the deposition of small Cu clusters [95]. The
development of allowing the generation of small metal clusters, with
the help of an STM tip, and placing them at will onto single crystal
Search WWH ::
Custom Search