4.2 Combination of UPD with Other Surface-Area-Limited Processes
109
graphite cathode. This configuration provides a sufficient electrical contact between
the particles in a stagnant solution where SLRR was shown to be effective at least
at the monolayer-level coverage [131]. Due to the accessibility of the deep regions
of the sediment, the SLRR reaction time for nanoparticle sediments was about two
orders of magnitude larger than for planar electrodes. A better mechanical control
on the assembly of nanoparticles is provided if they are pressed against each other
with small-porosity filters, introducing a current lead to the same chamber. This
compacted flow cell makes it possible to exchange the working solution around the
nanoparticles without loosing the potential control [153].
Another way for increasing the surface area of a catalyst is to apply a porous
material as substrate [126, 139]. Dealloyed Ag–Au alloys proved to be an ideal
catalyst support when the internal surface was modified with SLRR-produced Pt
[144], taking advantage of the conformal deposition characteristics of the SLRR
process.
It is not only the efficiency but also the degradation of a catalyst can be studied
by using SLRR layers. When a catalyst degrades, the corrosion rate can be estimated
from the outflow of a reactor, but this method requires the measurement of very small
concentrations, which is often a problem. When ultrathin layers are studied, the loss
of the catalyst can be followed with the surface analysis of the catalyst itself since
the substrate underneath is a different material than the ultrathin catalyst layer. This
approach has been taken advantage of for Au-supported Pt catalysts formed with
SLRR [112].
Finally, it has to be mentioned that catalysis is by far not the only field of the
potential application of SLRR-wise metal deposition. In microelectronics, the everdecreasing size of circuit elements due to the ultra-large-scale integration (ULSI)
may require the deposition of even metallic layers, which can be carried out in a
feasible manner by SLRR [155].
4.3 Non-UPD Deposition of Ultrathin Metallic Layers
4.3.1 Electrodeposition of Ultrathin Layers with Self-limiting
Processes
It is needless to say that any deposition process can lead to the formation of some
nanoscale objects if the deposition is stopped early enough after the start of the
process. However, an interruption of the deposition process shortly after the onset of
the deposition does not necessarily result in a structure that is different from the bulk
and what deserves the name “nanostructure”. Therefore, the common feature of the
cases discussed in Sect. 4.3 is that some particular observation which is normally not
observed in the bulk form of the same material can be made that is closely related to
the nanoscale nature of the deposits.
109
graphite cathode. This configuration provides a sufficient electrical contact between
the particles in a stagnant solution where SLRR was shown to be effective at least
at the monolayer-level coverage [131]. Due to the accessibility of the deep regions
of the sediment, the SLRR reaction time for nanoparticle sediments was about two
orders of magnitude larger than for planar electrodes. A better mechanical control
on the assembly of nanoparticles is provided if they are pressed against each other
with small-porosity filters, introducing a current lead to the same chamber. This
compacted flow cell makes it possible to exchange the working solution around the
nanoparticles without loosing the potential control [153].
Another way for increasing the surface area of a catalyst is to apply a porous
material as substrate [126, 139]. Dealloyed Ag–Au alloys proved to be an ideal
catalyst support when the internal surface was modified with SLRR-produced Pt
[144], taking advantage of the conformal deposition characteristics of the SLRR
process.
It is not only the efficiency but also the degradation of a catalyst can be studied
by using SLRR layers. When a catalyst degrades, the corrosion rate can be estimated
from the outflow of a reactor, but this method requires the measurement of very small
concentrations, which is often a problem. When ultrathin layers are studied, the loss
of the catalyst can be followed with the surface analysis of the catalyst itself since
the substrate underneath is a different material than the ultrathin catalyst layer. This
approach has been taken advantage of for Au-supported Pt catalysts formed with
SLRR [112].
Finally, it has to be mentioned that catalysis is by far not the only field of the
potential application of SLRR-wise metal deposition. In microelectronics, the everdecreasing size of circuit elements due to the ultra-large-scale integration (ULSI)
may require the deposition of even metallic layers, which can be carried out in a
feasible manner by SLRR [155].
4.3 Non-UPD Deposition of Ultrathin Metallic Layers
4.3.1 Electrodeposition of Ultrathin Layers with Self-limiting
Processes
It is needless to say that any deposition process can lead to the formation of some
nanoscale objects if the deposition is stopped early enough after the start of the
process. However, an interruption of the deposition process shortly after the onset of
the deposition does not necessarily result in a structure that is different from the bulk
and what deserves the name “nanostructure”. Therefore, the common feature of the
cases discussed in Sect. 4.3 is that some particular observation which is normally not
observed in the bulk form of the same material can be made that is closely related to
the nanoscale nature of the deposits.