442
12 Localized or Spatially Selective Electrodeposition Methods
salts containing tertaalkylammonium cations with relatively long carbon chains are
typical, and the anion is usually also large such as tetrakis(pentafluorophenyl)borate.
It has to be kept in mind that not only is the liquid–liquid interface polarized
but charge transfer has to take place therein at the same time. This means that one
of the contacting phases contains the reagent to be deposited and the other phase
also must contain an electron donor/scavenger compound. The variety of the redox
couples largely depends on which of the contacting phases contains the reactant. If
the reactant is present in the aqueous phase (e.g., PdCl 2 when Pd nanoparticles are to
be deposited at the interface), the reduced form of a redox couple has to be dissolved
in the organic phase. Butylferrocene and decamethylferrocene are common that can
be oxidized easily, and they can provide the electron for the metal ion reduction. In the
opposite case when the reactant is in the low-polarity phase, another compound of the
same role is to be dissolved in the aqueous phase. For the reduction of [AuCl 4 ]
– that
is initially present in the organic phase, K 4 [Fe(CN) 6 ] is a suitable electron exchange
partner that is present in the aqueous phase. The electron transfer partner compound in
the phase containing no precursor compound for the deposition may vary as a function
of the nature of the entire system. However, similarly to the supporting electrolytes,
they also have to exhibit a large partition coefficient between the contacting phases.
The features of the deposition processes taking place at the bare liquid—
liquid interface without the assistance of any electrode (electron conductor) will
be discussed in Sects. 12.3.2–12.3.3. Beside these conventional deposition systems,
there are additional methods making use of the liquid–liquid interface in some other
means, also with a special electrode configuration. Sect. 12.3.4 will enumerate the
studies where a macroscopic planar electron conductor crosses the liquid–liquid
interface vertically, but the reaction zone is restricted to the triple-phase boundary
line. Finally, in Sect. 12.3.5, the cases will be discussed when either a tip or a filament is applied that touches or crosses the liquid–liquid interface, respectively, but
the apolar phase has no role in the electrochemical reactions apart from forming the
growth-regulating interface with the aqueous electrolyte solution.
12.3.2 Particle Deposition at the Liquid–Liquid Interface
The main reason of the particle deposition studies at ITIES is the opportunity of the
controlled size regulation and the availability of small particles without the necessity of their release from a surface. The typical cell arrangement can be seen in
Fig. 12.6. The cell contains two electrodes for passing the current which are the
counter electrodes in the two contacting liquid phases. These are usually made of
platinum gauze. The exact position of the counter electrodes is not crucial; nevertheless, the symmetry of the cell and the even current distribution has to be taken into
account. In order to measure the potential difference across the interface, one needs
two reference electrodes which remain unpolarized during the entire experiment. For
reducing the ohmic drop contribution that arises between the junction point of the
end of the reference capillary and the interface, the endings of the capillary of the
12 Localized or Spatially Selective Electrodeposition Methods
salts containing tertaalkylammonium cations with relatively long carbon chains are
typical, and the anion is usually also large such as tetrakis(pentafluorophenyl)borate.
It has to be kept in mind that not only is the liquid–liquid interface polarized
but charge transfer has to take place therein at the same time. This means that one
of the contacting phases contains the reagent to be deposited and the other phase
also must contain an electron donor/scavenger compound. The variety of the redox
couples largely depends on which of the contacting phases contains the reactant. If
the reactant is present in the aqueous phase (e.g., PdCl 2 when Pd nanoparticles are to
be deposited at the interface), the reduced form of a redox couple has to be dissolved
in the organic phase. Butylferrocene and decamethylferrocene are common that can
be oxidized easily, and they can provide the electron for the metal ion reduction. In the
opposite case when the reactant is in the low-polarity phase, another compound of the
same role is to be dissolved in the aqueous phase. For the reduction of [AuCl 4 ]
– that
is initially present in the organic phase, K 4 [Fe(CN) 6 ] is a suitable electron exchange
partner that is present in the aqueous phase. The electron transfer partner compound in
the phase containing no precursor compound for the deposition may vary as a function
of the nature of the entire system. However, similarly to the supporting electrolytes,
they also have to exhibit a large partition coefficient between the contacting phases.
The features of the deposition processes taking place at the bare liquid—
liquid interface without the assistance of any electrode (electron conductor) will
be discussed in Sects. 12.3.2–12.3.3. Beside these conventional deposition systems,
there are additional methods making use of the liquid–liquid interface in some other
means, also with a special electrode configuration. Sect. 12.3.4 will enumerate the
studies where a macroscopic planar electron conductor crosses the liquid–liquid
interface vertically, but the reaction zone is restricted to the triple-phase boundary
line. Finally, in Sect. 12.3.5, the cases will be discussed when either a tip or a filament is applied that touches or crosses the liquid–liquid interface, respectively, but
the apolar phase has no role in the electrochemical reactions apart from forming the
growth-regulating interface with the aqueous electrolyte solution.
12.3.2 Particle Deposition at the Liquid–Liquid Interface
The main reason of the particle deposition studies at ITIES is the opportunity of the
controlled size regulation and the availability of small particles without the necessity of their release from a surface. The typical cell arrangement can be seen in
Fig. 12.6. The cell contains two electrodes for passing the current which are the
counter electrodes in the two contacting liquid phases. These are usually made of
platinum gauze. The exact position of the counter electrodes is not crucial; nevertheless, the symmetry of the cell and the even current distribution has to be taken into
account. In order to measure the potential difference across the interface, one needs
two reference electrodes which remain unpolarized during the entire experiment. For
reducing the ohmic drop contribution that arises between the junction point of the
end of the reference capillary and the interface, the endings of the capillary of the