400
11 Templated Systems
the original template. With the same templating principle, ZnO nanodots can also be
synthesized [314].
In a variation of the double-templating process, the secondary template is prepared
with a much smaller thickness than the particle diameter of the primary template. If
the thickness of the first deposit is relatively small, it does not determine a spherical
cavity for the secondary deposit but rather provides a surface pattern at which the
second deposit can nucleate and then grow. With this method, polymer-separated
nanodots can be deposited along a hexagonal pattern of the same unit cell size as
that of the primary template [315, 316].
In contrast to the above-mentioned method in which the goal is the surface
patterning with a thin layer, thick inverse opal structures with a thickness of several
times the colloidal particle diameter can be used as substrate. If the plating of the
second deposit into the inverse opal structure is carried out under carefully adjusted
circumstances, the second deposit can nucleate and grow along the entire surface of
the secondary template. The feasibility of this method was evidenced for the deposition of Si coatings on Ni inverse opal secondary template [317]. If conformal deposit
cannot form, the inverse opal structure hosts seeds of the secondary deposit, such as
it was demonstrated with Fe 2 O 3 deposition onto macroporous Ni scaffold [318].
In nanosphere lithography, chemical and electrochemical steps can be combined.
For instance, the primary colloidal template can be filled up with a salt, namely
Al(NO 3 ) 3 by solvent evaporation, whose annealing results in an Al 2 O 3 secondary
template that can be used in the forthcoming electroplating process [319]. If the
inverse opal structure is electroplated, it can be used as secondary template for
chemical synthesis of spherical particles that is hard to produce as free nanoparticles
without a size-limiting template [320].
11.4 Soft Templates Formed by Molecular Self-assembly
Processes
11.4.1 Lyotropic Systems Suitable for Templates
in Electrodeposition Processes
Lyotropic systems consist of amphiphilic molecules as solute and a solvent. For the
framework of this monograph, it is an acceptable simplification that water will be
considered as solvent in each case. The liquid crystalline properties of the water–
amphiphilic solute systems stem from the ordering of the molecules in the lyotropic
mixture [321]. This is governed by the preferred interaction of the hydrophilic part
of the amphiphilic molecules with water and the hydrophobic (or oleophilic) part,
usually a long apolar chain, with the similar parts of other species present in the
system. As the amphiphilic solute-to-water ratio increases, the following phases can
form (see also Fig. 11.18 and note that Arabic and Roman numbers both occur in
various sources as type identifiers):
11 Templated Systems
the original template. With the same templating principle, ZnO nanodots can also be
synthesized [314].
In a variation of the double-templating process, the secondary template is prepared
with a much smaller thickness than the particle diameter of the primary template. If
the thickness of the first deposit is relatively small, it does not determine a spherical
cavity for the secondary deposit but rather provides a surface pattern at which the
second deposit can nucleate and then grow. With this method, polymer-separated
nanodots can be deposited along a hexagonal pattern of the same unit cell size as
that of the primary template [315, 316].
In contrast to the above-mentioned method in which the goal is the surface
patterning with a thin layer, thick inverse opal structures with a thickness of several
times the colloidal particle diameter can be used as substrate. If the plating of the
second deposit into the inverse opal structure is carried out under carefully adjusted
circumstances, the second deposit can nucleate and grow along the entire surface of
the secondary template. The feasibility of this method was evidenced for the deposition of Si coatings on Ni inverse opal secondary template [317]. If conformal deposit
cannot form, the inverse opal structure hosts seeds of the secondary deposit, such as
it was demonstrated with Fe 2 O 3 deposition onto macroporous Ni scaffold [318].
In nanosphere lithography, chemical and electrochemical steps can be combined.
For instance, the primary colloidal template can be filled up with a salt, namely
Al(NO 3 ) 3 by solvent evaporation, whose annealing results in an Al 2 O 3 secondary
template that can be used in the forthcoming electroplating process [319]. If the
inverse opal structure is electroplated, it can be used as secondary template for
chemical synthesis of spherical particles that is hard to produce as free nanoparticles
without a size-limiting template [320].
11.4 Soft Templates Formed by Molecular Self-assembly
Processes
11.4.1 Lyotropic Systems Suitable for Templates
in Electrodeposition Processes
Lyotropic systems consist of amphiphilic molecules as solute and a solvent. For the
framework of this monograph, it is an acceptable simplification that water will be
considered as solvent in each case. The liquid crystalline properties of the water–
amphiphilic solute systems stem from the ordering of the molecules in the lyotropic
mixture [321]. This is governed by the preferred interaction of the hydrophilic part
of the amphiphilic molecules with water and the hydrophobic (or oleophilic) part,
usually a long apolar chain, with the similar parts of other species present in the
system. As the amphiphilic solute-to-water ratio increases, the following phases can
form (see also Fig. 11.18 and note that Arabic and Roman numbers both occur in
various sources as type identifiers):