11.2 Nanochannel Templates Obtained with Top-Down Synthesis Methods
371
This is to be taken into account during the optimization of the templated deposition
processes.
11.2.5 Electrodeposited Non-metallic Nanowires
Although the electrodeposition of a large number of non-metallic materials has been
established, some deposits are not compact but rather porous. The interesting feature
of the template systems is that the strong spatial constraint makes it possible to obtain
these materials as compact nanowires. Among the motivation of the electrodeposition
of non-metallic nanowires, we have to highlight the application of semiconductors
in optoelectronic devices. The band gap of the semiconductors can be tuned by
the size of the deposit element, which opens a way to prepare custom-designed
devices. Another important property is the thermoelectricity which can be potentially
exploited in both refrigerating and waste heat harvesting devices. Below, a short
summary of the materials suitable for nanowire preparation will be given with a
short description of the conditions of their electrodeposition.
Oxides and hydroxides. Recipes elaborated for reductive electrodeposition of
various oxides and hydroxides in the form or either films or porous coatings work with
minor modification for nanochannel templates, too. Among others, such processes
are suitable to produce ZnO [114], Cu 2 O [115, 116] and Cd(OH) 2 [117] nanowires.
All above-mentioned processes are based on the production of alkaline reagents by
the reduction of a suitable co-reactant other than the metal ions in an aqueous solution.
For ZnO, an alternative of the deposition from aqueous solution is the application
of dimethyl sulphoxide as solvent and the alkalization of the media by reducing
the dissolved molecular oxygen [118]. Several oxide nanowire arrays reported were
produced in PAA membranes [115–118]. It seems that the pH increase needed for
the production of the oxide/hydroxide nanowires is moderate enough so that it does
not lead to the destruction of the alumina structure.
Electrodeposition of oxide nanowires involving metal atoms of higher oxidation number is carried out by oxidizing dissolved metal ions of lower oxidation
number. Such anodic processes can be used to synthesize PbO 2 [119] and MnO 2
[120] nanowires. For PbO 2 , the careful selection of the reactants and that of the pH
of the solution lead to the formation of various crystalline forms of the oxide, while
MnO 2 is obtained in an amorphous state.
Besides the direct synthesis of oxide nanowires, there is also an indirect synthesis
route. An example is the deposition of Cu nanowires and their transformation to
CuO nanowires by oxidation in air at high temperature [62]. Although there is a
small roughness increment during the oxidation, the shape of the metal nanowires
could be retained during the oxidation process.
Compounds of metals with the elements of Groups 5A and 6A. The nature of
the precursor materials used for the electrosynthesis of compound semiconductors
differs for aqueous and non-aqueous solutions. Therefore, a better insight can be
given if these methods are discussed separately, irrespectively of the fact that some
371
This is to be taken into account during the optimization of the templated deposition
processes.
11.2.5 Electrodeposited Non-metallic Nanowires
Although the electrodeposition of a large number of non-metallic materials has been
established, some deposits are not compact but rather porous. The interesting feature
of the template systems is that the strong spatial constraint makes it possible to obtain
these materials as compact nanowires. Among the motivation of the electrodeposition
of non-metallic nanowires, we have to highlight the application of semiconductors
in optoelectronic devices. The band gap of the semiconductors can be tuned by
the size of the deposit element, which opens a way to prepare custom-designed
devices. Another important property is the thermoelectricity which can be potentially
exploited in both refrigerating and waste heat harvesting devices. Below, a short
summary of the materials suitable for nanowire preparation will be given with a
short description of the conditions of their electrodeposition.
Oxides and hydroxides. Recipes elaborated for reductive electrodeposition of
various oxides and hydroxides in the form or either films or porous coatings work with
minor modification for nanochannel templates, too. Among others, such processes
are suitable to produce ZnO [114], Cu 2 O [115, 116] and Cd(OH) 2 [117] nanowires.
All above-mentioned processes are based on the production of alkaline reagents by
the reduction of a suitable co-reactant other than the metal ions in an aqueous solution.
For ZnO, an alternative of the deposition from aqueous solution is the application
of dimethyl sulphoxide as solvent and the alkalization of the media by reducing
the dissolved molecular oxygen [118]. Several oxide nanowire arrays reported were
produced in PAA membranes [115–118]. It seems that the pH increase needed for
the production of the oxide/hydroxide nanowires is moderate enough so that it does
not lead to the destruction of the alumina structure.
Electrodeposition of oxide nanowires involving metal atoms of higher oxidation number is carried out by oxidizing dissolved metal ions of lower oxidation
number. Such anodic processes can be used to synthesize PbO 2 [119] and MnO 2
[120] nanowires. For PbO 2 , the careful selection of the reactants and that of the pH
of the solution lead to the formation of various crystalline forms of the oxide, while
MnO 2 is obtained in an amorphous state.
Besides the direct synthesis of oxide nanowires, there is also an indirect synthesis
route. An example is the deposition of Cu nanowires and their transformation to
CuO nanowires by oxidation in air at high temperature [62]. Although there is a
small roughness increment during the oxidation, the shape of the metal nanowires
could be retained during the oxidation process.
Compounds of metals with the elements of Groups 5A and 6A. The nature of
the precursor materials used for the electrosynthesis of compound semiconductors
differs for aqueous and non-aqueous solutions. Therefore, a better insight can be
given if these methods are discussed separately, irrespectively of the fact that some