362
11 Templated Systems
feature size will be followed. The discussion will be started with the self-assembly
of solid particles in which the particle size may be even in the micrometre scale.
Finally, the template obtained with molecular-level self-assembly will be detailed.
The literature of the template-based synthesis methods of nanostructures is particularly rich. The number of works dealing with each topic of the present chapter
ranges to thousands, and the careful selection of the relevant works is really hard.
Therefore, the literature list cited in connection with each template type is meant
to be representative. Neither of these lists can be taken as exclusive, and the further
literature search of the reader is highly encouraged. Review works published on electrochemical applications of templates give an ample selection of additional examples
[1–12].
11.2 Nanochannel Templates Obtained with Top-Down
Synthesis Methods
11.2.1 Comparison of the Templates Suitable
for Electrodeposition of Nanowires
The research on nanochannel templates started in 1970 when the first article was
published on the electrochemical treatment of ion-irradiated and etched MICA
template with nanochannels [13]. Although the instrumentation used for electrodeposition was not truly professional and a part of the observations made were abandoned
later, the basic experimental setup with the nanochannel templates and their singleside metal coverage used as electrode was laid down and has been followed ever
since. The deposition method based on ion track-etched MICA was improved later,
making it possible to deposit nanowires with a diameter as small as 8 nm [14]. It was
recognized right at the time of the introduction of the technique that it has a unique
potential to produce quasi-one-dimensional materials. Although MICA templates
were used in a few studies for both electrochemical [15] and electroless [16] depositions of one-dimensional nanomaterials, this template family was suppressed by
anodized porous alumina and ion track-etched polymer membranes. The latter two
dominate the market of nanochannel templates in electrochemical research nowadays. The distinctive feature of MICA is that, due to its crystalline nature, the cross
section of the track-etched channel is rhombohedral, not circular.
The principle of the preparation of track-etched membranes is as follows. The foils
are bombarded with heavy ions of energy typically larger than 10 MeV. In velocity
equivalence, this means that the speed of the particles is more than 10% of the speed
of the light. Although the collision cascade within a polymer material decelerates
the heavy ions, their penetration depth is larger than 100 μm. During the sequential
collisions, the bonds in the membrane are destroyed in a cylindrical zone of a fewnanometre radius along the heavy ion trajectory. The small molecules produced leave
the membrane easily, and the ion track can be further etched chemically to fully open
11 Templated Systems
feature size will be followed. The discussion will be started with the self-assembly
of solid particles in which the particle size may be even in the micrometre scale.
Finally, the template obtained with molecular-level self-assembly will be detailed.
The literature of the template-based synthesis methods of nanostructures is particularly rich. The number of works dealing with each topic of the present chapter
ranges to thousands, and the careful selection of the relevant works is really hard.
Therefore, the literature list cited in connection with each template type is meant
to be representative. Neither of these lists can be taken as exclusive, and the further
literature search of the reader is highly encouraged. Review works published on electrochemical applications of templates give an ample selection of additional examples
[1–12].
11.2 Nanochannel Templates Obtained with Top-Down
Synthesis Methods
11.2.1 Comparison of the Templates Suitable
for Electrodeposition of Nanowires
The research on nanochannel templates started in 1970 when the first article was
published on the electrochemical treatment of ion-irradiated and etched MICA
template with nanochannels [13]. Although the instrumentation used for electrodeposition was not truly professional and a part of the observations made were abandoned
later, the basic experimental setup with the nanochannel templates and their singleside metal coverage used as electrode was laid down and has been followed ever
since. The deposition method based on ion track-etched MICA was improved later,
making it possible to deposit nanowires with a diameter as small as 8 nm [14]. It was
recognized right at the time of the introduction of the technique that it has a unique
potential to produce quasi-one-dimensional materials. Although MICA templates
were used in a few studies for both electrochemical [15] and electroless [16] depositions of one-dimensional nanomaterials, this template family was suppressed by
anodized porous alumina and ion track-etched polymer membranes. The latter two
dominate the market of nanochannel templates in electrochemical research nowadays. The distinctive feature of MICA is that, due to its crystalline nature, the cross
section of the track-etched channel is rhombohedral, not circular.
The principle of the preparation of track-etched membranes is as follows. The foils
are bombarded with heavy ions of energy typically larger than 10 MeV. In velocity
equivalence, this means that the speed of the particles is more than 10% of the speed
of the light. Although the collision cascade within a polymer material decelerates
the heavy ions, their penetration depth is larger than 100 μm. During the sequential
collisions, the bonds in the membrane are destroyed in a cylindrical zone of a fewnanometre radius along the heavy ion trajectory. The small molecules produced leave
the membrane easily, and the ion track can be further etched chemically to fully open