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nanoregime. To move towards this goal, it will be necessary to control the binding
interaction of the respective molecules with the carbon nanotube surface selec-
tively via suited linkers (e.g., pyrene groups).
12.5. CONCLUSIONS
Highly ordered supramolecular metal ion arrays (MIAs) and metal ion networks
(MINs) can be constructed on surfaces by using two different general approaches:
(A) a three-tiered hierarchical synthesis/self-assembly/deposition protocol or (B)
by one-step 2D confined coordination of the metal ions/atoms through organic
ligands directly under assistance of the surface. Both strategies lead to nanometer
sized, highly symmetric regular arrangements of metal ions on surfaces, whereby
the components (organic ligands and metal ions) can be changed in their size,
identity, and electronic properties. This modular approach enables a deliberate
choice of the nature as well as the relative positioning of the metal ions, in
addition to the fine-tuning of their electronic environment. Remarkably, indivi-
dual metal ions can be effectively imaged and addressed by scanning tunneling
microscopy (STM) and spectroscopy (STS) techniques. In the future, direct
addressing of electronic properties of the metal ion states (redox, spin states,
magnetic anisotropy) might lead to the exploitation of bi- or even multistability
at the single ion level, e.g., within the 1 nm regime. Such possibilities posit the ion
dot concept in analogy to the well established quantum dot approach. In addition
to the possibility of controlled nanopatterning, new horizons in (molecular) data
storage are opened. We are given access to completely new avenues in view of
alternative information processing technologies (e.g., cellular automata, quantum
computing) [11]. If one considers each metal ion within the extended network as
addressable (still) bistable data point with an averaged metal ion distance of ca.
2 nm, a functional MIN nanostructure would easily lead to data storage
capacities in the several hundreds of Tb/in
2
. This is clearly above the actual
state-of-the-art of storage devices (below 1 Tb/in
2
), but it is also more than what
might be achievable by 2D monodomain cluster deposition (without organic
molecules) on Au (788) surfaces (26 Tb/in
2
) [40]. The additional use of the
intrinsic multistability of metal ions through the ion dot concept would go
beyond these numbers; this might be a strong motivation to implement molecular
metal ion components into the nanoscale devices. However, the implementation
and controlled exploitation of metal ion arrays (MIAs) and networks (MINs)
within device architectures must find a way to bridge the gap between the
molecular nano- and the environmental macrodimensions. Highly integrated
carbon nanotube-electrode structures can act as the appropriate connector tool,
linking the nanoworld of supramolecular metal ion assemblies with the macro-
scopic device environments. In sum, such molecule-based device geometries
comprising (i) metal ion assemblies, (ii) carbon nanotubes, and (iii) nanostruc-
tured metallic electrodes would combine the advantages of both bottom-up
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