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Rational Design and Characterisation of Supramolecular Architectures on Surfaces

Final Report Summary - RADSAS (Rational Design and Characterisation of Supramolecular Architectures on Surfaces)

Nanoscale science has experienced a tremendous growth in importance over recent years. The main focus of current research is on understanding, utilising and eventually applying the enormous richness of phenomena on this scale. However, looking closely at the present situation, we still encounter a substantial bottleneck in our attempts at building nanoscale devices. It is not sufficient to show that nanoscale assembly is feasible on the laboratory level, but it also has to be shown that massively parallel fabrication of nano-devices on an industrial scale is feasible.

Here, chemical methods of bottom-up construction become important, because only with these methods are the growth processes of complicated systems fast enough for an efficient production procedure. In this sense, the concept of bottom-up construction using methods of chemical synthesis becomes important, because only using these concepts the growth of complex systems is fast enough and provides sufficient quantity to allow an efficient production procedure.

The 'Rational design and characterisation of supramolecular architectures on surfaces' (Radsas) project aimed at developing efficient strategies for parallel, two-dimensional molecular self-assembly on surfaces, which is consider an indispensable prerequisite for the technical realisation of supramolecular design and engineering. Radsas combined the specific knowledge existing in surface science with the most advanced methods of chemical synthesis to obtain supramolecular structures with unique electronic and transport properties, tailored to reflect the desired behaviour in a wide range of technical applications.

The central aspect of our approach was to introduce site selectivity not only in the molecular building blocks but also in the interaction with the substrate surface. This was accomplished by fabricating surfaces with well defined nucleation sites for the subsequent molecular self-assembly process. Such templates with a regular array of nucleation centres were realised by two-dimensional strain relief and dislocation networks obtained by deposition of one or two monolayers of a metal on a single-crystalline substrate with a different lattice constant - such as Ag/Pt - and by vicinal Au surfaces exhibiting a rectangular superlattice of steps and discommensuration lines.

These template surfaces were thoroughly investigated with respect to their site-selectivity upon molecular adsorption. It was shown that both Ag/Pt and Au template surfaces could successfully be used for the site-specific anchoring of molecular building blocks. Furthermore, the intended directional guiding of (supra-)molecular self-assembly by the nanostructured template surfaces could be demonstrated. Using specifically functionalised entities, we successfully fabricated binary supramolecular wires and ribbons exhibiting undirectionality and an extremely regular wire-to-wire distance. Using the concepts developed in the project, the successful fabrication of a whole series of supramolecular architectures could be demonstrated.

Last but not least, the processes involved in the self-assembly and the properties of the resulting supramolecular structures were studied using a wide range of experimental as well as theoretical methods. The success of the Radsas project is largely based on a truly multidisciplinary approach, bringing together researchers in physical surface science, chemical synthesis and theoretical modelling.

The achievement of the ambitious goals of the Radsas project relied on a close collaboration between all project partners, and thus between researchers in physical surface science, chemical synthesis and theoretical modelling. Only in this strongly interdisciplinary approach could the processes involved in the self-assembly and the properties of the resulting supramolecular structures be studied using a wide range of experimental as well as theoretical methods. All partners are proud of the success of the Radsas project, which has clearly highlighted the potential of a combination of nanostructured template surfaces and appropriately functionalised molecular building blocks for the controlled self-assembly of specific supramolecular architectures on surfaces.

New opportunities for the future fabrication of nanoscale devices will critically depend on the controlled fabrication of surface-supported functional supramolecular structures. A promising strategy is to guide the molecular self-assembly by a combination of specific molecular functionalisation and anisotropic molecule-substrate interactions.