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Single-Molecule Resonant Tunnelling in Small Transition Metal Complexes - Towards Molecular Electronics

Final Activity Report Summary - TOMECS (Single-Molecule Resonant Tunnelling in Small Transition Metal Complexes - Towards Molecular Electronics)

Continued ultra-miniaturisation of electronic components such as transistors and diodes is of utmost technological and social importance. Overarching TOMECS objectives were to:
1. understand how electronic components operated at the ultimate scale of the single molecule;
2. design, prepare and explore target molecules in this new molecular electronics concept; and
3. develop theoretical frames for the single-molecule charge transport phenomena.

Molecules that could undergo redox processes, i.e. exchange electrons with other molecules or metallic electrodes, offered much more sophisticated electronics features than non-redox molecules. TOMECS identified, prepared and characterised a class of chemical compounds with such molecular electronics' properties. The transition metal osmium was the central ion in coordination chemical complexes with large organic molecules (bipyridine and terpyridine), such as ligand spheres.

The Os-complexes could be enclosed between a macroscopic but atomically planar gold or platinum surface and a thin metallic tip in a scanning tunnelling microscopy (STM) configuration. STM was used in the in-situ mode in aqueous solution and included an electrochemical reference electrode, entirely analogous to the source, drain, and gate electrode of a single-molecule transistor. The complexes could both be imaged to single-molecule resolution by in-situ STM and be brought to display interfacial electron transfer (electrical currents) of the single molecule. The current / bias and current / gate voltage (current / overpotential) correlations showed amplification and rectification effects that were large at the molecular scale, i.e. up to two orders of magnitude. These data were the first of their kind and were supported by parallel theoretical frame development in TOMECS.

By its combination of theoretical basis, chemical design and synthesis, and novel nanoscale approach, TOMECS offered new approaches to molecular charge transport at these ultra-small size scales and pointed to the powerful tools of electrochemistry and in-situ STM in molecular electronics.

The TOMECS perspectives could also be more broadly applied. Polynuclear transition metal complexes with more sophisticated electronics function were designed. The molecules could also be inserted in other, identified multifariously designed molecular scale 'circuits'. Finally, by its concept and in contrast to virtually all previously reported cases of single-molecule electronics which only operated at cryogenic temperatures and in ultra-high vacuum, the new TOMECS-based complexes operated at room temperature and in condensed matter environment.