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Probing single molecule-metal contacts and electronic transport by STM-STS

Final Activity Report Summary - STMolTranSTS (Probing single molecule-metal contacts and electronic transport by STM-STS)

The project aimed to obtain a microscopic understanding of the transport through single molecules and nanostructures in atomistically controlled environments. In order to accomplish this aim it was mandatory to acquire an excellence control of the atomistic structure of the electrode surface and the molecular or nanostructure adsorption geometry.

This goal was achieved by combining in situ analysis with scanning tunnelling microscopy at very low temperatures, less than one Kelvin, and ultra-high-vacuum preparation techniques. This unique combination provided us an atomistic control of the shape and cleanness of the molecules and nanostructures studied and allowed us to investigate their local electronic properties, e.g. transport, superconductivity and magnetism, with ultimate energy resolution. During this project we characterised the electronic transport through single molecules and nanostructures adsorbed at metal and insulating surfaces using the tip of a scanning tunnelling microscope (STM) as a second electrode.

The most important scientific achievements made during the project can be summarised as follows:

1. optimisation of the performance of the experimental system, a step which was crucial for the excellence of the results achieved in the project.
2. control at the atomic scale of the environment where the individual molecules and nanostructures were deposited or grown. We proved that the exceptional electronic properties of the boron nitride (BN) nanomesh and of epitaxatial graphene on SiC made these two substrates ideal hosts to adsorb single molecules and nanostructures.
3. controlled deposition and characterisation of the molecules on the different substrates. We overcame the challenge of depositing complex functional molecules by means of electrospray ionisation. Thanks to this pioneering methodology we were able, for the first time, to bring the spin crossover complex [Fe(bpp)2]2+ intact into a surface.
4. study of the electronic properties of isolated superconducting and magnetic nanostructures. With the combination of very low temperature ultra high vacuum (UHV)-STM experiments with in situ growth of clean isolated superconducting Pb and Sn nanoparticles on top of a BN ultrathin insulating spacer layer, we were able to study for the first time the evolution of superconductivity in isolated single superconducting nanoparticles as a function of size and temperature.