"À la carte" manufacture of electrodes on the atomic scale

One of the key problems in nanotechnology is the formation of electrical contacts at the atomic scale. This requires characterized in detail the current that flows through circuits extremely small, so small that its components become individual atoms or molecules. It is precisely in the smallness of the system, typically of nanometer dimensions (1 meter = 1 billion nanometers), where lies the difficulty of this problem still not solved. In particular, unions made up of a single molecule has found that the number of individual atoms which make up the contact and their positions are crucial in determining the electrical current that can pass. Until now, there has been no experiment where will have been able to control these parameters with sufficient accuracy.

Thanks to a collaboration between scientists in San Sebastian and at the University of Kiel (Germany) has been demonstrated that it is possible to determine and control the number of atoms in contact between a molecule and a metal electrode copper, as shown in the figure, while simultaneously registers the current that passes through the Union *. In this way, these scientists have discovered and explained the changes suffered by the electric current through a molecular Union (metal/molecule/metal) depending on the area of the contacts that unite the molecule to the metallic electrodes. The bottom line is that changing the number of atoms in the molecule contact one at a time, becomes a regime of low (poor contact) to another (good contact) high driving. In the poor contact current is limited by the area of contact, while for a good contact current is limited by the intrinsic properties of the molecule.

Figure: Graphical representation of a tip of STM (STM) tunnel with a molecule of C60 in its apex on a surface of copper, which has been manipulated on the atomic scale to build aggregates with different numbers of atoms of copper. These aggregates are used to make contact between the molecule and the metal surface. The colored surface that appears at the bottom shows a real image obtained with the STM of the surface of copper and various metal additions deposited on it.

(*) Atomic-scale engineering of electrodes for single-molecule contacts, g. Schull, th. Frederiksen, a. Arnau, D. Sanchez-Portal, r. Berndt, Nature Nanotech. (in press).

Dr. Thomas Frederiksen, who now works in the Donostia International Physics Center (DIPC) as a 'fellow Guipúzcoa' programme funded by the Gipuzkoako Foru Aldundia, has been one of the scientists who participated in this project in collaboration with Dr. Daniel Sánchez Portal in the Centre of Physics of materials of the Center joint CSIC-UPV/EHU and Professor Andrés Arnau of the Department of Physics of materials in the Faculty of chemistry of the BASQUE country. The results have been published in the prestigious journal Nature Nanotechnology.

Researchers.

The work is an example of the fruits of a strategic alliance of the University of the Basque country with the Donostia International Physics Center (DIPC) and Tecnalia Corporación Tecnológica, articulating a joint project, Euskampus, which has been the Campus of international excellence recognition.