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Touching From A Distance - How Weak Contacts Solve A Long-Standing Problem in Molecular Electronics

13.03.2015

Dr Damien Thompson          TOC

Researchers at the University of Limerick are working to get miniaturised devices out of research labs and into mass production. A major bottleneck is the realisation of dependable atomic-scale switches, which hampers the production of useful nanoscale circuits. Dr Damien Thompson of the Physics and Energy department and Materials and Surface Science Institute models the structure, dynamics and energetics of these materials at the atomic scale. His work has produced design rules that allow molecules with useful functions such as electronic decoupling and cell adhesion to be integrated into devices.

In new work published in the March 2015 edition of Nature Communications (doi:10.1038/ncomms7324), Thompson collaborated with Prof Christian Nijhuis at National University of Singapore and co-workers to design, synthesise and test the electrical properties of a new class of reversible molecular switches. The study has produced exciting results demonstrating that large rectification ratios can be obtained by means of non-covalent contacts formed by self-assembled monolayers (SAMs) of long alkane chains with a ferrocene unit. Furthermore, the direction of rectification can be switched simply by “walking” the ferrocene up and down the chain, demonstrating a remarkable degree of control of macroscopic device properties through atomic scale engineering.

Most of the molecular electronics community chases strong coupling as the key to making stable contacts but, Thompson explains, this new work demonstrates that these alternative “van der Waals” contacts can provide a Goldilocks effect, contacts that are strong enough to allow electronic function but weak enough to prevent broadening of energy levels (which turns the device off). Thompson recently demonstrated similar beneficial van der Waals effects in collaboration with Peter Nirmalraj and co-workers at IBM-Zurich in which an insulating layer of alkanes allowed fullerene molecules (and also graphene) to sit near gold without damaging their electrical properties (doi:10.1038/nmat4060).

The research is supported on Thompson's side by a Starting Investigators Research Grant from Science Foundation Ireland and is enabled by high-performance computing facilities at the Irish Center for High-End Computing (ICHEC). The collaboration with experimental partners, says Thompson, evolved out of informal meetings that very quickly spawned new ideas by convergence of mutual interests and complementary skills. "The push and pull of the collaborations with fellow young(ish) scientists is very stimulating. We dare each other to advance our methods beyond the current state of the art, and we can pool our data from different fields to form new ideas that will enable new technologies".