Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 44: Focussed session: Functional molecules at surfaces II

O 44.2: Topical Talk

Mittwoch, 28. März 2012, 11:00–11:30, A 053

Conductance switching and quantum interference in molecular junctions — •Sense Jan van der Molen — Kamerlingh Onnes Laboratorium, Leiden University, Leiden, The Netherlands

A fascinating prospect in nanoscience is to externally manipulate the conductance of molecular junctions. For this, an impressive set of (switchable) molecules has been synthesized in organic chemistry. However, once contacted, switchable molecules may easily lose their functionality, e.g. due to quenching of molecular excitations. Surprisingly, the opposite is possible too: junctions containing passive molecules may become switchable. I will give examples from our research, with a special focus on (arrays) of molecular junctions containing light-sensitive diarylethene molecules. The conductance properties of these devices can be switched reversibly by illumination, although the on/off ratio is limited. Next, I will deviate a bit from molecular switching and focus on the quantum aspects of charge transport through organic molecules. In some cross-conjugated molecules, destructive interference of electron waves can take place, leading to a dramatically low conductance. I will present experimental evidence for destructive quantum interference in (anthraquinone-based) molecular junctions. Remarkably, the large energy level spacing allows this interference phenomenon to be observed at room temperature, unlike the traditional case of Aharanov-Bohm rings. By turning quantum interference on and off, switchable molecular junctions with very high on/off ratios are anticipated shortly.