Exploring the molecular toolkit

Molecular engine designed by Seldenthuis and Prins. (Illustration: Marijn van der Meer)

Make a nanogap, stick a molecule across and see what it does. Ferry Prins’ experiments could lead to molecular memories, more efficient solar cells and the tiniest motor ever.

He is basically a chemist, although he mainly worked with physicists during his PhD project. Dr Ferry Prins just loves molecules and is excited that the latest technologies at Applied Sciences allowed him to almost put his finger onto these tiniest building blocks of chemistry. What’s more: he did most of his experiments at room temperature.
A whole lot of tricks are required to get in contact with single molecules. A 1 to 2 nanometer wide gap for example cannot be made by lithography. Instead, a current is fed through a thin platinum wire until it locally ‘evaporates’ and leaves a nanogap between the electrodes. Now try to stick a molecule across the gap – another nasty hit and miss affair, which requires patience and persistence.

Prins’ patience was rewarded with the discovery of very useful molecular traits. For example, he reports the discovery of a molecular switch – a molecule able to switch between two spin states. Moreover, the iron-based polymer works at room temperature and its spin state is externally readable. That sounds like a promising candidate for yet smaller memory devices.
Prins also used lead-selenide quantumdots as photodetectors. Resting between two electrodes only 5 nanometers apart, the quantumdots readily pass on any electrons freed by incident photons. The electronic efficiency is much higher than in traditional solar devices, but in the present configuration no external current is generated. Prins’ successors are busy inventing solutions for that.

Lastly, Prins also designed a molecule that can serve as a rotor in a molecular engine. At two extremes the (flat) molecule has two rings, which should bind to two gold electrodes. The other two extremes of the molecules are electrically charged, which makes the molecule sensitive to the electric fields. Prins, and his colleague Jos Seldenthuis (MSc), hope to demonstrate that the application of an alternating electric field to an adjacent electrode will nudge the molecular engine into rotation.

Ferry Prins, ‘Molecular functionality in nanoelectronic devices’, 16 September 2011, PhD supervisor: Professor Herre van der Zant (AS)