Credit: © 2008 ACS

Understanding the electronic properties of single molecules is a major challenge in nanotechnology. Experiments in this field generally involve the use of anchoring groups to attach the molecule of interest to a pair of metal electrodes so that its electrical conductance can be measured. Thiol groups have long been favoured for such experiments, although amine groups have become popular in recent years. Now Christian Martin and co-workers1 at Delft University of Technology, Leiden University and the University of Copenhagen have shown that anchoring groups based on fullerene molecules have certain advantages over thiols and amines.

Martin and co-workers prepared three different benzene derivatives — benzene molecules with either two fullerene molecules, two thiol groups (which contain sulphur) or two amine groups (which contain nitrogen) attached — and compared their electronic properties in mechanically controlled break junctions. This involved fabricating gold electrodes on a flexible substrate, and depositing the benzene derivatives onto the electrodes from solution at room temperature. The conductance of the resulting molecular junctions was then measured while a rod pushed on the substrate from below, gradually increasing the separation of the electrodes.

The Delft–Leiden–Copenhagen team found that the experimental signature of BDC60 — the benzene derivative containing two fullerene molecules — was more pronounced than those of benzene derivatives containing the amine or thiol groups. Moreover, the BDC60 was able to stretch further in the junction before breaking.