Molecular Wires

This illustration was made to visualise Andrea Vezzoli and his colleague's study on how electricity passes through single molecules containing an iron-based chemical unit called ferrocene. These molecules can act as wires, but there has been debate over how they carry electrical charge. The team compared ferrocene wires with their oxidised counterparts, called ferrocenium, which have lost one electron.

The team placed individual molecules between two gold contacts and measured their electrical behaviour under different conditions. At lower voltages, charge mainly crossed the molecules through quantum tunnelling, a process that allows electrons to pass through an energy barrier. At higher voltages, or when the electrical conditions favoured a change in the molecule’s charge, another route became important: charge moved in two separate steps, temporarily changing the molecule’s electrical state along the way.

The study shows that the same molecular wire can carry electricity through more than one process, depending on the conditions. A simple conductivity measurement cannot reliably distinguish these routes, so the team combined several electrical tests with computer calculations to reveal what was happening. This distinction matters for designing molecular electronic devices, because higher conductivity alone does not show whether a molecule preserves the quantum behaviour needed for certain applications.