Credit: © 2008 APS

Electrons on the surface of a noble metal behave like a free electron gas, and can be used to affect the movements of atoms on the surface. Now, Gerhard Meyer at the IBM Zurich Research Laboratory, and co-workers in France and Germany have demonstrated control over the diffusion of copper atoms, by trapping this electron gas between two barriers1.

The researchers used a scanning tunnelling microscope at very low temperatures to build a 'quantum resonator', consisting of two parallel chains of copper atoms, 55 ångströms apart, on a flat copper surface. The researchers found that a single copper atom placed between the two chains tended to move parallel to both chains, along one of three possible diffusion channels.

These distinct diffusion channels are caused by electrons, which experience quantum confinement between the copper-atom chains. The confined electrons set up standing waves, and the copper atoms are more likely to travel along the 'troughs' of the waves.

Meyer and co-workers show that the number of diffusion channels can be tuned by varying the width of the resonator. Interestingly, the copper atom usually stays in the resonator even though the ends of the nanostructure are open.