When the two clean metals in the set up (a tungsten needle and gold surface) meet for the first time, they cling to each other with great adhesive force. As a result, a large amount of mechanical energy must be applied to separate the metals. The separation process is accompanied by some gold atoms sticking to the tungsten needle and altering its surface composition. Surprisingly, after a number of repeated contacts (a few dozen), it becomes much easier – about six times easier – to separate the materials.

The scientists propose that surface diffusion of adatoms – single atoms whizzing around on the surface of materials – might help mediate the separation. In fact, this kind of "self healing" mediated by adatoms has already been seen in studies of other types of phenomena, such as friction.

In the McGill group’s experiments, when the mobile gold atoms ‘wet’ the surface of the tungsten needle, the electronic conductance through the metal nanocontact also dramatically reduces. The order­-of­-magnitude drop in conductance stems from the increased number of interfaces between different crystalline configurations, causing electrons to bounce around at the junction rather than zip right through.

We believe that this work may help guide the design of more reliable nanoscale switches in the future – for example, ones that open and close without sticking and that conduct electrons with ease.

More information can be found in the journal Nanotechnology 24 475704

Further reading

SPM tip apex defined using field ion microscopy (Sep 2012)