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Waterwheels have been used for centuries to harness the energy of flowing water. Simulations reported in Nature Nanotechnology show that the same idea could be transferred to the atomic scale — a 'waterwheel' made of just a few atoms that is driven by a stream of electrons.

Advances in computational techniques have made it possible to investigate the ways in which a current affects individual atoms in a conductor. This power has provided a better understanding of the damage that can be done to electrical interconnects by the current-induced forces that act on atoms, a consideration that becomes increasingly important as circuitry gets smaller and smaller.

Daniel Dundas and his colleagues wondered, however, whether these forces could be put to a more productive use (Nature Nanotech 4, 99–102; 2009). To phrase it more technically, is the energy conserved by the current-induced forces or is there some spare that can be put to work? It is a question that has been considered before but no clear answer had been found — until now.

The system that Dundas et al. investigated is a simple one, comprising a line of atoms — an atomic wire — with an electrode attached at each end to enable a voltage to be applied. The wire is given a sharp bend in the middle, at an atom that is of a different type from the others. In the simulations, this atom is allowed to move and its trajectory is calculated when a bias is applied.

When the wire is bent by 70° and 1 volt is applied, the central atom eventually settles into an orbital trajectory, the radius of which slowly increases. This demonstrates that net work is being done during each revolution: that is, the current-induced forces are non-conservative.

This current-driven atomic motor is, of course, overly simple. However, it represents a formal solution to an important question. And if nanotechnology continues to advance at the rate at which it has over the past decade or so, it may not be that long before devices based on this initial concept are realized in practice.