The effect of atomic bonds on friction has been demonstrated, for the first time, at the scale of just a few atoms. Variations in atomic surfaces are thought to modulate the force of friction in a way that depends on the direction in which objects are moved, but this has been difficult to show experimentally. Jay Weymouth of the University of Regensburg in Germany and his colleagues have now done so. They passed the tip of a tungsten lateral-force microscope between regions of a silicon crystal surface, on which pairs of silicon atoms were oriented at right angles to each other. Oscillations of the tip varied depending on whether it was sliding along or across the direction of the paired atoms.
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