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It's no surprise that a block sliding across a table is slowed by friction, but for small enough crystals, theory and a few experiments suggested that frictionless motion may be the norm. We investigated nanoscale friction by pushing Antimony particles over a graphite surface using atomic force microscopy techniques. The sliding friction during particle pushing showed two distinct states: Either the friction scales linear with the island-substrate contact area or it is hardly detectable at all [1]. This frictional duality can be understood if partial contamination of the interface by mobile surface molecule is assumed. New experiments with improved sensitivity shed light on the 'zero' friction state: Here the pushing resistance scales roughly with the square root of the contact area, a dependence predicted by current theories of superlubricity [2].
[1] D. Dietzel et al., Phys. Rev. Lett. 101, 125505 (2008) [2] M. Müser et al., Phys. Rev. Lett. 86, 1295 (2001) |
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