Observation of Superlubricity by Scanning Tunneling Microscopy

Experimental evidence of superlubricity, the state of vanishing friction, is obtained by examining systems of sliding atomically clean surfaces by using ultrahigh vacuum scanning tunneling microscopy. The experimental results agree with theoretical predictions: Friction is not observed in the superlubricity regime in measurements capable of resolving a friction force of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\mathrm{N}$, whereas friction of $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\mathrm{N}$, which is comparable to theoretical values, is observed in the friction regime.