Why do we “feel” atoms in nano-scale friction?

Atomic stick-slip patterns are readily observed in experiments. The traditional description of atomic-scale friction in terms of mechanical stick-slip instabilities (the Prandtl−Tomlinson model) appears so successful, that it obscures the actual mechanisms of energy dissipation. Here, we show that the conventional model fails completely, because it can only explain the atomic resolution of surface force maps at a level of dissipative forces that is many orders of magnitude higher than what we should expect for the slipping nano-contact. We demonstrate that we can “feel” atoms in nano-scale friction only because there is always a tiny mass that rapidly slips between atomic positions, well before the rest of the moving body follows.