In this talk it is shown that FFM experiments can be highly misleading, almost completely masking the relevant fine structure in the relative motion and energy dissipation of sliding bodies. We will start by inspecting thermal effects that manifest themselves in the form of noise and lowering of the average friction force. In extreme cases, this can result in the near vanishing of friction: ‘thermolubricity’ [1].
For a fully quantitative interpretation of these effects we explicitly take into account the flexibility of the FFM tip. In fact, it is the final section of the tip, the apex, that dominates this flexibility. The extremely small effective mass of the apex introduces an extremely short characteristic timescale for position fluctuations of the apex, which tends to be masked by the sluggish dynamics of the rest of the tip and the macroscopic cantilever. Calculations will be shown that demonstrate bizarre consequences of the presence of these two different time scales, such as situations in which the tip apex is fully free to move (fully ‘thermolubric’) while the cantilever seems to perform ordinary stick-slip motion [2]. Our calculations also predict that there should be a variety of slip (and thus energy dissipation) scenarios, including erratic back-an forth jumps during slipping, slipping via an intermediate non-lattice position and ultraslow slipping [3], thus providing a natural explanation for the results of the first time-resolved slip measurements [4].
These effects, revealed here for FFM experiments, can possibly also play a role in the much more general context of the asperities that establish the contact between macroscopic sliding bodies.
[1] S.Yu. Krylov, et al., Phys. Rev. E 71, 065101(R) (2005).
[2] S.Yu. Krylov, et al., Phys. Rev. Lett. 97, 166103 (2006).
[3] D. Abel et al., to be published.
[4] S. Maier et al., Phys. Rev. B 72 , 245418 (2005).
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