Anisotropy Effects in Atomic-Scale Friction
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The static and kinetic friction experienced by a point mass elastically driven at different angles on surface lattices with square, hexagonal, and honeycomb symmetries are estimated by analytical and numeric calculations based on the Prandtl–Tomlinson (PT) model. Assuming a strong surface coupling, the anisotropy of static friction increases from 3.7 up to 46.3% when the density of packing of the surface atoms is reduced, but this is not the case for kinetic friction, the anisotropy of which is maximal on a square lattice. Although these results have not been supported by accurate experimental verifications so far, the PT model was successfully applied to interpret anisotropy effects in the friction force profiles measured, among other surfaces, on rectangular lattices with complex unit cells and on stepped crystal surfaces.
KeywordsNanotribology Friction mechanisms Stick-slip Static friction AFM
Prof. Riccardo Ferrando from the University of Genova is gratefully acknowledged for scientific discussion. Our collaboration was promoted thanks to the EUROCORES programme ‘Friction and Adhesion in Nanomechanical Systems’ (FANAS) of the European Science Foundation. OYF and JJM acknowledge Spain MICINN under Projects No. FIS2008-01240 and FIS2011-25167 cofinanced by FEDER funds.