Nanoscale sliding friction versus commensuration ratio : molecular dynamics simulations

Abstract

The pioneer work of Krim and Widom [Phys. Rev. B 38, 12184 (1988)] unveiled the origin of the viscous nature of friction at the atomic scale. This generated extensive experimental and theoretical activity. However, fundamental questions remain open like the relation between sliding friction and the topology of the substrate, as well as the dependence on the temperature of the contact surface. Here we present results, obtained using molecular dynamics, for the phononic friction coefficient (nph) for a one-dimensional model of an adsorbatesubstrate interface. Different commensuration relations between adsorbate and substrate are investigated as well as the temperature dependence of nph. In all the cases we studied nph depends quadratically on the substrate corrugation amplitude, but is a nontrivial function of the commensuration ratio between substrate and adsorbate. The most striking result is a deep and wide region of small values of nph for substrate-adsorbate commensuration ratios between ≈0.65 and 0.9. Our results shed some light on contradictory results for the relative size of phononic and electronic friction found in the literature.