Molecular dynamics simulations of the isotopic effect on nanoscale friction

Abstract

Computer simulations are becoming increasingly useful for studying friction, enabling the application of controlled conditions, uncoupling mechanisms, and set-ups that are not usually achievable in physical experiments, ensuring that no other undesirable variable is acting on the system. In this work, molecular dynamics (MD) simulations were used to systematically explore the isotope's mass effect on the phononic contribution to friction by simulating different load conditions, sliding direction, and surface coverage of H-passivated fat [111] single-crystal diamond surfaces. Simulations were performed using the Adaptive Intermolecular Reactive Empirical Bond-Order (AIREBO) potential, including van der Waals interactions. The coeffcient of friction was found to be independent of the adsorbate atomic mass for both sliding directions simulated. Furthermore, at least in the simulated conditions, a simple reduction in surface coverage also did not signifcantly affect the coefficient of friction. A marked increase of friction force was observed only when the passivation layer was modified by introducing highly reactive defects. Accordingly, the results from MD simulations give support to an indirect isotopic effect on friction, but only to the extent that defects created in the passivation layer lead to the formation of highly reactive surfaces. [resumo fornecido pelo autor]