Measuring sliding friction at the atomic scale

Abstract

Sliding friction is a nonconservative force in which kinetic energy is dissipated via various phenomena. We used lateral force microscopy to measure the energy loss as a tip oscillates laterally above a surface with sub-Angstrom amplitudes. By terminating the tip with a single molecule, we ensure the tip ends in a single atom. We have reported that energy is dissipated as a CO molecule at the tip apex is oscillated over pairs of atoms. This is a result of the CO being bent in different directions as the tip moves in one direction and then in the other. We confirm this with a model that describes the CO on the tip as a torsional spring. Surprisingly, we only observe dissipation within a small range of tip heights. This allows us to determine the necessary components to model friction and shows how sensitive friction is to the local potential energy landscape.