Friction Fluctuations of Gold Nanoparticles in the Superlubric Regime

TL;DR

This study investigates the sudden, reversible friction fluctuations of gold nanoparticles on graphite during AFM experiments, attributing these to nanoparticle rotations affecting superlubricity.

Contribution

It demonstrates that nanoparticle rotations within superlubricity can cause significant friction changes, supported by theoretical simulations linking size, shape, and orientation.

Findings

Friction fluctuations are reversible and linked to nanoparticle rotations.

Small rotations can cause large changes in friction levels.

Particle size and shape influence the friction-orientation relationship.

Abstract

Superlubricity, or alternatively termed structural (super)lubrictiy, is a concept where ultra-low friction is expected at the interface between sliding surfaces if these surfaces are incommensurate and thus unable to interlock. In this work, we now report on sudden, reversible, friction changes that have been observed during AFM based nanomanipulation experiments of gold nanoparticles sliding on highly oriented pyrolythic graphite. These effects are can be explained by rotations of the gold nanoparticles within the concept of structural superlubricity, where the occurrence of ultra-low friction can depend extremely sensitively on the relative orientation between the slider and the substrate. From our theoretical simulations it will become apparent how even miniscule magnitudes of rotation are compatible to the observed effects and how size and shape of the particles can influence the dependence between friction and relative orientation.