Ballistic nanofriction

TL;DR

This paper introduces and characterizes a novel high-speed 'ballistic' friction regime in nanosystems, revealing unique temperature and velocity dependencies and the interplay of rotations and translations in atomic-scale friction.

Contribution

It uncovers a new ballistic friction regime at high speeds in nanosystems, distinct from low-speed drift, with detailed analysis of temperature effects and rotational- translational correlations.

Findings

Ballistic friction is viscous and velocity-dependent.

Temperature effects on slip distance differ between regimes.

Rotations and translations are anticorrelated in ballistic sliding.

Abstract

Sliding parts in nanosystems such as Nano ElectroMechanical Systems (NEMS) and nanomotors, increasingly involve large speeds, and rotations as well as translations of the moving surfaces; yet, the physics of high speed nanoscale friction is so far unexplored. Here, by simulating the motion of drifting and of kicked Au clusters on graphite - a workhorse system of experimental relevance -- we demonstrate and characterize a novel "ballistic" friction regime at high speed, separate from drift at low speed. The temperature dependence of the cluster slip distance and time, measuring friction, is opposite in these two regimes, consistent with theory. Crucial to both regimes is the interplay of rotations and translations, shown to be correlated in slow drift but anticorrelated in fast sliding. Despite these differences, we find the velocity dependence of ballistic friction to be, like drift, viscous.