Non-monotonic velocity dependence of atomic friction

TL;DR

This paper investigates how atomic-scale friction varies with velocity, revealing non-monotonic behavior due to memory effects and thermal fluctuations, which explains recent experimental observations of decreasing friction with increasing velocity.

Contribution

It introduces a theoretical model incorporating memory effects and thermal fluctuations to explain non-monotonic velocity dependence of atomic friction.

Findings

Friction force can decrease with increasing velocity under certain conditions.

Memory effects and low-frequency surface modes are crucial for non-monotonic behavior.

The model supports experimental observations of decreasing friction on monolayer-covered surfaces.

Abstract

We study the velocity dependence of the frictional force of the tip of an atomic force microscope as it is dragged across a surface, taking into account memory effects and thermal fluctuations. Memory effects are described by a coupling of the tip to low frequency excitation modes of the surface in addition to the coupling to the periodic corrugation potential. We find that when the excitation mode frequency is comparable to the characteristic frequency corresponding to the motion of the tip across the surface, the velocity dependence of the frictional force is non monotonic, displaying a velocity range where the frictional force can decrease with increasing velocity. These results provide theoretical support for the interpretation of recent experiments which find a frictional force that decreases with velocity on surfaces covered with a monolayer.