Imaging high-speed friction at the nanometer scale

TL;DR

This paper introduces a novel high-speed friction measurement technique at the nanometer scale, enabling detailed force mapping across velocities from zero to several centimeters per second with high spatial resolution.

Contribution

The authors develop a rapid, high-sensitivity method for measuring frictional forces on a single asperity at nanometer scales and high velocities, filling a gap in experimental capabilities.

Findings

Transition from stick-slip to smooth sliding observed

Force measurements match a modified Prandtl-Tomlinson model

Surface mapping of velocity-dependent friction achieved

Abstract

Friction is a complicated phenomenon involving nonlinear dynamics at different length and time scales[1, 2]. The microscopic origin of friction is poorly understood, due in part to a lack of methods for measuring the force on a nanometer-scale asperity sliding at velocity of the order of cm/s.[3, 4] Despite enormous advance in experimental techniques[5], this combination of small length scale and high velocity remained illusive. Here we present a technique for rapidly measuring the frictional forces on a single asperity (an AFM tip) over a velocity range from zero to several cm/s. At each image pixel we obtain the velocity dependence of both conservative and dissipative forces, revealing the transition from stick-slip to a smooth sliding friction[1, 6]. We explain measurements on graphite using a modified Prandtl-Tomlinson model that takes into account the damped elastic deformation of the asperity. With its greatly improved force sensitivity and very small sliding amplitude, our method enables rapid and detailed surface mapping of the full velocity-dependence of frictional forces with less than 10~nm spatial resolution.