Gigantic Maximum of Nanoscale Noncontact Friction

TL;DR

This study observes a gigantic maximum in noncontact friction at nanometer distances between NbSe2, SrTiO3, and a Pt-Ir tip at 4.2 K, linked to a relaxation mechanism with multiple time scales.

Contribution

It reports the first observation of a giant maximum in noncontact friction at nanoscale distances, revealing a new relaxation mechanism influencing friction behavior.

Findings

Giant maximum in noncontact friction at nanometer distances

Correlation between friction maximum and cantilever spring constant

Distance-dependent relaxation mechanism explains the phenomena

Abstract

We report measurements of noncontact friction between surfaces of NbSe$_{2}$ and SrTiO$_{3}$, and a sharp Pt-Ir tip that is oscillated laterally by a quartz tuning fork cantilever. At 4.2 K, the friction coefficients on both the metallic and insulating materials show a giant maximum at the tip-surface distance of several nanometers. The maximum is strongly correlated with an increase in the spring constant of the cantilever. These features can be understood phenomenologically by a distance-dependent relaxation mechanism with distributed time scales.