Anomalous friction in suspended graphene

TL;DR

This paper reveals an unusual increase in friction with distance in suspended graphene, challenging traditional tribological expectations and highlighting unique 2D material behaviors.

Contribution

It demonstrates a novel frictional phenomenon in suspended graphene through molecular dynamics simulations, contrasting with established 3D material behavior.

Findings

Friction increases as the tip retracts from suspended graphene.

The behavior is explained by unique properties of 2D materials.

This phenomenon is not observed in isotropic 3D materials.

Abstract

Since the discovery of the Amonton's law and with support of modern tribological models, friction between surfaces of three-dimensional materials is known to generally increase when the surfaces are in closer contact. Here, using molecular dynamics simulations of friction force microscopy on suspended graphene, we demonstrate an increase of friction when the scanning tip is retracted away from the sample. We explain the observed behavior and address why this phenomenon has not been observed for isotropic 3-D materials.