Velocity-dependent friction enhances tribomechanical differences between monolayer and multilayer graphene

F Ptak,C M Almeida,R Prioli

doi:10.1038/s41598-019-51103-1

Abstract

The influence of sliding speed in the nanoscale friction forces between a silicon tip and monolayer and multilayer graphene were investigated with the use of an atomic force microscope. We found that the friction forces increase linearly with the logarithm of the sliding speed in a highly layer-dependent way. The increase in friction forces with velocity is amplified at the monolayer. The amplification of the friction forces with velocity results from the introduction of additional corrugation in the interaction potential driven by the tip movement. This effect can be interpreted as a manifestation of local thermally induced surface corrugations in nanoscale influencing the hopping dynamics of the atoms at the contact. These experimental observations were explained by modeling the friction forces with the thermally activated Prandtl-Tomlinson model. The model allowed determination of the interaction potential between tip and graphene, critical forces, and attempt frequencies of slip events. The latter was observed to be dominated by the effective contact stiffness and independent of the number of layers.

Highlights

Graphene, a layered material composed of carbon atoms structured on a hexagonal lattice, has attracted much attention in the scientific community[1], being a candidate for the fabrication of electronic devices[2], gas sensors[3] as well as micro- and nano-electromechanical systems (MEMS and NEMS, respectively)[4,5]
The barrier ΔV is defined as ΔV = V(xmax, t) − V(xmin, t), where xmax and xmin give the maxima and minima of the potential V(x, t) at a time t, and can be parametrized in terms of the friction force fL while Fc is a critical force at which the barrier vanishes[40], given by: ΔV = V0 1 − FfLc 3/2 (2)
We studied friction mechanisms on monolayer and multilayer graphene with an AFM, focusing on probing the friction-velocity relation for different number of graphene layers

Summary

Introduction

A layered material composed of carbon atoms structured on a hexagonal lattice, has attracted much attention in the scientific community[1], being a candidate for the fabrication of electronic devices[2], gas sensors[3] as well as micro- and nano-electromechanical systems (MEMS and NEMS, respectively)[4,5]. Many efforts have been reported on this issue, from both experimental[6,12,13,14,15,16,17,18,19,20,21] and theoretical[15,22,23,24,25,26] approaches Such studies show that friction in graphene is influenced by parameters such as the number of graphene layers[12,15], interaction with the substrate[14,15,19], surface roughness[25,27,28] and crystallographic orientation[17,21,29,30].

Methods

Results

Discussion

Conclusion