Effect of elastic deformation on frictional properties of few-layer graphene

Abstract

We describe the results of Brownian dynamics (BD) simulations of an atomic force microscope (AFM) tip scanned on locally suspended few-layer graphene. The effects of surface compliance and sample relaxation are directly related to the observed friction force. We demonstrate that the experimentally observed reduction of friction with an increasing number of graphene layers in case of a narrow scanning tip can be a result of decreased sample deformation energy due to increased local contact stiffness under the scanning tip. Simulations with varying scan rates indicate that surface relaxation at a given temperature can affect the frictional characteristics of atomically thin sheets in a manner not explained by conventional thermally activated models.

An atomistic investigation of the effect of strain on frictional properties of suspended graphene

“…3 For the non-pre-strained model (υ=0), µ decreased with the increase of k. But for the pre-strained models, µ increased linearly with the increase of k which is not corresponding to the theory of Ref. 25. Meanwhile, 1/k decreased by up to 51% during the pre-strain increased from 0 to 0.12, so it would be less likely to result in a sharp decrease in friction coefficient µ.…”

“…It has been reported that the friction properties of non-strained suspended graphene are mainly affected by elastic deformation energy and thus µ is approximately proportional to the reciprocal of contact stiffness k=F N /δ, 25 whereF N is the vertical load applied on diamond tip and δ is the deflection of the graphene layer. As shown in Fig.…”

“…The loading and friction simulation were performed under Langevin thermostat 27 with a damping constant of γ=3.32·10 −12 Kg/s. 25 The temperature in all of the simulations was controlled at 10K. To avoid the boundary effects, periodic boundary conditions (PBC) were applied in X-direction and the atoms along Y-boundaries were fixed to support the sample.…”

“…23 For the suspended graphene, the elastic deformation, dominated by out-of-plane stiffness, is the major factor contributing to friction. [24][25][26] To our knowledge, little work about the effect of strain on the friction of suspended graphene has been reported until now. In this paper, molecular dynamics (MD) simulation was applied to study the sliding interaction between the diamond AFM probe and the strained suspended graphene to explore the effect of strain on atomic-level frictional properties.…”

Current trends in the physics of nanoscale friction

“…Friction increases because graphene deformations enhance the real contact area at the tip apex. In this interpretation, the amount of deformation decreases with increasing number of layers, as revealed by computer simulations [109][110][111][112], with the result that friction diminishes for increasing graphene thickness.…”