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

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.

Speed dependence of friction on single-layer and bulk MoS2 measured by atomic force microscopy

“…[10][11][12][13][14][15][16][17] Despite the extensive amount of work performed toward elucidating friction mechanisms on 2D materials, very few results were published on the dependence of friction forces on sliding speed. 18 This is potentially a critical concern, as components in various micro-and nano-scale mechanical systems designed to be lubricated by 2D materials are expected to move in a wide range of speeds during operation. As such, a potential degradation of lubricative character at certain sliding speeds could result in unexpected device failure and consequently necessitate new approaches in component design.…”

“…20 No significant change in k eff values was observed with respect to scanning speed, in accordance with previous results. 18 Figure 1(a) shows a three-dimensional representation of a topographical AFM image, which comprises the multi-layer MoS 2 flake on which the experiments were performed and the SiO 2 substrate on which the flake was deposited. The shallowest part of the flake is about $1.0 nm higher than the underlying SiO 2 substrate; the highest part of the flake is at a height of $20 nm and can thus be considered "bulk."…”

“…Remarkably, the dependence of the experimentally acquired friction data on speed is very similar for both single-layer and bulk MoS 2 , in contrast to results published recently for graphene. 18 The logarithmic increase in friction with sliding speed can be understood by means of the thermally activated Prandtl-Tomlinson (PTT) model. 21,34 In the classic Prandtl-Tomlinson model, 35,36 a point mass (that represents the tip apex in AFM) is attached to a base (that represents the cantilever's fixed base in AFM) by means of an elastic spring (which represents the effective lateral stiffness of the sample-tip-cantilever system), whereby the base and consequently the point mass are moved laterally over a one-dimensional, periodic potential energy landscape that arises due to energy interactions between the tip apex and the sample surface.…”

Graphene Synthesis: Method, Exfoliation Mechanism and Large-Scale Production

“…The exfoliation method, using flake graphite or pyrolytic graphite with high crystallinity as raw material, separates the stacked sheets through external forces such as impact, [35], shear [36], friction [37], airflow expansion [38], blasting [39], chemical intercalation [40], redox [41], and electrode reactions [42], which significantly weaken and destroy the Van der Waals forces between graphite sheets to form single-layer, doublelayer, or few-layer graphene. According to the "power source" in the peeling process, it is categorized into electrochemical exfoliation [8,12,13,[25][26][27][28], oxide-assisted liquid phase exfoliation [6,9,43], mechanical exfoliation [27,[44][45][46][47], and three other categories.…”

Nanotribologia Em Grafeno E Outros Materiais Atomicamente Finos

“…As medidas e análises referentes ao grafeno aqui descritas nos rendeu uma publicação no periódico Scientific Reports [96].…”