Adhesion-dependent negative friction coefficient on chemically modified graphite at the nanoscale (original) (raw)

Nanoscale friction properties of graphene and graphene oxide

Diamond and Related Materials, 2014

Achieving superlow friction and wear at the micro/nano-scales through the uses of solid and liquid lubricants may allow superior performance and long-lasting operations in a range of micromechanical system including micro-electro mechanical systems (MEMS). Previous studies have indicated that conventional solid lubricants such as highly ordered pyrolitic graphite (HOPG) can only afford low friction in humid environments at micro/macro scales; however, HOPG is not suitable for practical micro-scale applications. In this study, we explored the nano-scale frictional properties of multi-layered graphene films as a potential solid lubricant for such applications. Atomic force microscopy (AFM) measurements have revealed that for high-purity multilayered graphene (7-9 layers), the friction force is significantly lower than what can be achieved by the use of HOPG, regardless of the counterpart AFM tip material. We have demonstrated that the quality and purity of multilayered graphene plays an important role in reducing lateral forces, while oxidation of graphene results in dramatically increased friction values. Also, for the first time, we demonstrated the possibility of achieving ultralow friction for CVD grown single layer graphene on silicon dioxide. This confirms that the deposition process insures a stronger adhesion to substrate and hence enables superior tribological performance than the previously reported mechanical exfoliation processes. 1. Introduction.

Friction and degradation of graphite: a nanotribological approach

Research Square (Research Square), 2023

We investigated the friction and wear of graphite by atomic force microscopy in sliding contact with SiO x , Pt, and diamond tips with contact forces up to several micronewtons. Graphite's tribology strongly depends on the chemistry of the counter body. With a SiO x tip, friction is governed by puckering. Wear initiates at surface steps by mechanical destabilization of folds. With a Pt tip, the adhesive effects lead to the exfoliation of graphite. At higher loads, friction crosses over from exfoliation to puckering. For SiO x and Pt, the wear rate is low in ambient conditions. In the case of diamond tips, we measured a friction coe cient and a wear rate of an order of magnitude larger than with SiO x or Pt tips.

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

Physical Review B, 2012

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.

Graphene Confers Ultralow Friction on Nanogear Cogs

Small, 2021

Friction‐induced energy dissipation impedes the performance of nanomechanical devices. Nevertheless, the application of graphene is known to modulate frictional dissipation by inducing local strain. This work reports on the nanomechanics of graphene conformed on different textured silicon surfaces that mimic the cogs of a nanoscale gear. The variation in the pitch lengths regulates the strain induced in capped graphene revealed by scanning probe techniques, Raman spectroscopy, and molecular dynamics simulation. The atomistic visualization elucidates asymmetric straining of CC bonds over the corrugated architecture resulting in distinct friction dissipation with respect to the groove axis. Experimental results are reported for strain‐dependent solid lubrication which can be regulated by the corrugation and leads to ultralow frictional forces. The results are applicable for graphene covered corrugated structures with movable components such as nanoelectromechanical systems, nanoscale...

Effect of surface morphology on friction of graphene on various substrates

Nanoscale, 2013

The friction of graphene on various substrates, such as SiO 2 , h-BN, bulk-like graphene, and mica, was investigated to characterize the adhesion level between graphene and the underlying surface. The friction of graphene on SiO 2 decreased with increasing thickness and converged around the pentalayers due to incomplete contact between the two surfaces. However, the friction of graphene on an atomically flat substrate, such as h-BN or bulk-like graphene, was low and comparable to that of bulklike graphene. In contrast, the friction of graphene folded onto bulk-like graphene was indistinguishable from that of mono-layer graphene on SiO 2 despite the ultra-smoothness of bulk-like graphene. The characterization of the graphene's roughness before and after folding showed that the corrugation of graphene induced by SiO 2 morphology was preserved even after it was folded onto an atomically flat substrate. In addition, graphene deposited on mica, when folded, preserved the same corrugation level as before the folding event. Our friction measurements revealed that graphene, once exfoliated from the bulk crystal, tends to maintain its corrugation level even after it is folded onto an atomically flat substrate and that ultra-flatness in both graphene and the substrate is required to achieve the intimate contact necessary for strong adhesion.

Giant and Tunable Anisotropy of Nanoscale Friction in Graphene

Scientific Reports, 2016

The nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction forces in graphene are highly dependent on the scanning direction: under some conditions, the energy dissipated along the armchair direction can be 80% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations.

Friction and Adhesion of Different Structural Defects of Graphene

ACS Applied Materials & Interfaces, 2018

Graphene structural defects, namely edges, step-edges and wrinkles are susceptible to severe mechanical deformation and stresses under frictional operations. Applied forces cause deformation by folding, buckling, bending and tearing the defective sites of graphene, which lead to a remarkable decline in normal load and friction bearing capacity. In this work, we experimentally quantified the maximal normal and friction forces corresponding to the damage thresholds of the different investigated defects as well as their pull-out (adhesion) forces. Horizontal wrinkles (with respect to the basal plane, i.e. folded) sustained the highest normal load, up to 317 nN, during sliding, whereas for vertical (i.e. standing collapsed) wrinkles, step-edges and edges, the load bearing capacities are up to 113 nN, 74 nN and 63±5 nN, respectively. The related deformation mechanisms were also experimentally investigated by varying the normal load up to the initiation of the damage from the investigated defects and extended with the numerical results from Molecular Dynamics and Finite Element Method simulations.

Atomic scale mechanisms of friction reduction and wear protection by graphene

Nano letters, 2014

We study nanoindentation and scratching of graphene-covered Pt(111) surfaces in computer simulations and experiments. We find elastic response at low load, plastic deformation of Pt below the graphene at intermediate load, and eventual rupture of the graphene at high load. Friction remains low in the first two regimes, but jumps to values also found for bare Pt(111) surfaces upon graphene rupture. While graphene substantially enhances the load carrying capacity of the Pt substrate, the substrate's intrinsic hardness and friction are recovered upon graphene rupture.