Observation of Superlubricity by Scanning Tunneling Microscopy

Hirano, Motohisa; Shinjo, Kazumasa; Kaneko, Reizo; Murata, Yoshitada

doi:10.1103/physrevlett.78.1448

Cited by 261 publications

(149 citation statements)

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“…For narrow ranges of orientations corresponding to commensurate contacts, stick-slip motion was observed and friction was high (typically 250 pN). A few earlier experiments [6,7] also provided indications of the superlubricity phenomenon in dry friction.Measuring friction between graphite flakes and an underlying graphite surface we found that the ''lifetime'' of a superlubric state can be finite and therefore, superlow friction does not persist. We demonstrate that the dominating contribution to such residual friction in contacts lubricated by lamellar solids may stem from torque-induced reorientation of the flakes attached to the tip.…”

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Torque and Twist against Superlubricity

et al. 2008

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Superlubricity between incommensurate surfaces provides a desired low-friction state essential for the function of small-scale machines. Here we demonstrate experimentally and theoretically that superlubricity in contacts lubricated by lamellar solids might be eliminated due to torque-induced reorientation coupled to lateral motion. We find that the possibility of reorientation always leads to stabilization of a high frictional state which corresponds to a commensurate configuration. DOI: 10.1103/PhysRevLett.100.046102 PACS numbers: 68.35.Af, 07.79.Sp, 46.55.+d, 68.37.Ps The practical importance and the relevance to basic scientific questions have motivated studies towards understanding the conditions which lead to superlow friction. A mechanism for superlow dry friction, which arises from the structural incompatibility of two contacting solids, was first suggested by Hirano and Shinjo [1,2]. This phenomenon is also referred to as superlubricity. However, incommensurability of the interfaces results in a cancellation of only one of the channels of energy dissipation, which originates from a stick-slip instability. Other dissipative processes, such as electronic and phononic friction, etc., still persist, and therefore even in the case of complete incommensurability the net friction force will not be identical to zero. Nonetheless, typical to the superlubricity state is a reduction of the friction force by orders of magnitude.Detailed experimental studies of superlubricity have been performed recently by , who measured friction between a graphite flake attached to the tip of a frictional force microscope (FFM) and an atomically flat graphite surface. Superlow friction forces (<50 pN) have been found for most relative orientations of the flake and the substrate, for which the contacting surfaces find themselves in incommensurate states. For narrow ranges of orientations corresponding to commensurate contacts, stick-slip motion was observed and friction was high (typically 250 pN). A few earlier experiments [6,7] also provided indications of the superlubricity phenomenon in dry friction.Measuring friction between graphite flakes and an underlying graphite surface we found that the ''lifetime'' of a superlubric state can be finite and therefore, superlow friction does not persist. We demonstrate that the dominating contribution to such residual friction in contacts lubricated by lamellar solids may stem from torque-induced reorientation of the flakes attached to the tip. Dynamics of the flake reorientation result in irregular sharp peaks of the lateral force shown in Fig. 1, which are observed during the restoration of the high friction state. The lifetime may depend on the structure of the tip and the density of defects on the graphite surface. Our calculations show that the possibility of flake rotation always stabilizes the high frictional state which corresponds to the commensurate configuration of the contacting surfaces in relative motion. Reorganization of a sliding layer leading to a locking in a ''comme...

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Torque and Twist against Superlubricity

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“…For commensurate conditions, a dissipative stick-slip motion is typically observed 14 . In contrast, at incommensurate interfaces, atomic friction studies revealed a superlubrication regime, where the friction coefficient vanishes 15,16 . This behaviour can be explained by simple mechanical models such as the FrenkelKontorova model, a generalized Prandtl-Tomlinson scheme or the double-chain model [17][18][19][20] .…”

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Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces

2011

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Friction between solids is responsible for many phenomena such as earthquakes, wear or crack propagation 1-4 . Unlike macroscopic objects, which only touch locally owing to their surface roughness, spatially extended contacts form between atomically flat surfaces. They are described by the FrenkelKontorova model, which considers a monolayer of interacting particles on a periodic substrate potential 5-8 . In addition to the well-known stick-slip motion, such models also predict the formation of kinks and antikinks 9-12 , which greatly reduce the friction between the monolayer and the substrate. Here, we report the direct observation of kinks and antikinks in a two-dimensional colloidal crystal that is driven across different types of ordered substrate. We show that the frictional properties only depend on the number and density of such excitations, which propagate through the monolayer along the direction of the applied force. In addition, we also observe kinks on quasicrystalline surfaces, which demonstrates that they are not limited to periodic substrates but occur under more general conditions.Friction is important in our daily life and it is not surprising that systematic investigations date back more than 300 years. According to Amontons and Coulomb, friction between solids is proportional to the normal force but independent of the contact area. This intriguing result was explained by realizing that macroscopic objects touch at asperities that are deformed by the normal force 13 . A different situation occurs when atomically flat surfaces slide against each other, as for example encountered in micro-or nanoelectromechanical systems. Then, extended contacts arise and the degree of commensurability between the surfaces determines the friction. For commensurate conditions, a dissipative stick-slip motion is typically observed 14 . In contrast, at incommensurate interfaces, atomic friction studies revealed a superlubrication regime, where the friction coefficient vanishes 15,16 . This behaviour can be explained by simple mechanical models such as the FrenkelKontorova model, a generalized Prandtl-Tomlinson scheme or the double-chain model [17][18][19][20] . In the Frenkel-Kontorova approach the interface between two solids is described by a monolayer of elastically interacting beads on a periodic substrate potential [5][6][7][8] . In addition to stick-slip motion, the Frenkel-Kontorova model also predicts the formation of topological solitons, so-called kinks and antikinks [9][10][11][12] . These excitations are believed to dominate the frictional properties at atomic length scales because they provide an efficient mechanism for mass transport; so far, such excitations have never been observed in sliding friction experiments 21 .Here, we report the observation of kinks and antikinks in a colloidal system that is driven across commensurate and incommensurate substrate potentials. We use highly charged polystyrene spheres with radius R = 1.95 μm, which are suspended in water. In the presence of gravitational and op...

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“…10 K3 ). Scanning tunnelling microscopy measurements in UHV (Hirano et al 1997) of a W(011) wire in contact with Si(001) showed that the friction is below the detection limit for incommensurate contacts. Recently, Dienwiebel et al (2004) used a novel friction force microscope, which allows for quantitative measurement of the friction force in three directions, to examine friction between a tungsten tip and graphite.…”

Section: Friction Of Crystalline Surfaces (A ) Friction Of Diamondmentioning

confidence: 99%

Friction between solids

Harrison

Gao

Schall

et al. 2007

Phil. Trans. R. Soc. A.

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The theoretical examination of the friction between solids is discussed with a focus on self-assembled monolayers, carbon-containing materials and antiwear additives. Important findings are illustrated by describing examples where simulations have complemented experimental work by providing a deeper understanding of the molecular origins of friction. Most of the work discussed herein makes use of classical molecular dynamics (MD) simulations. Of course, classical MD is not the only theoretical tool available to study friction. In view of that, a brief review of the early models of friction is also given. It should be noted that some topics related to the friction between solids, i.e. theory of electronic friction, are not discussed here but will be discussed in a subsequent review.

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Observation of Superlubricity by Scanning Tunneling Microscopy

Cited by 261 publications

References 12 publications

Torque and Twist against Superlubricity

Torque and Twist against Superlubricity

Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces

Friction between solids

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