Control of Nanoscale Friction on Gold in an Ionic Liquid by a Potential-Dependent Ionic Lubricant Layer

Sweeney, James; Hausen, Florian; Hayes, Robert A.; Webber, Grant B.; Endres, Frank; Rutland, Mark W.; Bennewitz, Roland; Atkin, Rob

doi:10.1103/physrevlett.109.155502

Cited by 207 publications

(300 citation statements)

References 29 publications

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“…In spite of the first successful experimental studies of nanoscopic friction under potential control [5][6][7][8][9][10], so far there have been no theoretical or numerical studies of the effect of electric fields on friction. We do not know what the mechanism is behind the observed variation of friction with electrostatic potential, nor in which systems significant reversible variation of the friction can be achieved.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…By varying the applied potential, the electrode surface can quickly and reversibly be modified either with adsorbed (sub)monolayer or multilayers, or via the oxidation and reduction of surfaces, or deposition of ultrathin films [3,4]. Thus, friction force microscopy (FFM) measurements under electrochemical conditions [5][6][7][8][9][10] may offer significant advantages in comparison to those between dry surfaces.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…Recent FFM measurements in UHV have also shown strong sensitivity of nanoscopic friction to the orientation of surface molecules [18]. Investigating the impact of potentialdependent orientation of adsorbed molecules on friction offers a new perspective on active control of friction forces through reversible molecular reorientation.In spite of the first successful experimental studies of nanoscopic friction under potential control [5][6][7][8][9][10], so far there have been no theoretical or numerical studies of the effect of electric fields on friction. We do not know what the mechanism is behind the observed variation of friction with electrostatic potential, nor in which systems significant reversible variation of the friction can be achieved.…”

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Nanoscopic Friction under Electrochemical Control

et al. 2014

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We propose a theoretical model of friction under electrochemical conditions focusing on the interaction of a force microscope tip with adsorbed polar molecules of which the orientation depends on the applied electric field. We demonstrate that the dependence of friction force on the electric field is determined by the interplay of two channels of energy dissipation: (i) the rotation of dipoles and (ii) slips of the tip over potential barriers. We suggest a promising strategy to achieve a strong dependence of nanoscopic friction on the external field based on the competition between long range electrostatic interactions and short range chemical interactions between tip and adsorbed polar molecules. PACS numbers:Control of friction during sliding is extremely important for a large variety of applications [1,2]. A unique path to control and ultimately manipulate the forces between material surfaces is through an applied electric field. By varying the applied potential, the electrode surface can quickly and reversibly be modified either with adsorbed (sub)monolayer or multilayers, or via the oxidation and reduction of surfaces, or deposition of ultrathin films [3,4]. Thus, friction force microscopy (FFM) measurements under electrochemical conditions [5-10] may offer significant advantages in comparison to those between dry surfaces.Several experimental and theoretical studies of electrochemical interfaces demonstrated that the orientation of polar molecules adsorbed at electrode surfaces is potential dependent. Water molecules at electrode/electrolyte interfaces reorient from "oxygen-up" to "oxygen-down" as the potential on the electrode changes from negative to positive [11][12][13][14]. Another extensively studied system is pyridine adsorbed on gold electrodes [15,16]. Recent FFM measurements combined with cyclic voltammetry [17] have shown that friction depends strongly on the orientation of the molecules and is five times higher when the molecules are parallel to the substrate compared to their vertical orientation. The molecule orientation can be changed either by changing their concentration or by an external field. In the latter case, the friction shows an intense peak around values of the field where the change of orientation takes place. Recent FFM measurements in UHV have also shown strong sensitivity of nanoscopic friction to the orientation of surface molecules [18]. Investigating the impact of potentialdependent orientation of adsorbed molecules on friction offers a new perspective on active control of friction forces through reversible molecular reorientation.In spite of the first successful experimental studies of nanoscopic friction under potential control [5][6][7][8][9][10], so far there have been no theoretical or numerical studies of the effect of electric fields on friction. We do not know what the mechanism is behind the observed variation of friction with electrostatic potential, nor in which systems significant reversible variation of the friction can be achieved.In this Letter we propose a m...

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Section: Pacs Numbersmentioning

confidence: 99%

Section: Pacs Numbersmentioning

confidence: 99%

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confidence: 99%

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Nanoscopic Friction under Electrochemical Control

et al. 2014

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“…For instance, driving a system through a ferroelectric phase transition can give rise to a non-trivial behaviour of friction at the critical point; friction control can be also reached through the application of an external electric field [4]. Using organic ionic liquids as lubricants, the lubrication properties can be again controlled by an electric field [22], but such phenomenology is not easily and completely exploitable toward a full friction control. In this work we move instead to the mesoscale realm, namely to the study of two micron-sized plates coated with ferromagnetic films.…”

Section: Introductionmentioning

confidence: 99%

Microscale Motion Control through Ferromagnetic Films

Benassi

Schwenk

Marioni

et al. 2014

Adv Materials Inter

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Actuation and control of motion in micromechanical systems are technological challenges, since they are accompanied by friction and wear, principal and well-known sources of lifetime reduction. In this theoretical work we propose a non-contact motion control technique based on the introduction of a magnetic interaction, i.e., non-contact magnetic friction. The latter is realized by coating two non-touching sliding bodies with ferromagnetic films. The resulting dynamics is determined by shape, size and ordering of magnetic domains arising in the films below the Curie temperature. We demonstrate that the domain behavior can be tailored by acting on handles like ferromagnetic coating preparation, external magnetic fields and the finite distance between the plates. In this way, motion control can be achieved without mechanical contact. Moreover, we discuss how such handles can disclose a variety of sliding regimes. Finally, we propose how to practically implement the proposed model sliding system.

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“…The application of external fields (electric, magnetic, etc.) to the sliding contact was also exploited to tune effectively the frictional response in different kind of tribological systems [5][6][7][8] . Another, subtler route worth exploring is the possible change of adhesion and friction experienced by a nanoslider when a collective property of the substrate, for example some pre-existing ordering is altered under the action of an external field, or of temperature.…”

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Does rotational melting make molecular crystal surfaces more slippery?

et al. 2014

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The surface of a crystal made of roughly spherical molecules exposes, above its bulk rotational phase transition at T= T r , a carpet of freely rotating molecules, possibly functioning as "nanobearings" in sliding friction. We explored by extensive molecular dynamics simulations the frictional and adhesion changes experienced by a sliding C 60 flake on the surface of the prototype system C 60 fullerite. At fixed flake orientation both quantities exhibit only a modest frictional drop of order 20% across the transition. However, adhesion and friction drop by a factor of ∼ 2 as the flake breaks its perfect angular alignment with the C 60 surface lattice suggesting an entropy-driven aligned-misaligned switch during pull-off at T r . The results can be of relevance for sliding Kr islands, where very little frictional differences were observed at T r , but also to the sliding of C 60 -coated tip, where a remarkable factor ∼ 2 drop has been reported.Exploring novel routes to achieve friction control by external physical means is a fundamental goal currently pursued 1 in nanoscience and nanotechnology. The traditional lubrication control of frictional forces in macroscopic mechanical contacts is impractical at the nanoscale, where contacting surfaces are likelier to succumb to capillary forces. Novel methods for control and manipulation of friction in nano and intermediate mesoscale systems are thus constantly being explored. As an example, mechanically induced oscillations were recently shown to reduce friction and wear, an effect that has been experimentally demonstrated 2,3 . Mismatch of relative commensurability of mutually sliding lattices may prevent interlocking and stick-slip motion of the interface atoms, with a consequent friction drop (superlubricity) 4 . The application of external fields (electric, magnetic, etc.) to the sliding contact was also exploited to tune effectively the frictional response in different kind of tribological systems 5-8 . Another, subtler route worth exploring is the possible change of adhesion and friction experienced by a nanoslider when a collective property of the substrate, for example some pre-existing ordering is altered under the action of an external field, or of temperature. In a given state of the substrate, its order parameter magnitude, polarization, critical fluctuations, etc., determines in a unique manner the friction, affecting both the efficiency of * andrea. the slider-substrate mechanical coupling, and the rate of generation and transport of the frictional Joule heat away from the sliding contact. A toy-model study 9 showed that the variation of stick-slip friction, caused by a structural order parameter switching between order and disorder, can indeed be large and observable. Hard to predict on general terms, the frictional variation occurring in a real case will depend on the system, the mechanism, the material. In this work we study the friction experienced by a nanosized island or tip-attached flake sliding over the surface of a molecular crystal made up o...

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Control of Nanoscale Friction on Gold in an Ionic Liquid by a Potential-Dependent Ionic Lubricant Layer

Cited by 207 publications

References 29 publications

Nanoscopic Friction under Electrochemical Control

Nanoscopic Friction under Electrochemical Control

Microscale Motion Control through Ferromagnetic Films

Does rotational melting make molecular crystal surfaces more slippery?

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