Orientation dependent molecular friction on organic layer compound crystals

Fessler, Gregor; Zimmermann, Iwan; Glatzel, Thilo; Gnecco, Enrico; Steiner, Pascal; Roth, Raphael; Keene, Tony D.; Liu, Shi‐Xia; Decurtins, Silvio; Meyer, Ernst

doi:10.1063/1.3559227

Cited by 24 publications

(28 citation statements)

References 28 publications

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“…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.…”

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confidence: 99%

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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confidence: 99%

Nanoscopic Friction under Electrochemical Control

et al. 2014

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“…This was indeed possible on another organic crystal, where Fessler et al were recently able to distinguish between two differently oriented molecules forming the unit cell of a surface lattice, although the direction of motion of the tip was kept fixed. 9 In this article we have chosen the (104) cleavage surfaces of dolomite and calcite as prototype systems for studying the influence of the sliding direction on atomic stick-slip on surfaces of intermediate crystallochemical complexity. Mainly due to their interest for earth and environmental sciences, calcite and dolomite (104) surfaces have been extensively studied with numerous surface sensitive techniques.…”

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Anisotropic surface coupling while sliding on dolomite and calcite crystals

Pina¹,

Miranda²,

Gnecco³

2012

Phys. Rev. B

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High-resolution friction force microscopy has been performed on the (104) surfaces of dolomite and calcite in deionized water. The two rows of oxygen atoms alternating in a zigzag way on top of both surfaces are resolved with similar contrast while scanning along the [421] direction. Along the [010] direction, only one row is resolved, provided that the normal loading is large enough. The direction-dependent interaction between the probing tip and surface atoms is explained by numeric calculations based on the Prandtl-Tomlinson model. With the exception of a few noticeable superlubric effects, 1 the sliding of two solid surfaces past each other is accompanied by stick-slip events due to the continuous formation and rupture of interatomic bonds. 2 On geological scales stick-slip is responsible for earthquakes and notoriously difficult to predict. The scenario radically changes at the nanoscale, where the loading and friction forces on sharp tips terminated by just a few atoms can be easily controlled and monitored by atomic force microscopy (AFM) in contact mode. 3 In the first approximation, the probing tip of an AFM can be considered a point mass driven by a lateral spring. This spring is associated with the torsion of a cantilever beam supporting the tip combined with the shear deformation of the contact region. 4 On a crystal surface the tip sticks to a lattice site till the spring elongation reaches a critical value and the tip suddenly jumps and binds again to another site in a stick-slip fashion. The friction forces developed in this process peak while scanning along a main crystallographic direction, the peak intensity being determined by the density of packing of the surface atoms.5 Systematic measurements of such "friction anisotropy" were reported on highly oriented pyrolitic graphite, 6 metallic quasicrystals, 7 and organic crystals.8 However, the results of the first study could only be explained by assuming the presence of a graphite flake attached to the tip apex, the second investigation did not report any friction maps on the atomic scale, and the third one did not reveal sublattice features in the complex surface structure. This was indeed possible on another organic crystal, where Fessler et al. were recently able to distinguish between two differently oriented molecules forming the unit cell of a surface lattice, although the direction of motion of the tip was kept fixed. 9In this article we have chosen the (104) cleavage surfaces of dolomite and calcite as prototype systems for studying the influence of the sliding direction on atomic stick-slip on surfaces of intermediate crystallochemical complexity. Mainly due to their interest for earth and environmental sciences, calcite and dolomite (104) surfaces have been extensively studied with numerous surface sensitive techniques.10-12 However, their tribological properties have scarcely been investigated. 13 The structure of the two surfaces is shown in Fig. 1 (104) one of the Ca atoms is ideally replaced by Mg. Here we show how, depending on th...

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“…This behaviour was related to the rheological properties of such molecular adsorbates, since the coefficients of viscosity for flow parallel to the rod axis are lower than those for flow perpendicular to it. When point resolution can be reached, AFM analysis showed that adjacent molecular rows can give rise to different friction, depending on the orientation of protruding molecular moieties such as phenyl rings [16]. Furthermore, for loads as small as 3.5 nN, a distortion of the surface structure can be induced, giving rise to an abrupt change of friction.…”

Section: Resultsmentioning

confidence: 98%

“…Since this property is strictly related to surface structure, crystallographical aspects are of great help for understanding friction anisotropy. In the case of organic molecular materials, the strong anisotropy among molecular interactions was correlated with the anisotropy of friction, under the assumption of a partial compliance of the molecular layers under the action of loading and sliding [15][16][17][18]. In the case of physisorbed layers of tilted rod-like molecules, it was observed that friction is lowest when sliding parallel to the tilt direction and maximal when sliding perpendicular [15,17,18].…”

Section: Resultsmentioning

confidence: 99%

Nanoscale Mapping of Frictional Anisotropy

2011

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Friction hodographs contain all the information related to the intensity and symmetry of the friction phenomenon. We show how an atomic force microscope can be used to collect friction hodographs at the nanoscale and how to carry out data interpretation to unravel the frictionsurface structure relationship. As a model system, we analyzed the basal plane of orthorhombic b-alanine single crystals, and interpreted the data in terms of a constitutive model of orthotropic friction with slip direction-dependent friction coefficients.

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Orientation dependent molecular friction on organic layer compound crystals

Cited by 24 publications

References 28 publications

Nanoscopic Friction under Electrochemical Control

Nanoscopic Friction under Electrochemical Control

Anisotropic surface coupling while sliding on dolomite and calcite crystals

Nanoscale Mapping of Frictional Anisotropy

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