Andrea Vanossi

Empa - Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Zurich, Switzerland

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Publications (68)308.82 Total impact

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    ABSTRACT: The surface of a crystal made of roughly spherical molecules exposes, above its bulk rotational phase transition at T= Tr, 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 C60 flake on the surface of the prototype system C60 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 C60 surface lattice suggesting an entropy-driven aligned-misaligned switch during pull-off at Tr. The results can be of relevance for sliding Kr islands, where very little frictional differences were observed at Tr, but also to the sliding of C60 -coated tip, where a remarkable factor 2 drop has been reported.
    Nanoscale 09/2014; · 6.73 Impact Factor
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    ABSTRACT: Recent highly idealized model studies of lubricated nanofriction for two crystalline sliding surfaces with an interposed thin solid crystalline lubricant layer showed that the overall relative velocity of the lubricant $v_{\rm lub} / v_{\rm slider}$ depends only on the ratio of the lattice spacings, and retains a strictly constant value even when system parameters are varied within a wide range. This peculiar "quantized" dynamical locking was understood as due to the sliding-induced motion of misfit dislocations, or soliton structures. So far, the practical relevance of this concept to realistic sliding three dimensional crystals has not been demonstrated. In this work, by means of classical molecular dynamics simulations and theoretical considerations, we realize a realistic three-dimensional crystal-lubricant-crystal geometry. Results show that the flux of lubricant particles associated to the advancing soliton lines gives rise here too to a quantized velocity ratio. Moreover, depending on the interface lattice spacing mismatch, both forward and backward quantized motion of the lubricant is predicted. The persistence under realistic conditions of the dynamically pinned state and quantized sliding is further investigated by varying sliding speed, temperature, load, and lubricant film thickness. The possibilities of experimental observation of quantized sliding are also discussed.
    02/2014; 89(9).
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    ABSTRACT: We investigate the frictional sliding of an incommensurate chain of interacting particles confined in between two nonlinear on-site substrate potential profiles in relative motion. We focus here on the class of Remoissenet-Peyrard parametrized potentials V_{RP}(x,s), whose shape can be varied continuously as a function of s, recovering the sine-Gordon potential as a particular case. The observed frictional dynamics of the system, crucially dependent on the mutual ratios of the three periodicities in the sandwich geometry, turns out to be significantly influenced also by the shape of the substrate potential. Specifically, variations of the shape parameter s affect significantly and not trivially the existence and robustness of the recently reported velocity quantization phenomena [A. Vanossi et al., Phys. Rev. Lett. 97, 056101 (2006)], where the chain center-of-mass velocity to the externally imposed relative velocity of the sliders stays pinned to exact "plateau" values for wide ranges of the dynamical parameters.
    Physical Review E 07/2013; 88(1-1):012810. · 2.31 Impact Factor
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    ABSTRACT: The physics of sliding friction is gaining impulse from nanoscale and mesoscale experiments, simulations, and theoretical modeling. This Colloquium reviews some recent developments in modeling and in atomistic simulation of friction, covering open-ended directions, unconventional nanofrictional systems, and unsolved problems.
    Review of Modern Physics 04/2013; 85(2). · 44.98 Impact Factor
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    Davide Mandelli, Andrea Vanossi, Erio Tosatti
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    ABSTRACT: Stick-slip -- the sequence of mechanical instabilities through which a slider advances on a solid substrate -- is pervasive throughout sliding friction, from nano to geological scales. Here we suggest that trapped cold ions in an optical lattice can also be of help in understanding stick-slip friction, and also the way friction changes when one of the sliders undergoes structural transitions. For that scope, we simulated the dynamical properties of a 101-ions chain, driven to slide back and forth by a slowly oscillating electric field in an incommensurate periodic "corrugation" potential of increasing magnitude U0. We found the chain sliding to switch, as U0 increases and before the Aubry transition, from a smooth-sliding regime with low dissipation to a stick-slip regime with high dissipation. In the stick-slip regime the onset of overall sliding is preceded by precursor events consisting of partial slips of few ions only, leading to partial depinning of the chain, a nutshell remnant of precursor events at the onset of motion also observed in macroscopic sliders. Seeking to identify the possible effects on friction of a structural transition, we reduced the trapping potential aspect ratio until the ion chain shape turned from linear to zigzag. Dynamic friction was found to rise at the transition, reflecting the opening of newer dissipation channels.
    Physical review. B, Condensed matter 03/2013; 87(19). · 3.66 Impact Factor
  • Davide Mandelli, Andrea Vanossi, Erio Tosatti
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    ABSTRACT: Trapped cold ions are known to form linear or planar zigzag chains, helices or clusters depending on trapping conditions. They may be forced to slide over a laser induced corrugated potential, a mimick of sliding friction [1,2]. We present MD simulations of an incommensurate 101 ions chain sliding subject to an external electric field. As expected with increasing corrugation, we observe the transition from a smooth-sliding, highly lubric regime to a strongly dissipative stick-slip regime. Owing to inhomogeneity the dynamics shows features reminiscent of macroscopic frictional behaviors [3]. While the chain extremities are pinned, the incommensurate central part is initially free to slide. The onset of global sliding is preceded by precursor events consisting of partial slips of chain portions further from the center. We also look for frictional anomalies expected for the chain sliding across the linear-zigzag structural phase transition. Although the chain is too short for a proper critical behavior, the sliding friction displays a frank rise near the transition, due to opening of a new dissipative channel via excitations of transverse modes.[4pt] [1] A. Benassi et al, Nature Comm. 2, 236;[0pt] [2] T. Pruttivarasin et al, New Jour. of Phys. 13, 075012;[0pt] [3] S.M. Rubinstein et al, Nature 4, 1005.
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    ABSTRACT: The increase of sliding friction upon increasing load is a classic in the macroscopic world. Here we discuss the possibility that friction rise might sometimes turn into a drop when, at the mesoscale and nanoscale, a confined lubricant film separating crystalline sliders undergoes strong layering and solidification. Under pressure, transitions from N to N-1 layers may imply a change of lateral periodicity of the crystallized lubricant sufficient to alter the matching of crystal structures, influencing the ensuing friction jump. A pressure-induced friction drop may occur as the shear gradient maximum switches from the lubricant middle, marked by strong stick-slip with or without shear melting, to the crystalline slider-lubricant interface, characterized by smooth superlubric sliding. We present high pressure sliding simulations to display examples of frictional drops, suggesting their possible relevance to the local behavior in boundary lubrication.
    Physical review. B, Condensed matter 01/2013; 87(4). · 3.66 Impact Factor
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    Andrea Vanossi, Nicola Manini, Erio Tosatti
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    ABSTRACT: In a pioneer experiment, Bohlein et al. realized the controlled sliding of two-dimensional colloidal crystals over laser-generated periodic or quasi-periodic potentials. Here we present realistic simulations and arguments that besides reproducing the main experimentally observed features give a first theoretical demonstration of the potential impact of colloid sliding in nanotribology. The free motion of solitons and antisolitons in the sliding of hard incommensurate crystals is contrasted with the soliton-antisoliton pair nucleation at the large static friction threshold F(s) when the two lattices are commensurate and pinned. The frictional work directly extracted from particles' velocities can be analyzed as a function of classic tribological parameters, including speed, spacing, and amplitude of the periodic potential (representing, respectively, the mismatch of the sliding interface and the corrugation, or "load"). These and other features suggestive of further experiments and insights promote colloid sliding to a unique friction study instrument.
    Proceedings of the National Academy of Sciences 09/2012; 109(41):16429-33. · 9.81 Impact Factor
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    ABSTRACT: Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the removal of the frictionally generated Joule heat. Building upon general pre-existing formulation, we implement a fully microscopic dissipation approach which, based on a parameter-free, non-Markovian, stochastic dynamics, absorbs Joule heat equivalently to a semi-infinite solid and harmonic substrate. As a test case, we investigate the stick-slip friction of a slider over a two-dimensional Lennard-Jones solid, comparing our virtually exact frictional results with approximate ones from commonly adopted dissipation schemes. Remarkably, the exact results can be closely reproduced by a standard Langevin dissipation scheme, once its parameters are determined according to a general and self-standing variational procedure.
    Tribology Letters 08/2012; 48(1). · 2.15 Impact Factor
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    ABSTRACT: The sliding friction during pressure squeezout of a boundary lubricated contact has been shown [1,2] to undergo upward jumps every time a lubricant atomic layer is expelled. Here we ask the question whether the jump could not be downward. Whereas most studies focus on the layered structure which the confined lubricant takes in the normal direction, the element we wish to consider is a possible change of parallel periodicity occurring at the squeezout transition. Such changes have been reported in simulations [3], but their effect has not been discussed so far. One possible effect could be a transition of the slider-lubricant interface commensurability, producing a switch of the frictional mechanism, from lubricant melting-freezing in a commensurate state, to superlubric in an incommensurate one -- in this case with a drop of friction for increasing load. We exemplify this effect by MD simulations, where we replace for convenience the open squeezout system with a closed system, where the lubricant is sealed between the sliders. As the number of layers drops under pressure, the planar lubricant structural lattice parameter also drops. This change reflects in a sliding friction jump, which is easily observed to be downwards. The potential observability of load-induced friction drops will be discussed. [4pt] [1] J.N. Israelachvili et al., Science 240, 189 (1988). [0pt] [2] J. Gao et al., J. Phys. Chem. B 102, 5033 (1998). [0pt] [3] U. Tartaglino et al., J. Chem. Phys. 125, 014704 (2006).
  • Andrea Vanossi, Erio Tosatti
    Nature Material 12/2011; 11(2):97-8. · 35.75 Impact Factor
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    ABSTRACT: The physics of sliding friction is gaining impulse from nano and mesoscale experiments, simulations, and theoretical modeling. This colloquium reviews some recent developments in modeling and in atomistic simulation of friction, covering open-ended directions, unconventional nanofrictional systems, and unsolved problems.
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    ABSTRACT: A Reply to the Comment by K. McLaughlin, D. Rabson, and P. Thiel.
    Physical Review Letters 11/2011; 107(20):209402. · 7.73 Impact Factor
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    Roberto Guerra, Andrea Vanossi, Michael Urbakh
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    ABSTRACT: We study in detail the recent suggestions by Tshiprut et al. [Phys. Rev. Lett. 95, 016101 (2005)] to tune tribological properties at the nanoscale by subjecting a substrate to periodic mechanical oscillations. We show that both in stick-slip and sliding regimes of motion friction can be tuned and reduced by controlling the frequency and amplitude of the imposed substrate lateral excitations. We demonstrate that the mechanisms of oscillation-induced reduction of friction are different for stick-slip and sliding dynamics. In the first regime the effect results from a giant enhancement of surface diffusion, while in the second regime it is due to the interplay between washboard and oscillation frequencies that leads to the occurrence of parametric resonances. Moreover we show that for particular set of parameters it is possible to sustain the motion with the only oscillations.
    Physical Review E - PHYS REV E. 06/2011; 78(3).
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    ABSTRACT: The effects of a displacive structural phase transition on sliding friction are in principle accessible to nanoscale tools such as the Atomic Force Microscopy, yet they are still surprisingly unexplored. We present model simulations demonstrating and clarifying the mechanism and potential impact of these effects. A structural order parameter inside the material will yield a contribution to stick-slip friction that is nonmonotonic as temperature crosses the phase transition, peaking at the critical Tc where critical fluctuations are strongest, and the sliding-induced order parameter local flips from one value to another more numerous. Accordingly, the friction below Tc is larger when the order parameter orientation is such that flips are more effectively triggered by the slider. The observability of these effects and their use for friction control are discussed, for future application to sliding on the surface of and ferro- or antiferro-distortive materials.
    Physical Review Letters 05/2011; 106(25). · 7.73 Impact Factor
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    A Benassi, A Vanossi, E Tosatti
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    ABSTRACT: Sliding friction between crystal lattices and the physics of cold ion traps are so far non-overlapping fields. Two sliding lattices may either stick and show static friction or slip with dynamic friction; cold ions are known to form static chains, helices or clusters, depending on the trapping conditions. Here we show, based on simulations, that much could be learnt about friction by sliding, through, for example, an electric field, the trapped ion chains over a corrugated potential. Unlike infinite chains, in which the theoretically predicted Aubry transition to free sliding may take place, trapped chains are always pinned. Yet, a properly defined static friction still vanishes Aubry-like at a symmetric-asymmetric structural transition, found for decreasing corrugation in both straight and zig-zag trapped chains. Dynamic friction is also accessible in ringdown oscillations of the ion trap. Long theorized static and dynamic one-dimensional friction phenomena could thus become accessible in future cold ion tribology.
    Nature Communications 03/2011; 2:236. · 10.74 Impact Factor
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    ABSTRACT: Rare gas islands adsorbed through van der Waals forces on metal surfaces do not slide freely, but exhibit static friction in QCM experiments. Static friction appears, unexpectedly, even for incommensurate and defect-free crystal surfaces, where sliding should be frictionless. Via atomistic simulations of Kr islands on Au(111), we show that the island edges may be the ultimate culprits. Adsorbate sliding requires the flow of solitons - tiny density and corrugation modulations with the beat periodicity between the two periodicities. For an island, we find an edge-originated energy barrier that blocks the soliton flow, keeping the island pinned. As the static friction force is reached, the barrier vanishes at one point on the edge, and new solitons enter the island, which becomes depinned. Unsurprisingly, we find that low surface corrugation and high temperature facilitate this edge depinning. However, the island's thermal expansion is large and leads to changeable commensurability upon heating, which gives rise to the possibility of re-entrant static friction.
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    ABSTRACT: In the last twenty years the Atomic Force Microscope (AFM) is become one of the most important instruments to perform characterization at the nanoscale and to achieve direct control of nano-objects. In this paper a quantitative method to estimate the detachment energy of gold spherical nanoclusters with typical diameters of 13, 24 and 42nm deposited on silicon dioxide and Highly Oriented Pyrolytic Graphite (HOPG) by AFM measures with Amplitude Modulation (AM-AFM) feedback is presented. It is based on the use of AFM tip oscillations to induce clusters detachments and on the substrate mapping with phase signal. With this powerful method is possible to move in a very controlled way nanoparticles selected by dimensions. All experiments have been performed in air conditions using a commercial AFM microscope with cantilevers characterized by nominal spring constants lying between 5 and 50N/m. KeywordsAFM–Nanotribology–Nanoclusters–Manipulation–Static friction–Nanoparticles
    Meccanica 01/2011; 46(3):597-607. · 1.75 Impact Factor
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    ABSTRACT: Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the way Joule heat is removed. We implement in a realistic frictional simulation a parameter-free, non-markovian, stochastic dynamics, which, as expected from theory, absorbs Joule heat precisely as a semi-infinite harmonic substrate would. Simulating stick-slip friction of a slider over a 2D Lennard-Jones solid, we compare our virtually exact frictional results with approximate ones from commonly adopted empirical dissipation schemes. While the latter are generally in serious error, we show that the exact results can be closely reproduced by a viscous Langevin dissipation at the boundary layer, once the back-reflected frictional energy is variationally optimized.
    Physical review. B, Condensed matter 08/2010; · 3.66 Impact Factor
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    ABSTRACT: Sliding parts in nanosystems such as nanoelectromechanical systems and nanomotors increasingly involve large speeds, and rotations as well as translations of the moving surfaces; yet, the physics of high-speed nanoscale friction is so far unexplored. Here, by simulating the motion of drifting and of kicked Au clusters on graphite--a workhorse system of experimental relevance--we demonstrate and characterize a new 'ballistic' friction regime at high speed, separate from drift at low speed. The temperature dependence of the cluster slip distance and time, measuring friction, is opposite in these two regimes, consistent with theory. Crucial to both regimes is the interplay of rotations and translations, shown to be correlated in slow drift but anticorrelated in fast sliding. Despite these differences, we find the velocity dependence of ballistic friction to be, like drift, viscous.
    Nature Material 08/2010; 9(8):634-7. · 35.75 Impact Factor

Publication Stats

363 Citations
308.82 Total Impact Points


  • 2014
    • Empa - Swiss Federal Laboratories for Materials Science and Technology
      Duebendorf, Zurich, Switzerland
  • 2009–2013
    • Scuola Internazionale Superiore di Studi Avanzati di Trieste
      Trst, Friuli Venezia Giulia, Italy
  • 2002–2011
    • Università degli Studi di Modena e Reggio Emilia
      Modène, Emilia-Romagna, Italy
  • 2007
    • University of Milan
      • Department of Physics
      Milano, Lombardy, Italy
  • 2005
    • National Academy of Sciences of Ukraine
      • Institute of Physics
      Kiev, Misto Kyyiv, Ukraine
  • 2000–2003
    • Los Alamos National Laboratory
      • Center for Nonlinear Studies
      Los Alamos, NM, United States
  • 2000–2001
    • University of Bologna
      Bolonia, Emilia-Romagna, Italy