Out-of-plane and in-plane actuation effects on atomic-scale friction

The influence of out-of-plane and in-plane contact vibrations and temperature on the friction force acting on a sharp tip elastically pulled on a crystal surface is studied using a generalized Prandtl- Tomlinson model. The average friction force is significantly lowered in a frequency range determined by the "washboard" frequency of the stick-slip motion and the viscous damping accompanying the tip motion. An approximately linear relation between the actuation amplitude and the effective corrugation of the surface potential is derived in the case of in-plane actuation, extending a similar conclusion for out-of-plane actuation. Temperature causes an additional friction reduction with a scaling relation in formal agreement with the predictions of reaction rate theory in absence of contact vibrations. In this case the actuation effects can be described by the effective energy or, more accurately, by introducing an effective temperature.Comment: To appear in Physical Review

Lateral vibration effects in atomic-scale friction

The influence of lateral vibrations on the stick-slip motion of a nanotip elastically pulled on a flat crystal surface is studied by atomic force microscopy (AFM) measurements on a NaCl(001) surface in ultra-high vacuum. The slippage of the nanotip across the crystal lattice is anticipated at increasing driving amplitude, similarly to what is observed in presence of normal vibrations. This lowers the average friction force, as explained by the Prandtl-Tomlinson model with lateral vibrations superimposed at finite temperature. Nevertheless, the peak values of the lateral force, and the total energy losses, are expected to increase with the excitation amplitude, which may limit the practical relevance of this effect.Comment: To appear in Applied Physics Letter

Anisotropy effects and friction maps in the framework of the 2d PT model

We present a series of numerical simulations on the friction-anisotropy behavior and stick-slip dynamics of a point mass in the framework of a 2d Prandtl-Tomlinson model. Results for three representative surface lattice are shown: square, hexagonal and honeycomb. Curves for scan angle dependence of static friction force, and kinetic one at T=0 K and T=300 K are shown. Friction force maps are computed at different directions.The authors acknowledge financial support from Spanish MINECO through Project no. FIS2011-25167, cofinanced by FEDER funds and Project no. MAT2012-34487. O.Y.F. acknowledges financial support from FPU grant by Ministerio de Ciencia e Inovación of Spain.Peer Reviewe

Lateral vibration effects in atomic-scale friction

The influence of lateral vibrations on the stick-slip motion of a nanotip elastically pulled on a flat crystal surface is studied by atomic force microscopy measurements on a NaCl(001) surface in ultra-high vacuum. The slippage of the nanotip across the crystal lattice is anticipated at increasing driving amplitude, similarly to what is observed in presence of normal vibrations. This lowers the average friction force, as explained by the Prandtl-Tomlinson model with lateral vibrations superimposed at finite temperature. Nevertheless, the peak values of the lateral force, and the total energy losses, are expected to increase with the excitation amplitude, which may limit the practical relevance of this effect

Nucleation and detachment of polystyrene nanoparticles from plowing-induced surface wrinkling

We report the formation of spherical particles (up to 250 nm in diameter) from polystyrene surfaces repeatedly scratched by atomic force microscopy nanotips (nominal radius < 10 nm) along a series of parallel lines. The particles nucleate from the crests of the ripple profiles formed in the beginning of the scratch process. They are subsequently detached and progressively displaced by the tip across the ripples till the edge of the scanned area, where they pile up without coalescing. The detachment occurs smoothly without static friction peaks, suggesting that the particles are torn off as a result of a crazing mechanism induced by the tip when it is pushed against the ripple crests. Considering the negative impact of nanoplastics on the environment and human health, and the absence of established methodologies for a quantitative analysis of these processes at the level of single particles, our results will help to promote systematic characterization of plowing wear on different polymeric materials and different environmental conditions. © 2021 The Author(s

Atomic structure of alkali halide surfaces

The atomic structure of surfaces of alkali halide crystals has been revealed by means of high-resolution dynamic force microscopy. True atomic resolution is demonstrated both on steps surrounding islands or pits, and on a chemically mixed crystal. We have directly observed the enhanced interaction at low-coordinated sites by force microscopy. The growth of NaCl films on metal surfaces and radiation damage in a KBr surface is discussed based on force microscopy results. The damping of the tip oscillation in dynamic force microscopy might provide insight into dissipation processes on the atomic scale. Finally, we present atomically resolved images of wear debris found after scratching a KBr surfac

Quantitative Nanofriction Characterization of Corrugated Surfaces by Atomic Force Microscopy

Atomic Force Microscopy (AFM) is a suitable tool to perform tribological characterization of materials down to the nanometer scale. An important aspect in nanofriction measurements of corrugated samples is the local tilt of the surface, which affects the lateral force maps acquired with the AFM. This is one of the most important problems of state-of-the-art nanotribology, making difficult a reliable and quantitative characterization of real corrugated surfaces. A correction of topographic spurious contributions to lateral force maps is thus needed for corrugated samples. In this paper we present a general approach to the topographic correction of AFM lateral force maps and we apply it in the case of multi-asperity adhesive contact. We describe a complete protocol for the quantitative characterization of the frictional properties of corrugated systems in the presence of surface adhesion using the AFM.Comment: 33 pages, 9 figures, RevTex 4, submitted to Journal of Applied Physic