Friction Force Spectroscopy in the Low-Load Regime with Well-Defined Tips

Schwarz, Udo D.; Zwörner, O.; Köster, Peter; Wiesendanger, R.

doi:10.1007/978-94-011-5646-2_15

Cited by 20 publications

(5 citation statements)

References 11 publications

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“…A topographic AFM image is actually a convolution of the tip and sample geometry. Separation of the tip and sample contributions by contact imaging sharp or at least known sample features allows, in situ , some determination of the overall tip shape on a namometer to micrometer scale. − Ex situ tip imaging by transmission electron microscopy has also been performed. , Some of these measurements have revealed that a majority of microfabricated cantilevers possess double tips and other unsuitable tip structures. , This convincingly proves that tip characterization is absolutely necessary for useful nanotribological measurements with AFM. Thin film coatings applied to the microfabricated levers can provide robust, smooth, and possibly conductive coatings. − Further work in this direction would be useful, so as to provide a wider array of dependable tip structures and materials.…”

Section: Probe Tip Characterizationmentioning

confidence: 94%

Scratching the Surface: Fundamental Investigations of Tribology with Atomic Force Microscopy

1997

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Section: Probe Tip Characterizationmentioning

confidence: 94%

Scratching the Surface: Fundamental Investigations of Tribology with Atomic Force Microscopy

1997

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“…The tips were formed by coating the tips of tungsten carbide-coated silicon cantilever probes (MikroMasch, Wilsonville, OR) with a smooth hydrogenated amorphous carbon film using electron beam induced decomposition (EBID) in a transmission electron microscope (TEM). 46,47 This process forms a dense hydrocarbon coating on the tip, but the exact composition and hybridizations of the carbon atoms are not known. Both tips were imaged at high resolution by TEM before and after the AFM experiments to measure tip shape and radius and to determine the extent to which the tip may have changed during the experiment.…”

Section: Methodsmentioning

confidence: 99%

Atomic-Scale Friction on Diamond: A Comparison of Different Sliding Directions on (001) and (111) Surfaces Using MD and AFM

et al. 2007

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Atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations were conducted to examine single-asperity friction as a function of load, surface orientation, and sliding direction on individual crystalline grains of diamond in the wearless regime. Experimental and simulation conditions were designed to correspond as closely as state-of-the-art techniques allow. Both hydrogen-terminated diamond (111)(1 x 1)-H and the dimer row-reconstructed diamond (001)(2 x 1)-H surfaces were examined. The MD simulations used H-terminated diamond tips with both flat- and curved-end geometries, and the AFM experiments used two spherical, hydrogenated amorphous carbon tips. The AFM measurements showed higher adhesion and friction forces for (001) vs (111) surfaces. However, the increased friction forces can be entirely attributed to increased contact area induced by higher adhesion. Thus, no difference in the intrinsic resistance to friction (i.e., in the interfacial shear strength) is observed. Similarly, the MD results show no significant difference in friction between the two diamond surfaces, except for the specific case of sliding at high pressures along the dimer row direction on the (001) surface. The origin of this effect is discussed. The experimentally observed dependence of friction on load fits closely with the continuum Maugis-Dugdale model for contact area, consistent with the occurrence of single-asperity interfacial friction (friction proportional to contact area with a constant shear strength). In contrast, the simulations showed a nearly linear dependence of the friction on load. This difference may arise from the limits of applicability of continuum mechanics at small scales, because the contact areas in the MD simulations are significantly smaller than the AFM experiments. Regardless of scale, both the AFM and MD results show that nanoscale tribological behavior deviates dramatically from the established macroscopic behavior of diamond, which is highly dependent on orientation.

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“…After exposure, the apex radii could be determined very accurately with nanometer precision from the electron micrographs. The exact procedure for the preparation of the spherical tip apexes is described in [13].…”

Section: Methodsmentioning

confidence: 99%

The velocity dependence of frictional forces in point-contact friction

Zwörner¹,

Hölscher²,

Schwarz³

et al. 1998

Applied Physics A: Materials Science & Processing

109

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The velocity dependence of point-contact friction is studied by means of friction force microscopy of different carbon compounds (diamond, graphite, amorphous carbon). The measured frictional force is found to be constant over a wide range of sliding velocities [nm/s to µm/s]. This result is substantiated by a simple mechanical model, where the frictional forces are shown to be constant at sliding velocities well below the slip velocity.Although frictional phenomena are familiar from daily life and the study of friction is one of the oldest topics in physics because of its technological relevance [1], there has been only little success in deriving an exact description of friction since the time the following phenomenological laws of dry friction were established by Amontons and Coulomb 200 years ago. These laws are: (i) the frictional force is proportional to the normal load; (ii) the frictional force is independent of the (apparent) contact area of the sliding surfaces; (iii) sliding friction is independent of the sliding velocity. These three laws of friction hold surprisingly well at the macroscopic scale, but cannot be explained by first principles. Nevertheless, with the advent of new experimental tools such as the surface force apparatus, the quartz crystal microbalance, and the friction force microscope, the expanding field of nanotribology has been established where the tribological properties of contacts with well-defined geometries are studied on the nanometer scale [2].By using the friction force microscope (FFM) [3], which is an extension of the scanning force microscope (SFM) [4], it is possible to examine the frictional properties of an (approximate) point contact at the nanometer scale. The observed frictional behavior differs significantly from the behavior expected from the macroscopic friction laws introduced above. In particular, it is found that frictional forces are proportional to the true area of contact, which is generally not proportional to the loading force [5]. Consequently, the laws (i) and (ii) are no longer valid at the nanometer scale. * Corresponding author In this study, we examine the validity of law (iii) for point contacts by using a friction force microscope. It is found that the frictional forces are independent of the sliding velocity in a wide range. This result is substantiated by a simple mechanical model based on the Tomlinson [6] and the independent oscillator [7, 8] models. Experiment SamplesIn order to investigate the velocity dependence of frictional forces in point-contact friction, three different modifications of carbon were studied as examples. (i) A diamond film deposited by chemical vapor deposition on a silicon (001) substrate which exhibited crystallites with flat, {100} oriented surfaces. The surfaces of individual crystallites were typically several 100 nm 2 up to somewhat more than 1 µm 2 . (ii) Highly oriented pyrolytic graphite (HOPG) with 99.99% purity [9]. The sample was cleaved each time right before measurement along its (0001) plane by using Scotch...

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Friction Force Spectroscopy in the Low-Load Regime with Well-Defined Tips

Cited by 20 publications

References 11 publications

Scratching the Surface: Fundamental Investigations of Tribology with Atomic Force Microscopy

Scratching the Surface: Fundamental Investigations of Tribology with Atomic Force Microscopy

Atomic-Scale Friction on Diamond: A Comparison of Different Sliding Directions on (001) and (111) Surfaces Using MD and AFM

The velocity dependence of frictional forces in point-contact friction

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