fundamentals of friction and wear on the nanoscale, 2007, p.713

[...]... dependence of FFM results itself can depend again on the temperature [37, 38] Consequently, an enclosure of FFM experiments for humidity control greatly enhances the reproducibility of results 1.3.1 Friction as a function of load One of the central experiments in tribology is the quantification of friction, i e the change of lateral force with increasing normal load on the sliding contact One of the questions... where for example friction on terraces and friction at steps could automatically be distinguished [40] When the normal load on the tip is varied the position of the contact may be displaced along the long axis of the cantilever This effect is caused by the tilt of the cantilever with respect to the surface On heterogeneous surfaces such displacement may distort the friction measurement and, therefore, has... 2 R Bennewitz Thermal fluctuations of the cantilever Calibration of the beam deflection scheme Spring constant of normal and torsional bending Environmental conditions, in particular humidity Stiffness of the tip apex Crosstalk between friction and topography signals Wear during friction measurement Sample surface quality Displacement of tip position parallel to the cantilever direction with increasing... studies of frictional properties in single-asperity contacts The biggest drawback within the method is the lack of methods for a reproducible preparation and characterization of tips on atomic scale, as compared to the surface preparation by means of methods of Surface Science Such control over the atomic constitution of the contact area would greatly advance our understanding of tribological processes on. .. surfaces, the refractive index of the film confined between the surfaces and the geometry of the contact region The SFA is one of few techniques in the field of tribology that allows to image in situ and in real time the geometry of the contact area, and probably the only one with subnanometric resolution Multiple Beam Interferometry (MBI ) is used for this purpose [11] A highly reflective layer is deposited on. .. to the friction sensing device and the piezoelectric bimorph slider, respectively MBI an image of the surfaces in contact can be obtained as the surfaces are slid, allowing monitoring of the size and the profile of the contact area and the distance between the surfaces, by observing the flat region on the FECO Shear-induced elastohydrodynamic deformation can also be distinguished In addition, damage of. .. Granick and coworkers [37, 38] The goal of these low amplitude studies is to focus the investigation on the linear response of the confined films By applying small deformations, the flow of fresh liquid in the contact zone is avoided This allows the study of long time relaxation process that may be occurring in the contact region A schematic of this device is illustrated in Fig 2.2 In this design, the bottom... Another effect that can seriously disturb friction experiments is the onset of wear and the concomitant increase of lateral forces Wear thresholds in FFM can be as low as a few nanonewton normal load, and wear at a constant low load may suddenly start after repeatedly scanning the same area [44] 1.3.2 Friction as a function of material On inhomogeneous surfaces Friction Force Microscopy can image contrasts... automate the procedure of measurement, in order to improve the accuracy and simplicity of the technique Second, the strategy used to determine the separation between the surfaces has been extended by using non-interferometric techniques Recently, Qian and co-workers extended the capabilities of the apparatus to include the movement of the surfaces and the measurement of the friction force between them... limits the molecules that can be studied to large dye molecules In addition, for best determination of the adsorption spectra of the confined dyes, relatively thick mica has to be used, reducing the accuracy of the film thickness determination In other order of ideas, Salmeron and coworkers suggested to couple second harmonic and sum-frequency generation to the SFA to study alignment and relaxation of confined . between friction and topography signals. Wear during friction measurement. Calibration of the beam deflection scheme. Spring constant of normal and torsional bending. Displacement of tip position parallel. to im- age and move particles in a controlled way. With a proper calibration of the excitation amplitude the energy dissipation and the frictional forces involved in the manipulation process can. research and is certainly one of the most im- portant ones from a practical point of view. The da Vinci-Amonton laws are common knowledge (1. Friction is independent of apparent contact area, 2. Friction