Friction force microscopy

Lateral force microscopy (LFM) has provided a new tool for the investigation of tribological (friction and wear) phenomena on a nanometre scale [110]. Alternatively known as friction force microscopy (FFM), this variant of AFM focuses on the lateral forces experienced by the tip as it traverses the sample surface, which... 

Overney R and Meyer E 1993 Tribological investigations using friction force microscopy MRS Bulletin XVIII-5 20... 

Carpick, R.W., Ogletree, D.F. and Salmeron, M., Lateral stiffness A new nanomechanical measurement for the determination of shear strengths with friction force microscopy. Appl. Phys. Lc//., 70(12), 1548-1550(1997). 

In Section 4.3, we introduce a Friction Force Microscopy (FFM), designed and made by one of the authors. Professor Luetal. [9]. 

Measurement for Microscale Friction Using Friction Force Microscopy... 

Ruan, J. and Bhushan, B., Atomic-Scale Friction Measurements Using Friction Force Microscopy Part 1. General Principles and New Measurement Techniques, ASME J. Tribol., Vol. 116,1994, pp. 378-388. 

Sundararajan, S., and Bhushan, B., Micro/Nanotribology of Ultra-thin Hard Amorphous Carbon Coatings Using Atomic Force/Friction Force Microscopy," Wear, Vol. 225-229, 1999, pp. 678-689. 

In 1987 Mate et al. [468] used, for the first time, an atomic force microscope (AFM) to measure friction forces on the nanometer scale (review Ref. [469]). This technique became known as friction force microscopy (FFM) or lateral force microscopy (LFM). To measure friction forces with the AFM, the fast scan direction of the sample is chosen perpendicular to the direction of the cantilever. Friction between the tip and the sample causes the flexible cantilever to twist (Fig. 11.7). This torsion of the cantilever is measured by using a reflected beam of light and a position-sensitive detector in the form of a quadrant arrangement of photodiodes. This new method made it possible for the first time to study friction and lubrication on the nanometer scale. 

In experiments with friction force microscopy, the tip forms a contact of a few nanometers in diameter with the substrate, a so-called nanocontact. In reality, friction of macroscopic bodies is determined by the interaction via m/crocontacts. One possibility of extending the method of friction force microscopy to larger contact areas is the use of the colloidal probe technique, where a small sphere is attached to the end of an atomic force microscope cantilever (see Section 6.4). Even for microcontacts, the proportionality between the true area of contact and the friction force was observed (see example 11.1). 

Example 11.4. McGuiggan et al. [492] measured the friction on mica surfaces coated with thin films of either perfluoropolyether (PFPE) or polydimethylsiloxane (PDMS) using three different methods The surface forces apparatus (radius of curvature of the contacting bodies R 1 cm) friction force microscopy with a sharp AFM tip (R 20 nm) and friction force microscopy with a colloidal probe (R 15 nm). In the surface force apparatus, friction coefficients of the two materials differed by a factor of 100 whereas for the AFM silicon nitride tip, the friction coefficient for both materials was the same. When the colloidal probe technique was used, the friction coefficients differed by a factor of 4. This can be explained by the fact that, in friction force experiments, the contact pressures are much higher. This leads to a complete penetration of the AFM tip through the lubrication layer, rendering the lubricants ineffective. In the case of the colloidal probe the contact pressure is reduced and the lubrication layer cannot be displaced completely. 

The lateral force microscope (LFM) is a modification of the standard contact mode SFM [87-90]. In addition to the normal forces, the friction forces exerted on the probe are measured via torsion of the cantilever (Fig. 5). This mode is sometimes called friction force microscopy . LFM can be used in combination with topographic imaging as it shows changes in material as well as enhanced contrast on sharp edges (Fig. 9). In addition to morphology, it provides information on the friction and wear properties (Sect. 3.4). 

Frictional Force Microscopy Fourier-transform infrared spectroscopy scanning electron microscope surface force apparatus Secondary ion mass spectroscopy scanning tunneling microscope X-ray photoelectron spectroscopy bovine serum albumin immunoglobulin G... 

After these initial and promising lateral-force results, the friction force microscopy (FFM) was introduced. The FFM is a modified SFM with a four-quadrant photodiode, based on the laser beam deflection technique (Meyer Amer 1988) (Fig. 2.17). The beam is emitted by a low-voltage laser diode and reflected from the rear side of the cantilever to the four-quadrant photodiode. With this detection scheme, normal and torsional forces can be measured simultaneously. The torsional forces correspond to the lateral forces measured with the instrument of Mate et al. (1987). In 1993, Ovemey introduced the threefold measurement of topography, friction and elasticity on a polymer sample using an ITM. With this latest achievement, a wide spectram of tribological information was opened up, limited only by the lattice parameters of the sample. 

In friction force microscopy, laser light interference may lead to artefacts that are often eliminated by subtracting trace and retrace (after scan line shift correction). 

Sundararajan, S. Bhushan, B. Micro/nanotiibology of ultra-thin hard amorphous carbon coatings using atomic force friction force microscopy. Wear 1999, 229, 678. 

Hammerschmidt, J.A. Gladfelter, W.L. Haugstad, G. Probing polymer viscoelastic relaxations with temperature-controlled friction force microscopy. Macromolecules 1999, 32, 3360-3367. 

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