Friction force microscope

Three scanning probe techniques are described in more detail below the scanning tunneling microscope, the atomic force microscope, and the friction force microscope. 

In order to study microscale friction and wear, scientists have developed the friction force microscope (FFM), nanoindentation and nanoscratch tester which serve as excellent tools in micro tribological research [1,6-9]. In this chapter, we first compare the differences between macro and micro friction and wear, and then introduce some results of our research group on microscale friction and wear of ordered films, thin solid films, and multilayers. 

The tests were carried out in an atomic force microscope and friction force microscope developed by the au-... 

Figure 11.7 Working principle of the lateral or friction force microscope (LFM or FFM).

Example 11.2. In Fig. 11.9 the experimental results from a friction force microscope experiment is compared to simulations based on an extended two-dimensional Tomlinson model [481], The tip was assumed to be connected elastically to the holder (coordinates (xo, yo) that is scanned with the velocity v relative to the sample surface. The path (x(t),y(t)) of the tip was calculated using effective masses m. , my, spring constants Kx, Ky, and damping constants jx, 7y. The equation of motion for this system is ... 

Figure 11.9 Friction force microscope pictures (a, b) of a graphite(OOOl) surface as obtained experimentally with FFM and results of simulations (c, d) of the stick-slip friction using a two-dimensional equivalent of the Tomlinson model. The friction force parallel to the scan direction (a, c) and the lateral force perpendicular to the scan direction (b, d) are shown. The scan size is 20 Ax 20 A. Pictures taken from Ref. [481] with kind permission from R. Wiesendanger.

MFM (magnetic force microscope), LFM (lateral force, or friction force microscope), etc. None of the above finds wide use for particle size determination. The AFM has however been used to determine the shape, size and types of particle on a polished silicon wafer surface [203]. 

Figure 2.17. Sketch of a friction force microscope (FFM) with a beam-deflection detection scheme. Cantilever movements are monitored by a laser beam with a four-quadrant photodiode. The topography (T) is measured simultaneously with the lateral forces (L). Irreversible lateral forces are by definition frictional forces. (From Ovemey, 1995.)...

The three major new atomic-scale experimental methods developed in the last decade are the quartz crystal microbalance (QCM) [2 4], atomic and friction force microscopes (AFM/FFM) [5,6], and the surface force apparatus (SEA) [7,7a,8]. These new tools reveal complementary information about tribology at the nanometer scale. The QCM measures dissipation as an adsorbed him of submonolayer to several monolayer thickness slides over a substrate. AFM and FFM explore the interactions between a surface and a tip whose radius of curvature is 10 100 nm [9]. The number of atoms in the contact ranges from a few to a few thousand. Larger radii of curvature and contacts have been examined by gluing spheres to an AFM cantilever [10,11]. SEA experiments measure shear forces in even larger-diameter ( 10 pm) contacts, but with angstrom-scale control of the thickness of lubricating hlms. 

A modified type of AFM, called a friction-force microscope (FFM), has been described." " This method was shown to be able to distinguish between fluorocarbons and hydrocarbons on a phase-separated LB film. This shows that although AFM has proven useful for imaging organic thin films on an atomic scale, the technique can also provide useful information about the composition of molecules, as well as their conformation. 

Fig. 6.22 Schematic of the detector system in a frictional force microscope. A laser beam is reflected off the back of the cantilever and onto the center of a four segment light sensor. When the cantilever bends, due to a normal force, there is an intensity difference between the top and bottom halves. When it twists, due to frictional forces, there is an intensity difference between the left and right halves. (From Ovemey and Meyer [201] reproduced with permission.)...

The lateral forces result in a torsion of the cantilever, and this can be measured using the same optical detection system that measures vertical deflection (see Fig. 2.8). This signal from the tip-specimen interaction leads to another operational mode, the lateral or frictional force microscope (LFM or FFM) [142, 143]. In LFM the cantilever is designed to be... 

Scanning Electron Microscopy (SEM) Transmission Electron Microscopy (TEM) Scanning Tunneling Microscopy (STM) Atomic Force Microscopy (AFM) Frictional Force Microscope (FFM). 

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