Friction Force Measurements

Fig. 17—Quantized changes in both film height and friction force, measured on an island of C12 thiols on Au(111) as a function of applied load (taken from Ref. [31]).

As it is known, during the micro friction force measurement, it is difficult to obtain the real and precise friction force due to the small size of cantilever as well as the slight difference between cantilevers. According to the principle of FFM, the friction force signal can be used as the representative of the real friction force. Therefore, a friction coefficient factor is introduced in order to compare the relative micro friction characteristics among the samples. Corresponding to the relationship between the friction force and the friction... 

As is known, microscale friction and wear is important in microtribology. However, it is not easy to get real friction force on micro/nano scale during the tests. The surface morphology at nanometer scale, the scanning direction of the FFM, etc., have significant effects on friction force measurement. Even nowadays for commercial SPM we are not quite sure if the friction force we get is a real one or not. 

Friction force measurements at Skega AB were carried out by the following procedure. A piston/cylinder type of test ring was used. The O-ring being tested was greatly stretched over the piston and fitted into the seal groove. The cylinder was carefully wiped and dried with a clean cloth before the piston was put into the... 

The friction force endurance of EPDM O-rings after XeF2 treatment in optimum mode can be illustrated by a graphic presentation of friction force measurements during 50 cycles in the compression test machine (L W TCT 50) (Figure 15.1). 

Tribological behavior has its origin at the molecular level. Current theories suggest that adhesive forces have an important effect on die magnitude of frictional forces measured between two surfaces. At the molecular level, the two... 

As described in the last section, the adhesion forces between the particles and the polished surface can provide insight into post-CMP cleaning mechanism and efficiency. As a matter of fact, measurements of adhesion force and alike can directly help in the understanding of CMP and post-CMP cleaning processes. In this section, some basic principles and applications of adhesion and friction force measurements in copper CMP will be presented. The discussion is certainly applicable to post-CMP cleaning processes when similar systems are involved. 

Faint contrast in the error signal is a good indication for an optimized feedback loop. At the same time the dimension and the habit and possible defects of the crystal, including the fold domain boundaries, are very well visualized. For several polymers including PE [49] and poly(4-methyl-l-pentene) [50], the friction forces measured on the surface of the lamellar crystals obtained from solution are anisotropic (Fig. 3.20 bottom right). This anisotropy is related to the direction of the folds on the crystal surface. 

The nano-friction force, measured in torsion mode, is directly proportional to the TMR value (trace minus retrace, in volts), which is given as the difference between the lateral forces scanning left-to-right and right-to-left. Absolute adhesion and friction forces can be obtained with calibration methods but such techniques... 

Figure 9.16, (a) Friction force measurements on crossed polylethylene tercphthalaic) fibers showing agreement with Equation (9.16) with friction coefficient = 0..T.3 and work of adhesion W = 0.01 m . (b) Contact between two crossed cylinders, equivalent to sphere on flat, showing the forces acting. 

Fig. 22 Effect of clay content of NC gels on the sliding frictional behavior. The force profiles were measured in air and wet for N-NC gels with different clay contents (NC1-NC5). Insef. The principle of sliding frictional force measurement on the gel surface and a picture of sliding friction measurement on NC gel. Reprinted from Haraguchi and Takada [98], Copyright 2005, with permission of Wiley...

Furthermore, many factors affect the frictional force measured. These include sample hardness, the load and speed used in the test, and the particular material and surface morphology of the surface against which the sample is pressed. Compounding differences of polymer type and especially additives (which can bloom to the surface) have major effects. Lubrication of surfaces by light oils or soapy water can render them very slippery. 

Figure 1.2 Friction force measurement during the CMP process [8].

Figure 1.3 Friction force measurement during the CMP process [8]. (a) Without polishing slurry and (b) with polishing slurry.

The friction force measurements were performed in two different configurations asymmetric, where only the fiat substrate surface was coated by PLL-g-PEG and the colloidal probe of the LPM remains bare, and... 

Figure . AFM results friction force measured as a function of increasing load for the contact of a bare silicon nitride tip and silicon wafers coated with PLL-g-dex copolymers.

Figure 2.14b shows the friction force measured on platinum patterns and the averaged scan pull-off force measured before and after each friction measurement for the same scanned area. In fig. 2.14b, both the friction and pull-off forces decreased as the asperity height increased, but not as rapidly as the forces with silicon groove depth (fig. 2.10b). The difference in contact conditions, as mentioned previously, possibly caused the differences in rates of decrease in the friction and pull-off forces. 

FIGURE 2.19 Comparison of friction force vs. pull-off force on platinum and silicon asperity arrays using data from fig. 2.18. The friction forces measured on each material were fitted with a line that passes through the origin. The gradient of each approximated line is shown in the parentheses in the inset box. 

Figure 2.29 shows the friction force measured for the asperity arrays covered with LB films as a function of the curvature radius of the asperity peaks. The error... 

The tests were conducted on aqueous solutions of SML/ESMIS mixtures at the concentrations of 0.01%, 0.1%, 1%, and 4 wt%. A T-11 tribometer (pin-on-disc) produced by ITeE Poland (Institute for Sustainable Technologies, National Research Institute, Radom, Poland) was used in the tests. The pins used were 3.0 mm in diameter and were made of LH15 steel or polyamide-6, while the discs were 25 mm in diameter and were made of polyamide-6. Before the tests, all components of the friction couples were thoroughly chemically cleaned. An ultrasonic cleaner was employed. The steel elements were cleaned in n-hexane, acetone, ethyl alcohol, and distilled water. The polyamide-6 elements were cleaned in ethyl alcohol and distilled water. After the cleaning process all friction-couple components were dried (50°C, 30 min). The time of the test run was 900 s, the friction-couple load was 10 N, and the sliding velocity was 0.1 m/s. The coefficient of friction was calculated from friction force measurements using... 

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