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Atomic force microscopy (AFM) measurements have shown that nanoscale interfaces in sliding contact frequently exhibit atomic lattice stick-slip friction. Using various material surfaces and AFM tips, including colloidal probes, and systematically varying applied load and lever stiffness, it is demonstrated that transitions can be repeatedly observed from smooth sliding to single unit-cell slips and then multiple slips. The behavior is dependent on the interplay between the stiffness of the contact zone, the measurement system (i.e., the AFM cantilever), and the interfacial potential. Atomic lattice stick-slip occurs with colloidal particle tip orders of magnitudes larger than those previously used. Stable atomically corrugated sliding in ambient conditions that cannot be seen elsewhere is reported. The generality of these conditions suggests that atomic-scale stick-slip behavior may be far more prevalent than previously appreciated. In addition, the friction-stiffness maps of various material surfaces in contact with a colloidal particle were reported, and the complex effects of system stiffness and pressure were discussed for chemical-mechanical polishing applications. [ABSTRACT FROM AUTHOR]

The friction behaviour of Si-wafer, diamond-like carbon (DLC) and two self-assembled monolayers (SAMs) namely dimethyldichlorosilane (DMDC) and diphenyl-dichlorosilane (DPDC) coated on Si-wafer was studied under loading conditions in milli-newton (mN) range. Experiments were performed using a ball-on-flat type reciprocating micro-tribo tester. Glass balls with various radii 0.25 mm, 0.5 mm and 1 mm were used. The applied normal load was in the range of 1.5 mN to 4.8 mN. Results showed that the friction increased with the applied normal load in the case of all the test materials. It was also observed that friction was affected by the ball size. Friction increased with the increase in the ball size in the case of Si-wafer. The SAMs also showed a similar trend, but had lower values of friction than those of Si-wafer. Interestingly, for DLC it was observed that friction decreased with the increase in the ball size. This distinct difference in the behavior of friction in DLC was attributed to the difference in the operating mechanism. It was observed that Si-wafer and DLC exhibited wear, whereas wear was absent in the SAMs. Observations showed that solid-solid adhesion was dominant in Si-wafer, while plowing in DLC. The wear in these two materials significantly influenced their friction. In the case of SAMs their friction behaviour was largely influenced by the nature of their molecular chains. [ABSTRACT FROM AUTHOR]