ABSTRACT
The loading force of a contact is not only given by the external force, but also by the interfacial adhesion forces between the two bodies in contact. The next chapter outlines the measurement of adhesion and pull-off forces by the scanning probe microscope. It is shown that heterogeneous samples can be segmented into their components by the adhesion force. Again one of the important questions still open is that of the applicability of continuum mechanics models. Molecular interaction might have a non-negligible influence for small tips. Increasing the resolution of the instrument, the chapter on the atomic scale friction measurements explains the theory and experimental details of this technique. On an atomic level, one can have dissipative, but not plowing friction. Mapping of the samples enables the seasoned researcher to extract important information on the surface and its interaction potential with the tip. This means that the very nature of the surface determines friction coefficients. Since the wear part of the friction is mostly
not
present at atomic scales, the friction can be much lower than in the macroscopic case. Even though the AFM can be operated in the wearless regime it is also possible to operate the
instrument at higher loads for friction studies as well as for scratch/wear and indentation studies. The nanoindentation and the nanoscratch operation allow us to probe the elastic/plastic response of nanometer films and of small amounts of material. The experiments are similar to the failure mechanism one would expect if a hard disk slider touched a surface or if a MEMS device were to undergo the first steps of a catastrophic failure. An overview of various tribological studies being conducted by scanning probe microscopy are given in the next chapter. Investigations of scratching, wear, and indentation on nanoscales using the AFM can provide insights into failure mechanisms of materials. Coefficients of friction, wear rates, and mechanical properties such as hardness have been found to be different on the nanoscale than on the macroscale; generally, coefficients of friction and wear rates on micro-and nanoscales are smaller, whereas hardness is greater. Therefore, micro/nanotribological studies may help define the regimes for ultra-low friction and near zero wear.
