Nanotribology

The study of friction and wear processes on the nanometer scale is related to the development of the atomic force microscope, where laser beams and piezoelectric elements are used to detect the motion of a micro tip across a surface in a controlled way. Friction on the nanometer scale has peculiar characteristics which are not revealed by macroscopic tools. Well-known concepts such as the coefficient of friction and the independence of friction from the scan velocity must be modified. The load dependence of friction is based on the non-linear relation f proportional to F-N(2/3); the velocity dependence is determined by thermally activated processes. The environment plays also an important role and different humidity conditions may lead to different friction, due to the formation of capillary necks in the contact area. A practical use of the atomic force microscope is to check the quality of surface preparation by comparing the responses of materials under different friction and wear conditions. Interesting applications are given by magnetic storage devices and micro-electromechanical systems.