2 - Superlubricity of clean surfaces

Abstract

This chapter describes the atomistics of friction—explaining the atomistic origin of the friction forces—and discusses the mechanisms of superlubricity based on a model from the atomistic theory. In Tomlinson's mechanism, the atoms change their equilibrium positions nonadiabatically, which leads to the energy transfer of the elastic energy into the kinetic energy of the atoms. Tomlinson's mechanism explains the energy dissipation; however, it is shown that Tomlinson's mechanism is unlikely to occur in the realistic frictional systems. The origin of the dynamic friction force explains the irreversible energy transfer of the translational kinetic energy into the internal kinetic energies. The translational kinetic energy is a constant for motion, and the frictional system is in a state of superlubricity. The superlubricity can appear when the sum of the forces of each atom vanishes. When the kinetic energy is given to a solid so that it is made to slide at a finite speed, it would come to a stop in a short time. In this case, the energy of the translational motion dissipates because of friction. This energy dissipation does not originate from the nonadiabatic motion of atoms.