Atomic-Scale Friction Measurements in Ultra-High Vacuum

This chapter reviews friction force microscopy experiments that reveal atomic-scale processes in single asperity contacts during sliding. Different regimes of atomic friction will be discussed including smooth sliding with low dissipation and the dissipative atomic stick-slip motion, where the tip jumps from one lattice site to the next. Furthermore, effects owing to finite temperatures, varying scan velocity and the influence of surface structures on the atomic friction are presented. Finally, the empirical Prandtl-Tomlinson model is introduced, which explains well the main observations in atomic-scale friction force microscopy experiments.