Friction force microscopy on well defined surfaces

Friction force microscopy is implemented in ultrahigh vacuum conditions. Atomic-scale friction is observed on clean surfaces. The onset of atomic-scale stick - slip is observed and discussed in relation to the plucking model. Comparative measurements of AgBr(001) versus NaCl(001) and versus NaCl(001) demonstrate the material-specific contrast of friction. Contrast mechanisms are discussed in relation to these experiments. The role of the chemical nature of the tip is exemplified for the case of Si(111) , where wearless sliding is achieved with a PTFE-coated probing tip.