Atomic friction studies on well-defined surfaces

Atomic friction studies have been performed by means of a friction force mi croscope (FFM) in ultrahigh vacuum, where well-defined surfaces can be prep ared. A home-built FFM allows us to study lateral forces as low as 0.05 nN using rectangular silicon cantilevers. Furthermore, comparison with dissipa tion measurements performed in non-contact mode are possible. Recent experi mental results are presented and discussed in the framework of a one-dimens ional Tomlinson model which includes thermal activation. Atomic-scale stick -slip processes on a metallic surface could be repeatedly measured on Cu(11 1), while the Cu(100) surface was distorted by the tip during the scanning process. A logarithmic velocity dependence of atomic friction has been meas ured on Cu(111) and NaCl(100) for low scanning velocities. The dissipation found in stick-slip measurements is compared to the power loss detected in dynamic non-contact measurement.