friction

A breakthrough in the exploration of friction on the atomic scale has recently become possible by means of friction force microscopy (see figure). The tip of an AFM-cantilever is brought into contact with an atomically flat surface, which moves with a constant speed v along the x-axis. The resulting torsion of the cantilever is observable by optical techniques, yielding the time resolved lateral force F(t) and its time average (effective friction force) as the quantity of foremost interest. From the dependence of this force on the sliding velocity v, the normal force FN, or the temperature T, one tries to gain insight into the specific molecular properties of the probed surface and into the general microscopic principles of surface friction within an exceptionally simple "minimal" system.